Ultrastructure of granulopoiesis in tunica propria of the bursa of fabricius

Abstract

Heterophilic and eosinophilic leukocyte series appear adjacent to blood vessels or surrounding the primordium of lymphoid follicles in the tunica propria at stages 38-45 (6) of chicken embryo bursa. Development of the heterophilic granulocytes promyelocytes are the largest of the heterophils (8~m diameter) and the first recognizable stage (fig. i). They have short, thick fingerlike cytoplasmic projections, an eccentric round nucleus with fine dense chromatin pattern, a small peripheral zone, central clumps of heterochromatin, and one or two nucleoli. Round and elongated mitochondria, free ribosomes and several cisternae of rough ER dilated to a variable degree can be seen. The juxtanuclear Golgi complex is surrounded by numerous medium dense vesicles. Spherical electron-dense granules (type I) of 0.1/~m diameter are present. Myelocytes are spherical cells of 7~m diameter (fig. 2) with an eccentric round and a slightly idented nucleus and more peripheral heterochromatin than in promyelocytes; one or two nucleoli were sometimes observed. Flattened cisternae of rough ER were arranged parallel to the cellular surface and free ribosomes were less numerous than in promyelocytes. Mitochondria were located in the cell periphery. A well developed Golgi complex surrounds the centrioles. Dense spherical and peripherally located (0.3-0.7~m of diameter) (type I), similar to those described in promyelocytes, and less dense spherical or oval granules (O.IXO.4~Im) of variable electron-density (type II) are distinguished.