The first study investigates the fundamental question of whether the immunotoxic 33-mer peptide is delivered intact across the intestinal epithelium in glutensensitive FH09, during both remission and relapse, as well as in healthy control FR26. We use mass spectrometry to detect for the first time the transepithelial delivery of a chemically-defined, immunotoxic gluten peptide in a gluten-sensitive organism. The second study investigates the practical question of whether oral protease therapy can protect a second gluten-sensitive animal, FH45, from gluten challenge-induced relapse. We present clinical and serological data for FH45, and for control FI96, showing that EP-B2, a gluten-specific endoprotease with potential as a therapeutic for celiac disease, prevents clinical relapse in FH45 in response to a gluten challenge. However, this treatment gives rise to an unexpected elevation in anti-gliadin and anti-TG2 antibodies, the implications of which are discussed. We exploited the gluten-sensitive rhesus macaque model to study two questions regarding gluten sensitive enteropathy that have not yet been investigated in humans or any other model organism. First, can appreciable quantities of immunotoxic gluten peptides be absorbed intact across the enterocyte barrier in glutensensitive animals? And second, can oral glutenases provide clinical benefit to these animals upon gluten exposure? To OTX015 investigate gastrointestinal absorption of intact gluten peptides, we dosed a gluten-sensitive macaque with an isotopically labeled form of the immunotoxic 33-mer gluten peptide, and measured its plasma concentration using a sensitive and specific mass spectrometric method. Nanomolar concentrations of the peptide were measured in peripheral blood, both in remission as well as in active disease, but not in control animals. Although the concentration of the 33-mer peptide in the intestinal mucosa is likely to be higher, low nanomolar concentrations of the 33-mer peptide are sufficient to stimulate proliferation of celiac patient-derived T cells in culture. Thus, gluten-sensitive macaques appear to exhibit enhanced intestinal permeability akin to celiac disease patients. If so, they may offer a unique opportunity to investigate the mechanisms underlying transport of immunotoxic gluten peptides across the enterocyte barrier, as well as the relevance of this aspect of celiac disease to overall disease pathogenesis. We also took advantage of these gluten-sensitive macaques to evaluate the clinical and serological efficacy of a therapeutically promising oral glutenase. The gluten detoxifying characteristics of the zymogen form of barley endoprotease EP-B2 have been extensively investigated as a stand-alone drug candidate and in combination with complementary glutenases. Our study revealed that clinically achievable oral doses of the EP-B2 proenzyme, but not placebo, could prevent dietary gluten from precipitating clinical relapse in a gluten-sensitive macaque. Remarkably, however, the levels of anti-gliadin antibodies underwent a dramatic increase, and, for the first time, we observed an anti-TG2 Masitinib antibody response to dietary gluten in macaques. We speculate that the spike in anti-gliadin antibody levels is due to delivery of a high dose of short gluten peptides into a permeable duodenum upon gastric emptying. Although these shorter peptides are expected to exhibit diminished T cell reactivity, their small size enables them to penetrate the enterocyte barrier more efficiently than the considerably longer peptides produced in the absence of EP-B2. In turn, systemic distribution of these absorbed peptides could elicit an anti-TG2 IgG response because even short gluten peptides are good substrates of mammalian TG2. If so, our findings have two important implications. First, if the goal of oral glutenase therapy is to protect a celiac disease patient from all gluten responses, including anti-gliadin and anti-TG2 antibodies, then gluten must be extensively proteolyzed in the stomach, not simply rendered non-reactive towards disease-specific Th1 cells. The use of combination enzyme therapies that cleave gluten into very short peptides may be beneficial in this regard. Regardless, our data suggest that careful monitoring of patient antibody levels is warranted in future clinical trials for glutenase therapies. Second, there has been considerable debate over the role of anti-TG2 antibodies in celiac disease pathogenesis.