The PC61.5 antibody specifically reacts with mouse CD25, the 55 kDa low-affinity Interleukin-2 Receptor α chain (IL-2R α), expressed on early progenitors of T and B lineage, and on B and T cells. Together with CD122 (IL-2 Receptor β) and CD 132 (IL-2 Receptor γc, the common gamma chain), CD25 forms high-affinity receptor complexes for IL-2. Resting B and T cells and natural killer cells do not express IL-2Rα. Cd25 is also expressed on the dendritic cells, and it enhances lymphocyte differentiation and activation.

The PC61.5 antibody blocks the binding of IL-2 to both high-affinity and low-affinity receptors.