Several studies have shown the ability of retinoids to modulate inflammatory response. CXCL16/SR-PSOX is a novel protein functioning as a chemokine and a scavenger receptor. We investigated effects of all-trans retinoic acid (atRA) on CXCL16/SR-PSOX expression in several cell types. Real-time PCR showed that atRA increased CXCL16/SR-PSOX mRNA expression in THP-1 and endothelial cells, which corresponded to increased release of CXCL16 protein from the cells, measured by ELISA. In THP-1 cells this effect was reduced by retinoic acid receptor (RAR) antagonist, which indicates receptor-mediated inhibition. RAR-α and RAR-γ agonists increased CXCL16 release, which suggests RAR-mediated effect of atRA, which is not selective for a particular RAR subtype. In smooth muscle cells, up-regulation of CXCL16 mRNA was observed only after 96 h of treatment, while protein expression did not change. These findings suggest that retinoid signaling might be a pathway modulating inflammatory response by regulating CXCL16 expression in a cell-specific manner.

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