title: Role of fibrinogen in complement inhibition by streptococcal M protein.
abstract: M protein, the major virulence factor of group A streptococci, has antiopsonic activity in that it inhibits activation of the alternative complement pathway on the streptococcal surface. Two properties of M protein have been claimed to account for the inhibitory activity, namely, (i) its binding affinity for complement factor H, which is an inhibitor of alternative pathway activation, and (ii) its high binding affinity for fibrinogen. We have recently shown that fibrinogen, like M protein, inhibits alternative pathway activation by possessing binding affinity for factor H. Here we report that fibrinogen effectively competes with factor H for binding to M protein but retains its own binding affinity for factor H. The presence of fibrinogen did not significantly affect alternative pathway inhibition on the streptococcal surface.
authors.affiliation: Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
authors.forename: R D
authors.initials: RD
authors.lastname: Horstmann
authors.forename: H J
authors.initials: HJ
authors.lastname: Sievertsen
authors.forename: M
authors.initials: M
authors.lastname: Leippe
authors.forename: V A
authors.initials: VA
authors.lastname: Fischetti
mesh_terms: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000494:pharmacology*; D002352:Carrier Proteins; D003179:Complement C3b / Q000378:metabolism; D017242:Complement Factor H / Q000378:metabolism; D003169:Complement Inactivator Proteins / Q000494:pharmacology*; D005340:Fibrinogen / Q000378:metabolism / Q000494:pharmacology*; D010587:Phagocytosis; D013291:Streptococcus / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003169:Complement Inactivator Proteins; C014689:streptococcal M protein; D003179:Complement C3b; D017242:Complement Factor H; D005340:Fibrinogen