بحث اجنبي جميل

Fine structure of the thymus gland in ostrich (Struthio camelus L)
By
El-Zoghby, I.M.A and Attia, H.F
Histology & Cytology Dept. Faculty of Vet Med. Benha University
Summry
Fifteen samples of the ostrich thymus glands were used to show the histological, histochemical and fine structure of the thymus glands. H&E, Gomori method and Crossman’s trichrome; PAS and alcian blue stain were used for histological and histochemical demonstration respectively. The gland consisted of lobes of different size separated from each other by fine strands of connective tissues. These lobes surrounded by CT capsule of collagen and reticular CT fibers. Each lobe was divided by the septa into numerous thymic lobules. Each lobule was consisted of cortex (Darkly stained area) and medulla (Lightly stained area). The parenchyma mainly consisted of lymphocytes (Thymocytes) and epithelial-reticular cells which were few in the cortex and numerous in the medulla. Hassal’s corpuscles were located in the center of the thymic lobules. It was consisted of concentric epithelial-reticular hyaline cells which appeared in different stages of degeneration. The ultrastructure of the thymic lobules showed numerous thymocytes of different size and epithelial-reticular cells between them.
Introduction
The thymus has attracted much attention in the recent literature, due in large part to its role in the immunological response. This role appears to be mediated by secretions (Trainin, 1974), the thymus gland of the ostrich lay at the base of the neck (Bezuidenhout, 1986). The ostrich are used principally for the production of meat of high protein value and low cholesterol level. Furthermore ostrich are used for the production of hides and feather (Horbanczuk, Sales, Cleeda, Konecka, zinab and Kawaka 1998).
Numerous papers were dealed with the histological structure of the thymus in poultry as, Hodges,1974, Kendall,1980 , Hashimoto et al.,1982 , Crivellato, Nico, Battistig, Beltrami and Ribatti ,2005 and Karaca , Yörük and Uslu, 2006 . The fine structure was discussed by Kendall and Frazier, 1979 and Chan, 1995.
Papers dealing with the structure of the thymus gland of ostrich were found to be rare from the anatomical point of view Bezuidenhout, 1986 and Wagner , Kirberger and Groenewald, 2001. Where, those discussed the histological structure were rare. (Elewa, 2005).
The aim of the current study is to throw focus spots of light on the histological , histochemical and fine structure of the ostrich’s thymus gland
Materials & Methods
The thymus glands of 15 mature ostrich of both sex, their ages ranges from 6 months-2.5 years. The specimens were collected from different abattoirs, put in Susa fluid fixative, dehydrated in ascending grades of alcohols, cleared in xylene and embedded in paraffin then cut at 4-5 U.
The histological, histochemical and ultrastructure of the thymus glands were studied using different histological stains. Hematoxyline & Eosin for general character , Crossman’s trichrome for identification of collagen fibers and Silver impregnation technique for identification of reticular fibers and combination of PAS and alcian blue for identification of both acid and neutral mucopolysacharides. (Bancroft et al., 1994)
A very small pieces of 1x1x1 mm were fixed in 2.5% glutaraldehyde in 1M phosphate buffer (pH. 7.3) for 24 hours then post fixed in cold 1M phosphate buffered 1% osmium tetroxide (pH. 7.3) for 3 hours, rinsed in phosphate buffer for 30 minutes then dehydrated (Hayat,1986). Semi-thin sections were stain by Toluidine blue. Ultra thin sections were obtained and mounted on copper grids then stained with uranyl acetate and lead citrate (Reynolds,1965). For the TEM picture in ( Faculty of science , Ain shams University )using Sumy Electron Optics SEO at 25 Kv.
Results
The thymus glands of the ostrich were large lobulated and consisted of numerous lobes. The thymus lobes were covered by CT capsule mainly consisted of collagen and fine reticular fibers (Fig.1). CT septa extended from the capsule divided it into thymic lobules. These septa contained the thymic blood vessels (Fig.2). The CT capsule and the thymic septa was contained dispersed single muscle cells (Fig.3). The stroma of these lobules was consisted of fine collagen and reticular fibers and reticular cells.
The thymic lobules divided into two definite parts, the cortex which was dark in staining and located in the peripheral part of the thymic lobules, and the medulla which appeared light in staining and located in the core of the thymic lobules (Fig.4).
