Human B lymphocytes express the p75 component of the interleukin 2 receptor

The nature of the interleukin 2 (IL-2) receptor on purified human B lymphocytes was examined. Both normal and malignant cells showed evidence of a 70-75,000 mol.wt (p75) IL-2 binding molecule as assessed by ¹²⁵I-labeled IL-2 binding and receptor cross-linking. On normal, Tac-negative B lymphocytes the estimated number of p75 binding sites was 1100 per cell and the dissociation constant (K_dd) was 1.7 nM. Consistent with this, cross-linking experiments demonstrated the presence of an IL-2 binding molecule of 70-75,000 mol.wt. Purified B cells from patients with hairy cell leukemia and chronic lymphocytic leukemia (CLL) also expressed the p75 IL-2 binding molecule. In the HCL samples, a small number of high-affinity IL-2 binding sites were detected (27-90) while the majority of binding sites (2100-10800) were typical of low-affinity p55 Tac binding. IL-2 added to the purified normal and CLL B lymphocytes led to the induction of p55 Tac expression and the generation of high-affinity IL-2 receptors. This response to IL-2 was equivalent to the response observed when normal B lymphocytes were stimulated by Staphyloccus aureus Cowan I.