CD74 Monoclonal Antibody [Bu45]CD74 Monoclonal Antibody (Bu45) recognizes human CD74, a type II transmembrane protein, also known as the MHC class II associated invariant chain. CD74 Monoclonal Antibody (Bu45) is validated in applucations, including ICC IF, Flow Cyt (unfixed cells). The Bu45 antibody recognizes 33, 35 and 41 kDa isoforms of CD74. The CD74 molecule plays a critical role in the presentation of peptides, by the MHC class II antigens, to CD4 positive lymphocytes.