In vitro augmentation of human natural killer (NK) cell activity by a streptococcal preparation OK-432 and its extracts, protein M and polysaccharides.

Effect of a streptococcal preparation OK-432 and its derivatives on the augmentation of human natural killer cell activity in vitro was examined. The strong augmentation was found by the OK-432 stimulation. Cell separation procedures revealed that cytotoxic activity augmented by the stimulant was considered to be mediated mainly by nonadherent, nonphagocytic, IgG-Fc receptor positive, non-T cells, i.e. NK cells. In addition, supernates cultured with OK-432 augmented NK activity, suggesting some kinds of soluble factors released in the supernates may be participating on the augmentation of human NK activity by OK-432.