Monocytes

MONOCYTES, non-granular leukocytes of the peripheral blood, normally occurring in the amount of 4-6-8% of all white blood cells. The name M. was given by Pappenheim, who united under this name large mononuclears and Ehrlich's transitional forms. Türk initially called them splenocytes, and later - large mononuclear leukocytes; Hell - leukocytoid lymphocytes. The M. is a large cell, 12-20 µm in size, with a centrally or eccentrically located nucleus. The latter is kidney-shaped, horseshoe-shaped, or less frequently, lobed, with numerous protrusions and depressions on the surface, and often, due to its indistinct structure, leaves the impression of a degenerative formation. The protoplasm of the M. is relatively wide, weakly basophilic, and contains delicate azurophilic granulation, often with small vacuoles. The perinuclear light zone is very weakly expressed, and more often completely absent. M. give a negative reaction to oxidase and only sometimes, when using stronger reagents, a dust-like positive reaction. Modern hematology believes that the term M. unites cells that are different in terms of their histogenesis, i.e., that M. is a collective concept that includes cells of bone marrow, splenic, lymphatic, and histogenous origin. However, recently, as a result of the use of the vital staining method, the view is strengthening regarding the origin of M. from the reticulo-endothelial system (i.e., that M. represents a cell of this system that has separated in a state of functional rest) and regarding the closeness of M. to macrophages of connective tissue. Aschoff calls M. blood macrophages (Blutmakrophagen) (see Wandering cells). Also included under M. is the endothelium of peripheral vessels that desquamates during various diseases (sepsis lenta, typhus, cholera). Cells of this kind (sometimes in the form of clusters) appear in large numbers after preliminary rubbing of the blood collection site (earlobe); they are larger than M., of irregular configuration with a shape of the nucleus unusual for M., sometimes with division figures and phagocytosed cells. They are called histiocytes, endothelial, endothelioid cells, macrophages. In some pathological conditions, young forms of leukocytes - leukoblasts, lymphoblasts - are difficult to distinguish from M. and are recognized and designated as atypical monocytes.