Expression and functional role of the p75 interleukin 2 receptor chain on leukemic hairy cells.

Hairy cell leukemia is a chronic lymphoproliferative disorder char-acterized by the expansion of neoplastic B-cells expressing the p55 chain of the interleukin 2 receptor (IL-2R) system that is recognized by anti-CD25 monoclonal antibodies (mAb) and binds interleukin 2 (IL-2) with low affinity. In the present study we investigated leukemic hairy cells (HC) for the presence of the p75 IL-2R chain which binds IL-2 with intermediate affinity and plays a crucial role in transducing the message to the cell. For this purpose, we tested highly enriched leuke-mic HC from six hairy cell leukemia patients for the presence of IL-2R transcripts and for the expression of the p55 and p75 IL-2R chains on their surface membrane by flow cytometry and immunoprecipitation analyses. The functional role of IL-2 in the regulation of HC prolifer-ation was also investigated. Our results indicate that freshly isolated HC express detectable mes-sages for both the p75 IL-2R and the p55 IL-2R. Flow cytometry anal...