Table 2 Proteins interacting with C3 and its proteolytic References fragments Protein Alternative pathway complement protein Houreade D.Garea AD.Post TW(naly is of the human Fa es C3bBb Factor H ine MD.Fearon DTand Austen KF(1)Hu Reconectin/FHL-I FHR Pron erdin CRI (CD35) Lambris JD(1988)The multifuncti DAF(CD55 the third como MCP(CD 46 iC3 Factor H Factor I IH.RosOA.Todd EW and Wardwach A CRI(CD35) ration and iC3b Factor H e1282 prop role i CRI (CD35) CR2 (CD21) CR2 (CD21) proteins:an expandi of proteins? FHR-3 Zipfel PF and Skerka C(99)FHL-/re onectin:a human complement FHR-4 C3a C3a receptor envelope.These host complement regulators help the virus Further Reading mplement control,host ntal In used hy (1997)The Complement System are not further accessible to complement.The CR2(CD21) nd Frar protein oteins MCP (CD46).and DAF(CD55)act ndad the CRI(CD (1997)Control of the complement system. Doods AW 8 ENCYCLOPEDIA OF LIFE SCIENCES/e 2001 Nature Publishing Group /www.els.netenvelope. These host complement regulators help the virus to inactivate complement attack. In addition to their role in complement control, host membrane regulators are used by microorganisms as entry points into cells. Following internalization, the pathogens are not further accessible to complement. The CR2 (CD21) protein on B and T lymphocytes serves as a receptor for Epstein–Barr virus (Nemerow et al., 1989), the RCA proteins MCP (CD46), and DAF (CD55) act as receptors for measles and echovirus, and the CR1 (CD 35) receptor seems to be recognized by a protein expressed on the surface of Plasmodium falciparum-infected erythrocytes. References Fishelson Z (1994) Complement-related proteins in pathogenic organ￾isms. Springer Seminars Immunopathology 15: 345–368. Hourcade D, Garcia AD, Post TW et al. (1992) Analysis of the human regulators of complement activation (RCA) gene cluster with yeast artificial chromosomes. Genomics 12: 289–300. Kazatchkine MD, Fearon DT and Austen KF (1979) Human alternative complement pathway: membrane associated sialic acid regulates the competition between B and B1H for cell bound C3b. Journal of Immunology 122: 75–81. Kotwal GJ and Moss B (1988) Vaccinia virus encodes a secretory polypeptide structurally related to complement control proteins. Nature 335: 176–178. Lambris JD (1988) The multifunctional role of C3, the third component of complement. Immunology Today 9: 387–393. Nemerow GR, Houghton RA, Moore MD and Cooper NR (1989) Identification of an epitope in the major envelope protein of Epstein– Barr virus that mediates viral binding to the B-lymphocyte EBV receptor. Cell 56: 369–377. Pillemer L, Blum L, Lepow IH, Ros OA, Todd EW and Wardwach AC (1954) The properdin system and immunity. I. Demonstration and isolation of a new serum protein, properdin and its role in immune phenomena. Science 120: 279–285. Rother RP, Rollins SA, Fodor WL et al. (1994) Inhibition of complement-mediated cytolysis by the terminal complement inhibitor of herpesvirus saimiri. Journal of Virology 68: 730–737. Zipfel PF and Skerka C (1994) Complement factor H and related proteins: an expanding family of complement-regulatory proteins? Immunology Today 15: 121–126. Zipfel PF and Skerka C (1999) FHL-1/reconectin: a human complement and immune regulator with cell-adhesive function. Immunology Today: 20: 135–140. Further Reading Prodinger W, Wu¨rzner R, Erdei A and Dierich MP (1998) Complement. In: Paul WE (ed.) Fundamental Immunology. New York: Raven Press. Rother K, Till GO and Ha¨nsch GM (1997) The Complement System Complement? Berlin: Springer-Verlag. Volonakis JE and Frank MM (1997) The Human Complement System in Health and Disease. New York: Marcel Dekker. Reid KBM and Day AJ (1996) Complement. Oxford: IRL Press. Liszewsky MK, Farries TC, Lublin DM, Rooney IA and Atkinson JP (1997) Control of the complement system. Advances in Immunology 61: 201–283. Doods AW and Sim RB (1997) Complement: A Practical Approach. Oxford: IRL Press. Table 2 Proteins interacting with C3 and its proteolytic fragments Protein Alternative pathway complement protein C3 Convertases C3bBb C3b Factor B Factor H Reconectin/FHL-1 FHR-3 FHR-4 Factor I Properdin CR1 (CD35) DAF (CD55) MCP (CD 46) iC3 Factor B Factor H Factor I CR1 (CD35) iC3b Factor H Factor I CR1 (CD35) CR2 (CD21) CR3 (CD11b/CD18) CR4 (CD11c/CD18) C3dg CR2 (CD21) FHR-3 FHR-4 C3a C3a receptor Complement: Alternative Pathway 8 ENCYCLOPEDIA OF LIFE SCIENCES / & 2001 Nature Publishing Group / www.els.net