Cellular Antigens

CD31 (PECAM1) is a member of the immunoglobulin (Ig) superfamily that is expressed on the surface of circulating platelets, monocytes, neutrophils, and particular T-cell subsets. CD31 is also a major constituent of the endothelial cell intercellular junction, where up to an estimated 1 million molecules are concentrated. Because of this cellular expression pattern, CD31 is implicated in several functions, including transendothelial migration of leukocytes, angiogenesis, and integrin activation. Ig superfamily members are known to mediate cell adhesion, or antigen recognition, e.g.

Immune costimulatory protein B7-H4 (B7-H4) is expressed on the surface of a variety of immune cells and functions as a negative regulator of T cell response. By arresting cell cycle, B7-H4 inhibits growth, cytokine secretion and cytotoxicity development. When expressed on the cell surface of tumor macrophages, B7-H4 plays an important role, together with regulatory T-cells (Treg), in the suppression of tumor-associated antigen-specific T-cell immunity. B7-H4 is also involved in promoting epithelial cell transformation. B7-H4 can be a predictive marker for renal cell carcinoma.