Chemokine stromal derived factor 1 (SDF-1) is involved in trafficking of hematopoietic stem cells (HSCs) from the bone marrow (BM) to peripheral blood (PB) and has been found to enhance postischemia angiogenesis. This study was aimed at investigating whether SDF-1 plays a role in differentiation of BM-derived c-kit ؉ stem cells into endothelial progenitor cells (EPCs) and in ischemia-induced trafficking of stem cells from PB to ischemic tissues. We found that SDF-1 enhanced EPC number by promoting ␣ 2 , ␣ 4 , and ␣ 5 integrinmediated adhesion to fibronectin and collagen I. EPC differentiation was reduced in mitogen-stimulated c-kit ؉ cells, while cytokine withdrawal or the overexpression of the cyclin-dependent kinase (CDK) inhibitor p16 INK4 restored such differentiation, suggesting a link between control of cell cycle and EPC differentiation. We also analyzed the time course of SDF-1 expression in a mouse model of hind-limb ischemia. Shortly after femoral artery dissection, plasma SDF-1 levels were up-regulated, while SDF-1 expression in the bone marrow was down-regulated in a timely fashion with the increase in the percentage of PB progenitor cells. An increase in ischemic tissue expression of SDF-1 at RNA and protein level was also observed. Finally, using an in vivo assay such as injection of matrigel plugs, we found that SDF IntroductionIt has been shown that endothelial progenitor cells (EPCs) play a role in vascular repair following ischemic injury. 1 EPCs give rise to endothelial-like cells in culture, growing as spindleshaped cells attaching to culture dishes coated with extracellular matrix (ECM) components. 2 However, the mechanisms driving EPC differentiation are largely unknown. Stromal-derived factor 1 (SDF-1) regulates adhesion/chemotaxis of bone marrow hematopoietic progenitor cells through activation/regulation of specific integrin molecules. [3][4][5] This factor is, therefore, suggested to play a major role in successful hematopoietic stem cell (HSC) engraftment in the bone marrow. 6 In vivo gene inactivation of SDF-1 and its receptor C-X-C chemokine receptor 4 in mice led to early embryonic lethality due to abnormal cerebellar, gastrointestinal vasculature, and hematopoiesis development. [7][8][9] A role for SDF-1 in HSC/EPC recruitment from bone marrow (BM) to peripheral blood (PB) has been proposed, based on the evidence that granulocyte colony stimulating factor (G-CSF)-mediated HSC/EPC mobilization causes an imbalance between the expression of BM SDF-1 and CXCR4 in HSCs, 10 and that SDF-1␣ adenovirus gene transfer enhances the number of circulating HSCs/EPCs. [11][12][13] Recently, overexpression of SDF-1 in ischemic tissues has been found to enhance EPC recruitment from PB and to induce neoangiogenesis. 14,15 In this paper, we show that SDF-1 increases EPC number through enhancement of (BM) c-kit ϩ stem cell adhesion onto extracellular matrix components by integrin receptors. Further, we show that treatment of c-kit ϩ cells with mitogenic cytokines abolished SDF-1-mediated EPC differen...

Chemokine receptors transduce signals important for the function and trafficking of leukocytes. Recently, it has been shown that CC chemokine receptor (CCR)8 is selectively expressed by Th2 subsets, but its functional relevance is unclear. To address the biological role of CCR8, we generated CCR8 deficient (−/−) mice. Here we report defective T helper type 2 (Th2) immune responses in vivo in CCR8−/− mice in models of Schistosoma mansoni soluble egg antigen (SEA)-induced granuloma formation as well as ovalbumin (OVA)- and cockroach antigen (CRA)-induced allergic airway inflammation. In these mice, the response to SEA, OVA, and CRA showed impaired Th2 cytokine production that was associated with aberrant type 2 inflammation displaying a 50 to 80% reduction in eosinophils. In contrast, a prototypical Th1 immune response, elicited by Mycobacteria bovis purified protein derivative (PPD) was unaffected by CCR8 deficiency. Mechanistic analyses indicated that Th2 cells developed normally and that the reduction in eosinophil recruitment was likely due to systemic reduction in interleukin 5. These results indicate an important role for CCR8 in Th2 functional responses in vivo.