Myeloblasts

Myeloblasts, the maternal form of granulocytes. It bears various names: large lymphocyte of Ehrlich, myeloblast of Naegeli-Schridde-Mosse, basophilic myelocyte of Dominici, lymphoidocyte, leukoblast of Pappenheim, hemocytoblast of Ferrata, homogeneous mononuclear cell of Schleip, myelogonium according to Klein, hemogonia of Mollier, and lymphoid maternal cell of various authors. To this day, it is still debated whether M. belongs only to the myeloid series or is identical to the lymphoblast of the lymphoid series. M. is a large cell of 12-20 µ (macromyeloblast), but medium-sized forms are encountered, and in pathological conditions (leukemias), small forms (micromyeloblasts) are also found in significant numbers. The outline of the cell is properly round. The nucleus is mostly round, rarely oval or kidney-shaped, occupies the larger part of the cell, has an exceptionally delicate fine-grained structure of chromatin, and contains 2-3-6 small nucleoli. The protoplasm is strictly basophilic with various nuances in the degree of basophilia. As in other leukocytes, it is divided into the intensely staining spongoplasm and the paler paraplasm. When stained according to Pappenheim, a dust-like granulation is found in the protoplasm of M., and there is no special granulation. The reaction to oxidase is positive, but not always. Normally, myeloblasts are not found in peripheral blood. In acute leukemias, a pathological form of M. is found in the blood, the so-called "Rieder form", characterized by an irregular shape of the nucleus, which has numerous indentations and sometimes takes on such a grotesque form [see separate table (Vol. XV, pp. 515-516), Fig. 5], that it resembles the nucleus of a polynuclear cell or megakaryocyte (see Hematopoiesis). Lit.: Timofeevsky A. and Benevolenskaya S., Culture of myeloblasts in vitro, Zh. exp. biol. i med., 1927, No. 14.