AbstractThe effects of purified protein A from Staphylococcus aureus Cowan I strain on induction of lymphokine (IL-2) activated killer (LAK) activity were studied in normal as well as melanoma patient's lymphocyte. The coculture of peripheral blood mononuclear cells (PBMC) with various doses of protein A (0.001, 0.01 and 0.1μmlg/ml) and IL-2 (100 U/ml) for 4 days produced synergistic effect on the LAK cells mediated cytotoxicity. The potentiation of cytotoxicity and lytic ability of LAK cells against NK sensitive (K-562) and NK-resistant (M1 4) tumor cells were observed. Further there was potentiation of DNA synthesis in PBMC after 4 days culture. Similar results were found when PBMC from melanoma patients were cultured with PA and IL-2. The potentiation of LAK cell induction associated with its cytotoxic and lytic potential by low doses of IL-2/PA regiment may be helpful in the development of LAK immunotherapy of the cancer patients.