The 1G9 monoclonal antibody reacts with mouse TIGIT (T cell immunoreceptor with Ig and ITIM domains). TIGIT is a 26 kDa, type I transmembrane protein and a member of the poliovirus receptor (PVR) family. TIGIT has been found to be expressed on follicular T helper cells in mice while in humans it's expressed by many T cell subsets including activated T cells, follicular T helper cells, memory T cells, and regulatory T cells as well as on NK cells. TIGIT can interact with certain members of the PVR and PVR-like families, including PVR, PVRL2, PVRL3, CD155, and CD112. TIGIT is thought to negatively regulate NK and T cell activation. Binding of TIGIT on T cells by dendritic cells results in their differentiation into a tolerogenic phenotype, with increased secretion of IL-10 and diminished production of IL-12. TIGIT knock-out mice are more susceptible to autoimmune disease.