Platelet receptor Gi24, also known as Dies1, VISTA, SISP1 and B7-H5, is a 5565kD transmembrane glycoprotein with homology to B7like immune costimulatory molecules (1, 2). Mature human Gi24 contains a 162 amino acid (aa) extracellular domain (ECD) with one Vtype Iglike domain, a 21aa transmembrane segment, and a 96 aa cytoplasmic domain. Within the ECD, human Gi24 shares 70% and 67% aa sequence identity with mouse and rat Gi24, respectively (3). The 30kD ECD can be shed by MT1MMP, with a 2530kD fragment remaining in the membrane (3). Gi24 promotes both MT1MMP expression and the MT1MMP mediated activation of MMP2 (3). Gi24 supports the differentiation of embryonic stem cells (ESC) and enhances BMP4 induced signaling in ESC, but is also downregulated following BMP4 exposure (4, 5). It binds to BMP4 directly, and also associates with the type I BMP receptor Activin RIB/ALK-4 (4, 5). Gi24 is expressed on the surface of naive CD4+ T cells and regulatory T cells (6). It is upregulated in vivo on activated monocytes and dendritic cells (5). Gi24 inhibits CD4+ and CD8+ T cell proliferation, and their production of IL2 and IFN-F (6). Its expression on tumor cells attenuates the antitumor immune response and enables more rapid tumor progression (6). In contrast, Gi24 limits disease progression in the autoimmune disease model EAE (6). Recombinant protein corresponding to aa33-194 from human Gi24/VISTA/B7-H5 NS0-derived N-terminus (Accession AAH20568). Moleclar weight ~44.8kD Endotoxin: <0.01EU/ug Biological Activity: Measured by its ability to inhibit anti-CD3 antibody induced IL-2 secretion in human T lymphocytes. The ED50 for this effect is typically 1-6ug/ml. Storage and Stability: Lyophilized and reconstituted products are stable for 6 months after receipt at -20C. Reconstitute with sterile PBS. Aliquot to avoid repeated freezing and thawing. Store at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer.
