Boshnakova, E.

Marinova, Tz.

English

Varna Medical University Press: Journals

IV. Experimental and Clinical Immunology ULTRASTRUCTURAL CHARACTERISTICS CF THYMOCYTE MICROENVIRONMENT E. Boshnakova, Tz. Marinova Key-words: thymocyte microenvironmenl — macrophages — special cells — granulocytes — labrocytcs It is accepted that non-lymph cells in thymus, so-called thymocyte microen-vironment are of great importance for Т-lymphocyte differentiation. Epithelial cells and macrophages play albasic role in this relation (11, 12). Data concerning the distribution, structure peculiarities and mechanisms of functioning of the cells of the thymocyte microenvironment are still scanty and even in some cases contradicting (6, 9, 12, 16). We have good reasons for enlarging our investigations on the ultrastructural characteristics of non-lymph cells in mice thymus cover­ing not only epithelial cells and macrophages but also special cells, plasmo-cytes, tissue basophils and granulocytes. Material and methods The study was carried out on 69 Swiss mice of both sexes at different ontoge­netic stages (13—14 days and 18—19 days old fetuses, new-born (12-hours after birth), 7 days, 14 days, 30 days, 40 days and 45 days; 3 months, 4 months, 7 months, 18 months and 24 months old animals). Thymus material of decapitated mice was processed according to the routine method for electron microscope study (3, 15). An electron microscope J E M 7 A was used for observation and electro-nogram taking. Results and discussion We observed the cells forming thymocyte microenvironment in thymus lo­bules of mice of any age groups studied. Some age and regional peculiarities cha­racterize the distribution and ultrastructure of certain kinds of these cells. Epithelial cells. Epithelial cells predominate amids non-lymph cells of thy­mus in close contact with lymphocytes. Epithelial cells are characterized with morphological heterogeneity (3). We reported in detail some kinds of close spa­tial relationships between epithelial cells and lymphocytes elsewhere (14) and data concerning the presence of morphological preconditions for direct influence of lymphocytes by epithelial cells in thymus cortex deserved a special attention. Macrophages. Ultrastructural peculiarities of macrophages in thymus cortex and medulla are in principle identical with those described in the same organ of other mammals (1, 3, 5, 7). These cells can be found in three thymus regions scat­tered singly amids thymocytes and epithelial cells. The wealth of primary and various kinds of secondary lysosomes as well as parts of phagocyted lymphocytes in macrophage gives evidence for the conclusion that macrophage functional activity in mice thymus consists mainly in phagocytosis of lymphocytes. 10 Scr ipta scientif ica medica ' л 146 Е. Boshnakova, Tz. Marinova Special cells. These cells as described by us (13) in thymus cortico-medullar transition region are mainly characteristic cf the early age (15 days old mice). The productive character of their cytoplasm with characteristic rocket-like gra­nules in it impresses deeply, indeed. Fig . 1. Spatial proximity between eosinophilic granulocyte and thymocyte in thymic lobule inside. Electron micrograph, Magn. X 10 000 Granulocytes. Granulocytes are observed in thymus of animals of any age groups studied. They are most frequently presented in sexually mature animals (3—4 months and 2 years old mice). Eosinophils predominate (fig. 1) together with neutrophil granulocytes while basophils are rarely seen. These cells are scat­tered amids lymphocytes and epithelial cells in three thymus regions. They are more frequently located in the cortex. Granulocytes are in the immediate spa­tial proximity of lymphocytes in their neighbourhood. There are no data about the presence of specialized contacts between both cell types. We observe granules and pieces of cytoplasm near to the cellular membrane (with intact or destroyed integrity) of neighbouring single eosinophils and neutrophil granulocytes. Tissue basophils (labrocytes). We observe tissue basophils in mice thymus of any age groups. Their permanent presence not only in connective-tissue septi but also in thymic stroma as well as their characteristic distribution mainly in the cortex allows us to consider them a component of thymocyte microenviron-ment. These basophils have a morphology which is typical of these cells (fig. 2). Their granules are with peculiarities which are characteristic of the species mouse (4), at a different degree of maturity, with non-equal size and content with dif­ferent electron density. We observe a relatively great number of tissue basophils in the thymus of fetuses (13—14 days) and of adult (2 years) old animals. These cells are in the immediate spatial proximity of lymphocytes in any cases. Plasmocytes. Single plasmocytes with typical morphology are seen in the thymus of any animals studied (fig. 3). Ultrastructural characteristics of thymocyte. 147 In concordance with other investigators' concepts concerning rat and guinea pig thymus (6, 9, 16) we assume that "thymocyte microenvironment" is a broader term and covers some cell types. In mice thymus elements of thymocyte microen-vironment are not only epithelial cells and macrophages but also some other ron micrograph, F ig . 