Ultrastructural studies on erythropoiesis in the avian thymus

Abstract

Thymus lobes from three species of birds, Quelea quelea, Passer domesticus and Sturnus vulgaris, have been examined ultrastructurally. The component cell types are compared with their counterparts in mammalian thymus glands, and found to be similar. Greater differences between small, intermediate and enlarged lobes of one species than exist between species. Developing erythroid cells are present in most enlarging and some enlarged glands. They appear to be developing at the expense of lymphoid cells in some birds. The origin of these cells is discussed. Cells that are possible candidates for the production of some thymic hormones are also described.

Hemopoiesis in the Thymus

“…Granulocytes in the connective tissues of the septa and capsule are generally recorded as more mature, and may be cells entering or exiting the thymus. In many avian thymuses, mature eosinophils were found within vacuoles in or close to the necrotic center of Hassall's corpuscles (Kendall and Frazier, 1979). Associations of this nature were also observed in children (Bhatal and Campbell, 1965;Muller, 1977) and in rabbits (Westermann and Engelbert, 1969b).…”

“…In several wild bird species, thymic erythropoiesis is a regular occurrence, especially during breeding and moult (Kendall and Ward, 1974;Bacchus and Kendall, 1975;Kendall, 1975aKendall, , 1975bKendall, , 1979Ward and Kendall 1975;Kendall and Frazier, 1979;Fronfria et al, 1985). It has been most extensively studied in the red-billed quelea, Quelea quelea (Fig.…”

Influence of partial decerebration and hypophyseal allograft on differentiation of thymic epithelial cells in chick embryos: an ultrastructural study

“…Previous ultrastructural studies in birds have classified these cells as "undifferentiated" (Frazier 1973), "pale RECs of the cystic associated type" (Kendall and Frazier 1979) or "medullary epithelial cells without synthethizing activity" (Sugimoto et al 1977).…”

“…Cytological analysis revealed the existence of multiple cell types within the thymic epithelium of birds by means of histochemical, electron microscopical (Frazier 1973;Isler 1976;Sugimoto et al 1977;Kendall and Frazier 1979;Kendall 1980;Chan 1991Chan , 1994 and immunohistochemical studies Wilson et al 1992). It is generally accepted that the lymphoid, nervous and endocrine systems cooperate in the regulation of the immune microenvironment (Freeman 1971;Jankovic et al 1981;Blalock 1989;Marsh and Scanes 1994).…”

Ultrastructure of myoid cells in the chick thymus

“…Endocrine-like cells secrete polypeptide hormones (Hakanson et al, 1974) and their close association with the myoid cells suggests that their secretion can modulate the functional activity of the latter. In some tropical birds, linkages between myoid and chromaffin-like cells have been reported (Kendall and Frazier, 1979), but the reason for the difference in cell type is not apparent.…”