Okajimas Folia Anat. Jpn., 56(2-3) : 91-158, August 1979
Karyorrhexis and Karyolysis of Mesenchymal Cells in the Intestinal Epithelium of Amphibians and Mammals
With Evidence for Successful Differentiation of Some Mesenchymal Cells into Epithelial Cells
By
WARREN ANDREW and NANCY V. ANDREW
Department of Anatomy, Indiana University, 1100 West Michigan Street, Indianapolis, Indiana 46202, U.S.A.
-Received for Publication, January 25, 1979-
Key Words : Karyorrhexis, Karyolysis, Mesenchymal cells, Intestinal epithelium, Differentiation of cells.
Summary : The nature of the migratory process and the role of the mesenchymal cells (primarily lymphocytes) have been studied by light and electron microscopy in the small and large intestines of the urodele amphibian, Ambystoma mexicanum, and in the mouse (C57 Black) and rat (Wistar Albino). In all three species the migration is intense and in all the large intestine shows a much higher proportion of mesenchymal cells in the apical position in the epithelium between the epithelial nuclei and the lumen. The mouse intestine was chosen for quantitative studies because of the genetic homogeneity of the material and the availability of animals of known age. A marked decrease in numbers of mesenchymal cells in epithelium is seen with ad- vaning age in our specimens. The total numbers. of migrating cells in the large intestine of the mouse do not seem to be greater than in the small intestine but the number in the apical position in the large intestine is approximately nine times that in the villi. It is in this apical position in all three species that degenerative change in the mesenchymal cells usually is seen. Degenerating mesenchymal cells (lymphocytes) are within epithelial cytoplasm. Condensation of nuclear chromatin is followed by nuclear breakdown (karyorrhexis) and solution of nuclear contents (karyolysis). The material of the lymphocyte nucleus seems either to be absorbed in the eyithelial cytoplasm or discharged to the intestinal lumen. The appearance of mesenchymal cells in the basal portion of the epithelium suggests strongly that some at least of them are undergoing a transformation, in all three species, in very much the way that Mori (1937) suggested as occurring in the intestine of the amphibian Megalobatrachus japonicus. Such transformation would appear to be occurring frequently enough to play a very significant role in replacement of epithelial cells.
91 92 W. Andrew and N. V. Andrew
Introduction than those in the cores of the folds. Mitotic division was seldom seen in the Susumu Mori undertook the study of connective tissue cells close to the the mode of development of the goblet epithelial layer. cells in the amphibian intestine (Mori, Two characteristics of the subepithelial 1936) and was impressed with the dif- cells were especially noteworthy to culty of equating his findings with the Mori : (1) they are mobile, moving up generally accepted view that these to make their way between the epithelial mucus-secreting cells arise only by a cells and drawing a cytoplasmic "train" functional modification of the cylindrical (Schleppe) behind them, and (2) they are epithelial cells which form the lining of able to secrete mucus while still beneath that organ. As perhaps would seem only the epithelial layer. natural, he had confined his observations Mori speaks of an individual migratory to the region alove the membrana cell as a cell unit (Zelleinheit) and propria, since he believed that he was describes these units as coming from dealing with processes occurring only the plasmodia, each of which contains a within the epithelium. Failing to find number of such units. The cell or cell the looked-for changes from lining to unit, then, frees itself from the so-called secreting cell, however, he initiated a plasmodium and moves into the epithelial second study. Mori says (1937' p. 1) : layer. Secretion of mucus, however, has "Diesmal mein Au genmerk auf das begun either during its migration or subepitheliale Bindegewebe richtend, while it is still in the plasmodium. It begegnete ich eine merkwurdige Erschei- seems highly probable to Mori that the flung, welche, scheint mir, uber die cell moving out of the plasmodium does Becherzellenfrage einen neuen Aufchluss attain an independent existence, while geben durfte." (Turning my attention the plasmodium proceeds to produce new this time to the subepithelial connective cells. He found mitotic division as an tissue, I encountered a noteworthy evidence of new cell production in the phenomenon, which, it seems to me, may plasmodia. give a new explanation for the goblet In Gekko japonicus although "plasmodia" cell problem). are not described by Mori, and apparently The observations which Mori describes do not occur in the small intestine of in this second article were made on this reptile, he does affirm an origin of small intestine from two species, one the goblet cells as from a kind of wandering urodele amphibian, Megalobatrachus cell which again makes its way between jaPonicus and the other the reptile, the ordinary epithelial cells. These, he Gekko japonicus. They were made with says, probably are the so-called "replace- the light microscope on sections 4-5 ment cells" which many earlier authors micra (micrometers) thick, stained with had described as occurring between the hemalum or iron hematoxylin (Regaud) basal parts of the cylindrical cells. and with mucicarmine. While commendably cautious on this In the interior of the mucosal folds of point, he states (p. 270) : "Deshalb neige Megalobatrachus japonicus, certain cells ich vielleicht zu denken, dass die were seen with deeply stained nuclei sogenannte Ersatzzelle nichts anderes als and with scanty cytoplasm, The more eine bindegewebige Zelle ist, welche aus deeply situated free cells in the loose dem Darmstroma in die Epithelschicht connective tissue had nuclei more rounded einwandert." (Therefore, I incline perhaps Karyorrhexis and Karyolytis of Mesenchymal Cellt 93 to think that the so-called replacement the blood of invertebrates (Andrew, cell is nothing other than a connective 1961, 1962), as well as the review of the tissue cell which migrates from the work of many authors on the blood, intestinal stroma into the epithelial lymph, and tissue fluid of lower verteb- layer). Settled between the epithelial rates which we carried out in the pre- cells, such a cell gradually changes paration of a book on "Comparative from its rounded form, pushing forward Hematology" (Andrew, 1965a) have shown a cytoplasmic extension toward the us the importance of the lymphocyte in surface to become at first an immature its multipotential characteristics. It is "goblet cell" without secretion , then this evidence, together with the results attaining to the lumen with its apical of the most recent work by a number end and actively producing mucus. of investigators in the fields of ultra- We have described the work of Mori structure, immunology, and tissue repair at some length here because, although it which we have brought together in the has not served as a basis for our monograph (Andrew, 1978). The broad research on the intestinal epithelium, we outlook on cell transformation and its have been impressed by the increasing role in the body economy has stimulated significance to some fundamental bio- us to re-investigate the phenomena in logical problems which it has presented the intestine of the urodele amphibians, in the development of our own concepts. especially in relation to the early work In the preparation of a monograph on of Mori. "The Lymphocyte in Evolution : New
Light on its Role as a Transforming Materials and Methods Cell in Blood and Tissues" (Andrew, 1978), we have found it necessary to In the present study observations have review a large amount of literature on been made on the relation between the relation between wandering cells migrating mesenchymal cells (largely and "stable" epithelial cells. We have classifiable as lymphocytes) and the found that the observations and con. intestinal epithelium in one species of clusions of Mori on the phenomena as amphibian and in several species of seen in urodele amphibians and in reptiles mammals. The amphibian species is the have received markably little attention Axolotl, Ambystoma mexicanum, which in the literature. has been much used in experimental It is true that Mori newhere uses the studies. An analysis of the literature term "lymphocyte", speaking of the on the viscera and lymphatic system of wandering cell as "eine bindegewebige this species has been made (Smith, R.B., Zelle" (connective tissue cell) which and H.M. Smith, 1969) and has been wanders out from the intestinal stroma useful to us. into the epithelium. There may indeed We have used 33 individuals of the be some room for discussion as to Axolotl, all of which came originally which term is preferable in describing from the laboratory of Rufus Richard the migrating cells. It seems to us, Humphrey in the Department of Zoology however, that Mori, intent on describing of Indiana University. On all of these the intestine, was not likely to have animals the time between spawning and been concerned about a more specific sacrifice is indicated as the age of the designation of such cells. The individual individual, which ranges from nine research studies which we have made on months to over eight years. 94 W. Andrew and N. V. Andrew
