The TC15-12F12.2 antibody reacts with CD150 (signaling lymphocyte activation molecule or SLAM), an ~75 kDa type I transmembrane glycoprotein that plays multiple roles in the immune response by serving as a cell adhesion molecule and/or coreceptor. It is differentially expressed by T cells, immature thymocytes, B cells, dendritic cells, macrophages, and endothelial cells. The expression pattern differs according to cell type and activation status. Expression is rapidly induced upon activation of T cells, B cells and dendritic cells, with synthesis by T cells being maintained on Th1 but not Th2 clones. CD150-mediated co-stimulation of TCR-activated T cells enhances the production of IFN-γ by Th1 cells, a response that can be augmented by binding of the TC15-12F12.2 antibody. CD150 is thought to mediate signal transduction by associating with the intracellular protein tyrosine phosphatase, SHP-2. CD150 also has functions in hematopoietic cell development and is a useful marker for detection of multipotent hematopoietic stem cells (in concert with other markers such as CD48 and CD41). CD150 is not expressed on non-multipotent hematopoietic progenitor cells.