In vitro augmentation of natural killing activity by OK-432

OK-432, a streptococcal preparation, augmented the natural killing (NK) activity of peripheral blood lymphocytes of normal donors and cancer patients against both NK sensitive and resistant human target cells in vitro. The enhancement of NK activity was evident after 4 h pretreatment and maximum by 16-24 h. The manifestation of OK-432 induced augmentation required active cell metabolism, RNA and protein synthesis but no DNA synthesis of lymphocytes. The supernatants produced by OK-432 stimulated lymphocyte cultures had no enhancing substance nor interferon. Anti-interferon antibodies did not inhibit boosting activity of OK-432. Large granular lymphocytes were involved in both spontaneous and OK-432 induced cytotoxic activity. The proportion of lymphocytes conjugating to target cells was not changed by OK-432. These results suggest that OK-432 augments cytotoxic activity of large granular lymphocytes having ability to recognize target cells independent of interferon induction.