Potentiation of natural killer cell activity of human lymphocytes in vitro: the participation of interferon in stimulation with Staphylococcus aureus Cowan I bacteria but not with protein A.

In the previous paper we reported that human natural killer (NK) cell activity was augmented greatly by preincubation with Staphylococcus aureus Cowan I bacteria (SpA CoI) or its Protein A. We examined here whether the augmentation with these stimulants is ascribable to the direct activation of NK cells or mediated by some soluble factors produced by the stimulants. It was found that a significant amount of interferon (IFN) was produced by the SpA CoI-stimulation but not by the Protein A-stimulation, although the latter usually induced augmentation of NK-cell activity not less than SpA CoI-stimulation. IFN produced by SpA CoI was considered to belong to alpha-type IFN, because it was stable at pH 2.0 and could be neutralized effectively by anti-IFN alpha antibody. Kinetics of NK-cell activation by SpA CoI (but not by Protein A) were very similar to those by IFN alpha. Furthermore, augmentation of NK-cell activity with SpA CoI-stimulated supernatant was inhibited almost completely by diluted anti-IFN alpha antibody, whereas augmentation with Protein A-stimulated supernatant could not be abolished by the same treatment. It was, therefore, suggested that augmentation of NK-cell activity with SpA CoI might be ascribable in most part to the IFN induced, whereas Protein A can stimulated NK or T cells directly or soluble factors other than IFN might work as well.