ACTA OTORHINOLARYNGOL ITAL 2003;23:98-101 Morphological study of development and functional activity of palatine tonsils in embryonic age Studio morfologico dello sviluppo e dell’attività funzionale delle tonsille palatine durante l’età embrionale G. NOUSSIOS, J. XANTHOPOULOS, T. ZARABOUKAS, V. VITAL, I. KONSTANTINIDIS Department of Otolaryngology Head and Neck Surgery, Hippokratio General Hospital, Thessaloniki, Greece Key words Parole chiave Palatine tonsils • Histology • Embryology • Lymphocytic Tonsilla palatina • Istologia • Embriologia • Tessuto lin- tissue fatico Summary Riassunto Palatine tonsils play an important role in the development La tonsilla palatina come tutti gli organi a struttura linforetico- of the immune system, being the first organ in the lymph lare esplica una funzione reattiva ed immunitaria nei confronti system which analyses and reacts to antigenic stimulation. dei complessi antigenici batterici e non batterici. In questo stu- In this study, the peritonsillar area of Waldeyer’s ring was dio sono state esaminate, attraverso preparati istologici ed im- investigated in 88 normal human embryos which were munoistochimici, le tonsille palatine di 88 embrioni umani sani examined histologically and immunohistochemically. The (4 embrioni per ogni settimana di sviluppo embrionale, dalla 14a progressive development of palatine tonsils during embry- alla 35a settimana), al fine di valutare lo sviluppo progressivo onic life is discussed. The first appearance of tonsils is in della tonsilla palatina nel corso della vita embrionale. Si è os- about the 14th-15th week followed by a parallel develop- servato che la tonsilla palatina inizia il suo sviluppo tra la 14a e ment of B- and T-cell regions which accounts for the high la 15a settimana di vita intrauterina, con uno sviluppo parallelo incidence of non mucosa-associated lymphoid tissue delle zone di T e B linfociti, il che giustifica l'elevata incidenza lymphomas among all tonsillar lymphomas and the higher di “non-tessuto linfoide mucosa-associato” linfomi tra le forme incidence of T-cell-lymphomas, in comparison to the linfoproliferative che interessano la tonsilla, e la più alta fre- mucosa-associated lymphoid tissue of the digestive system. quenza di linfomi a cellule T in confronto agli altri organi a The way in which the human body develops the palatine struttura linforeticolare annessi alle mucose. In seguito vengono tonsils quickly and prepares them to react to the first anti- discusse le modalità di sviluppo della tonsilla e le modalità di genic stimulation, are discussed. preparazione a rispondere agli stimoli antigenici. Introduction Patients and methods Palatine tonsils play an important role in the devel- This research was completed with the collection and opment of the immune system. Complete develop- systematic examination of 88 human embryos from ment of the tonsils is achieved after birth under the the 14th to 35th embryonic week. More specifically, 4 influence of antigens. The embryologic development embryos from every embryonic week. of palatine tonsils appears to be the same as that of Embryos were collected at the University Depart- the thymus gland. In the present investigation, 88 ment of Gynaecology Hippokratio General Hospital normal human embryos (4 embryos from each em- Thessaloniki, Greece. This procedure was performed bryonic week were studied). Multiple histological in accordance with the legal regulations for the col- sections were obtained and the study included also lection of human biological material, and with the immunohistochemical analyses. agreement of the parents and the Administration The progressive development of tonsils during em- Council of the Hospital. bryonic life are discussed and conclusions are drawn. The embryos collected were normal and intact and The purpose of this study was to show the way in referred to cases of abortion, premature birth, or de- which the human body develops the palatine tonsils tachment of the placenta. and how this knowledge can be used in managing re- Examination of the embryos was performed in the lated pathological conditions. Histopathology Laboratory of the Medical Faculty in the Aristotelian University of Thessaloniki, Greece. At the initial examination, all embryos with congen- ital abnormalities or syndrome were excluded. 98 MORPHOLOGICAL AND FUNCTIONAL STUDY OF TONSILS A total of 88 normal and intact embryos were, there- tures are the primary crypts of the embryonic pala- fore, available. At this stage, the head of each embryo tine tonsils. The primary lymph follicles often dis- was preserved in a 4% solution of formol for 48 h. play a central necrosis and are morphologically, sim- Removal of the tongue and the mandible was carried ilar in appearance to Hassall’s corpuscles in the thy- out in order to obtain histological sections from mus gland. Waldeyer’s area, and specifically from the palatine TH ND tonsils. 