The reactivity of a monoclonal antibody against cells of the monocyte-macrophage series in sections of normal and inflamed human tissues.

FMC-17a monoclonal antibody reactive with peripheral blood monocytes was used to identify cells of monocyte origin in sections of normal and inflamed human tissues. FMC-17 + ve cells were found in all samples tested. The distribution, HLA-DR staining characteristics, and enzyme profiles (ACP and ATPase) of FMC-17 + ve cells indicated that interdigitating (dendritic) cells, Langerhans cells, tissue histiocytes, and the classical inflammatory phagocytic macrophages belonged to the reactive population. The antigen recognized by this antibody was found on monocytic and promonocytic cells in bone marrow, yet appeared to be lost following activation in the later stages of inflammatory conditions. Further studies are necessary to elucidate at what stage in the differentiation/maturation pathway the antigen is acquired and again whether or not FMC-17--ve cells are an activated or degenerating population.