Regulation of IL-15-stimulated TNF-alpha production by rolipram

Agents that increase intracellular cAMP have been shown to reduce joint inf lammation in experimental arthritis, presumably by lowering the release of proinflammatory cytokines, such as TNF-alpha. Recent studies suggest that, in joints of patients with rheumatoid arthritis, TNF-alpha release from mac rophages is triggered by their interaction with IL-15-stimulated T lymphocy tes, In this report, we analyze the effect of rolipram, a cAMP-specific pho sphodiesterase inhibitor, on TNF-alpha production in this experimental syst em. Cocultures of U937 cells with IL-15-stimulated T cells, but not control T cells, resulted in increased release of TNF-alpha. Pretreatment of T cel ls with rolipram or cAMP analogues inhibited the IL-15-stimulated increases in proliferation, expression of cell surface molecules CD69, ICAM-1, and L FA-1, and release of TNF-alpha from macrophages, Addition of PMA. to T cell s dramatically increased the expression of cell surface molecules, but had little or no effect on TNF-alpha release from either T cells or from cocult ures, suggesting that other surface molecules must also be involved in T ce ll/macrophage contact-mediated production of TNF-alpha, Addition of PMA syn ergistically increased the proliferation of IL-15-stimulated T cells and th e secretion of TNF-alpha from IL-15-stimulated T cell/macrophage cocultures , Rolipram and 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) blocked these increas es. Measurement of protein kinase A (PKA) activity and the use of inhibitor y cAMP analogues (RpCPT-cAMP) confirmed that rolipram worked by stimulating PKA, These data suggest that PKA-activating agents, such as rolipram, can block secretion of TNF-alpha from macrophages by inhibiting T cell activati on and expression of surface molecules.