In the study of the intestinal epithe- the intestine of Ambystoma mexicanum lium of mammals, we have used chiefly (Andrew, 1972, 1975) we have discussed the C57 Black mouse and the Albino rat briefly the general histological structure of the Wistar Institute. The ages of of that organ. The cells have diameters all of the rodents were known and several times greater than those in the recorded. The mice are of both sexes mouse and rat. The greatest difference, and range in age from 88 to 849 days. however, is seen in the presence in this The rats all are 100 days of age. amphibian of "cell nests", generally solid Sestions of intestine from 20 mice and groups of cells lying beneath the ten rats were studied. The quantitative surface epithelium but usually connected studies of the small intestine represent to it by a narrow neck. These "nests" 18 mice (Table 1) and of the colon, 13 seem clearly to correspond to the mice (Table 2). The selection of these "plasmodia" of which Mori (1937) spoke ; animals depended chiefly on the quality but our thinner sections and also the of fixation for the light microscope electron microscope studies indicate that observation and for enumeration of cells. they do not have a syncytial character, Material for light microscopy was although a few clear instances of cyto- prepared by fixation in ten percent plasmic continuity between plasma cells neutral formalin, embedded in paraffin and epithelial cells have been seen. and sectioned at 5 or 6 micra (micro- Another feature of the general struc- meters). Regaud's fixative was used ture in the small intestine different from for mitochondria with staining with iron that described by earlier authors has hematoxylin after iron alum mordant. been noted by us in the present study. Acid fuschsin also was used as a mito- Having used both longitudinal and cross chondrial stain, observations then being sections, we conclude that finger-like made with a green filter in the micro- processes, apparently actual villi, do scope lamp. occur, whereas the earlier descriptions Specimens for electron microscope speak only of longitudinal folds of the study were fixed in three per cent mucosa. glutaraldehyde in phosphate buffer and In the present investigation we have post-fixed in 1 per cent osmic acid in concentrated our observations on the phosphate buffer. Embedment was in region of the surface epithelium. Our epon. primary purpose here has been to deter- Thick epon sections (0.5 p), stained mine the destination oi the wandering with toluidin blue, were very rewarding. mesenchymal cells (almost entirely Thin sections were studied on an RCA- lymphocytes) after they enter the layer. 3E microscope. The intensity of the migratory process We wish to express our sincere thanks can be seen in almost any light micro- to Dr. Ralph Jersild and Mrs. Joan scopic field (figs. 1 and 2). In the Simpson for aid in the work of prepa- Axolotl the variety in the appearance ration for eiectron microscopy. of the migrating cells is considerable. While there are many cells of spherical shape basal to the level of the epithelial Observations nuclei and also at the level of those A. The Axolotl nuclei, there also are numerous apparently 1. The Role of the Migratory Cells motile cells which have short or long In two preliminary reports of work on ovoidal nuclei and yet in the staining of Karyorrhexis and Karyolysis of Mesenchymal Cells 95 the karyoplasm resemble the cells which form (figs. 5 and 6). one would not hesitate to designate as It is true that it might be argued that lymphocytes. The presence of such some or all of the elongated cells with elongated cells in this amphibian might darker nuclei are themselves epithelial seem to be explainable on the basis of cells, perhaps in a different physiological movement upward of cells from the cell state, in some stage of a secretory cycle nests (the "plasmodia" of Mori). In fact, for example, or at a different stage of we believe that this is the source of the interphase portion of the mitotic many of these cells in the large intestine cycle, than the majority of the epithelial and in those portions of the small cells. Against such an argument, in our intestine where the surface epithelium opinion, there are several points (1) the overlies cell nests. The small intestine, great similarity in appearance of these however, has a large portion of its cells to many of those in the underlying mucosa in the form of long, very thin connective tissue, (2) the clear evidence "villi" . In the core of these villi we do that a migration of mesencymal cells is not find cell nests. Nevertheless, the occurring as seen by the cells with more epithelium contains, in addition to densely staining nuclei and rounded or spheroidal lymphocytes, many dark, oval bodies at different levels of the elongated nuclei. The counterparts of epithelial layer, and (3) the occasional such nuclei are seen in the core of the presence of a cell in which one can see villus and often present a picture as of both its location partially still in the a "stream" of cells moving upward and subepithelial zone and partly in the outward. epithelium. The first two of these points While the appearances are suggestive can be supported by any general study of a motion of the dark-nucleate cells of the intestinal mucosa. The third from the connective tissue into the point, in our experience, involves study epithelium, the much thinner sections of of a large extent of mucosa and a epon-embedded material, stained with willingness in some instances to accept toluidin blue, present us with a clearer information presented to us by an arte- picture of this cell population actually factual condition in the tissue. It is in the epithelial layer (fig. 2). Here the indeed the lifting up of the epithelial variety in appearance of the migrating layer somewhat from the underlying mesenchymal cells is seen. Some are tissue which reveals most clearly the rounded or short ovoidal in shape with position of some of the elongated cells densely staining nuclei. Others are as partially below and partially within elongated with nuclei staining somewhat the epithelial layer (fig. 6). That such more lightly, yet appearing darker in cells are taking a functional part in "epithelial" activity is seen by a clear general and with more densely concent- rated chromatin masses in their interior evidence of secretion, the secretory pro- than have the definitely epithelial nuclei. duct being discharged to the lumen. For the rounded mesenchymal cells there These phenomena of migration and seem to be definite transitional stages differentiation to become secretory cells to cells of epithelial type (figs. 3A and appear, then, to support and to add B, and fig. 4). The same appears to be weight to the concept of Mori. He true of the elongate cells with dark worked with one species, we will recall, nuclei, although they frequently appear in which the migrating cells were coming to be passing direetly into a secretory from the "plasmodia" (since called "cell 96 W. Andrew and N. V. Andrew
nests") and with another in which such in regard to our own conclusion. For cells seemed to come simply from the some reason, it has been difficult for a subepithelial connective tissue stroma. number of investigators to be convinced The former species was Megalobatra- or to convince others that relatively chus japonicus ; the latter, Gekko japonicus. stationary cells, such as those of the The first is a tailed amphibian, the intestine can tolerate the entrance of second a reptile. The cell nests are other cells. A striking instance of this structures which, among vertebrates, was seen at a national meeting in our seem to have been described only in the country (The United States), in the tailed amphibians (Urodela). In Amby- recent past in relation to another organ stoma mexicanum we find cells migrating but with a similar problem as to cell from both the cell nests and the general location. A speaker (Schmedtje, 1965) connective tissue stroma. As we have had published his abstract with an indicated in our preliminary papers apparently unequivocal statement that (Andrew '72, '75) the cell nests contain epithelial cells in a certain location (the numerous mesenchymal cells, both lym- appendix) in the rabbit often contain as phocytes and plasma cells. many as ten lymphocytes per epithelial 2. Position of the Migratory (Mesen- cell, the lymphocytes lying in a large chymal) cells in relation to Epithelial intracytoplasmic vacuole. Then, in an Cells informal discussion shortly before he The great majority of the mesenchymal was to speak from the platform, a cells in the epithelium are seen in the number of his colleagues expressed doubt basal portion, between the epithelial that such an intracellular location of cells. The more rounded ones are gene- lymphocytes was "possible". The speaker rally basal to the position of the epithelial was so affected by their opinion that nuclei while the elongated nuclei are when he presented his talk he had changed slightly lower than the level of the his own position and described the epithelial nuclei or at the same general lymphocytes as intercellular. level as such nuclei. Survey of consider- able extensions of the surface epithelium, A. The Axolotl however, shows the presence of some In the Axolotl the relatively great size mesenchymal cells in a position apical of the cells makes the relationship be- to the epithelial nuclei. The mesenchymal tween epithelial cell and lymphocyte a cells at this level differ in two important well defined one. The lymphocyte gener- respects from those at lower levels : (1) ally lies within a vacuole in a position they are within the cytoplasm of the