Mouse anti-Human HLA DP DQ DR monoclonal antibody for FC. The main function of human leucocyte antigen (HLA) molecules is to present antigenic peptides to the T-cell receptor, thereby regulating the induction of the immune response. The HLA molecules are encoded by a cluster of tightly linked genes located on the short arm of chromosome 6. Three classes of HLA molecules (I, II and III) have been denoted. Human class II genes are located in the HLA-D region, consisting of three families called DQ, DP and DR. The products of class II genes form a heterodimeric transmembrane protein, consisting of a heavy (~34 kDa) ?-chain and a light (~28 kDa) ?-chain. The DR ?-chain is expressed from one non-polymorphic gene, whereas the DR ?-chain originates from nine highly polymorphic genes. HLA-DR antigen is constitutively expressed on antigen-presenting cells, such as B lymphocytes, monocytes and dendritic cells but can also be detected on activated T lymphocytes and activated granulocytes. Occasionally, natural killer cells express HLA-DR antigen. The antigen has been found expressed in cases of different types of acute lymphoblastic leukaemias, acute myeloid leukaemias except AML-M3, chronic lymphoblastic leukaemias, chronic myeloid leukaemias and B- and T-cell non-Hodgkin's leukaemias. However, the antigen is normally not present on non-haematopoietic tumours and multiple myelomas.