Mouse platelet basic protein (CXCL7/mPBP) was cloned from thymic stromal cells and further identification indicated that it was expressed in thymic monocytes/macrophages (Mo/Mphis). Recombinant mPBP was chemoattractive for target cells of polymorphonuclear leucocytes, peritoneal Mo/Mphis and splenic lymphocytes with distinct potencies. CXCR2 was identified to be a cognate receptor for mPBP. Mouse thymocyte subsets of CD4(-)CD8(-) double-negative (DN), CD4(+)CD8(+) double-positive (DP), CD4(+)CD8(-) single-positive (CD4SP) and CD4(-)CD8(+) single-positive (CD8SP) expressed cell surface CXCR2 with different positive percentages and expression levels. mPBP was chemoattractive for thymocyte subsets with the potency order DN>DP> CD8SP>CD4SP, consistent with the levels of CXCR2 expressed on the respective cells. Thus, mPBP in thymus is functionally redundant with chemokine CXCL12/ SDF-1. Moreover, our finding that thymic Mo/Mphis can produce mPBP implies that they may have other functions apart from acting as scavengers in thymus.Biochemistry & Molecular BiologyCell BiologySCI(E)PubMed4ARTICLE151935-19456
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