just apical to the epithelial nucleus (figs. epithelial cells and (2) they are in various 7 to 10, inclusive). The appearances of stages of a degenerative process. the lymphocytes (mesenchymal cells) are, The statement that the mesenchymal however, remarkably varied. They ap- cells (lymphocytes) occupy an intra- parently represent stages in an elimi- cellular position is meant to be made nation of the lymphocyte, not by here without equivocation. In the Dis- extrusion into the lumen but rather by cussion of this paper we shall consider breakdown (karyorrhexis) and solution the question of the entrance of these (karyolysis) within the epithelial cells. cells into other cells as found in recent The changes occurring in this process experimental studies. We stress at this are not, it would seem, always the same. 14,y-ter.It nrirtagrear 44% e.4- iv,. et rtn elt0;1-0.1-;nri In some cases the nucleus and cytoplasm Karyorrhexis and Karyolysis of Mesenchymal Cells 97 are both diminished in size. In others clear spaces, conspicuous in the dark the nucleus appears shrunken and surrounding material (fig. 12 and especi- pycnotic, while a large amount of ally fig. 13). lymphocyte cytoplasm persists for a Between the very dense chromatin while. In other cases the breakdown masses the nuclei show minute, rather _ of the nucleus into separate fragments densely packed granules, which probaly is conspicuous. This may proceed to a indicate the reason for the deep stain of condition where numerous pieces of the karyoplasm seen in the light micro- nuclear debris of varying size are scope preparations. The nuclear mem- scattered in the epithelial cytoplasm brane itself is in the sections of some (figs. 11A and B). End-stages of the cells of a smooth and regular outline. process show such fragments as little In others there are many indentations. more than outlines or "ghosts", perhaps With the methods which we have to be extruded. employed on nuclear pores are observed The presence of degenerating mesen- occasionally. chymal cells is seen occasionally in An interesting fact about the nuclei is epithelial cytoplasm basal to the nuclei. the considerable variety in appearance Also, cells may be seen in vacuoles within the general picture which we without evidence of degenerative change. have just given. Thus in a number of Rarely we have seen a nucleus which them the dense chromatin is much less has the epithelial appearance and staining abundant (compare figs. 12 and 13). In qualities but which is itself within a such cases the degree of continuity conspicuous vacuole. The significance between chromatin masses appears less. of this not yet clear. The small granules between the dense Electron microscope observations on masses appear lighter and more widely the Axolotl intestine have been helpful spaced, so that the general density of especially in the elucidation of the the nucleus is due to differences both in ultrastructural characteristics of the these and in the pattern of the heavier cells with dark elongated nuclei. The chromatin. cytoplasm varies considerably in amount The smaller, rounded or ovoid mesen- but often is seen as a rather narrow chymal cells, which more often are called band on either side of the nucleus and simply "lymphocytes" share in some of extending from it at one or both poles. the nuclear characteristics of the larger, A moderate amount of rough endoplasmic elongated ones but also show important reticulum is present. The mitochondria differences. The coarse masses of chro- are generally spheroid or ovoid and matin tend to occupy a large part of relatively small as compared with those the volume of the nucleus and the of fully developed epithelial cells. bridges connecting the major subdivisions It is the nuclei, however, which are of chromatin are broad ones. The small most characteristic. In them the greater granules in the karyoplasm are densely part of the chromatin is in the form of crowded. Larger rounded or ovoid cells heavy-appearing, irregularly shaped show a shift from this heavy conden- masses which often show a high degree sation of chromatin to a generally of continuity (fig. 12). While these lighter appearance. As with the elon- masses are homogeneous for the most gated mesenchymal cells, the dense part, they frequently, near the periphery chromatin tends to be continuous, or of the nucleus, show numerous minute almost so, at the periphery of the 98 W. Andrew and N. V. Andrew
nucleus, in contact with the nuclear manner of cell replacement not depen- membrane. dent on cell nests, for they are lacking in the intestine of Gekko japonicus. Yet B. The Mouse this method resembled that which he In the observations on the mouse, we found in the urodele amphibian, in that have concentrated on the epithelium of in both cases the replacing elements are the villi in the small intestine and on migratory cells which enter the epithelial the surface epithelium in the colon. layer from below and then become This decision has been made primarily secreting cells. Since we had observed because of the complication of the this general type of replacement, by cells cytological picture in the crypts of from below, in the intestine of the Lieberkuhn by the presence of many Axolotl, the question almost immediately mitotic figures. It is understood, how- would arise : "Is there a similar pheno- ever, that an explanation of the cyto- menon in the intestine of the mammal?" logical phenomena in any part of the But for this comparison, it would seem epithelial layer must depend ultimately well, temporarily at least, to place aside on the understanding of the total or out of ones mind the long accepted picture. On the villi, and in the surface concept that mitotic division in the epithelium, nevertheless, one is better crypts, accompanied by a pushing or able to obtain definite ideas of the gliding of epithelial cells, both absorp- relationship of wandering mesenchymal tive and goblet, upwards along the villi, cells (lymphocytes) to the lining and accounts entirely for replacement of the secretory cells (epithelium). While the intestinal epithelium. quantitative study has been made on the Entering then, upon the observations villi, incidental observations on the on the intestine of the mouse as though crypts will be mentioned. we simply are ascending the evolution- The study of the mouse in this ary scale, our first question will be : "Is project, paralleling as it does, the there a population of mesenchymal observations on an amphibian, raises the migratory cells in the subepithelial question of what sort of comparisons connective tissue of the mammalian we may expect to find in fundamental intestine bearing a resemblance to that processes such as cell differentiation and which we have seen in the urodele replacement. Basic processes, such as amphibian ?" The answer is in the mitosis, for example, are seen in vast affirmative. The tissue of the tunica numbers of organisms, both plant and propria in the core of each villus and animal and show somewhat the same filling in between the crypts of characteristics in organisms which differ Lieberkuhn contains such large numbers widely in size, form and way of life. of lymphocytes, chiefly of the small It has seemed to us that we reasonably category, that it may be called diffuse could expect a general similarity in lymphoid tissue. Along with the lympho- manner of cell replacement for the cytes, as in the amphibian, are smaller epithelium of amphibia, reptiles and numbers of plasma cells. As important mammals. The cell nests in our elements of the loose "skeleton" of the Ambystoma rnexicanum and in the tunica propria are fixed mesenchymal Megalobatrachus japonicus studied by cells, apparently the producers and Susumu Mori appear similar. In the sustainers of the fibrous network within reptile, however, Mori described a the interstices of which the lymphocytes, Karyorrhexis and Karyolysis of Mesenchymal Cells 99 plasma cells and other "detached" cells, epithelium of the colon. Table 1 indi- such as macrophages, lie. Such fixed cates that there are large numbers of mesenchymal cells are primitive fibro- lymphocytes in the epithelial layer of blasts and resemble those seen in the the villi. In fact, a total of 2912 lympho- embryonal mesenchyme which, however, cytes are found in fields in which there has a fluid or semi-fluid material in its were approximately 12,780 epithelial cells. interstices, rather than with the dense Of this large number of lymphocytes, cell population seen there in the tunica 81.7 per cent were located basal to the propria of the intestine of the mature epithelial nuclei ; 15.3 per cent on the animal. level with the epithelial nuclei, and 3.7 Our second question will be whether, per cent apical to such nuclei. as in the amphibian, there is a migration In the surface epithelium of the colon of certain cells, primarily the lympho- (Table 2) we found 836 lymphocytes in cytes, from the tunica propria into the fields containing 6500 epithelial cells. epithelial layer covering the villi of the In regard to the position of the lympho- small intestine and into the surface cytes in the epithelial layer, the mouse
Table 1. Characteristics of lymphocytes in 20 oil immersion fields of the intestinal villi in each of 18 C57 black mice comprising a total count of 12780 epithelial cells. 100 W. Andrew and N. V. Andrew
Table 2. Characteristics of lymphocytes in fields inculuding 500 cells of surface epithelium of the colon in each of 13 C57 black mice comprising a total count of 6500 epithelial cells.
