Membrane Cofactor Protein

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Abstract
Membrane cofactor protein (MCP, CD46) is a widely distributed regulatory protein that inhibits complement activation on host cells. Except for erythrocytes, it has been found on every cell examined (Liszewski et al. 1991 ). Cole et al. (1985) originally identified MCP as a third class, in addition to CR1 and CR2, of electrophoretically distinct, C3 binding, membrane proteins of human peripheral blood leukocytes. Initially termed gp45–70, to reflect its electrophoretic mobility on SDS-PAGE, the common name was changed to MCP when its cofactor activity was recognized (Seya et al. 1986). MCP was hypothesized and subsequently found to belong to a family of structurally, functionally, and genetically related proteins collectively termed the regulators of complement activation (RCA) (DeCordoba et al. 1984, 1985; Holers et al. 1985; Hourcade et al. 1989). Recently, MCP was given its leukocyte differentiation number (CD46) and a monoclonal antibody (E4.3) was designated as the standard typing reagent (Hadam 1990; Purcell et al. 1989a). This chapter will review our current understanding of the structure and function of MCP, emphasizing recent contributions made possible by molecular analyses (Post et al. 1991).