Activation of macrophage CD8: Pharmacological studies of TNF and IL-1 betaproduction

Previously, we demonstrated that rat macrophages express CD8 and that Ab to CD8 stimulates NO production. We confirm that CDS is expressed by rat macr ophages and extend understanding of its functional significance. Activation of CD8 alpha (OX8 Ab) on alveolar macrophages stimulated mRNA expression f or TNF and IL-1 beta and promoted TNF and IL-1 beta secretion. Similarly, O X8 Ab (CD8 alpha) stimulated NR8383 cells to secrete TNF, IL-1 beta, and NO . Activation of CD8 beta (Ab 341) on alveolar macrophages increased mRNA ex pression for TNF and IL-1 beta and stimulated secretion of TNF, but not IL- 1 beta. Interestingly, anti-CD8 Abs did not stimulate IFN-gamma or PGE(2) p roduction, or phagocytosis by macrophages. OX8 (CD8 alpha)-induced TNF and IL-1 beta production by macrophages was blocked by inhibitors of protein ty rosine kinase(s), PP1, and genistein, but not by phosphatidylinositol-3 kin ase inhibitor, wortmannin. Moreover, OX8 stimulated protein tyrosine kinase activity in NR8383 cells. Further analysis of kinase dependence using anti sense to Syk kinase demonstrated that TNT, but not IL-1 beta, stimulation b y CD8 alpha is Syk dependent. By contrast, protein kinase C inhibitor Ro 31 -8220 had no effect on OX8-induced TNF production, whereas OX8-induced IL-1 beta production was blocked by Ro 31-8220, Thus, there are distinct signal ing mechanisms involved in CD8 alpha (OX8)-induced TNF and IL-1 beta produc tion. In summary, macrophages express CDS molecules that, when activated, s timulate TNF and IL-1 beta expression, probably through mechanisms that inc lude activation of Src and Syk kinases and protein kinase C. These findings identify a previously unknown pathway of macrophage activation likely to b e involved in host defense and inflammation.