The CD83 antigen is a 186 amino acid single chain glycoprotein. This molecule is a member of the immunoglobulin superfamily and is composed of an extracellular V type immunoglobulin-like single domain, a transmembrane region, and a short, 40 amino acid cytoplasmic tail. CD83 antigen undergoes extensive post translational glycosylation, as the determined Mr is twice the predicted size of the core protein. However, CD83+ cells have a unique cell surface immunophenotype that does not correlate with that of T cells, B cells, NK cells, or cells of the myelomonocytic lineage. CD83+ cells coexpress the highest levels of MHC class II molecules, when compared with other leucocyte lineages. They also coexpress T cell markers (CD2, CD5), B cell markers (CD40, CD78), myeloid cell markers (CD13, CD33, CD36) and cytokine receptors, as well as other cell surface molecules.