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Blood, 1 February 2005, Vol. 105, No. 3, pp. 1052-1059. Prepublished online as a Blood First Edition Paper on September 21, 2004; DOI 10.1182/blood-2004-06-2149.
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY FbsA, a fibrinogen-binding protein from Streptococcus agalactiae, mediates platelet aggregationFrom the University of Pavia, Department of Biochemistry, Pavia, Italy; Department of Microbiology and Biotechnology, University of Ulm, Ulm, Germany; and Microbiology Department, Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland.
The bacterium Streptococcus agalactiae is an etiologic agent in the pathogenesis of endocarditis in humans. FbsA, a fibrinogen-binding protein produced by this pathogen, is considered an important virulence factor. In the present study we provide evidence that S agalactiae clinical isolates bearing FbsA attach to fibrinogen and elicit a fibrinogen-dependent aggregation of platelets. Mutants of S agalactiae lacking the fbsA gene lost the ability to attach to fibrinogen and to aggregate platelets. Plasmid-mediated expression of fbsA restored the capability for fibrinogen binding and platelet aggregation in S agalactiae fbsA mutants, and allowed Lactococcus lactis to interact with fibrinogen and to aggregate human platelets. Moreover, a monoclonal anti-FbsA antibody inhibited bacterial adherence to fibrinogen and S agalactiaeinduced platelet aggregation. Platelet aggregation was inhibited by aspirin, prostaglandin E1, the peptide RGDS, and the antibody abciximab, demonstrating the specificity of platelet aggregation by S agalactiae and indicating an involvement of integrin glycoprotein IIb/IIIa in the induction of platelet aggregation. Aggregation was also dependent on anti-FbsA IgG and could be inhibited by an antibody against the platelet Fc
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