Macrophage subpopulations were detected immunohistochemically with the aid of monoclonal antibodies in tissue sections of 15 patients with posttraumatic osteomyelitis at the beginning of therapy and after combined operative/antibiotic treatment. Macrophages represent the majority of the immunocompetent cells in osteomyelitis tissue. Before the start of therapy, the acute inflammatory macrophage subtype 27E10 was absent or rarely found in 8/13 evaluable biopsies from the osteomyelitis focus, and a further decrease in the expression of these macrophage antigens was observed after treatment. The RM3/1-positive macrophage associated with the down-regulation of inflammation was detectable to a low extent in 4/13 evaluable biopsies from the osteomyelitis focus before the start of therapy. After treatment of the infection, an increase in this subtype was found in the cellular inflammatory infiltrates in the tissue samples examined. In 8/15 biopsies a marked expression of the RM3/1 antigen was observed. At the start of treatment, the macrophage 25F9, which dominates in the late phase of inflammation, was missing in 3/13 tissue samples. After combined operative/antibiotic treatment the 25F9-positive macrophage was found in all patients, having increased in 7/14 biopsies studied. These data suggest that treatment of posttraumatic osteomyelitis leads to a local macrophage subtype distribution in the osteomyelitis focus resembling the pattern of a late inflammatory reaction.
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