The murine chemokine receptor CXCR4 is tightly regulated during T cell development and activation

We have characterized the murine homolog of the HIV-co-receptor CXCR4 durin g T cell development and activation. Our data demonstrate that this chemoki ne receptor, although highly conserved between human and mouse, is differen tly expressed and regulated in both species. Mitogenic activation resulted in an increase of surface CXCR4 on murine T cells within 2 days, whereas th e receptor was strongly down-regulated on human T cells during this period. Furthermore, intraperitoneal immunization of mice resulted in a strong inc rease of splenic and mesenteric cytotoxic T cells co-expressing CXCR4. It i s interesting that, on thymocytes, expression of CXCR4 is restricted to CD4 (+)CD8(+) cells. Stromal cell-derived factor-lau, a natural Ligand of CXCR4 , induced chemotaxis of thymocytes and Tvas found to counteract dexamethaso ne-induced apoptosis to a certain extent in these cells. Thus, our data sho w that expression of CXCR4 is tightly controlled on murine T cells and indi cate that this highly conserved chemokine receptor might serve different fu nctions in humans and mice.