Enhancement of mouse natural killer cell activity by type II interferon.

It is likely that interferons are key molecules in the physiological regulation of natural killing (NK) activity. This assumption is based on the strong enhancing effect exerted by type I interferon on NK cells. The aim of this study was to examine whether type II interferon, released upon activation of T lymphocytes by a mitogen, had the same enhancing effect. Crude PHA-induced interferon was purified on affinity chromatography columns (Blue Sepharose), and the eluted fractions were tested in parallel for antiviral activity and for in vitro boosting effect on spleen cell natural cytotoxicity. We found that both activities were unseparable. Acid pretreatment of purified type II interferon, as well as addition of anti-type II interferon serum, greatly decreased the enhancement of the spleen cell cytotoxic response. Responder cells to type II interferon are NK cells (surface Ig-negative, Thy-1-negative, devoided of acid Fc receptors) as assessed by classical spleen cell fractionation procedures based on cell surface markers. Comparison between the dose-response curves obtained with type I and type II interferons suggest that both interferon preparations stimulate NK activity in a comparable manner. We could conclude that interferon molecules (type I as well as type II) display a positive immunoregulatory function on NK cells.