Functional expression of CCR1, CCR3, CCR4, and CXCR4 chemokine receptors on human platelets

Platelets are known to contain platelet factor 4 and beta -thromboglobulin, alpha -chemokines containing the CXC motif, but recent studies extended th e range to the beta -family characterized by the CC motif, including RANTES and Gro-alpha. There is also evidence for expression of chemokine receptor s CCR4 and CXCR4 in platelets. This study shows that platelets have functio nal CCR1, CCR3, CCR4 and CXCR4 chemokine receptors. Polymerase chain reacti on detected chemokine receptor messenger RNA in platelet RNA. CCR1, CCR3, a nd especially CCR4 gave strong signals; CXCR1 and CXCR4 were weakly positiv e. Flow cytometry with specific antibodies showed the presence of a clear s ignal for CXCR4 and weak signals for CCR1 and CCR3, whereas CXCR1, CXCR2, C XCR3, and CCR5 were all negative. Immunoprecipitation and Western blotting with polyclonal antibodies to cytoplasmic peptides clearly showed the prese nce of CCR1 and CCR4 in platelets in amounts comparable to monocytes and CC R4 transfected cells, respectively. Chemokines specific for these receptors , including monocyte chemotactic protein 1, macrophage inflammatory peptide 1 alpha, eotaxin, RANTES, TARC, macrophage-derived chemokine, and stromal cell-derived factor 1, activate platelets to give Ca++ signals, aggregation , and release of granule contents. Platelet aggregation was dependent on re lease of adenosine diphosphate (ADP) and its interaction with platelet ADP receptors. Part, but not all, of the Ca++ signal was due to ADP release fee ding back to its receptors. Platelet activation also involved heparan or ch ondroitin sulfate associated with the platelet surface and was inhibited by cleavage of these glycosaminoglycans or by heparin or low molecular weight heparin. These platelet receptors may be involved in inflammatory or aller gic responses or in platelet activation in human immunodeficiency virus inf ection. (C) 2000 by The American Society of Hematology.