colon shows : total basal, 57.1 per cent ; using more strictly comparable methods. total level, 10.4 per cent, and total apical, The percentages of the total numbers 32.5 per cent. of lymphocytes in colonic epithelium in The relation of the total numbers of the three positions—basal, apical, and lymphocytes in the epithelial layers to level—on the other hand should be the number of epithelial cells cannot, in strictly comparable with those for the this study, be compared with strict villi. In like manner, the percentages accuracy for the villi and the colon ; of lymphocytes classified as "degenerate" since the basis of counting for the villi and as "unaltered or transforming" is by numbers of oil immersion fields, should be able to be compared from while for the colon it is by actual small intestine (villi) and large intestine numbers of epithelial cells. We used (colon). When we compare the numbers the latter method for the colon because as to position, we find : total basal, it is much easier there to distinguish villi, 81.7 per cent, colon, 57.1 per cent ; individual epithelial cells. Still, the total at level, villi, 15.3 per cent, colon, comparison should be close enough, it 10.4 percent ; and total apical, villi, 3.7 seems, to be able to say that the per cent, colon, 32.5 per cent. It is clear number of lymphocytes in the colonic that in the surface epithelium of the epithelium is not greater than that in colon there are many more lymphocytes epithelium of the villi. It is planned to in the apical position and this difference make a further study of this matter seems to be primarily "at the expense" Karyorrhexis and Karyolysis of Mesenchymal Cells 101 of lymphocytes in the basal position. The qualitative aspects of the lympho- In the epithelium of the villi the cytes in epithelium have been studied number of degenerating lymphocytes is with special regard to the relation very small, a total of 32 among 2912, or between individual cells in these two 1.1 per cent ; in the colon, the number parts of mouse intestine. The picture is 216 out of 836, or 25.8 per cent, over is a varied one, yet certain appearances 25 times as high a proportion of the total indicating the lymphocyte-epithelial number of lymphocytes as on the villi. relationship recur frequently enough that The nature of the luminal contents of they soon become familiar to the the small intestine and the colon are, of observer. Figure 14 presents two fields course, very different. It is not clear, from the epithelium of the villi. The however, at this stage of our work phenomenon of apparent "pushing" of whether the high degree of degeneration the lymphocyte against an epithelial of lymphocytes in colonic epithelium is cell or its nucleus is seen in both 'A' related to that fact or to the far greater and In 'A' the lymphocyte nucleus frequency of lymphocytes in an apical still appears dense and is in sharp position in the colon. The difference in contrast to the somewhat crescent- position of lymphocytes may itself, of shaped epithelial nucleus. In 'B' the course, be related to the different nucleus of the "lymphocyte" is far less nature of the luminal contents between dense, yet is easily distinguishable from small and large intestine. From the that of the epithelial cell just apical to quantitative study of the villi and the it. surface epithelium of the colon, it is The advancing lymphocyte, when it is clear that there is a great difference in alongside or parallel to an epithelial numbers of lymphocytes in the two age nucleus, often is elongated. In many groups, with a marked decrease from instances such a nucleus is clearly young to old (Tables 3 and 4). distinguishable from the epithelial ones
Table 3. Total numbers of lymphocytes per animal in the epithelial layer of the villi (20 oil immersion fields) in young and old C57 black mice. The mean and its probable error is given for each age group.
Table 4. Total numbers of lymphocytes per animal in a segment of surface epithelium (500 cells) in young and old C57 black mice. The mean with its probable error is given for each age group. 102 W. Andrew and N. V. Andrew
(fig. 15) in some instances the distinc- The manner of loss of epithelial cells tion is difficult. A most interesting has been dealt with by several authors. appearance is that of the cell which In a columnar epithelium, it is perhaps seems not yet fully integrated into the not appropriate to speak of "desqua- epithelial layer (fig. 15B). Here a cyto- mation" which gives an idea of the plasmic body of considerable size is seen shedding of flat, scale-like objects. "Sloughing" may be used and its elongated, somewhat pyramidal , but this might shape is well outlined, while the nucleus seem to indicate a massive process with is often, as here, spheroidal in form. the breaking away of groups of cells. In rare instances in the mouse villi, Our observations indicate that the we have seen what appears to be a shedding of single cells, often somewhat subepithelial secretion of mucus. Clearly altered in form, is the most common identifiable goblet cells lie below the manner of epithelial cell elimination surface epithelial cells (fig. 16). An (figs. 19A and B). outlet for the mucus in these cases may The crypts of Lieberkuhn are a lie in the intercellular spaces. The prominent feature of both small and probable explanation of this phenomenon, large intestine in the mammal. In many it seems to us, is a process of differenti- of the cold-blooded vertebrates, there ation of wandering mesenchymal cells seem to be no clearly homologous (lymphocytes) into mucus-secreting structures. In the Axolotl the cell nests "epithelial" cells before they have which we have described earlier in this entered the epithelial layer. paper probably have an homology to the Our observations have shown numerous mammalian crypts, although the nests instances of a process of elimination generally are solid. There are at least both of the lymphocytes and of the some mammals in which the "crypts", epithelial cells on the villi and in the although having a long tubular form, colon (figs. 17A and B, 18B, and 19A have no lumen and hence, like the and B). The eliminative process for the urodele amphibian nests, are solid lymphocytes seems to be primarily structures. An example is the long- within the epithelial cytoplasm, as we nosed bandicoot, Perameles nasuta Geoffroi had observed in the Axolotl. A common (Van Lennep, 1962). feature is condensation of the chromatin In the mouse and rat, however, all of in which it often forms a dense mass the crypts are tubular structures. We against the nuclear membrane. Karyor- have not found quantitative studies on rhexis, the breaking of the nucleus into the size of the lumen, but in sections it a few or many fragments also is seen varies considerably, from very small to (fig. 17B), again as in the Axolotl (figs. very large. Such variation probably is 7-10. inclusive). The ultimate fate of due in part to the angle of section, the these fragments appears to be a solution distance from the base, and perhaps the into the epithelial cytoplasm, although region of the intestine, as well as to the product of the solution may be changes occurring during technical extruded. In rare cases a degenerating preparation. lymphocyte may be cast out into the Lymphocytes are readily identifiable in lumen while in process of degeneration, the epithelium of the crypt (fig. 18A). but we are inclined to believe that this Large numbers of lymphocytes in the is a departure from the common or crypts are undergoing degenerative normal process. change. In some cases the nuclei of Karyorrhexis and Karyolysis of Mesenchymal Cells 103 such lymphocytes are of normal or below fications are in many instances even normal size but show a homogeneous more difficult than with the oil immer- karyoplasm, without nucleoli or chromatin sion lens of light microscopy. particles (fig. 18B). In other cases the One process which it seems necessarily nuclei are enlarged, generally showing would be involved in a transformation aggregation of the chromatin just beneath of mesenchymal wandering cells into the nuclear membrane. columnar epithelial cells would be the Another feature in the crypts which formation of surface modifications includ- adds somewhat to the difficulty of ing the microvilli. That such structures identification of cell type is the fact can be formed even deep within a cell that the mitotic figures generally do not has been shown for the ciliated epithelium show the chromosomes in a discrete of the respiratory tree, where intracellular fashion, chromosome bridges being vesicles serve as a "lumen" into which present in many cases (fig. 18B). Not cilia sprout and by which they actually infrequently the two groups of chromo- are carried to the surface. somes appear more like two large masses We as yet have not been able to trace of dense chromatin material. in any detail the production of surface The interesting process of direct trans- modifications of differentiating cells of formation of wandering mesenchymal the intestinal epithelium. In our light cells into epithelial ones appears to be microscope pictures we seem to have occurring in the crypts as well as on the cells present which would be in a stage villi. This seen by the presence of cells, in which such production would be often with spheroidal nuclei and "pushing occurring. In electron micrograph aside" the cytoplasm and nuclei of pictures we see some cells which do not adjoining epithelial cells. extend to the surface and in which the What evidence is there of the elimi- contents of the cytoplasm are different nation of epithelial cells ? The classical from those in adjoining cells. Clearly a and widely accepted "wander theory" more sophisticated study of serial sections would hardly see the need, or indeed should be made in the future. the possibility, of such elimination (see The identification of wandering mesen- Discussion). We do see, however, single chymal cells (lymphocytes) which have cells being cast off from surface entered the epithelial layer is not epithelium (fig. 19A). Careful study difficult. Striking features of some of shows that degenerate cells do occur these is the almost "empty" cytoplasm also in the crypt lumen (fig. 19B). It is and its extension upward in the form of not easy to be certain about the identity a column (fig. 20). of such cells but the density of their We have described an intracellular cytoplasm and their general appearance position of the lymphocytes. This pheno- make it seem probable to us that they menon has seemed especially conspicuous are epithelial cells from the walls of the in our light microscope pictures of the crypts. Axolotl intestine. With the electron The study of the mesenchymal wander. microscope we can see details of the ing cells in the mouse and rat with lymphocytes within epithelial cytoplasm. electron microscopy and of their relation. The nuclei of such lymphocytes differ ship to the epithelial cells has furnished greatly in appearance, being in various some additional details. Problems oi stages of a degenerative process which cell identification at the high magni. itself may not always show the same 104 W. Andrew and N. V. Andrew
