ABSTRACT
T lymphocytes are present in the mucosal epithelial layer as intraepithelial lymphocytes. They are also found in the lamina propria of the mucosa, where they serve as an integral component of the cellular immune system. These T lymphocytes function in the induction and regulation of responses by antigen-specific IgA B cells as well as effector T cells. The epithelial cells lining mucosal surfaces furnish signals that are significant for the initiation of the mucosal inflammatory response and critical communications between epithelial cells and mucosal lymphoid cells. The immune response to oral antigens differs from the response to parenterally administered immunogens. Oral tolerance may follow the ingestion of some protein antigens, but a vigorous local mucosal immune response with the production of high concentrations of IgA may follow oral immunization with selected vaccines such as the Sabin oral polio vaccine.
