Interleukin‐2 Receptor β‐Chain (p70–75) Expressed on Leukemic Cells from Adult T Cell Leukemia Patients

To determine whether the interleukin‐2 receptor (IL‐2R) β‐chain (p70–75) is expressed on lenkemic cells from patients with adult T cell leukemia (ATL) as well as α‐chain (p55, Tac), we performed radiolabeled interleukin‐2 (IL‐2) binding assay, chemical crosslinking of radiolabeled IL‐2 and flow cytometric analysis using a newly‐developed anti‐IL‐2R β‐chain antibody. The results showed that leukemic cells from all the 12 ATL patients we examined expressed the IL‐2R β‐chain together with the α‐chain, whereas there was no detectable β‐chain expression on unstimulated peripheral blood CD4(+) T cells from healthy volunteers. Southern blot analysis revealed that this abnormal expression was not caused by the structural change of IL‐2R β‐chain gene. Though leukemic cells from all ATL patients examined expressed high‐affinity IL‐2Rs, leukemic cells from only 25% of all ATL patients proliferated in response to IL‐2. These results showing abnormal expression of IL‐2R β‐chain on leukemic cells from ATL patients (ATL cells) suggest a close association between HTLV‐I infection and abnormal β‐chain expression as well as α‐chain expression.