The different effects of recombinant human interferon-gamma and recombinant human interferon-beta on the activation of natural killer cells.

Highly purified recombinant human interferon-gamma produced by Escherichia coli (ReIFN-gamma) was examined for ability to stimulate natural killer (NK) cell cytotoxic activity and antibody-dependent cell-mediated cytotoxicity in human peripheral blood lymphocytes (PBLs) in comparison with natural human interferon-gamma (IFN-gamma) and with recombinant human interferon-beta produced by E. coli (ReIFN-beta). The activity of ReIFN-gamma to stimulate NK cell cytotoxicity was about 10 times greater than that of ReIFN-beta and similar to that of IFN-gamma when PBLs were pretreated with each interferon for 16 hr. The effects of ReIFN-gamma were completely neutralized by a rabbit anti-ReIFN-gamma antibody, but not by a rabbit anti-ReIFN-beta. ReIFN-gamma did not show any significant NK-enhancing effect when it was added directly to the killing phase of standard 51Cr-release assay for 4 hr, while ReIFN-beta showed a marked effect. The time course study showed that the NK-activating effect of ReIFN-gamma was not expressed until 2 hr after the start of incubation, while that of ReIFN-beta was expressed rapidly and sufficiently within 15 min. This kinetic difference between ReIFN-gamma and ReIFN-beta was confirmed by an experiment using the Ca2+-pulse method, in which the killing rate in the Ca2+-dependent stage of NK cytolysis was increased by ReIFN-gamma, but only after 6 hr of preincubation, while the effect by ReIFN-beta was expressed rapidly at 30 min. These findings suggest that ReIFN-gamma and ReIFN-beta may stimulate NK cell cytotoxicity through different intracellular events after they bind to their receptors on the surface of NK cells.