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Vol. 280 19 July 1979 193 monoclonal eliminates the possibility that These data lend support to the proposal their nonspecificity is apparent rather than that the immense polymorphism of the of real, and that the cells are really producing MHC antigens is due to the massive a very large number of different specific selective advantage of heterozygosity: if factors. the combination of one parent's MHC from Peter D. Moore A similar collection of hybridomas antigen and does not elicit a response, producing helper factors would be a great the other parent's may (indeed this has partitioning in is less well asset. The biochemical elucidation of been shown9). documented than among and this helper factors lags well behind that of However, this begs the question of why is not surprising, for the on which suppressors. There is now evidence for antigens that fail to elicit an immune plants depend are fewer and idiotype-bearing, antigen-specific factors response should survive in the . which could be referred to as partitioning which replace T help in the production The answer may lie in the of are generally more subtle than is the case of antibodies against phosphorylcholine selective recognition. It is now clear that with animals. This is probably why (M. Feldman, University College London) some combinations of MHC antigen and ecophysiologists have eagerly grasped the 10 and (T,G)-A--L (ref.6) but the relationship virus cross-react with alloantigens : it is thus opportunities presented by the gradual

of such specific factors to nonspecific highly likely that the combination of some exposition of the extent of the C4 and helper factors remains unclear. J.D. viral antigens with self antigens will cross­ crassulacean acid (CAM) Watson (University of California at react with other self antigens. Since any cell photosynthetic adaptations among plants. Irvine), for example, reported that T cell reacting strongly against self must be It is well established that both of these

growth factor(s) from supernatant of eliminated, it follows that cells reacting modifications to the basic C3 Calvin spleen cells treated with concanavalin A against certain combinations of self and photosynthetic system are associated with would act both as a nonspecific growth virus will sometimes be eliminated too. certain ecologically selective advantages in factor and as a nonspecific helper factor in While it is clear that to avoid conditions of high , high antibody production or the generation of autoimmune reactions T cells with high­ intensity and stress. This has led to cytotoxic T cells; but if microcultures of ten affinity receptors for self must be many investigations into the or so cells are expanded with the use of the eliminated, it has been suggested that biogeographical significance of the .growth factor, their supernatants are active receptors with weak affinity for self adaptations, mainly by mapping their only on some cells. This , which antigens are the basis for MHC restricted distributions on a continental scale (see is similar to that of Waldmann and recognition 11 • Tentative evidence in Nature 272,400; 1978). Information is now Lefkowitz 7 suggests that 'nonspecific' support of this theory was presented by H. accumulating concerning the ecological growth factors from concanavalin A Wigzell (Uppsala University), who has value of such adaptations in the local supernatants may be mixtures of antigen or used an anti-idiotypic serum raised against composition of plant . idiotype-specific factors; it remains to be immune T cells specific for an allogeneic To search for correlations between the seen whether such mixtures include a antigen to extract the T cell receptor for success of one particular type of genuinely nonspecific T factor. that antigen. He then labelled internally the photosynthetic system and an MHC restriction, which limits T cell allogeneic antigen, the self antigen of the , such as aridity or recognition of viral antigens to infected immune and a third-party antigen, and elevation, is not new. In 1974, Mooney, cells bearing the same MHC antigens, can ran them on Sepharose columns to which Troughton and (Carnegie Inst. Ybk. be seen as a special case of antigen the receptor was bound. Three labelled 73, 793; 1974) reported a survey they had specificity applied to T cells. It has now polypeptides from the third-party control conducted along the coastal strips of become clear that, like any other kind of passed straight through the ; two California and Chile, where the antigen recognition, MHC restricted chains from the cells of the immunising shifts from a Mediterranean to a recognition is subject to cross-reaction. strain were stopped; and one chain from type with decreasing latitude. They found Cross-reactions have been demonstrated the self strain was retarded. in both locations that increasing aridity was in in which allogeneic virus­ Wigzell interprets this as evidence not associated with an increasing proportion of infected cells are killed by cytotoxic cells only for weak binding of alloreactive CAM plants in the . Among C3 plants, depicted of alloreactivity by passage receptors to self, but also as evidence that there was a change from evergreen to

through the appropriate mouse strain different polypeptides are involved in the drought-deciduous forms, but C4 plants (J.R. Bennink, University of recognition of self MHC and allo- or viral were virtually absent from all stations. Philadelphia). The cross-reaction may not determinants. It is still a of disupte They explain this as a consequence of the be reciprocal: for example, b haplotype whether T cell receptors 'see' virus and low prevailing at the of cells may kill infected k haplotype targets MHC antigen as a complex, with only water availability. while k cells will not kill infected b targets 8• one receptor for both ('altered self), or More recent work in the cold winter The converse can also occur: certain whether they see the two antigens with of Utah by Caldwell, White, Moore combinations of haplotype and virus can different receptors ('dual recognition') 12• and Camp (Oeco/ogia, Berl. 29,275; 1977)

