MANNOSE-BINDING PROTEIN (MBP) ENHANCES MONONUCLEAR PHAGOCYTE FUNCTION VIA A RECEPTOR THAT CONTAINS THE 126,000 M(R) COMPONENT OF THE C1Q RECEPTOR

Mannose-binding protein (MBP), Clq, the recognition component of the classical complement pathway, and pulmonary surfactant protein A (SP-A) are members of a family of molecules containing a collagen-like sequence contiguous with a noncollagen-like sequence, and usually having the properties of a lectin. Clq and SP-A have been shown to enhance monocyte FcR- and CR1-mediated phagocytosis, suggesting that the common structural features of the collagen-like domains may provide a basis for this immunologically important function. Results presented here demonstrate that MBP also enhanced FcR-mediated phagocytosis by both monocytes and macrophages, and stimulated CR1-mediated phagocytosis in human culture-derived macrophages and in phorbol ester-activated monocytes. Furthermore, a monoclonal antibody that recognizes a 126,000 M(r) cell surface protein and inhibits Clq-enhanced phagocytosis, inhibited the MBP-mediated enhancement of phagocytosis. Thus, the receptors that mediate the enhancement of phagocytosis by MBP and Clq share at least one critical functional component, the 126,000 M(r) ClqRp.