The gastrointestinal tract is a major reservoir of a wide variety of microorganisms. The role of the colonizing microorganisms in contributing to host metabolic processes and overall gastrointestinal health is becoming more widely recognized. Recent work in our laboratory has revealed that bacteria residing in the oral cavity, the entrance to the gastrointestinal tract, are able to degrade dietary gluten. Glutens elicit immunologic reactions and serious clinical conditions in patients suffering from celiac disease. The basis of this disease is an auto-immune disorder in which a host-anti-self response is triggered by gluten-derived cytotoxic peptides. Patients with overt celiac disease suffer from gastroenteropathy and are at risk for malnutrition, anemia, osteoporosis and gastrointestinal malignancies such as lymphoma and adenocarcinoma. To avoid gluten toxicity, patients are required to adherence to a strict gluten-free diet, which is currently the only treatment option available. However, the dietary restriction approach requires a life-long commitment and represents a significant burden to the patient. The discovery of natural gluten degrading microorganisms from the oral cavity opens a promising new avenue in the quest to neutralize the deleterious effects of glutens. The current application seeks to explore the proteolytic activities of resident gastrointestinal microorganisms and study their potential to fragment gluten proteins into non-toxic peptides. The specific aims are: (1) To identify gluten-degrading microorganism(s) in dental plaque and fecal specimens; (2) To define protease cleavage site specificity and assess the abolishment of immunogenic gliadin regions, and to determine pH activity profiles; (3) To assess gliadin detoxification by selected microbes and purified enzyme preparations in a T-cell proliferation assay and in an in vivo model for celiac disease; (4) To characterize, clone and recombinantly express the gene(s) of the most promising enzyme(s). Reduction of gluten toxicity by natural colonizers of the gastrointestinal tract would offer novel treatment perspectives in the form of probiotics or applications of pure gluten-degrading enzymes.