sequences. The cytoplasm of the we found additional evidence of the lymphocyte often has an almost chaotic entrance of lymphocytes into intestinal appearance. In some cases we have seen epithelial cells in the mouse and in the the loss of continuity of the cell Wistar Institute rat. In the earlier and membrane of the lymphocyte with a later studies we described a degeneration resulting continuity of lymphocyte and of some lymphocytes within the epithelial epithelial cytoplasm at a time when cytoplasm in the crypts of Lieberkuhn. chromatin condensation is far advanced In both of these studies the small intestine in the nucleus of the lymphocyte (fig. only was used. 21-23). An important feature of the An investigation of the lymphocyte- intracellular lymphocyte is its closeness epithelial relationships in the rabbit to the nucleus of the epithelial cell. appendix (Shimizu, Y. and W. Andrew, This conceivably could indicate an 1967) was of special interest in showing absorption of cytoplasmic or nuclear the occurrence of groups or "nests" of material of the degenerating lymphocyte lymphocytes which seemed to lie within by the epithelial nucleus. epithelial cells covering the lymphoid nodules of that organ. Intracellular Discussion bacteria also were found in that covering epithelium. The method of cell dissoci- The Questions of Position of Lympho- ation was useful in considering whether cytes and of the Degeneration of such lymphocytes and bacteria are actually Cells in the Epithelium within the epithelial cells and gave af- A conclusion of importance from this firmative evidence. comparative study of amphibian (Axolotl) Later, Nieuwenhuis (1971) described and mammalian (mouse and rat) intestine the intracellular lymphocytes of the is the similarity in these forms, widely rabbit appendix and spoke of the separated in the "biological scale", of the epithelial cells which contain them as relationship between mesencymal cells "nurse cells ." (lymphocytes) and epithelial cells. One Meader and Landers (1967) came to aspect of this relationship which has conclusions very different from ours. been a matter of considerable controversy They studied the duodenum and ileum is the question whether some of the in mice (Swiss Albino), rats "(Sprague- lymphocytes actually are located within Dawley), Syrian hamsters, and man (five the cytoplasm of epithelial cells. From autopsy cases and two biopsy cases). a study with light microscopy on the They describe their investigation as small intestine of C57 Black mice of ages consisting of "correlated electron and ranging from young adult (118 days) to light microscopic studies of the distribu- extreme senility (818 days) we reported tion, position, appearance, migration and that many lymphocytes in the crypts of fate of lymphosytes.. .." (p. 763). They Lieberkuhn are within the epithelial stress the predominantly basal position cells (Andrew, W. and N.V. Andrew, of lymphocytes in all of their material. 1957). Their presence appears to cause Averaging the three groups of (non- deformation of epithelial nuclei, the human) animals, they found that 97.6 per most common form being a partial cent of the total 54,700 lymphocytes invagination of the apical aspect of the were below the level of the epithelial epithelial nucleus. nuclei in the human material there was In a later study (Andrew, W., 1965b), 98.7 per cent of a total of 15,875 lympho- Karyorrhexis and Karyolysis of Mesenchymal Cells 105 cytes in that basal position. These data 7, 8, 9 and 10) and electron microscopy are of much interest when we compare (fig. 21). them with those from our quantitative Another error into which Meader and study on C57 Black mice. There, on the Landers have fallen is to deny the villi of the jejunum, we found that of presence of degenerative change in any 2912 lymphocytes, 81.7 per cent were in of the lymphocytes within intestinal the basal position, 15.3 on a level with epithelium, a very serious error indeed, the epithelial nuclei, and 3.7 per cent since this process, occurring in normal apical to them. While Meader and animals, almost certainly is of a funde- Landers do not distinguish the three mental significance in relation to their different levels at which lymphocytes in functional role, much of which is still the epithelium may be found, we would obscure. not consider their data as markedly The fact that lymphocytes and related different from ours for the small intestine. cells can enter into other cells of various Meader and Landers failed to make any types has been shown in several studies. study of the large intestine (colon). Ioachim and Furth (1964) found leukemic There we found in C57 Black mice the lymphocytes entering into the cytoplasm percentage of basally located lympho- of the reticular cells in thymic tissue cytes as only 57.1, while 32.5 per cent cultures and multiplying there. Furth were in the apical position, the remaining (1964) tells us that the intracellular lymphocytes (10.4 per cent) being at the position of lymphocytes has been con- same level as the epithelial nuclei. In firmed by cinematography and their our Axolotl material the numbers of entry into and exit from other types of lymphocytes in the apical position were cells have been demonstrated. Trowell conspicuous. (1958) accepted the idea of the occurrence Another important factor which seems of lymphocytes within cells of the to have led these authors astray is found intestinal epithelium in rat, cat, dog and in their statement (p. 796) : "Areas of frog and cited supporting evidence of the section in which lymphocytes were earlier workers. As early as 1956 atten- counted included only the epithelium of tion had been called to a type of bio- the villi since it was not always possible logical interaction between lymphocytes to distinguish lymphocytes from mitotic and other types of cells by Humble, stages of other cells in the epithelium of Jayne and Pulvertaft. It was seen by the crypts." The reason given for ex- them in serum-organ cultures of a cluding the crypts from their study, variety of tissues, both normal and while it may have some validity, does pathological. Their material included not excuse the failure to make and human bone marrow and lymph nodes, describe qualitative observations on the pleural and ascitic fluids, and primary lymphocytes in the crypts immediately and secondary malignant tumors of man ; underlying the villi which were studied. also bone marrow, exudates, and malig- Had they done so, it seems probable that nant tissue of the mouse. In these they would not have fallen into the cultures a "peculiar and hitherto undes- error of denying the intracellular position cribed relationship between lymphocytes of any of the lymphocytes in the and malignant cells, also cells in mitosis intestinal epithelium, which we have and megakaryocytes." (p. 293) was demonstrated in the present paper by observed. When lymphocytes come into both light microscopy (especially figs. 6, contact with other cells, probably through 106 W. Andrew and N. V. Andrew
random wandering, they move around and a settling into place. Certainly the the perimeter of such individual cells for mechanical effect of the lymphocyte on hours at a time, then attach themselves the nucleus of the host cell is similar to the cells, and finally, at least in to that described by Humble, et al. (see many of the cases, effect an entry. especially figs. 7, 8, 9, 10 and 21 of our Within the cell, the lymphocytes do not present paper). seem to degenerate but rather move Another important body of evidence about actively. For this reason, these on the ability of lymphocytes to enter authors have suggested that this the cell bodies of other cells and to be phenmenon be called "emperipolesis" completely enclosed by their cytoplasm (inside-round-about wandering). is seen in the study by Marchesi and What is the function of the lymphocytes Gowans (1964) on the emigration of these in this process ? Humble, et al. suggest cells from the lumen of venules. Gowans that the invaders are actually helpful to and Knight (1964) had shown that the invaded cells, whether they be radioactively-labelled small lymphocytes, malignant or otherwise, perhaps serving which were transfused into the blood of as a source of enzymes or general rats, migrated rapidly into the lymph metabolites, the lymphocytes carrying nodes by crossing the walls of the so- such products. Such activity could be called post-capillary venules. The mi- helpful, of course, at the cellular level, grating cells pass then into the medull- yet in the case of malignancies, harmful ary sinuses of the lymph nodes from to the organism. This study certainly which they are carried back into the shows the ability of lymphocytes