The monoclonal antibody 4APD7/26 recognizes CD45RB, which is an isoform of the Leukocyte Common Antigen (LCA) also known as CD45. CD45RB is a protein tyrosine phosphatase receptor that is present on most hematopoietic cells and absent on non-hematopoietic cells. Expression of CD45RB is more restricted than CD45 and can only be found on T cell subsets, B, NK, and myeloid cells. Regulatory T cells (Tregs) have been show to express low levels of CD45RB, which may correlate with increased migration to sites of infection. In contrast, high CD45RB expression results in IL-2 and IFN gamma production instead of IL-4 in vitro.