Macrophage membrane molecules: Markers of tissue differentiation and heterogeneity

Monoclonal antibodies directed against murine macrophage differentiation antigens provide tools to characterize novel glycoproteins, their expression by different macrophage subpopulations in situ and regulation by cytokines and other agents in vitro. Studies are in progress to determine ligands for these molecules, and to establish possible functions. We summarize current knowledge of the following molecules: F4/80, a glycoprotein with homology to the G-protein linked transmembrane 7 hormone receptor family; macrosialin, a member of the lysosomal-associated membrane protein [lamp] family with a macrophage-specific mucin-like extracellular domain also present in its human homologue, CD68; sialoadhesin, a sialic acid binding lectin with multiple Ig superfamily domains; mannosyl receptor, a lectin-like molecule with multiple C-type lectin domains; type 3 complement receptor, a β2 integrin involved in cell migration and adhesion; scavenger receptor, a transmembrane homotrimer with a collagenous domain.