The BC96 antibody is specific for human CD25, a 55 kDa surface protein also known as the Interleukin-2 Receptor alpha chain, or IL-2R alpha. CD25 may bind IL-2 by itself, although with low affinity and without induction of cell signaling. CD25 is also expressed within a high-affinity complex, along with the IL-2R beta chain (CD122) and the common gamma chain (CD132), to form a signaling receptor complex. Signaling via CD25 may modulate Th17 and Treg cell differentiation, and has been shown to play a role in the function of dendritic cells. The BC96 antibody may be used as a marker for expression of CD25 during T and B cell development, on activated mature T and B cells, and for its expression at high levels on natural T regulatory cells (nTreg cells) in the thymus or periphery, and on “induced” peripheral Tregs. This antibody is cross-reactive with CD25 in several non-human species, including Baboon, Chimpanzee, Cynomolgus and Rhesus.