REGULATION OF IL-17, IFN-γ AND IL-10 IN HUMAN CD8+T CELLS BY CYCLIC AMP-DEPENDENT SIGNAL TRANSDUCTION PATHWAY

In the present study, the expression of interleukin 17 (IL-17) by human CD8+T lymphocytes and its regulation following PKA activation was determined and compared with that of interferon γ (IFN-γ) and IL-10. IL-17 mRNA was highly expressed in human CD8+T lymphocytes at least at the same level than in CD4+T cells that were isolated from peripheral blood mononuclear cells (PBMC). Expression of IL-17 mRNA in CD8+T cell was induced by prior activation of PBMC for 18 h with Ca2+ionophore and phorbol myristate acetate (PMA). Furthermore, our results clearly showed that CD8+T cells are sensitive to elevation of cAMP and PKA activation pathway. Data demonstrated a significant inhibition of IL-17 as well as of IFN-γ mRNA expression in CD8+T cells isolated from activated PBMC cultured in the presence of either dibutyryl cAMP (db-cAMP) or PGE2. In contrast, IL-10 mRNA expression was strongly enhanced in the same experimental conditions. The differential expression of IL-10 and IFN-γ production in CD8+T cells was also observed at the protein level as it was measured by a double immunofluorescence technique and flow cytometry analysis. Taken together, these results provide evidence that human CD8+T cells are also the source of massive expression of IL-17, and that PKA plays a prominent role in the switch of CD8+T cells to a Th2 like profile and an inhibition of IL-17 expression, thus suggesting that the activation of cAMP signal transduction pathway may have consequences for the relative role of CD8+T cells in the immune and inflammatory process.