Development of granulocytes and monocytes in adult rabbit bone marrow ultrastructural aspects

ABSTRACT

The hematopoietic tissue of bone marrow constitutes a heterogeneous family of indistinguishable pleuripotential stem cells; they subsequently pass through a series of developmental stages that are microscopically identifiable. The aim of the present work was to throw mor light on the development of blood granulocytes in the red bone marrow of adult rabbit using the electron microscope.in bone marrow, developing granulocytopoietic series appeared to be grouped into clusters. Among these cells, myeloblasts were characterized by a relatively large nucleus with fully granular chromatin. The cytoplasm contained much free eibosomes. During the prom yelocyte stage, Iry granules being to be formed, while the maturation sequence was evidenced by change in the nuclear configuration and size and by the appearance 2ry granules which later on dominated over the Iry type. In this study it was observed that the myelocytes nuclei were rounded or oval in shape. However, gradual elongation and indentation of the nucleus was the initial sign of maturation from myelocyte to metamyelocyte. After that, nucear remodeling continued forming the staff granulocyte, and later on constrictions appeared to segment the nucleus into two or more lobes and thus a muture segmented granulocyte was formed. A characteristic feature in eosinophilic granulocytes was their 2ry specific granules which contained electron dense crystals. Monoblasts had similarities with their mature forms, but the chromatin was homogeneously fine and granular and the cytoplasm was entirely devoid of granules, while promonocytes contained small clear vesicles. The maturation of the latter cell into monocyte was associated with development of lysosomal granules and an increase of condensed chromatin with a progressive decrease in the number of ribosomes