The cortex was studded by numerous small size lymphocytes (Thymocytes) with darkly stained basophilic centrally located nuclei and peripheral rim of cytoplasm and numerous lymphoblasts with vesicular, centrally located nuclei (Fig.5).
The medulla was appeared lightly stained in compared to the cortex due to it was occupied by the large size lymphocytes with centrally located nuclei and acidophilic cytoplasm. Epithelial-reticular cells were located between the lymphocytes. The epithelial reticular cells were numerous and characterized by distinct cell boundaries and faint basophilic cytoplasm and central to some what eccentric nuclei (Fig. 6). The small lymphocytes were few in comparison to that of the cortex.
The fine structure of the thymocytes consisted of large centrally located nuclei and condensed chromatin. Electron lucent non granular thin rim of cytoplasm (Fig.7).While the lymphoblasts were characterized by large nuclei with numerous islets of heterochromatin, nucleolus and fine granular cytoplasm (Fig..
Epithelial-reticular cells were located between the lymphocytes but they were few. They were large cells with eccentric nuclei and faint acidophilic cytoplasm. The epithelial-reticular cells were large cells with oval nuclei with prominent nucleolus and fine granular dust like cytoplasm (Fig. 7&11).
The cortex of the young immature ostrich thymic lobules was studded with numerous eosinophilic cells (granular leucocytes), with shiny granular acidophilic cytoplasm and basophilic nuclei (Fig. 9).
The epithelial reticular cells might be arranged in the form of corpuscula thymica (Hassal’s corpuscles) which consisted of degenerated epitleilal -reticular cells and lymphocytes. (Fig. 10). The epithelial-reticular cells gathered with the lymphocytes to form the Hassal’s corpuscle which was characterized by degenerated structurless, hyalinized center and peripheral concentric arranged epithelial-reticular cells ( Fig.11).
Few plasma and macrophage cells were located between the lymphocytes (Fig.12). Different stages of mitotic figures was noticed in the cellular elements of the thymus gland especially in the cortex .
The thymus gland of the adult ostrich was characterized by vacuolation in the cortex and the medulla, single and multiple vacuoles was located in the architecture of the thymic lobules ( Fig. 13and 14 and 15 ). Cellular degeneration was recorded in the lymphocytes and the epithelial-reticular cells. The epithelial reticular cells were collected together as double cells or group of cells which appeared homogenous light eosinophilic masses (Fig.16) . Large eosinophilic masses located in the medulla of the thymic lobules which appeared homogenous structurless, none nucleated (Fig.18).
The CT capsule and the CT septa were strong PAS positive reaction and the cellular elements of the cortex were moderate PAS positive reaction (Fig.17). While the cellular elements of the medulla were very faint PAS reaction except the large eosinophilic mass which appeared moderate PAS positive reaction.( Fig.18).
Discussion
The thymus gland is necessary for normal development and function of gonads and thyroid gland as well as body growth (Azab et al., 2004).
The thymus gland of the ostrich located at the base of the neck as lobulated oval structure ( Elewa, 2005 and Bezuidenhout, 1999). The thymus gland was covered by CT capsule from which septa extended into the architecture of the gland dividing it into numerous thymic lobules. This statement was clarified in the ostrich and fowls thymus gland (Elewa, 2005 and Hodges, 1974) respectively. The lobulation is prounounced in the ostrich and chicken than that of the guinea fowl ( Onyenanous et al., 1994).
The thymic lobules were divided into outer dark cortex and inner light medulla without any line of demarcation. The light and dark appearance due to the types of the lymphocytes colonized in the cortex (small and medium size lymphocytes) and in the medulla (few numbers, this finding was augmented by Kendall, 1981 and Mahmoud, 1987 in chicken and Elewa, 2005 in ostrich.
The epithelial-reticular cells were few in the cortex and numerous in the medulla, while the macrophage and the plasma cells were abundant in the cortex (Bradley and Grahame, 1960) than that of the medulla, while ( Thorbecke et al., 1957) noted that the plasma cells only present in the outer part of the medulla . This finding may explain the suggestion of the microphagic role of these cells to remove the residual structure of the cortical dead cells as in the chicken (Mahmoud, 1987).