to enter blood by way of the lymph vessels. into the cytoplasm of other cells. The The post-capillary venules are easily effect on the host cell is of interest recognized in the cortical region of the also from the standpoint of our obser- lymph nodes, for their endothelial cells vations on the frequent deformation of project into the lumen as irregular, epithelial nuclei by the presence of the finger-like structures. Cervical, mesente- lymphocyte. They say (p. 286) : "In many ric and popliteal nodes were studied. cases the lymphocytes appear to be The common manner of migration of actuallly inside cells, and present a most the lymphocytes consists of several steps : peculiar appearance when the accelerated first, their attachment to an endothelial film is projected. The nucleus of the cell ; second, their penetration into its investing cell is pressed to one side, and cytoplasm, so that they are intracellular the lymphocytes circulate for hours at a lymphocytes ; third, the protrusion of time, never leaving the confines of the pseudopods by the lymphocyte through invested cell's margin. Sometimes only the base of the endothelial cell ; and one lymphocyte is confined in a relatively fourth, penetration of the basement large space ; more frequently the whole membrane and of the periendothelial available space is filled by crowded, freely sheath by the lymphocyte, bringing it moving lymphocytes up to a dozen in out into the masses of lymphocytes number." outside of the post-capillary venule. While we would not wish to indicate Stages in this process are illustrated in that we believe that there is very much detail in the electron micrographs of "inside round -about wandering" in the these authors. There appears to be no intestinal epithelial cells, there must be damage either to lymphocyte or endo- an entry into them by the motile cells thelial cell during the process. In normal Karyorrhexis and Karyolysis of Mesenchymal Cells 107 lymph nodes it is only the small lympho- involves the change from an amoeboid cytes which are migrating. In inflamed flowing cell to a columnar, stable one. nodes polymorphonuclear leucocytes and In many instances the extension of the monocytes also migrate through the cytoplasm of the lymphocyte to the walls of the post-capillary venules, but lumen is initially in the form of a long, they pass between the endothelial cells. clear, more or less pointed process." We did not have a reference to the * * * * * work of Susumu Mori (1937) at the time We have felt it important to give of the writing of our 1957 paper, attention to these articles in the litera- although we had, with S.F. Patten, paid ture on the relation of lymphocytes to attention to the cell nests and their other types of cells for two reasons : (1) possible function in urodele amphibians the question of whether or not the (Patten, S. F. and W. Andrew, 1954). lymphocytes in the intestinal epithelium In the present study we have been at times occupy an intracellular position able to use epon embedded material to is closely related to the general potenti- obtain very well defined views of cells alities of this type of cell in its by both light and electron microscopy. widespread occurrence throughout the It is true, however, that even well fixed body and in its relations with many and stained sections of paraffin-embedded other types of cells, and :2 a number of material give good evidence of the other authors, including Meader and relationship between the lymphocytes Landers, have failed to consider these (mesenchymal cells) and the cells of the broader aspects and have made very epithelium and of transitional stages meager references to the important between the two types of cells. literature in the field. Of particular interest in the Axolotl The Question of the Probability of are the different appearances of the Differentiation of Lymphocytes in the mesenchymal cells (lymphocytes) within Intestinal Epithelium and its Relation the epithelial layer (figs. 1-4). Some of to the Broader Problem of "Specificity them are rounded, some are short ovoids, of the Germ Layers". and some are elongated, with sausage- In an early paper (Andrew, W. and shaped, dark nuclei parallel to those of N. V. Andrew, 1957), in which we were the epithelial cells. Study with high describing an involutionary change in power of the stained, epon-embedded the small intestine of the mouse in old material has been especially helpful in age, we made what may have seemed showing the interior of the nuclei of the to be a very bold statement concerning migrating cells (fig. 2). In sections the lymphocytes (p. 141): "The trans- prepared in this way there seems to be formation of lymphocytes to epithelial a continuous series of transitional stages cells on the viii is indicated by their from densely stained, often clearly taking up a position in which their lymphocytic nuclei up to those of nuclei are at the same level as those of epithelial type. These migrating cells the epithelial nuclei ; by the intercalation appear clearly to correspond to the "cell of their bodies snugly between those of units" (Zelleinheiten) of Mori (1937. He the epithelial cells ; by the enlargement describes the deeper-lying cells in Mega- of these bodies; and by the internal lobatrachus japonicus as having nuclei changes in the nuclei toward the lighter more rounded than those in the cores epithelial type. This transformation of the folds. We have found the majority 108 W. Andrew and N. V. Andrew
of the cells in the rather restricted in the intimacy of the tissues ?") "cores" to be a deeply staining , elongated To an observer who has seen over and type. These elongated cell enter the over again the lymphocytes intercalated epithelial layer as do many of the between epithelial cells with consequent rounded ones (figs. 1,3A and B, and 12 change in shape of those cells and their and 13). nuclei, and who has identified cells in In the intestine of the mouse the the same type of location and of topo- elongated, densely stained nuclei are graphical relation to the epithelial cells not as numerous or conspicuous, most of but appearing to be transitional between the mesenchymal cells showing more lymphocytes and epithelial cells, the field rounded nuclei. The elongated nuclei of shown in Figure 4 can mean only that mesenchymal type, however, are not we are looking at an epithelial cell entirely lacking from the epithelium newly differentiated from a mesenchymal (fig. 15A). It seems, indeed, that differ- cell (lymphocyte). entiation of such cells may proceed far * * * * * in the "epitheloid" direction while still retaining the spheroid shape of the In stating our conclusion that great nucleus (fig. 15B). numbers of cells in the mucous lining of The picture of the mesenchymal cells the intestine are transforming, or differ- and of their relationship to the epithelial entiating, from one type into another, cells, it should be emphasized, is a com- and this under normal conditions, we plicated one both in our amphibian and realize that we are placing ourselves in mammalian material. Yet it presents opposition to at least three concepts the same general phenomena in the two which have been very widely, although classes, including the migration, the not universally, considered as true and penetration of some mesenchymal cells important generalizations : (1) the method into the cytoplasm of epithelial cells, of replacement of cells of the intestinal and most important of all, evidence of epithelium is always by mitosis of pre- transformation of the one cell type existing epithelial cells ; (2) cells do not (mesodermal mesenchymal) into the other enter into the cytoplasm of other cells (endodermal epithelial). In this latter under normal conditions (the process of phenomenon it should be acknowledged fertilization would be, of course, an that we are relying upon our interpret- exception to this rule) ; and (3) cells of ation of the histological and cytological mesodermal origin do not give rise to appearances. We are describing a cells which are derived originally from dynamic process from observation of one of the other germ layers, endoderm what generally are considered "static" or ectoderm. We already have discussed images in histological sections. This the evidence for our negating of the first kind of procedure, however, it seems to two concepts. While both have been us, is still one upon which we must widely considered as valid, and while largely rely in our description of rela- evidence that they are not correct tions of cells within the tissues. As a generalizations has been rather sparse South American colleague, whose name until recently, we believe that the unfortunately is not +now available once literature which we have cited in this said after a discussion of certain in vitro paper and our own observations indicate processes : "Pero, que pase en la intimidad that neither of them can remain an de los tejidos ?" ("But what is occurring acceptable statement. Karyorrhexis and Karyolysis of Mesenchymal Cells 109
