Role of γδ T cells in mucosal intranet

Abstract

Intraepithelial γδ T cells appear to be an essential regulatory T cell subset for the induction and regulation of humoral and cellular immune responses in the mucosa-associated tissues. These cells form a mucosal internet and intranet with epithelial cells which lead to a reciprocal regulation for activation and cell growth. Removal of the TORS gene (γδ-/- mice) results in a reduction of epithelial cell turnover and downregulates the expression of major histocompatibility complex class II molecules on epithelial cells. Epithelial cells are capable of producing interleukin (IL)-7 and stem cell factor which can activate mucosal γδ T cells expressing IL-7R and c-kit. Further, cell surface immunoregulatory molecules expressed on epithelial cells inhibit the proliferation and cytokine synthesis of γδ T cells stimulated via the TOR-OD3 complex. Thus, direct cell-to-cell interactions between mucosal γδ T cells and epithelial cells occur via their secreted cytokines and their cell surface immunoregulatory molecules to maintain the homeostatic regulation of the mucosal immune system. γδ-/- mice possess significantly lower numbers of immunoglobulin A (IgA) producing cells in mucosa- associated tissues, including intestinal lamina propria and salivary glands, when compared with normal control mice. Furthermore, the levels of antigen- specific IgA B cell responses in γδ-/- mice decreased when they were immunized orally. Mucosal γδ T cells possess an ability to maintain an IgA response in the presence of systemic tolerance. These results clearly indicate that γδ T cells play an important role in the regulation of antigen-specific mucosal IgA responses. Taken together, a triad mucosal lymphocytes intranet which connects among γδ T cells, αβ T cells and IgA B cells is necessary for the induction and regulation of IgA antibody responses in mucosal areas.