Project Summary/Abstract Viridans streptococci commonly found in the oral cavity as commensal bacteria can turn into opportunistic pathogens if they gain access to the bloodstream where they can cause systemic disease. Neutrophils at the gingival margin form a first line of defense by recognizing and destroying invading bacteria before they enter the bloodstream. The mechanisms facilitating recognition of streptococci by neutrophils that result in phagocytosis and killing of the streptococci are not completely understood. Many streptococcal strains express serine-rich repeat protein adhesins (SRRPs) which facilitate host colonization by recognizing and binding to sialic acids, the most common terminal glycans on glycoproteins in saliva and oral epithelial cells. Neutrophils also express sialylated proteins, but sialic acid-dependent interactions between oral streptococci and neutrophils have not yet been studied in sufficient detail. Recent work by our lab has identified strains of streptococci, obtained from the human oral cavity, which exhibit differential binding to the two most common forms of mammalian sialic acids, N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), the latter of which humans are unable to synthesize. The unexpected finding of streptococci in the human oral cavity which preferentially bind to Neu5Gc led us to question whether this preference prevents these bacteria from being recognized and killed by neutrophils. The question of whether human neutrophils, lacking Neu5Gc, are able to efficiently eliminate Neu5Gc-binding streptococci will be addressed by this proposal. Our central hypothesis is that streptococcal preference for specific sialic acid-containing epitopes results in different responses of neutrophils encountering these streptococci. We will test this hypothesis by incubating streptococcal strains which exhibit differential binding to Neu5Ac and Neu5Gc with neutrophils displaying either Neu5Ac, Neu5Gc, or which are devoid of sialic acids. In Aim 1, neutrophil activation and phagocytosis of streptococci based on sialic acid subtype preference is examined. Aim 2 will identify specific sialoglycoproteins on the surface of neutrophils which are bound by either Neu5Ac- or Neu5Gc-specific streptococci or their purified adhesin proteins. We will also test how these interactions with cell surface sialoglycoproteins contribute to neutrophil activation and phagocytosis of the streptococci. This project advances the trainee’s knowledge and skills in glycobiology and immunology acquired during his PhD dissertation research. The project will also permit the trainee to gain new knowledge and skills in microbiology and innate host defense as it pertains to the oral cavity. The applicant’s advisory committee members are committed to helping him develop the professional and academic skills necessary to achieve the long-term goal of establishing an independent research laboratory. The project is designed to pro...