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Functional and structural characteristics of interleukin 2 (IL-2) receptors on B-cell chronic lymphocytic leukemia (B-CLL) cells were analyzed by a proliferation assay, IL-2 binding assay and cross-linking study. In the 3H-thymidine incorporation assay, purified B-CLL cells from four out of sixteen cases, in which the percentage of Tac antigen (Tac Ag) positive cells in peripheral blood lymphocytes ranged from 0 to 48.8%, responded to IL-2 (100 U/ml) after both 3- and 6-day incubation. No relationship was found between the responsiveness to IL-2 and the percentage of Tac Ag positive cells. In the radiolabeled IL-2 binding assay, however, B-CLL cells from all seven cases examined, including three cases with mitogenic response to IL-2 and four cases without mitogenic response, were shown to have both high- and low-affinity receptors. The number of high- and low-affinity receptors per cell ranged from 29-186 and from 420 to 1,800, respectively. Furthermore, with the affinity cross-linking method p55 (Tac Ag) and p70/75 were found even in cases without mitogenic response in their B-CLL cells. In conclusion, the B-CLL cells so far examined possessed high-affinity IL-2 receptors consisting of p55 and p70/75; nevertheless, this was not sufficient to respond to the mitogenic signal of IL-2.