There remains, then, the question of of its companions ; and therefore all the germ layers and especially of the three, until each has reached a specific potentialities of the cells of the meso- level, work mutually together although dermal layer. There is general agree- destined for different ends." It was ment that the "germ layer" concept has Pander who first described the trilaminar been a useful one and has been of structure of the chick embryo in 1817. considerable importance in the descrip- In the above quotation he is pointing out tion of the complicated changes which the dependence of the layers upon one occur during development and of the another in the embryo. It appears to changing relationships between the parts us that the dependence of the tissues of the embryonic body. It is clear, of which are their derivatives in the adult course, that in the several systems of body is as great or greater and that the the body cells of diverse germ layer attempt to make a sharp division of origin are in close spatial and functional tissues solely on the basis of germ layer relationship to one another. It is true derivation may tend to prevent conside- also that cells of generally similar ration of observations and hypotheses morphological characteristics, such as which would act against the doctrine those belonging to simple cuboidal or (or dogma) of specificity. simple columnar epithelium, do not By the year 1884 the idea of the present any visible criteria as to the specificity of the germ layers had germ layer from which they have been attained considerable strength. Yet derived. While the concept that cells of K011iker raised major objections to it, a particular type, such as the columnar stressing the diverse types of tissues secreting and absorbing cells of endoder- and cells which can be derived from one mal origin must always be derived from germ layer, as from the ectoderm, which other cells of endodermal origin, has gives rise to nerve cells, neuroglia, long held sway, we may consider it as pigment epithelium of the eye, the a non-sequitur from the embryonic de- epidermis and even smooth muscle or its velopment of the gastro-intestinal tract. equivalent, as in the sweat glands. In other words, the chief objection to the Experimental studies, especially those idea of an origin of at least some of the on the embryos of the Axolotl, have intestinal epithelial cells from cells of given results which contradict the idea mesodermal origin rests on what we may of any rigid specificity. Mangold (1923) call a doctrine, or even a dogma, that found that presumptive ectoderm, when cells of a certain type and in a certain grafted into appropriate places, would location must always be derived from from somites, chorda, and pronephric cells of a particular one of the three structures, all of which ordinarily are germ layers and from such cells only. mesodermal derivatives. Later Bruns In this regard, it is interesting to see (1931) showed that if large defects were what an early worker, Christian Pander praduced in the ectodermal medullary (1817) says of the germ layers : "Actually plate, they could be repaired by mesoderm. there begins in each of these three Of special interest for the consider- layers a particular metamorphosis, and ations in the present paper are the each one strives to achieve its goal ; only finding in the chick by Hunt (1937a and each is not yet sufficiently independent b) that after removal of the presumptive by itself to produce that for which it is endoderm, the mesoderm can form gut . destined. Each one still needs the help Even nervous tissue can be formed 110 W. Andrew and N. V. Andrew
under certain conditions by mesoderm, 1961. as demonstrated for the fishes by Oppen- 2) Andrew, W.: Cells of the blood and heimer (1938). Oppenheimer (1940) also coelomic fluids of tunicates and echino- derms. Am., Zool. 2: 285-297, 1962. stresses the multipotentiality of the 3) Andrew, W.: Comparative Hematology. cells of the neural crest which form not Grune and Stratton (1965a.) pp. 180. only the spinal ganglia, the sheath of 4) Andrew, W.: Lymphocyte transfor- Schwann in peripheral nerves, melano- mation in epithelium. J. Nat. Cancer phores and xanthophores, but also Inst. 35: 113-137, 1965h. inesenchyme, the branchial skeleton and 5) Andrew, W.: DNA and mitochondrial probably the pia-arachnoid membranes. patterns of migrating and epithelial cells Oppenheimer (1940) summarizes the of intestine in Axolotl. Proc. fourth situation as of that date (p. 23) : "The in Congr. Histochem. and Cytochem. only conclusion that can be maintained, Kyoto : 219-220, 1972. as a result of all the experiments that 6) Andrew, W.: Origin and life history of have been enumerated, is that the plasma cells in the intestinal mucosa of the Axolotl, Ambystoma mexicanum, doctrine of the absolute specificity of the Proc. 10th Int. Congr. Anat. Tokyo, 380, germ layers as enunciated in the last 1975. century must be abandoned." Later 7) Andrew, W.: The Lymphocyte in studies (such as those of Gavin DeBeer, Evolution, New Light on its Role as a 1947) would strengthen this couclusion. Transforming Cell in Blood and Tissues. A recent article (Baxter, 1977) reviews New York. Pergamon Press, 1978. much of the early work on the problems 8) Andrew, W. and N.V. Andrew : An age of homology of the embryonic layers in involution in the small intestine of the the various groups of the invertebrates, mouse, with a description of the fund- which eventually led Edmund B. Wilson amental process of lymphoepithelial metamorphosis in intestinal mucosa. J. to a deep dissatisfaction with the germ Geront. 12: 136-149, 1957. layer theory. 9) Baxter, A.L. : E.B. Wilson's "Destruc- As with theories and attitudes in a tion" of the Germ-Layer Theory. Isis number of fields of science, the germ 68, No. 243: 363-374, 1977. layer theory has served as a basis for 10) Bruns, E.: Experimente fiber das Regu- many observations and descriptive studies lationsvermogen der Blastula von Triton which have contributed much to the taeniatus and Bombinator pachypus. field. It seems to us highly important, Arch. f. Entw. mech. 123: 682-718, however, that this theory, or doctrine, 1931. should not interfere with the acceptance 11) DeBeer, G.R. The differentiation of of observations such as those presented neural crest cells into visceral cartilages by Mori and extensively supported by and odontoblasts in Amblystoma, and a the present study. re-examination of the germ-layer theory. Proc. Roy. Soc., Ser. B. 134: 377-381, 1947. References 12) Furth, I.: Personal communication, 1965, 13) Freeman, J.A. : Fine structure of the 1) Andrew, W.: Phase microscope studies goblet cell mucous secretory process of living blood cells of the tunicates Anat. Rec. 144: 341-357, 1962. under normal and experimental con- 14) Gowans, J.L. and E.J. Knight : The routt ditions, with a description of a new type of re-circulation of the lymphocyte ir, of motile cell appendage. Quart. J. the rat. Proc. Roy. Soc., Series B, 159 Microsc. Science, 102, Part 1: 89-105, 257-282, 1964. Karyorrhexis and Karyolysis of Mesenchymal Cells 111
15) Humble, J.G., W.H. Jayne and R.J.V. 41 : 265-272, 1937. Pulvertaft : Biological interactions be- 25) Nieuwenhuis, P.: On the origin and fate tween lymphocytes and other cells. of immunologically competent cells. Brit. J. Hem. 2: 283-294, 1956. Wolters-Noordhoff Publishing Company 16) Hunt, T.E.: The development of gut Groningen, 161 pp., 1971. and its derivatives from the mesectoderm 26) Oppenheimer, J.M.: Potencies for differ- and mesentoderm of early chick blasto- entiation in the teleostean germ ring. derms. Anat. Rec. 68: 349-369, 1937a. J. Exp. Zool. 79: 185-212, 1938. 17) Hunt, T.E.: The origin of entodermal 27) Oppenheimer, J.M.: The non-specificity cells from the primitive streak of the of the germ-layers. Quart. Rev. Biol. chick embryo. Anat. Rec. 68: 449-459, 15:1-27, 1940. 1937b. 28) Pander, C.: Beitrage zur Entwicklungs- 18) Ioachim, H. and J. Furth : Intrareticular geschichte des Hiihnchens im Ei. Wurz- cell multiplication of leukemic lympho- burg, 1817. blasts in thymic tissue cultures. J. Nat. 29) Patten, S.F. and W. Andrew : Replace- Cancer Inst. 32 : 339-359, 1964. ment and differentiation of the intestinal 19) K011iker, A. von : Die embryonalen epithelium in the urodele. Anat. Rec. Keimblatter und die Gewebe. Zeit. wiss. 118: 338, 1954. Zool. 40 : 179-213, 1884. 30) Schmedtje, J.F. : Some histochemical 20) Mangold, 0.: Transplantationversuche characteristics of lymphoepithelial cells zur Frage der Spezifitat und der Bildung of the rabbit appendix. Anat. Rec. 151 : Keimblatter in der Entwicklung. Arch. 412-413, 1965. f. mikr. Anat. und Ent.-gesch. 100: 198- 31) Shimizu, Y. and W. Andrew : Studies 301, 1923. on the rabbit appendix. I. Lymphocyte- 21) Marchesi, V.T. and J.L. Gowans The epithelial relations and the transport of migration of lymphocytes through the bacteria from lumen to lymphoid nodule. endothelium of venules in lymph nodes ; J. Morph. 123: 231-250, 1967. an electron microscope study. Proc. 32) Smith, R.G. and H.M. Smith : An analy- Roy. Soc. London, Ser. B. 159: 283-290, sis of the literature on the viscera and 1963. lymphatic system of the Mexican Axolotl. 22) Meader, R.D. and D.F. Landers : Electron Bull. Phil. Herpet. Soc. 17: 36-46, 1969. and light microscope observations on 33) Trowell, 0.A. : The lymphocyte. Int. relationships between lymphocytes and Rev. Cytol. : 236-293, 1958. intestinal epithelium. Am. J. Anat. 121 : 34) Van Lennep, E.W. : The histology of 763-773, 1967. the mucosa of the small intestine of the 23) Mori, S.: Ueber die Entwicklung der long-nosed bandicoot (Marsupialia : Bechergelle. Nagasaki Igakkwai Zassi 14, Perameles nasuta Geoffroi) with special S. 54-72, S. 1229-1233, 1936. reference to intestinal secretion. Acta 24) Mori, S.: Ueber die Entwicklung der Anat. 50: 73-89, 1962. Becherzelle. Z. f. mikroskanat. Forsch. 112 W. Ancrew and N. V. Andrew
Explanation of Figures
Plate I
Fig. 1. Surface epithelium of small intestine of female Axolotl seven months of age. There are several migrating mesenchymal cells (lymphocytes). The apparent plasticity of the epithelial cell bodies and nuclei is seen here. Epon "thick section", 0.5 micrometer, toluidin blue stain. x 1000. 113
Plate I
W. Andrew and N. V. Andrew 114 W. Andrew and N. V. Andrew
Plate II
Fig. 2. Surface epithelium of small intestine of male Axolotl 20 months of age. Nuclei of several cells of migrating type are seen. The resemblance to the epithelial nuclei of the elongated nucleus on the right (1) is noteworthy. Epon thick section", 1,0 micrometer, toluidin blue stain. x 800. 115
Plate 11
W. Andrew and N. V. Andrew 116 W. Andrew and N. V. Andrew
Plate III