fail to elicit a cytotoxic response even when Attempts to resolve this question at a has also shown that such C4 as MHC restriction requirements are met. cellular level are all open to doubt: it is A triplex confertifolia fail to achieve many Much of the interest in such failures of probable that only can of the advantages normally associated with

recognition is of course due to their produce the answer, and Wigzell's the C 4 system when they commence growth possible bearing on susceptibility to disease experiment may be a first step. D in the cool of . They may, however, in man. A McMichael (Oxford University) still match the growth of their C 3 reported that lymphocytes of competitors and gain the advantage of a certain haplotypes will not show MHC­ 1Eichmann, K. Eur. J. lmmun. 5, 511 -51 7 (1975). longer growing as summer aridity 2Eichmann, K. & Rajewski, K. Eur. J. lmmun. 5, 661-666 restricted killing in association with g97S). sets in. It is difficult, therefore, to explain influenza virus antigens, whereas others Langman. R. Nature 177,517 (1979) . the lack of C species in the Californian and 4Ben-Nevia el al. Eur. J. lmmun. I, 797 (1978). 4 do. Similarly, S. Shaw (US National 5Taniguchi, M. el al. Nature (in the prc,s). Chilean coastal deserts. Institute of Health) reported that some ~Mozes, E. & Haimovich, J. Nature 171, 56-57 (1979). Eickmeier has now published the results HLA haplotypes elicit much stronger anti­ Lefkowitz, I. & Waldmann, H. 31,915 (1977). of a similar environmental gradient study 8Doherty, P. &Bennink, J .R. J. exp. Med. 149, 150-157 (1979). influenza cytotoxic responses than others. 9~haw, S. & Biddison, W.E. J. exp. Med. 149, 565-575 (1979) from Texas (Photosynthetica 12, 290; 1 Finbcrg, R. Burakoff, S.J. Cantor, H . & Benacerraf,, B. ffoc. natn. A cad. Sci. U.S.A. 75, 5145-5149 (1978). Peter D. Moore is a Senior Lecturer in the Miranda Robertson is an Associate Editor of Janeway, C.A. Wigzcll, H. & Binz, H. Scand. J. /mmun. 5, Department of Plant Sciences, King's College, Nature. 993-1001 (1976). London.

0028-0836/ 79/290193-02$01.00 (S'=::: Macrnillan Journals Ltd 1979 194 Nature Vol. 280 19 July 1979

