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

Human macrophage inflammatory protein-1 alpha (hMIP-1 alpha), 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-1 alpha in eosinophilic myelocytes in human bone marrow. We further examined the expression of hMIP-1 alpha mRNA in human bone tissue by in situ hybridization. A high level of hMIP-1 alpha mRNA expression was detected in eosinophilic myelocytes in bone marrow, confirming these cells as the site of hMIP-1 alpha synthesis. hMIP-1 alpha mRNA expression was also detected in osteoblasts in the bone-remodeling sites, and osteoclasts were frequently observed in the vicinity of these osteoblasts. hMIP-1 alpha was also able to induce osteoclastogenesis on calcified matrices in the absence of any other osteotropic hormones. These results strongly suggest that hMIP-1 alpha is involved not only in the regulation of hematopoiesis but also in the modulation of bone remodeling.