Certain streptococci isolated from dental plaque (or blood) bind and activate (shape change reaction, granule release) human platelets, which then aggregate into a septic thrombus. These interactions mimic in vitro the formation of the intracardiac vegetations characteristic of subacute bacterial endocarditis (SBE), a systemic complication associated with dental care. The definable platelet resonse end points of binding, activation and aggregation also provide a unique model to explore the molecular basis of interaction between the various surface components of oral streptococci and other essentially passive, mammalian cells and tissues. During years 04-06, class I, II and III components of S. sanguis (a prototypic SBE microorganism originating in dental plaque) implicated (years 01-03) in the sequence of binding, activation aggregation of platelets, will be purified and characterized. Biochemical purification will combine conventional column chromatography with high performance liquid chromatography. Purification using immunoaffinity techniques will employ existing polyclonal and new monoclonal antibody reagents. Since platelet interactions with solubilized components differ from that seen with native components, development of monoclonal antibodies to native, exposed surface epitopes on S. sanguis will identify and distinguish interacting components associated with the ascribed platelet responses prior to their extraction or fractionation. Characterization will include chemical, physical and immunological criteria of purity, chemical composition and key structural features, correspondence of function-associated antigen with a macromolecular component(s), localization of functional antigens in situ (on wall of S. sanguis) and determination of the number and affinity of platelet binding or interaction sites for the purified S. sanquis components. These data will refine the in vitro model for platelet-streptococcal interactions. Understanding the molecular basis of these interactions may pinpoint new strategies for prevention, diagnosis and treatment of SBE and related oral streptococcal infections.