Description: The monoclonal antibody NIMR-4 reacts specifically with a non-polymorphic I-A-encoded epitope on MHC Class II antigens. Class II antigens are predominantly expressed on antigen-presenting cells including B lymphocytes, macrophages, dendritic cells and certain epithelial cells. MHC Class II molecules are important for the selection of the TCR repertoire during the processes of positive and negative selection. MHC Class II expression is required for the positive selection of CD4+ T cells.