The YTH 76.3rMAb is a recombinant monoclonal antibody that specifically recognizes a monomorphic epitope on the extracellular region of the Human Leukocyte Antigen-B (HLA-B) heavy chain. This major histocompatibility complex (MHC) class I antigen is comprised of a polymorphic HLA-B heavy chain, a ~45 kDa type I transmembrane glycoprotein encoded by HLA-B, that is noncovalently associated with the invariant ~12 kDa Beta-2 (β2)-microglobulin light chain encoded by B2M. Hundreds of HLA-B alleles have been reported. HLA-B is expressed on most nucleated cells and leucocytes including specialized antigen presenting cells such as thymic epithelial cells and dendritic cells. HLA-B plays a major role in the MHC-restricted presentation of small peptides, including those derived from self or foreign antigens, that can be bound by TCR expressed on CD8+ thymocytes or T cells leading to either immune tolerance, the maturation of naïve CD8+ T cells, or the activation and differentiation of CD8+ cytotoxic effector T cells or memory CD8+ T cells. HLA-B also functions as a ligand for regulatory CD8 coreceptor molecules and some CD158 molecules that serve as regulatory MHC class I antigen receptors expressed by CD8+ T cells and NK cells. The YTH 76.3rMAb is derived from the hybridoma clone YTH 76.3, with Rat IgG2a, κ isotype. YTH 76.3rMAb has variable region sequences from the original YTH 76.3 clone appended to Rat IgG1 and kappa constant region sequences.