. Chronic allergy to dietary ovalbumin induces lymphocyte migration to rat small intestinal mucosa that is inhibited by MAdCAM-1. Am J Physiol Gastrointest Liver Physiol 286: G702-G710, 2004. First published December 11, 2003 10.1152/ajpgi.00183.2003.-Few models have described a chronic food allergy with morphological changes in the intestinal mucosa. Here we established an ovalbumin (OVA)-induced, cell-mediated, allergic rat model and examined lymphocyte migration in the gut. Brown Norway rats were intraperitoneally sensitized to OVA and then given 10 mg OVA/day by gastric intubation for 6 wk. Lymphocyte subsets and adhesion molecules were examined immunohistochemically, and the migration of T lymphocytes to microvessels of Peyer's patches and villus mucosa was observed by using an intravital microscope. Serum OVA-specific IgG and IgE levels were increased in animals repeatedly exposed to OVA. Significant villus atrophy and increased crypt depth was accompanied by increased infiltration of T lymphocytes in the small intestinal mucosa of the group given OVA. Expression of rat mast cell protease II and of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was also increased in these groups. The administration of anti-MAdCAM-1 antibody significantly attenuated the OVA-induced changes in the mucosal architecture and in CD4 T lymphocyte infiltration. Intravital observation demonstrated that in rats with a chronic allergy, T lymphocytes significantly accumulated in villus microvessels as well as in Peyer's patches via a MAdCAM-1-dependent process. Our model of chronic food allergy revealed that lymphocyte migration was increased with MAdCAM-1 upregulation.Brown Norway rats; rat mast cell protease II; delayed type hypersensitivity; Peyer's patch; intercellular adhesion molecule-1 THE CLINICAL MANIFESTATIONS of allergic reactions from food intolerance may be localized to the gut, including abdominal discomfort, nausea, vomiting, and diarrhea. Type I or IgEmediated allergic reactions are involved in early-phase symptoms of food allergy (6,8). On the other hand, cell-mediated reactions are also involved in the late phase and symptoms are often prolonged, causing mucosal damage such as crypt hyperplasia, villus atrophy, and lymphocyte infiltration (11,13,27,30). Because human research is restricted, animal models of food allergies would be of significant value. Several efforts have been made to develop rodent models of food allergy (10,14,32). However, few models have been validated for studying the effects of chronic antigen exposure or for relevance to clinical situations involving both IgE-and cell-mediated reactions (21,22,28). Although several groups (10) have investigated the effect of repeated oral challenge in rats with IgEmediated hypersensitivity, lymphocyte infiltration was not obvious in the intestinal mucosa of these animals. Only a recent report by Yang et al. (36) has demonstrated that the oral antigen challenge of sensitized Sprague-Dawley rats induces sustained epithelial dysfunction with inflammator...