Induction of activated killer cells from human lymphocytes by medullasin (a serine protease in bone marrow cells)

Medullasin, a serine protease found in human bone marrow cells, has been shown to induce activated killer (AK) cells that lyse both natural killer (NK)-sensitive and -resistant cloned target cells from human lymphocytes. In addition to all the tested malignant cell lines, malignant cells obtained from all patients with acute myelocytic leukaemia, chronic lymphocytic leukaemia and lymphoblastic leukaemia were lysed by AK cells induced by medullasin. Maximum induction was achieved when lymphocytes were incubated at 37 degrees for 60 min in the presence of medullasin (20 micrograms/ml). The cytotoxicity of AK cells induced by medullasin treatment (200 micrograms/ml, 37 degrees for 60 min) was greater than that of lymphokine-activated killer (LAK) cells produced by 500 U/ml of interleukin-2 (IL-2). Cytokines such as IL-2 or interferon (IFN) are not considered to be involved in the medullasin induction of AK cells for the following reasons: (1) neither IL-2 nor IFN activity were detected in the supernatant of lymphocytes treated with medullasin; (2) the supernatant of lymphocytes treated with medullasin failed to induce AK cells; and (3) the presence of antibodies against IL-2 or IFN did not influence the effect of the protease. By employing monoclonal antibodies to the surface antigens of lymphocytes and a panning method using plastic dishes coated with anti-mouse IgG goat Fab', progenitor as well as effector cells were found to be CD16-positive cells.