Cyclic AMP suppresses interleukin‐5 synthesis by human helper T cells via the downregulation of the calcium mobilization pathway

To delineate the mechanism by which cyclic AMP (cAMP) suppresses interleukin (IL)‐5 synthesis, the effects of prostaglandin (PG) E 2 , forskolin, dibutyryl (db)‐cAMP and the Ca 2+ ionophore, ionomycin on cytokine synthesis, proliferation and CD25 expression of human T cells were investigated. Further studies were performed by measurement of the intracellular concentrations of cyclic AMP ([cAMP] i ) and Ca 2+ ([Ca 2+ ] i ) and by electrophoretic mobility shift analysis (EMSA). PGE 2 , forskolin and db‐cAMP suppressed IL‐5 production by human T cell line following T cell receptor (TCR)‐stimulation. PGE 2 suppressed TCR‐induced messenger RNA (mRNA) expression of IL‐2, IL‐4 and IL‐5, as well as proliferation and CD25 expression. Cyclic AMP‐mediated suppression of cytokine synthesis, proliferation and CD25 expression in human T cells were attenuated by ionomycin. [cAMP] i was increased by PGE 2 and forskolin. PGE 2 suppressed the TCR‐induced biphasic increase in [Ca 2+ ] i . EMSA revealed that four specific protein‐DNA binding complexes related to NF‐AT were detected at the IL‐5 promoter sequence located from −119 to −90 relative to the transcription initiation site. The slowest migrating complex induced by TCR stimulation was enhanced by PGE 2 and further upregulated by ionomycin. Another binding which did not compete with cold AP‐1 oligonucleotides, was constitutively present and was unaffected by PGE 2 but enhanced by ionomycin. The suppressive effect of cyclic AMP on human IL‐5 synthesis is mediated by interference with intracellular Ca 2+ mobilization but distinct from the NF‐AT‐related pathway.British Journal of Pharmacology (1999) 127 , 521–529; doi: 10.1038/sj.bjp.0702558