Fig. 3. A. A lymphocyte in the basal portion of the surface epithelium. It has caused a deformation of the epithelial cell to the right and of its nucleus. Large intestine of three year old female Axolotl. Epon section, 0.5 micrometer, toluidin blue stain. x 1500. B. Transitional cell in basal portion of the epithelium. The nucleus has more of the characteristics of those of the epithelium. The deforming effect on the adjoining epithelial cells again is seen. The cytoplasm is moderate in amount but more definitely stained than in 'A'. Preparation as for 'A'. x 1500. 117
Plate III
W. Andrew and N. V. Andrew 118 W. Andrew and N. V. Andrew
Plate IV
Fig. 4. A cell in the basal portion cf the epithelium which we believe to be a newly difier- entiated epithelial cell. Its topographical relation to the adjoining epithelial cells is similar to that of the lymphocyte in '3A' and the transitional cell in 'B'. Epon section, 0.5 micrometer, toluidin blue stain. x 1500. 119
Plate IV
W. Andrew and N. V. Andrew 120 W. Andrew and N. V. Andrew
Plate V
Fig. 5. Mucus-secreting cell in large intestine of male Axolotl 15 months of age. The dark elongated nucleus is in contrast to those of adjoining epithelial cells but similar to those of many "mesenchymal" cells in the subepithelial connective tissue. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. 121
Plate V
W. Andrew and N. V. Andrew 122 W. Andrew and N. V. Andrew
Plate VI
Fig. 6. Small intestine of male Axolotl 15 months of age. The cell of chief interest here has a dark, elongated nucleus lying somewhat below the level of the nuclei of the clearly epithelial cells. Its apical end contains mucus which is being poured out onto the surface of the "villus". Its most important feature, however, is the basal cytoplasm, which appears to be clearly in relation to subepithelial tissue, presenting the picture of a cell migrating into the epithelium to become a functional part of that epithelium. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. 123
Plate VI
W. Andrew and N. V. Andrew 124 W. Andrew and N. V. Andrew
Plate VII
Fig. 7. Large intestine of a 15 month male Axolotl. One of the cells of the surface epithelium shows an altered lymphocyte within its cytoplasm, contiguous to the nucleus. Lymphocyte cytoplasm is not seen and there has been some condensation of the chromatin. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. 125
Plate VII
W. Andrew and N. V. Andrew 126 W. Andrew and N. V. Andrew
Plate VIII
Fig. 8. Large intestine of a 15 month old male Axolotl. An altered lymphocyte., again contiguous to the epithelial nucleus, is seen. The cell, within a clear vacuole, shows a large cytoplasmic body but a pycnotic nucleus. Note also the apparent effects of pressure on the epithelial cell to the left. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. 127
Plate V111
W. Andrew and N. V. Andrew 128 W. Andrew and N. V. Andrew
Plate IX
Fig. 9. Large intestine of a 15 month old male Axolotl. Here the vacuole containing an altered lymphocyte is even larger than in "Fig. 7". Again, it seems directly contiguous to the epithelial nucleus. There is a moderate amount of lymphocyte cytoplasm. The lymphocyte nucleus is pycnotic and partially fragmented. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. 129
Plate IX
W. Andrew and N. V. Andrew 130 W. Andrew and N. V. Andrew
Plate X
Fig. 10. Another very large intracellular vacuole containing the remains of a lymphocyte. Here the deformation of the epithelial nucleus by the expanding vacuole is well seen. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. 131
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Plate XI
Fig. 11. Evidence of marked karyorrhexis and of karyolysis of lymphocytes in surface epithelial cells of a 15 month old male Axolotl. Paraffin, 5 micrometer section, hematoxylin and eosin stain. x 1000. A. Fragments of condensed chromatin of various sizes, still surrounded by the nuclear membrane. B. The membrane is no longer in evidence, and fragments of condensed chromatin lie freely in the epithelial cytoplasm. 133
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Plate XII
Fig. 12. Elongated cell of the "dark nucleus" type in cell nest of small intestine of a 14 month old female Axolotl. The massive blocks of chromatin show a conspicuous con- tinuity while the intervening karyoplasm contains prominent granules, many of which are coarse or in clusters. The dense chromatin shows a few clear spaces. Epon, thin section. x 9,600. 135
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Plate XIII
Fig. 13. Nuclei in small intestine, same animal as in "Fig. 12". These nuclei seem to have progressed in the process of "clearing". The dense chromatin masses are smaller and granules in the intervening karyoplasm seem smaller and more evenly distributed. Epon, thin section. x 5,760. 137
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Plate XIV
Fig. 14. The relation between individual lymphocytes and epithelial cells on the villi of the small intestine of the mouse. Hematoxylin and eosin stain. x 1995. A. Phenomenon of "pushing" of a lymphocyte against the nucleus of an epithelial cell, which has taken on a crescent shape. The lymphocyte nucleus is deeply stained. Young adult female. B. Another example of apparent "pushing" of an epithelial nucleus by a lymphocyta. Here, however, the lymphocyte nucleus has become clear, although still distinguishable in pattern from the epithelial nuclei. Young adult female. 139
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Plate XV
Fig. 15. Further aspects of individual cells on the villi. A. Three lymphocytes in the epithelium. The basally located one is somewhat rounded, the two higher ones are elongated, the one to the left, close to the epithelial nucleus, being club-shaped. Young adult male. B. A cell of large size, with smoothly rounded nucleus, which does not seem fully integrated into the epithelial layer. It seems to us probable that such cells, of which we have found a number of examples, represent mesenchymal cells (lymphocytes or former lymphocytes) far along the road of differentiation. Young adult female. 141
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Plate XVI
Fig. 16. Two mucus-secreting cells in a subepiThelial position on the villus of small intestine of the mouse. We interpret this unusual phenomenon as probably the result of a some what premature differentiation of mesenchymal cells before they have entered the epithelial layer. Young adult female. Hematoxylin and eosin stain. x 1995. 143
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Plate XVII
Fig. 17. Degenerative changes of lymphocytes in surface epithelium of mouse. Young adult male. Hematoxylin ane eosin stain. x 1995. A. Lymphocyte showing a cap of condensed chromatin at the apical side of its nucleus, which is just apical to an epithelial nucleus. Small intestine of mouse. B. Karyorrhexis of a lymphocyte. Two small fragments, eosinophilic in character, lie just above a larger one which shows a cap of condensed chromatin. 145
Plate XVII
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Plate XVIII
Fig. 18 Lymphocytes and their transformations in the crypts of Lieberkuhn of the mouse. Hematoxylin and eosin stain. x 1995. A. Crypt of Lieberkuhn of the colon of an adult mouse. A lymphocyte with small nucleolus-containing nucleus has entered the epithelial layer. Above it is a ring-shaped mitotic figure, which we interpret in the crypts as a prophase. B. Crypt of Lieberkuhn of the colon of an abult male mouse. Three lymphocytes are seen in vacuoles. While the size varies, the nuclei do not show nucleoli nor any well- defined chromatin masses and are in process of degeneration. The mitotic figure is of a type commonly seen in which there are chromatin bridges or what appears to be a delay in the clear separation of the chromosome groups of the daughter cells. 147
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Plate XIX
Fig. 19. A. Elimination of one surface epithelial cell. We feel that epithelial cells being "shed" can be distinguished readily from lymphocytes . The cytoplasm, while altered, seems clearly epithelial. Hemaloxylin and eosin stain. Colon of mouse. x 1995. B. Cast-off epithelial cell in the lumen of a crypt of the colon of an adult mouse. Such cells are seen not infrequently in our material and seem to indicate that loss of individual epithelial cells is occurring in the intestine even at the level of the crypts. Hematoxylin and eosin stain. x 1995. _ 149
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Plate XX
Fig. 20. Lymphocyte in the basal position, lying between epithelial cells in the duodenum of an adult (100 day) Wistar Albino rat. The cytoplasm of lymphocytes in this position generally is clear, showing a paucity of cell organs. A column of cytoplasm often extends upware toward the lumen, as in this case. x 21,600. 151
Plate XX
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Plate XXI
Fig. 21. Topographical view of a lymphocyte in the apical position, within an epithelial cell. Degenerative changes are seen in the lymphocyte. The chromatin is largely condensed in a peripheral position beneath the nuclear membrane. Cytoplasm of the lymphocyte is well seen near to the concave nucleus of the epithelial cell. The cell membrane of the lymphocyte seems to be breaking down, with discontinuities in several places. x 9,920. 153
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Plate XXII
Fig. 22. More detailed view of an intracellular lymphocyte. The paucity of cytoplasmic organelles is seen. Portions of Golgi apparatus of the epithelial cell (stacked lamellae) appear to be in close relation to the lymphocyte. x 16,800. 155
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Plate X XIII
Fig. 23. Highly magnified view of the portion of the lymphocyte resting in the concavity of the epithelial nucleus. Some groups of ribosomes are seen in the lymphocyte cytoplasm and ribosomes stud the surface of its nucleus in places. A mitochondrion can be made out in the lymphocyte cytoplasm at the far right, between two dense bodies. x 31,200. 157
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