Eosinophilic masses of different size were formed as change in the reticular cells which started as small vacuoles appeared spherical in shape and later on filled with various amount of homogenous eosinophilic substances were located in the medulla of the thymic lobules (Payne, 1971). These masses are somewhat considered as a step of Hassle’s corpuscle formation. (Oneynanous et al., 1994).
The typical structure was consisted of round-laminated cornified epithelial reticular cells with homogenous structurless mass center. The typical structure of the Hassle’s corpuscle was augmented by the findings of Elewa, 2005; Firth, 1977 and Mahmoud, 1987 in ostrich, fowl and chicken respectively.
The thymus gland has defense mechanism action via the produced T-lymphocytes (Nickel et al., 1977 and Adkins et al., 1987). The thymus-dependent development is represented morphologically by the small lymphocytes of the circulation and the white pulp type of development in the tissues. As in mammals, the thymus-dependent tissues of the chicken are basic to the ontogenesis of cellular immunity Copper et al., 1966 and Aviles-Trigueros and Quesada, 1995).
The involutions start in the thymus gland of the ostrich and characterized by vacuolation of the epithelial-reticular cells with degree of cellular degeneration and appearance of some fatty vacuoles in the gland parenchyma (Elewa, 2005; Hodges, 1974 and Mahmoud, 1987). The involution start at the sexual maturity and characterized by loss of the cortical substance leaving the medullary tissues with few lymphocytes Karakoz et al., 1976 and Eliwa, 2005).
References

Adkins,B; Muller,C; Okada,C.V; Reichert,R.A; Weissman,I.L and Spangrude,G.J (1987): Early events in T-cell maturation . Ann.Rev. Immunol.,5:325-365.

Aviles-Triguueros, M and Quesada, J.A (1995): Myelopoiesis in the thymus of the Sea Bass, Dicentraarchuslabrax L. Anat.Rec.,242:83-90.

Azab, M.E; Fathalla, S.I and Emara, S.A (2004): Effect of thymoectomy on some physiological aspect in Japanese quails (Coturnix, coturnix japonica ). Egypt.J.Basic Appl. Physiol., 3(1): 121-135.

Bancroft, J.D; Cook,H.C; Stirling, R.W and Turner,D.R( 1994): '' Manual of histological techniques and their diagnostic application' .2nd Ed.,Churchill Livingstone, Edinburgh, London, New York.

Bezuidenhout AJ. ( 1986): Anatomy of ostrich . In Deeming, D.C.(ed.): The ostrich biology, production and health. 1st Ed. CABI publishing , Wallingford, Oxon, pp.13-49.

Bezuidenhout AJ. ( 1999): The topography of the thoraco-abdominal viscera in the ostrich (Struthio camelus). Onderstepoort J Vet Res. 1986 Jun;53(2):111-117.
Bradley,O.C and Grahame,T (1960): The structure of the fowl.Oliver and Boyd, Edinburgh.
Chan AS (1995): Ultrastructure of myoid cells in the chick thymus. Br Poult Sci. 1995 May;36(2):197-203.
Cooper M D., RD. Peterson , MA South and R A. Good (1966): The functions of the thymus system and the bursa system in the chicken. Experimental Medicine, Vol 123, 75-102
Crivellato,E, B Nico, M Battistig, C A Beltrami, D Ribatti (2005): The thymus is a site of mast cell development in chicken embryos. Anat Embryol (Berl). 2005 Feb ;209 (3):243-249 .

