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.1-5 CD86 expression is rapidly upregulated by B-cell specific stimuli with peak expression at 18-42 hours after stimulation.1, 5 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.1-9 The monoclonal antibody GL1 blocks mixed lymphocyte reactions and stimulation of T cells by antigen-presenting cells.1, 3, 5