| dc.description.abstract | IFNγ-induced protein 10 (IP-10), also known as CXCL10, is a chemokine that can be produced by a variety of immune and non-immune cells during an inflammatory condition, and is associated with several inflammatory disorders. Accumulating evidence indicates that IP-10 is secreted by macrophages in response to various pro-inflammatory mediators, including lipopolysaccharide（LPS）. The regulatory mechanism underlying the production of IP-10, however, remains unclear. Activation of cAMP signaling is known to have negatively modulatory effects on cytokine production in most inflammatory cells. Type 4 phosphodiesterases（PDE4）, the enzymes responsible for cAMP degradation, play a key role in regulation of cAMP concentration in inflammatory cells. Thus, in this study, we aimed to determine whether and how PDE4 is involved in regulation of IP-10 production in macrophages in response to LPS. By stimulation of Raw 264.7 and mouse peritoneal macrophages with LPS, we observed that the IP-10 release increased in a time- and dose-dependent manner, and the PDE4 inhibitor rolipram effectively suppressed the IP-10 release with the IC50 of approximately 0.2 μM and 0.02 μM, respectively. The inhibition of IP-10 by rolipram was also obtained at the transcriptional level. Additionally, the LPS-induced IP-10 release was does-dependently inhibited by the PKA activator 6-Bnz-cAMP, but less effectively by the Epac activator 8-pCPT-2’-O-Me-cAMP. Moreover, the rolipram-inhibited IP-10 release was partially reversed by the PKA inhibitor Rp-8-CPT-cAMPS. These results indicated that the effect of rolipram on the IP-10 response was primarily mediated by the PKA activation. Using PDE4-deficient peritoneal macrophages treated with LPS, we found that the release of IP-10 in PDE4B-/- macrophages, but not PDE4A-/- or PDE4D-/- macrophages, was significantly decreased, to the level similar to that in the PDE4B+/+ macrophages treated with rolipram. Moreover, rolipram did not further decrease the IP-10 release in PDE4B-/- macrophages. These results demonstrated that the effect of rolipram on the IP-10 release was mediated by inhibition of PDE4B activity. Using mouse splenic T cells in a chemotactic reaction, we found that the IP-10-induced migration of T cells was also attenuated by rolipram. Taken together, these findings demonstrate that PDE4B is essential in the LPS-stimulated IP-10 production in mouse macrophages, and by activation of cAMP/PKA signaling ablation or inhibition of PDE4B can downregulate the IP-10 response. | en_US |