Lymphocyte emperipolesis into autologous monocytes in leukocyte cultures exposed to mitogenic lectins

Lymphocyte-monocyte synergistic interaction in cooperative response to mitogens and antigens is well established. This paper describes a less known--antagonistic (effector-target)--lymphocyte-monocyte interaction that came into existence in a leukocyte culture after the commencement of cellular response to concanavalin A, phytohemagglutinin and Wistaria floribunda mitogen. An invasion of lymphocytes into monocytes and monocyte polykaryons has been found 24-48 h after exposure to mitogens. The invasion is not followed by lysosome fusion with lymphocyte-bearing vacuoles, but is associated with a sequential destruction of the vacuole wall, and eventual disintegration of some affected cells. The expression of pan-T-cell surface antigens, staining patterns for nonspecific esterase and acid phosphatase as well as ultrastructural features show that the lymphocytes entering into and those located within monocytes and polykaryons represent activated T-cells. The presence of developed Golgi complexes associated with coated and smooth vesicles, and lysosomal bodies with microvesicles, tubular arrays or dense cores suggest that these T-cells belong to subpopulations which possess cytolytic activities. The lymphocyte invasion is considered cytolytic emperipolesis directed towards some autologous cells of the mononuclear phagocyte series. Its extent depends upon the mitogen concentration, and density of cell population in the culture. It also shows individual variability. The relationship of cytolytic emperipolesis to phagocytosis, and its possible significance as a mechanism of cell-mediated elimination of undesirable cells is discussed.