Characterization of mouse natural killer cell activating factor (NKAF) induced by OK-432: evidence for interferon- and interleukin 2-independent NK cell activation.

The bacterial immunopotentiator OK-432 induced natural killer cell activating factor (NKAF) from mouse spleen cells. OK-432-induced NKAF showed a single peak with an apparent mol. wt of 70 Kd by Sephadex G-100 chromatography and OK-432-induced interleukin 2 (IL-2) had the same mol. wt as NKAF. However, OK-432-induced interferon (IFN) showed molecular heterogeneity with two peaks at 90 Kd and 45 Kd. Further purification was achieved by Blue Sepharose affinity chromatography which copurified NKAF and IFN. The affinity-purified NKAF, however, was stable to heat (56 degrees C) and acid (pH 2) treatments. Moreover, anti-IFN failed to abolish NKAF activity and this activity was not absorbed by IL-2 dependent T cells. From isoelectric focusing analysis, a dissociation of NKAF and IFN was observed over the range of pI 6.5 to 8.0. Based on these results, KNAF appears to be a new kind of cytokine distinguishable from IFN and IL-2.