Comparison of the effects of interleukin-1 alpha, interleukin-1 beta and interferon-gamma-inducing factor on the production of interferon-gamma by natural killer

Interferon-gamma inducing factor (IGIF) is a recently identified cytokine which stimulates the production of interferon-gamma (IFN-gamma) by T cells and enhances natural killer (NK) cell cytolytic activity. Protein fold recognition, structure prediction and comparative modeling have revealed that IGIF is a member of the interleukin (IL)-1 cytokine family and has prompted the designation IL-1 gamma. Here we report functional similarities between members of the IL-1 family by comparing the effects of IL-alpha, IL-beta and IGIF on NK cell production of IFN-gamma. All three IL-I types enhanced NK cell production of IFN-gamma when induced by IL-2 or IL-12, although at high concentrations (>10 ng/ml), IGIF was five-to tenfold more potent than IL-1 alpha or IL-1 beta. This effect correlated with enhanced levels of mRNA for IFN-gamma when NK cells were stimulated with IGIF plus IL-12. In contrast to IL-12 and IL-2, the ability of IGIF to stimulate NK cell production of IFN-gamma was not increased by IL-1 alpha or IL-1 beta. The ability of IGIF to enhance IFN-gamma production was independent of the type I and type II IL-1 receptors or the IL-IR accessory protein. Together, these results identify IGIF as a potent stimulator of NK cell production of IFN-gamma and demonstrate that the effect of IGIF on Mt cell production of IFN-gamma is similar to that of IL-1 alpha and IL-1 beta but distinct from that of IL-12.