Description: The JJ319 monoclonal antibody reacts with the rat CD28 molecule, expressed by thymocytes, mature T cells, and a subset of NK cells. CD28 is a ligand for CD80 (B7-1) and CD86 (B7-2) and is a potent costimulator of T cells. Signaling through CD28 augments IL-2 and IL-2 receptor expression as well as cytotoxicity of CD3-activated T cells. No reactivity of JJ319 is observed on mouse T cells.