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We analyzed the expression of the interleukin-2 receptor (IL-2R) β chain (p70-75) on various leukemic cells from 44 patients by flow cytometric analysis using the IL-2Rβ chain-specific monoclonal antibody (MoAb), designated Mik-β1, which has been recently developed. Flow cytometric analysis demonstrated the expression of the IL-2Rβ chain on granular lymphocytes (GLs) from all eight patients with granular lymphocyte proliferative disorders (GLPDs), on adult T-cell leukemia (ATL) cells from all three patients with ATL, and on T-cell acute lymphoblastic leukemia (T-ALL) cells from one of three patients with T-ALL. Although GLs from all the GLPD patients expressed the IL-2Rβ chain alone and not the IL-2Rα chain (Tac-antigen: p55), ATL and T-ALL cells expressing the β chain coex-pressed the α chain. In two of seven patients with common ALL (cALL) and in both patients with B-cell chronic lymphocytic leukemia, the leukemic cells expressed the α chain alone. Neither the α chain nor the β chain was expressed on leukemic cells from the remaining 28 patients, including all 18 patients with acute nonlymphocytic leukemia, five of seven patients with cALL, all three patients with multiple myeloma, and two of three patients with T-ALL. These results indicate that three different forms of IL-2R chain expression exist on leukemic cells: the α chain alone; the β chain alone; and both the α and β chains. To examine whether the results obtained by flow cytometric analysis actually reflect functional aspects of the expressed IL-2Rs, we studied the specific binding of 126l-labeled IL-2 (125l-IL-2) to leukemic cells in 18 of the 44 patients. In addition, we performed 125l—IL-2 crosslinking studies in seven patients. The results of IL-2R expression of both 125l-IL-2 binding assay and crosslinking studies were in agreement with those obtained by flow cytometric analysis. These results indicate that flow cytometric analysis using MoAbs, anti-Tac, and Mik-β 1 is useful for detecting the expression of the IL-2R chains.

L-selectin is an adhesion molecule of the selectin family that mediates the initial step of leukocyte adhesion to vascular endothelium. Upon cellular activation, expression of the L-selectin gene is downregulated at both the protein and mRNA levels. To understand the mechanism of leukemic cell infiltration into organs, we studied the expression and regulation of L-selectin mRNA in fresh leukemic cells of adult T-cell leukemia (ATL) patients and investigated the response of the L-selectin promoter to human T-cell lymphotropic virus type 1 (HTLV-1) Tax, which is a viral transcriptional trans-activator. Flow cytometry showed that L-selectin was expressed on fresh ATL cells along with other activation antigens. Northern blot analysis showed that ATL cells over-expressed the L-selectin mRNA and that the level was aberrantly upregulated after PMA stimulation. Studies using in situ hybridization showed expression of the L-selectin mRNA in the infiltrating leukemic cells in the liver of two ATL patients. Intravenous injection of a rat T-cell line that overexpresses L-selectin showed increased organ infiltration. The induction of Tax expression in JPX9 cells resulted in about a twofold increase in the mRNA expression levels compared with the basal level. Chloramphenicol acetyrtrans-ferase (CAT) assay after transient cotransfection showed about a fivefold transactivation of the L-selectin promoter by Tax. The serum level of the shed form of L-selectin was significantly increased in ATL patients (mean ± SD, 4,215.4 ± 4,111 ng/mL) compared with those of asymptomatic carriers and healthy blood donors (mean ± SD, 1,148.0 ± 269.0 ng/ mL and 991.9 ± 224 ng/mL, respectively). These results indicated that ATL cells constitutively overexpress the L-selectin gene that can be transactivated by HTLV-1 Tax. The overexpression of L-selectin, as well as of inflammatory cytokines, by ATL cells may provide a basis for ATL cells to attach the vascular endothelium, leading to transmigration and organ infitration.