The BC96 antibody reacts with human CD25, a 55 kDa type I integral transmembrane glycoprotein. CD25 is involved in the activation and proliferation of lymphocytes and can be used in the identification of T cell subsets in viral infections like HIV and HTLV. CD25 is present on activated T and B cells, monocytes, macrophages, and regulatory T cells. Expression of CD25, together with CD4 and FOXP3, is considered a phenotypic signature for regulatory T cells. CD25 has a low affinity for its IL-2 ligand but associates with IL-2 receptor β (CD122) and common γ (CD132) chains to form a high affinity IL-2 receptor.