The 1G9 antibody reacts with mouse TIGIT (T cell Ig and ITIM domain), a 26 kDa member of the CD28 receptor family which is reported to regulate T cell receptor (TCR) activation. Within the CD28 family of receptors there are those which have co-stimulatory activity, such as CD28 and CTLA-4, as well as more recently identified receptors like TIGIT which are proposed to provide co-inhibitory signals. TIGIT is expressed and upregulated on activated T cells, and is also expressed on memory and regulatory T cells. Upon engagement by its ligands, CD112 and CD155, TIGIT signaling inhibits T cell proliferation and suppresses T cell responses, without triggering cell deletion. A second inhibitory effect of TIGIT signaling is the generation of immunoregulatory dendritic cells, which secrete IL-10 and TGF-beta to further inhibit T cell function.

The 1G9 antibody may be used for flow cytometric analysis of TIGIT, which is expressed at very high levels on T regulatory cells (Tregs) and activated conventional T cells, as well as memory T cells and NK cells.