CD45RB is a splice isoform of CD45 (also called protein tyrosine phosphatase, receptor type, C), a glycoprotein receptor that is required for T-cell activation. Several different splice isoforms of the extracellular domain of CD45 are expressed on T cells, and the isoform expressed depends on the particular subpopulation of cell, the state of cell maturation, and whether the cells have been exposed to antigen. CD45RB is expressed in bone marrow and immune system tissues, on naive T cells, peripheral B cells, thymocytes, dendritic cells, and macrophages. CD45RB expression decreases as T cells progress from naive T cells to memory cells. It is positive in most leukemias and lymphomas, but negative in Langerhans cells and plasma cell tumors. References: J Exp Med. 1987;166(5):1548-1566. doi: 10.1084/jem.166.5.1548;Proc Natl Acad Sci U S A. 1988;85(19):7182-7186. doi: 10.1073/pnas.85.19.7182;Trends Immunol. 2006;27(3):146-153. doi: 10.1016/j.it.2006.01.001;Immunol Cell Biol. 1997;75(5):430-445. doi: 10.1038/icb.1997.68;Eur J Immunol 1995 25(2):317.