Macrophage inflammatory protein-1α (LD78) expressed in human bone marrow: Its role in regulation of hematopoiesis and osteoclast recruitment

Human macrophage inflammatory protein-1α (hMIP-1α), also known as LD78, is a member of the chemokine/intercrine family and an inhibitor of the proliferation of the hematopoietic stem cells in vitro. Using a specific monoclonal antibody, we observed significant localization of hMIP-1α in eosinophilic myelocytes in human bone marrow. We further examined the expression of hMIP-1α mRNA in human bone tissue by in situ hybridization. A high level of hMIP-1α mRNA expression was detected in eosinophilic myelocytes in bone marrow, confirming these cells as the site of hMIP-1α synthesis, hMIP-1α mRNA expression was also detected in osteoblasts in the bone-remodeling sites, and osteoclasts were frequently observed in the vicinity of these osteoblasts, hMIP-1α was also able to induce osteoclastogenesis on calcified matrices in the absence of any other osteotropic hormones. These results strongly suggest that hMIP-1α is involved not only in the regulation of hematopoiesis but also in the modulation of bone remodeling.