The high concentration of foreign antigen in the lumen of the gastrointestinal tract is separated from the underlying lymphocytes by a single cell layer of polarized epithelium .
the high concentration of foreign antigen in the lumen of the gastrointestinal tract is separated from the underlying lymphocytes by a single cell layer of polarized epithelium .
O O O O B-protein_family_or_group I-protein_family_or_group O O B-cell_type O O B-body_part I-body_part O O O O O B-cell_type O O O O O O B-tissue I-tissue O