Gametocytogenesis of Leucocytozoon smithi.

Development of young gametocytes of Leucocytozoon smithi into morphologically mature forms was studied using electron microscopy. Gametocytogenesis began on day seven post inoculation when merozoites, released from ruptured hepatic schizonts, developed into gametocytes within mononuclear phagocytes or leukocytes (monocytes or lymphocytes). No gametocytes were observed in any erythrocytes or polymorphonuclear leukocytes. Two gametocyte forms, round and elongate, were observed. Immature round gametocytes occurred on days 7-10 post inoculation in the deep vasculature of liver, lung and spleen. Mature elongate gametocytes were observed beginning on day 12 post inoculation in both the deep tissue vasculature and peripheral circulation of the turkey host. Growth and elongation of the gametocyte resulted in distortion of the host cell and its nucleus. The host cell nucleus initially was elongated and displaced to one side or indented by the growing parasite. Eventually, the nucleus was laterally compressed or split into two or three fragments. The compressed host cell cytoplasm was displaced longitudinally and stretched over the parasite to form horn-like cytoplasmic extensions from each end. The potential role of microtubules in the elongation of the gametocyte and its host cell, and possibly in the indentation and splitting of the host cell nucleus, is discussed.