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(wandering cells at rest; polyblasts; clasmatocytes), cells of reticular connective tissue in vertebrate animals and humans. Histiocytes are sharply contoured, with basophilic cytoplasm, in which there are often vacuoles and inclusions. The shape of the cell varies owing to its capacity for amoeboid movement. Histiocytes perform a protective function by trapping and digesting various foreign particles, including bacteria. In various types of irritations—for example, in inflammatory reactions—the histiocytes are activated and transformed into typical macrophages. Sometimes the cytoplasm of histiocytes forms short, rounded projections that break away from the body of the cell (clasmatosis). In embryos, histiocytes develop from the mesenchyme, and in the adult body they develop from undifferentiated cells of reticular connective tissue, reticular tissue, and certain kinds of blood cells—lymphocytes and monocytes.
E. S. KIRPICHNIKOVA