Elewa,Y.H.A (2005): Some morphological studies on immunological organs in ostrich. M.V.Sc. Thesis. Fac. Of Vet. Med. Zagazig. Univ.
Firth, G.A (1977): The normal lymphatic system of the fowl.Vet.Bull.47:167-179.
Hashimoto Y, Kitagawa H, Kudo N, Sugimura M.(1982): Fine structural and immunohistochemical studies on the thymic cysts in ducks. Nippon Juigaku Zasshi. 1982 Aug;44(4):597-605.
Hayat, M. A. (1986):- Basic techniques for transmission electron microscopy. 1st Ed.Academic Press, Inc. Florida.

Hodges,R.D (1974): The histology of the fowl. Academic press. London., N.Y. Sanfrancisco.

Horbanczuk,J; Sale,J;Celeda, T; Konecka, A; Zinaba, G and Kawaka, P (1998): Cholesterol content and fatty acid composition of ostrich meat as influenced by subspecies. Meat Sci., (50): 385-388.

Karaca T, Yörük M, Uslu S.(2006): Age-related changes in the number of mast cells in the avian lymphoid organs. Anat Histol Embryol. 2006 Dec;35(6):375-379 .

Karakoz I, Hasek M, Kohoutová L. (1976): The role of bursa of Fabricius and thymus in antibody-mediated allograft rejection in ducks. Folia Biol (Praha). ;22(5):304-11.

Kendall, M.D. (1980): Avian thymus glands: A review. Dev. Comp. ImmunoL, 4 : 191-209.

Kendall, M.D. (1981): Cells of the thymus. In : The thymus gland, Kendall, M.D.(ed.), Academic Press, London, PP. 63-83.

Kendall, M.D. and Frazier, J.A. (1979): Ultrastructural studies on erythropoiesis in the avian thymus .1. Description of cell types. Cell Tissue Res., 199:37-61.

Mahmoud,M.H.M (1987): Some histological studies on the immune system of chickens. Ph.D . Thesis, Fac of Vet.Med, Cairo University.


Nickel.R; Schummer,A and Seiferle, E (1977): Anatomy of the domestic birds. 4th Ed. S.S. Verlag Paul Parey, Berlin, Hamburg.

Onyeanusi,B.I, J C Onyeanusi, A N Emma, C D Ezeokoli (1994): The thymus of the guinea fowl from the eighteenth day of incubation until maturity. Anat Histol Embryol. 1994 Dec ;23 (4):320-329

Payne, L.N(1971): the lymphoid system. In’’ Physiology and biochemistry of domestic fowl’’. 2nd Ed. Edited by Bell,D.J and Freeman, B.M. Academic press.London.PP.985-1037.

Reynolds, E. S. (1965): The use of lead citrate at high ph as an electron opaque in electron microscopy. J. Cell 26: 208-215.
Thorbecke , G.J; Gordor,H.A; Wostman, B.S ; Wagner, M and Reyniers, J.A (1957): Lymphoid tissue and serum gammaglobulins in young germ free chickens. J.Infect.Dis., 101:237-257.

Trainin, N. (1974). Thymic hormones and the immune response. Physiol. Rev. 54, 272-315.
Wagner WM, Kirberger RM, Groenewald HB.(2001): Radiographic anatomy of the thoraco-abdominal cavity of the ostrich (Struthio camelus). J S Afr Vet Assoc.Dec;72(4):203-8







التركيب الدقيق للغده التيموسيه في النعام
ايهاب محمود عبد العال الزغبي و حسام فؤاد عطيه
كليه الطب البيطري- جامعه بنها

