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.