CD86, also known as B7-2, is a type I transmembrane glycoprotein and a member of the immunoglobulin superfamily of cell surface receptors. It is expressed at high levels on resting peripheral monocytes and dendritic cells and at very low density on resting B and T lymphocytes. CD86 expression is rapidly upregulated by B-cell specific stimuli with peak expression at 18-42 hours after stimulation. CD86, along with CD80 (B7-1), is an important accessory molecule in T cell costimulation via its interaction with CD28 and CD152 (CTLA-4). Since CD86 has rapid kinetics of induction, it is believed to be the major CD28 ligand expressed early in the immune response. The monoclonal antibody GL1 blocks mixed lymphocyte reactions and stimulation of T cells by antigen-presenting cells.