19 -22 WEEK All this material was embedded in paraffin cubes The crypts are becoming more complex and numer- from which thin section of 3-5 µ were cut and stained ous and the follicular- parafollicular areas are more in preparation for microscopic examination. visible. There is a progressive development of fibrot- The study was completed under the microscope using ic tissue and this tissue, under the pressure of lym- multiple histological sections stained by haema- phocytic growth, is becoming the primary tonsillar toxylin-eosin (H&E) which in the stain routinely em- capsule. ployed for specimens in the Histopathology Labora- RD TH tory. 23 -28 WEEK This examination revealed the progressive develop- The above areas are now clear. The well-organised ment of the epithelial and lymphoid tissue of the em- lymph follicles have a relation with the bottom of bryonic palatine tonsils. this crypt branches and the addition of fibrotic septu- Some sections studied immunohistochemically were la has, as a result, the primary functional tonsillar stained using the peroxidase-antiperoxidase (PAP) units (crypt – primary lymph follicle – parafollicular method. The purpose was to identify B-lymphocytes area). with the L26 marker, T-lymphocytes with the UCHL- 1 marker and epithelial cells with the epithelial mem- 29TH-35TH WEEK brane antigens (EMA) and keratin. There is a progressive development in the lympho- cytic tissue which is characterised by an increased population of lymphocytes in the primary follicles Results (B-zone) and parafollicular area (T-zone), with a syn- chronous development of reticulocytes in the above areas and post-capillary venules in the T-zone. An- TH TH 14 -15 WEEK other interesting observation is that, in embryonic In the area of palatine tonsils, the epithelium of the life, germinal centres, in tonsillar lymph follicles, are embryonic oropharynx is becoming thicker. This ep- never observed. ithelium forms invaginations inside the underlying mesenchymal cells with multiple branches at each end. Some of these are becoming independent ep- Results of immunohistochemical study ithelial “islands”. In some epithelial invaginations or islands, a central From the 14th week, lymphoid cells are positive to necrosis and the start of a canal formation can be lymphoid markers. The majority of positive cells to recognised. Parallel to the former procedure, marked infiltration of the epithelial and mesenchymal cells, by lymphoid cells, is observed. Another significant point is the appearance of post-capillary venules, at this stage. 16TH-17TH WEEK The development of lymphocytic tissue results in the formation of primary lymph follicles. At the same time, the appearance of primary T-cells is the first stage in the formation of the parafollicular areas. A progressive development of complex epithelial inva- givations can be found with formation of tubules and the appearance, in the above-mentioned structures, of primary Langerhan’s cells. 18TH WEEK Fig. 1. Early epithelial invaginations (solid or with The formation of tubules in the epithelial invagina- tubules) in the mesenchymal cells. The beginning of tonsil formation (14th embryonic week) (H&E x100). tions is completed and the above-mentioned struc- 99 G. NOUSSIOS ET AL. ithelial invaginations and crypts. In the majority of the above structures, there is a central canal forma- tion (tubules) with a parallel creation of independent epithelial islands, some with central necrosis, and others without which are similar to Hassall’s corpus- cles of the thymus gland 4. The mechanism of the canal formation, in the crypts, probably plays a role in the development of lympho- cytic tissue. It is possible that substances from the necrotic epithelial cells act as a local antigenic stim- ulation for the local development of immature lym- phoid cells. We agree with many scientists especially von Gan- decker 5 and Slipka 6 concerning the time of appear- Fig. 2. Embryonic palatine tonsil with multiple epithelial ance of the palatine tonsils (14th-15th week), and the invaginations. Canal formation with central necrosis is appearance within them of primary lymph follicles noted in some. Peripheral lymphocytic infiltration cre- th th ates the primary follicles (16th embryonic week) (H&E and parafollicular areas at about the 16 -17 week. 7 x40). We also agree with the more recent literature that germinal centres were never observed in the tonsillar lymph follicles. L-26 marker (marker of B-lymphocytes) were subep- After birth, tonsils are one of the first organs to ac- ithelial cells and cells positive to UCHL-1 marker cept external antigenic