CLONING OF A NOVEL BACTERIA-BINDING RECEPTOR STRUCTURALLY RELATED TO SCAVENGER RECEPTORS AND EXPRESSED IN A SUBSET OF MACROPHAGES

A novel murine plasma membrane protein has been identified in subpopul ations of macrophages. It has an intracellular N-terminal domain, a tr ansmembrane domain, and an extracellular region with a short spacer, a n 89 Gly-Xaa-Yaa repeat-containing collagenous domain, and a C-termina l cysteine-rich domain. In situ hybridization and immunohistochemical staining have localized the protein to a subset of macrophages in the marginal zone of the spleen and the medullary cord of lymph nodes. No expression was observed in macrophages of liver or lung. Transfected C OS cells synthesized a native trimeric plasma membrane protein that bo und labeled bacteria and acetylated LDL, but not yeast or Ficoll. The results suggest that the novel protein is a macrophage-specific membra ne receptor with a role in host defense, as it shows postnatal express ion in macrophages, which are considered responsible far the binding o f bacterial antigens and phagocytosis.