Studies of the enhancement of natural cytotoxicity by the streptococcal immunopotentiator OK432.

The immunopotentiator OK432, a product of Streptococcus pyogenes A3, enhanced the natural killer (NK) activity of unseparated human peripheral blood mononuclear cells (PBM) and separated, nonadherent lymphocytes (PBL) containing less than 0.5% contamination with monocytes. Following treatment with OK432, both unseparated and non-adherent cell preparations produced interferon (IFN) alpha and gamma and low levels of interleukin-2 (IL-2). However, in the presence of neutralising amounts of anti-IFN alpha and gamma antisera, the NK enhancing effect of OK432 was not fully inhibited. Filtered supernatants derived from OK432-treated PBM or PBL also enhanced the NK activity of fresh PBM. In this instance, in most experiments, the NK enhancing effect of supernatants (from non-adherent cells) was fully inhibited by anti-IFN antisera. However, in some experiments, enhancement of NK activity by anti-IFN antisera-treated supernatants was still found. It is suggested that the presence of IL-2 or, possibly, other as yet uncharacterized factors secreted following OK432 treatment, account for this residual enhancement of NK activity.