Production of factor(s) that render polymorphonuclear leukocytes cytostatic from spleen cells stimulated with a streptococcal preparation, OK-432.

We previously reported the augmentation of tumor cytotoxicity of polymorphonuclear leukocytes (PMN) by in vivo administration of a streptococcal preparation, OK-432 (S. Watabe et al., J. Natl. Cancer Inst., 72: 1365-1370, 1984). The present study was undertaken to elucidate the mechanisms of the phenomena. Mouse and rat spleen cells were stimulated in vitro with OK-432. The culture supernatants from the stimulated spleen cells (OK sup) contained factor(s) that rendered mouse and rat PMN cytostatic [neutrophil activating factor (NAF)]. The stimulation of spleen cells with a small dose of OK-432 (0.05 micrograms/ml) resulted in the production of maximum NAF, and NAF was produced soon (12 h) after OK-432 stimulation. NAF was partially inactivated with 60 degrees C 30-min treatment, and completely inactivated with 100 degrees C 10 min. NAF was sensitive to pH 2 treatment. The treatment of PMN with OK sup for 5 min at 37 degrees C was sufficient to induce cytostatic activity of PMN. That OK sup contained gamma-interferon and recombinant gamma-interferon showed NAF activity indicate that gamma-interferon is a NAF in OK sup.