IL-2R (T-cell growth factor receptor) consists of a chain of 55kDa (also known as Tac antigen or p55 or alpha chain) and a p75 or Beta chain. IL-2Ralpha is over-expressed on the surface of activated T-cells,HTLV-1 or -2 positive T-cell lines,and moderately expressed on activated B-cells,NK-cells,and macrophages.