لقد أجريت هذه الدراسه علي الغده التيموسيه لخمسه عشرنعام وكانت سليمه وخاليه من الامراض*
تم تجهيز العينات للميكروسكوب الاليكتروني النافذ والصبغ العام والخاص والهستوكيميائي
تتكون الغده التيموسيه من فصوص عديده محاطه بكبسوله من الالياف تخرج منها فواصل تقسم الغده الي فصيصيات صغيره
يتكون كل فصيص من قشره خارجيه داكنه اللون ونخاع داخلي داكن اللون
توجد خلايا طلائيه شبكيه قليله في القشره وكثيره في النخاع وهذه الخلايا تتجمع مع الخلايا البلعميه لتكون حويصلات هاسلس
الخلايا البلعميه الصغيره توجد بكثره في القشره وقليله في النخاع
الخلايا تتكسر في الغده التيموسيه ووجود بعض الفجوات واجسام غير مميزه كبيره الحجم في النخاع مما يدل علي ضمور الغده التيموسيه.


















List of figures
Fig.1: Photomicrograph of the thymic lobes showing the collagen fibers capsule ( C ) and the thymic lobules ( l).
Crossman’s trichrome…………………………………………………..X20
Fig.2: Photomicrograph of the thymic lobes showing the blood vessels in the septa (Bv) and the CT septa (s).
Crossman’s trichrome…………………………………………………..X10
Fig.3: Photomicrograph of the thymic lobes showing the dispersed muscle cells in the CT septa (m)
Crossman’s trichrome…………………………………………………..X40
Fig.4: Ostrich thymic lobules to identify the dark staining cortex (c ) and lightly staining medulla (M).
H&E……………………………………………………………………..X10
Fig.5: The thymic cortex at 1 years old ostrich showing the numerous thymocytes (L) and lymphoblasts (Lb) with few epithelial reticular cells in between ( r ).
H&E…………………………………………………………..………..X100
Fig.6: The ostrich thymus cortex showing the thymocytes (L), Epithelio-reticular cells (r). X……………………………………………...40
Fig.7: TEM photography of the thymus cortex showing the thymocytes (L), and reticular fibers (rf)X……………………………………….4000

Fig.8: TEM photography of the thymus cortex showing the lymphoblast (Lb), X………………………………………………………….6000

Fig.9: Photomicrograph of the 6 months ostrich thymus gland cortex showing numerous eosinophils ( e).
H&E……………………………………………………………………..X100

Fig.10: Ostrich thymic medulla showing typical Hassal’s corpuscle (h)
H&E…………………………………………..………………………..X100
Fig.11: TEM photography of the thymus medulla showing the typical Hassal’s corpuscle (h) with degenerated center and epithelial reticular cells ( r ). X………..………………………………….3000
Fig.12: Photomicrograph of the thymic cortex showing the plasma cells (p) and the thymocytes with different stages of mitotic figures (m).
H&E……………………………………………………………………..X100
Fig.13: Photomicrograph of the 2 years ostrich thymus gland cortex showing the involuted thymic cortex with different size single vacuoles (v).
H&E……………………………………………………………………..X40
Fig.14: Photomicrograph of the 2 years ostrich thymus gland medulla showing the involuted thymic medulla with grouped vacuoles (v).
H&E……………………………………………………………………..X40
Fig.15: TEM photography of the thymus medulla showing the vacuolation (v) and the collected epithelial reticular cells ( r ).X ………….5000
Fig.16: Photomicrograph of the thymus gland of mature ostrich showing collected epithelial reticular cells ( r)
H&E…………………………………………………………………..X100
Fig.17: Photomicrograph of the thymus gland cortex showing positive PAS in the capsule (**) and moderate PAS positive in the cortex thymocytes ( * ).Alcian blue-PAS combination…………….. X40

Fig.18: Photomicrograph of the thymus gland medulla showing positive PAS in the large eosinophilic mass (**) and very faint PAS reaction in the medulla thymocytes ( * ).Alcian blue-PAS combination… X40