The phagocytosis of yeast cells by blood monocytes. Effects of therapeutic concentrations of Vinca alkaloids.

The role of cytoplasmic microtubules in the phagocytosis of yeast cells by blood monocytes was studied by means of therapeutic concentrations of the Vinca alkaloids vincristine, vinblastine, and vindesine. Phagocytosis was measured in a monolayer of glass-adherent monocytes fed with fluorescein-labelled yeast cells. Phagocytosis was composed of two sequential processes, yeast cell adherence to the monocyte and yeast cell engulfment by the monocyte. Monocyte phagocytosis was significantly inhibited by the Vinca alkaloids, mainly due to inhibition of engulfment but probably also due to inhibition of adherence. Since the Vinca alkaloids are microtubule antagonists it is reasonable to assume that monocyte phagocytosis, both adherence and engulfment, are partially microtubule-dependent processes. It is suggested that Vinca alkaloid inhibition of monocyte phagocytosis is of value in the treatment of type II-III autoimmune disorders, such as idiopathic thrombocytopenic purpura and autoimmune haemolytic anaemia.