Natural Killer Cells from Mice Deficient in Protein Kinase C-theta Have Reduced Production of Interferon-gamma After Stimulation with Interleukin-12

Résumé du livre

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