1978). Of 88 non-herbaceous species found capacity to withstand water stress. the molecular level, in the functioning of the peptides and nucleic acids of which along a 1,300-m elevation gradient, 22 were The greater competitive success of C3 are made. B. Fields (Harvard CAM, three were C4 and the remaining 63 species in higher altitude, more mesic • has now been Medical School) gave an example of what were C3 Ten samples were taken at 150-m conditions in the tropics altitude intervals; density, frequency and demonstrated by Tieszen, Senyimba, can be done, when he described his study of area cover values were used to determine an lmbamba and Troughton (Oecologia, two pairs of , represented by the importance value for each species at each Berl. 37, 337; 1979) along an altitudinal RN As S 1and M2 of reoviruses types I and elevation. The main peak in the importance and moisture gradient in Kenya. They have 3. He studied parent viruses and a of CAM species was found to occur at low found that nearly all the grass species of the collection of recombinants (or reassortants) and showed that S1 nucleic altitude, that of C3 species at higher low altitude grasslands in Kenya are of a C3 Some grass tribes, acid specifies the haemagglutinin altitudes and the C 4 peak was intermediate photosynthetic type. between the other two. Eickmeier such as Paniceae and Andropogoneae of the virus and that this is responsible for ) the ability to agglutinate cells and for considers this sequence to reflect both the (both exclusively C4 were most frequently adaptational significance of the encountered at intermediate altitudes. The serological specifity. It is also responsible for cell tropism in the , so that the physiological variations and also the exclusively C3 tribes (such as Festuceae, respective responses to biotic, competitive A veneae and Agrostideae) were found only type 3 virus causes a necrotising factors. For example, the CAM plants are at high altitude. No Ci species were found encephalitis due to a specific attack on the most suited to the low altitude, arid below an altitude of 2,000 m and no C4 neurones. It also determines the extent to environment, where competitive interplay species above 3,000 m. which the virus inhibits DNA synthesis with other plant species may be regarded as Evidently the complex adaptational when absorbed to cells. M2 RNA on the , C and CAM other hand, which is abundant on the minimal (but see Nature op. cit). C3 plants, significance of · C 3 4 he claims are evolutionarily attuned to photosynthetic systems is profoundly surface of the virus determines competitive situations with low abiotic influential on the floristic composition of whether the virus resists inactivation by both, having plant communities both on a chymotrypsin. M2 RNA from type 3 makes stress; C 4 plants can cope with potentially high and the biogeographic and an ecological scale. the virus resistant to and hence able to infect when given by mouth. Discussion of this work showed that the next step was to determine at which site on Viral pathogenesis and the surface of the neurone the virus attached. This is probably a part of the from D.A.J. Tyrrell chemical which has some other physiological characteristic of IT is easy to say ''The influenza virus causes however, survive and migrate up to cover neurones. Reassortants were also made influenza", while having really no the villi again, but while they are doing this which were infectious when given by scientific explanation of many of the signs and differentiating into mature mouth, like type 1, and caused central and symptoms of the disease, for instance enterocytes, there are profound nervous system disease, like type 3, and so, the headache or the depressed white blood physiological disturbances - lack of by the oral route, were more pathogenic cell count. This meeting• would have jolted absorption, excess , lack of than either parent. This type of anyone out of such a complacent view and digestive function (for instance the manipulation confirms earlier conclusions also gave some good examples of how splitting of lactose by disaccharidase) - about the functions of the genes. patient, thoughtful research is building a leading to marked diarrhoea, which can kill It is very difficult to evaluate the way in more complete picture of what happens in a piglet from dehydration unless it is which the host defences interact with the some virus infections - how the virus enters treated. On the other hand, another pig virus, sometimes preventing its and spreads through the body, enters cells, coronavirus causes vomiting and wasting multiplication, sometimes causing disturbs their function, interacts with the disease. M. Pensaert and K.L. Andries immunological damage to infected . host defence mechanisms (such as (State University of Ghent) described how For instance, P.A. Neighbour and B.R. interferon or humoral or cellular this virus affects the upper respiratory tract Bloom (Albert Einstein College of immunity) and disturbs normal body and Jung, the tonsil and the jejunum; it Medicine, New York) described some of functions to produce what we recognise as affects the cells of the plexus of Auerbach their work which started when they a clinical disease. and Meissner in the gut and seems to spread analysed why the lymphocytes of patients What seem in the laboratory to be very from them. It spreads through the nervous with multiple sclerosis show an unusual similar viruses may nevertheless produce system to the brain stem and later to the reactivity to measles virus; they tracked either different diseases or similar diseases spinal cord and the rest of the brain. All down the fault to a defect in the ability of by different methods. There was for this was established in great detail by their lymphocytes to produce type I instance a session on coronaviruses, which painstaking serial virus assay and immuno­ interferon (Neighbour & Bloom Proc. all look the same and are similar in fluorescent microscopy of experimentally natn. Acad. Sci. U.S.A. 76,476; 1979). biochemical composition. Yet the different infected animals. This suggests how the The success of the meeting was obvious, coronaviruses are specific to particular disease develops - probably the virus and there were many other interesting species - mouse coronaviruses never seem spreads from the respiratory tract and gut papers besides those mentioned here, to affect man or vice versa, for example - along peripheral nerves to the brain stem including whole sessions on herpes viruses and sometimes even to a very limited where the lesions give rise to vomiting, and rhabdoviruses. There were clear signs variety of cells in one species. P.A. while the damage to neurones in the that pathogenesis not only holds scientific Bachmann ( Health , plexuses prevents normal peristalsis, interest, but may be a source of practically Munich) described how the coronavirus of leading to wasting. Furthermore, knowing useful knowledge: vaccines and antiviral transmissible gastroenteritis of pigs (TOE) that the virus invades the nervous system treatments do not always work - sometimes affects only the differentiated enterocytes widely, it is not surprising that a virtually because we guess too much and know too of the villi of the small intestine which may identical virus has been recovered from little about the process by which viruses almost disappear. The crypt cells, pigs diagnosed as having encephalitis, and produce disease. 0 so was named haemagglutinating encephalitis virus. *A symposium on Mechanisms of Viral Pathoacncsis and D.A.J. Tyrrell is in the Division of Virulence was held in Munich on 6 and 7 June, 1979 and Explanations of these important and Communicable Diseases, Clinical Research organised by P.A. Bachmann. mysterious tropisms of viruses must lie at Centre, Harrow.

© Macmillan Journals Ltd 1979