3. Part of plasmocyte in thymic lobule cortex. Electron micrograph, Magn. X 5000 cells — special cells, labrocytes, granulocytes, and plasmocytes. The role of close spatial relationships between epithelial cells and lymphocytes in thymus cortex is emphasized by the data of other authors about the nature of TNC-phe-148 Е. Boshnakova, Tz. Marinova nomenon (8, 9, 17). It is presumed that lympho-epithelial complexes (TNC) have a key position in the mechanisms of intrathymic Т-lymphocyte differentiation (17). Concerning the interesting suggestions reported in the literature about the secretory function of macrophages and their participation in the process of re­gulation of lymphocyte differentiation through monokines (1, 4, 5) they require additional purposeful investigations of mice thymus. The data received by us about the morphological peculiarities of the special cells as well as some cytoche-mical data about them (6) confirm the concept of their participation in the syn­thesis of thymic humoral factors (THF) (7, 16). Probably, special cells realize their influence upon lymphocytes of the corresponding area through T H F (6) and their ascertaining as antigen-receptor cells (16). The features of eosinophils and neutrophil granulocytes observed by us do not demonstrate any differences as compared with the same cells of other mammals (1, 2, 4, 16). Granulocyte loca­lization and ultrastructural peculiarities in mice thymus insists to consider them an element of thymus microenvironment. The data obtained about thymus labro-cytes present an interest with a view to the peculiarities of mast-lymphocytic ro­settes observed in vitro (2) and Е. V. Gyuling's et al. (2) presumption that the immediate contact between labrocytes and thymocytes is a precondition for the influence of labrocytes on thymocytes even in cases when biologically active sub­stances containing in their granules are still not accumulated in the intercellular space. The data presented concerning plasmocytes are in concordance with the accepted view that these cells participate in thymocyte differentiation by means of immunoglobulins secreted by themselves (1). The outlined variety of cells of thymocyte microenvironment according to origin, kind and function depends on the age and regional affiliation thus enables to consider them a complex system of multidirectional and mutually related cell interactions, indeed (6, 16, 17). These interactions are probably based mainly on the immediate cellular contact in the cortex and on humoral factor release acting within the limits of the corresponding region — predominantly in the medulla and corticomedullar thymus transition zone. The interpreted peculiarities of thy­mocyte microenvironment in mice thymus are important for the understanding of the complex and still not enough clarified mechanism of intrathymic T-lym-phocyte differentiation (10, 16, 17). R E F E R E N C E S 1. А г е е в , А. К Гистопатология вилочковой железы человека. Л . , Медицина, 1973, 127 с. — 2. Г ю л л и н г, Э. В . , Л . А. Д я г о в с к а я. Уси. соер. виол., 88, 1979, № З, (6), 401—409. — З. М а р и н о в а, Ц. Ултраструктура на епителните клетки на тимуса . Канд. дис. Варна, 1982. — 4. С е р о в , В. В . , А. Б . Ш е х т е р . Соединительная ткань (функциональная морфология и общая патология). М., Медицина, 1981, 312 с. — 5. В е а -v a n , М. J . , P . J . F i n k. Immunol. Rev., 42, 1978, З—19. — 6. B r e l i n s k a , R . Fo­lia histochem. cijtochem., 19, 1981, No 3, 46—47. — 7. B u r n e t , F . M. Cell. Immunol., 30, 1977, 358—360. — 8. С s a b a, G . , I . Toro. Acta biol. Acad. Sci. Hung., 25, 1974, No 1 — 2, 131. — 9. D u i j v е s t i j n, A . M. , Е. C. H o e f s m i t . Cell Tissue Res., 218, 1981, 279—292. — 10. G a 1 1 i , S. J . , et a l . J . Cell Biol., 95, 1982, 435—444. — 11. G a 1 1 i 1 y , R . , N . S a v i о n. Immunology, 50, 1983, No 1, 139—148. — 12. J о r d a n, R . K- J . Ant., 132, 1981, No 3, 441. — 13. M a r i n o v a , T z . , E . B o s h n a k o v a . C. R . Acad, Sci. Bulg., 36, 1983, No 1, 141—143. — 14. M a r i n о v a, T z . , E . B o s h n a k o v a . Scr . Sc i . Med., 21 , 1984, 130—1ЗЗ. — 15. R е у n о 1 d s, E . S. J. Cell Biol., 17, 1963, 208. — 16. T o r б, I . , et a l . Acta Morphol. Acad. Sci. Hung., 28, 1980, No 4, 375. — 17. W e k e r -l e , H . , et a l . J . Experim. Mel., 151, 1980 925—944. Ultrastructural characteristics of thymocyte. 149 УЛЬТРАСТРУКТУРНАЯ ХАРАКТЕРИСТИКА ТИМОЦИТНОГО МИКРООКРУЖЕНИЯ Е. Бошнакова, Ц. Маринова Р Е З Ю М Е С помощью стандартного метода электронномикроскопического исследования прове­дена характеристика нелимфатлческих клеток вилочковой железы конвенциональных м ы ­шей различного возраста (от фегусов 13—14 дней до двухлетних животных). В дольках ж е ­лезы наблюдаются эпительные клетки, макрофаги, специальные клетки, гранулоциты, л а б -роциты, плазматические клетки. Установлены вэзрасгные и региональные особенности в распределении этих клеток среди лимфоцитов. Обсуждается роль описанных видов к л е ­ток как элементов тимоцитного микроокружения в вилочковой железе мышей, а т а к ж е и х роль в внутритимусной дифференциации Т-лимфоцитов. 

ULTRASTRUCTURAL CHARACTERISTICS CF THYMOCYTE MICROENVIRONMENT

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ULTRASTRUCTURAL CHARACTERISTICS CF THYMOCYTE MICROENVIRONMENT

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