DESCRIPTION: Bacteroides forsythus is a Gram-negative oral anaerobe implicated in the development of periodontal disease pathogenesis. Although, very little is known about the virulence factors of this organism, based on our recent in vitro and in vivo studies, a surface-associated 98-kDa protein (BspA) has been suggested as a virulence factor. The BspA protein contains homologous sequences belonging to the leucine-rich repeat motif family (LRR), and to motifs belonging to the immunoglobulin superfamily (Ig-SF). In vitro, the BspA protein binds to extracellular matrix components fibronectin and fibrinogen, and to epithelial cells, and induces release of proinflammtory cytokines from monocytic cells. Further, a mutant of B. forsythus defective in BspA expression constructed in our laboratory has been found to be significantly attenuated in its ability to bind to fibronectin, fibrinogen, and epithelial cells. The studies proposed here will address the hypotheses that LRRs and IgSF domains are critical for host cell interactions via binding to specific cellular receptors, and that the BspA protein plays important roles in pathogenesis via mediating bacterial colonization and triggering of host cellular responses, such as release of cytokines and other mediators. The experimental design will include: 1) studies to determine the specific BspA-domains involved in host cell (epithelial and monocytic cells) interactions (Specific Aim 1a), and investigate intracellular signaling events resulting from BspA binding (Aim 1b); 2) biochemical characterization of epithelial (Aim 2a) and monocyte receptors (Aim 2b) that bind BspA protein; and 3) assessment of the in vivo role of BspA protein as judged by studies in a mouse model of periodontal disease (Aim 3a), and by evaluating the host immune response against the BspA protein in patients with a history of periodontitis (Aim 3b). The findings will be important in determining the roles of BspA protein, and the underlying contribution of its domains in bacterial pathogenesis. The studies will also be critical from a proteomic standpoint in defining the roles of LRR and Ig-like signatures found in other bacterial proteins in general. In the long term, understanding the basic mechanisms of the BspA-mediated pathogenesis of B. forsythus will be vital in developing intervention strategies against periodontal disease.