Intestinal Intraepithelial TCRγδ+ T Cells are Activated by Normal Commensal Bacteria

TCR gamma delta(+) T cells play a critical role in protecting the intestinal mucosa against pathogenic infection. In the absence of infection, TCR gamma delta(+) T cell activation must be continuously regulated by T regulatory cells (Treg) to prevent the development of colitis. However, the activation of intestinal TCR gamma delta(+) T cells under normal conditions has not been clearly resolved. In order to determine TCR gamma delta(+) T cell activation in vivo, we designed an NF-kappa B based reporter system. Using the recombinant lentiviral method, we delivered the NF-kappa B reporter to isolated TCR gamma delta(+) T cells, which were then adoptively transferred into normal mice. Our data indicate that the NF-kappa B activation level in TCR gamma delta(+) T cells is higher in the intestinal intraepithelial layer than in the lamina propria region. In addition, the surface expression level of lymphocyte activation marker CD69 in TCR gamma delta(+) T cells is also higher in the intestinal intraepithelial layer and this activation was reduced by Sulfatrim treatment which removes of commensal bacteria. Collectively, our data indicate that the TCR gamma delta(+) T cell population attached to the intestinal lumen is constitutively activated even by normal commensal bacteria.