Cd3 is initially expressed in the cytoplasm of pro-thymocytes, the stem cells from which t-cells arise in the thymus. The pro-thymocytes differentiate into common thymocytes, and then into medullary thymocytes, and it is at this latter stage that cd3 antigen begins to migrate to the cell membrane. The antigen is found bound to the membranes of all mature t-cells, and in virtually no other cell type, although it does appear to be present in small amounts in purkinje cells. A t cell is a type of lymphocyte, which develops in the thymus gland (hence the name) and plays a central role in the immune response. T cells can be distinguished from other lymphocytes by the presence of a t-cell receptor on the cell surface. These immune cells originate as precursor cells, derived from bone marrow, and develop into several distinct types of t cells once they have migrated to the thymus gland. T cell differentiation continues even after they have left the thymus. Following t cell development in the thymus, these cells (termed recent thymic emigrants (rte)) egress from the thymus and home to secondary lymphoid organs (slo spleen and lymph nodes). Maturation of rte in slo results in the generation of mature naive t cells (nave t cells are those t cells that have never been exposed to the antigen that they are.). The tcrcd3 complex has a fundamental role in the maturation of thymocytes from immature precursors. The t cell receptor is composed of an or heterodimer associated with invariant chains, cd3, cd3, cd3, and cd3, four transmembrane proteins forming dimer modules , , and (figure 4. The , , and genes are located on chromosome 11q23, while tcr is on.). Both are made in your bone marrow, but b cells stay there to mature while t cells move the thymus to mature. B cells produce antibodies, which help your body destroy abnormal cells and harmful micro-organisms,. Cd5 is a good immunohistochemical marker for t-cells, although not as sensitive as cd3. About 76 of t-cell neoplasms are reported to express cd5, and it is also found in chronic lymphocytic leukemia and mantle cell lymphoma (both being b cell malignancies), that do not express cd3. It is commonly lost in cutaneous t-cell lymphoma, and its absence can be used as an.