Background: Phosphodiesterase (PDE4) inhibitors prevent breakdown of cAMP and affect the increase in cellular levels of cAMP, which is known to regulate immune cell functions. Because IL-4 plays a causal role in the pathogenesis of allergic disorders, we were interested to study the modulatory mechanisms of a PDE4 inhibitor, rolipram, in IL-4-mediated signaling in T cells. Methods: Human peripheral T cells were stimulated with IL-4 in combination with rolipram, and RT-PCR was performed using primers specific for IL-5. To monitor activation of transcription factors, immunostaining was employed. Results: Rolipram or a cAMP-analogue, 8-Br-cAMP, significantly downregulated IL-4-induced expression of IL-5 mRNA. The rolipram-induced inhibition of IL-5 mRNA was mediated by activation of protein kinase A (PKA), because rolipram-downregulated mRNA expression of IL-5 was restored by PKA inhibitors. Immunostaining revealed that rolipram interfered with IL-4-induced nuclear translocation of activator protein (AP)-1 components. Conclusions: This is the first demonstration of suppression of IL-4 signaling by PDE4 inhibitors via prevention of nuclear translocation of AP-1.

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