Potentiation of natural killer activity of human lymphocytes by Staphylococcus aureus bacteria and its protein A

Cytotoxic activity of human lymphocytes against the myeloid cell line K-562 was augmented greatly by 24-h incubation with Staphylococcus aureus Cowan I bacteria (SpA CoI) and its protein A. This effect was not observed when these stimulants were added after preincubation, suggesting that this activity was different from so-called lectin-induced cellular cytotoxicity. Potentiation required at least 12 to 18 h incubation of lymphocytes with these stimulants. Macrophage depletion did not affect the potentiation by protein A or SpA coI, although the potentiation by poly I:C or OK-432, an immunopotentiator of Streptococcus pyogenes was completely reduced. Further cell separation procedures revealed that neither T cells nor FcR- cells, which showed little natural killer (NK) activity, were enhanced by protein A or SpA coI. On the other hand, (a) null cells which were obtained from nylon column (NC)-passed fraction by depleting T cells and surface membrane Ig-positive cells, and (b) FcR+ E- cells which were obtained from NC-passed fraction by depleting FcR- cells and T cells, showed marked NK activity by themselves and were further augmented by these stimulants. FcR+ E+ cells failed to show NK activity even if they were stimulated by these stimulants. Thus, it was found that protein A and SpA CoI, as well as human interferon, could stimulate NC-non-adherent, FcR+, E- NK cells and potentiate markedly their NK activity.