Natural killer cells from mice deficient in protein kinase C-theta have reduced production of interferon-gamma after stimulation with interleukin-12

Natural killer (NK) cells play a key role in immune responses to viruses, bacteria and parasites. NK cell effector mechanisms include interferon-gamma (IFNgamma) production and cytolysis of infected cells. Protein Kinase C theta (PKCtheta) is important for T cell activation, but is also expressed in NK cells.{09}Evidence is presented to support the hypothesis that PKCtheta is involved in regulation of NK cell effector mechanisms. NK cells from PKCtheta -/-and wild-type mice were enriched from splenocyte cultures by incubation with IL-15 for one week and then treated for 24 hours with IL-12 or IL-18, cytokine activators of NK cell IFNgamma production. IFNgamma protein was measured by ELISA or intracellular cytokine staining. Cytotoxicity of NK cells from PKCtheta-/- and wild-type mice was activated in vivo with poly I:C or in vitro with cytokines, and target cell specific killing measured by 51chromium release assay.; NK cell-enriched splenocytes from PKCtheta-/- animals produce significantly less IFNgamma in response to IL-12, but not in response to IL-18. In contrast, NK cell mediated cytotoxicity is unaffected by the absence of PKCtheta. T cells, which can also make IFNgamma, are not a source of the cytokine in these experiments, nor do they affect the ability of NK cells to produce IFNgamma. Additional studies explored the mechanism behind the reduced IFNgamma production by NK cells from PKCtheta -/- mice. No differences in spleen NK cell numbers or viability are detected in PKCtheta-/- mice as compared to wild-type. In response to IL-12, NK cells from PKCtheta-/- mice also exhibit normal expression of TGFbeta1, IL-12 receptor-beta 1 (IL-12Rbeta1), and signal transducer and activator of transcription 4 (STAT4) proteins. There is also normal IL-12-induced phosphorylation of STAT4. Phosphorylation of threonine 538 (T538) within the catalytic domain of PKCtheta is detectable in NK cells from wild-type mice, but not enhanced by IL-12. IFNgamma mRNA increases to a similar extent in NK cells from wild-type and PKCtheta-/- mice in response to IL-12. IFNgamma mRNA stability is unaffected by the absence of PKCtheta. These findings support a role for PKCtheta in the post-transcriptional regulation of IL-12-induced IFNgamma.