Reacts with a common epitope of human major histocompatibility (MHC) class II antigens, HLA-DR and DP. Human MHC class II antigens are transmembrane glycoproteins composed of an alpha chain (36 kDa) and a beta chain (27 kDa). They are expressed primarily on antigen presenting cells such as B lymphocytes, monocytes, macrophages, and thymic epithelial cells and are also present on activated T lymphocytes. Human MHC class II genes are located in the HLA-D region that encodes at least six and ten chain genes. Three loci, DR, DQ and DP, encode the major expressed products of the human class II region. The human MHC class II molecules bind intracellularly processed peptides and present them to T-helper cells. They, therefore, have a critical role in the initiation of the immune response. It has been shown that some autoimmune diseases are associated with certain class II alleles.Primary antibodies are available purified, or with a selection of fluorescent CF® Dyes and other labels. CF® Dyes offer exceptional brightness and photostability. Note: Conjugates of blue fluorescent dyes like CF®405S and CF®405M are not recommended for detecting low abundance targets, because blue dyes have lower fluorescence and can give higher non-specific background than other dye colors.