Growth of malignant histiocytic cells induced by phorbol myristate acetate

Cells from the spleen of a patient with malignant histiocytosis were cultured in methyl cellulose with and without 100 ng/mL of phorbol myristate acetate (PMA). Colony growth occurred only with PMA; comparing surface marker studies of the cells before and after culture, it was evident that proliferation had occurred among the histiocytic cells as well as the lymphocytes. After exposure to PMA in organ culture for ten days, the histiocytes appeared to be differentiated and showed evidence of continuing phagocytosis by electron microscopy. This suggests that PMA is a mitogen for the histiocytes in this condition and maintains differentiation of the cells.