EXCEED THE SPACE PROVIDED. Abscess formation is a classic host response to bacteria during sepsis. Certain bacterial species, particularly Bacteroides fragilis and Staphy/ococcus aureus are particularly predisposed to induce abscesses. The essential bacterial virulence factor required for abscess induction by these two pathogens is a capsular polysaccharide with a zwitterionic charge motif. These zwitterionic polysaccharides (ZPS) induce the host to form abscesses by their ability to activate T cells initiating a proinflammatory Thl cytokine response. In contrast to the immunologic paradigm defining polysaccharides as T cell independent antigens, ZPS activate T cells in vitro as well as in vivo when incubated with antigen presenting cells (APC). There is currently no immunologic model that describes how purified polysaccharides can activate T cells. We have shown that ZPS are internalized and can be detected in lysates of intracellular vesicles from the APC. Blocking of endosomal acidification results in the failure of ZPS to activate T cells. ZPS recovered from endosomal vesicles has a substantially reduced molecular size, indicating processing. Fixation of the APC with paraformaldehyde blocks T cell activation by ZPS. We have demonstrated that MHC class II DR appears to be the molecule used by the APC to present ZPS to the T cell and that TCR (_ is required for T cell activation. We hypothesize that ZPS are internalized and cycle through the APC, and that this process is required for presentation of the ZPS to the T cell. We intend to define a novel immunologic paradigm that describes how an important class of biologic molecules (carbohydrates) is recognized by the cell-mediated immune system. This will be done by investigating the cellular pathway by which ZPS cycle through the APC and activate CD4+ T cells. We have defined four specific aims: 1) Determine whether ZPS are degraded and bind to MHC class II molecules in the endocytic pathway; 2) Determine whether ZPS are presented, after internalization, on the APC surface; 3) Characterize the binding interactions of the MHC class II DR molecule with ZPS; 4) Determine whether T-cell activation results from 'processed antigen' presentation or superantigen presentation. The delineation of a mechanism for carbohydrate processing and presentation has broad relevance to the fields of microbiology and immunology and could lead to new concepts for enhancing T cell recognition of other polysaccharides. PERFORMANCE SITE ========================================Section End===========================================
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