INTERLEUKIN-15 TRIGGERS THE PROLIFERATION AND CYTOTOXICITY OF GRANULAR LYMPHOCYTES IN PATIENTS WITH LYMPHOPROLIFERATIVE DISEASE OF GRANULARLYMPHOCYTES

The recently cloned cytokine interteukin-15 (IL-15) shares several fun ctional activities with IL-2 in different cell systems. Although IL-15 does not show sequence homology with IL-2, it uses components of the IL-2 receptor (IL-2R) for binding and signal transduction, namely, p75 (beta) and the p64 (gamma) chains of IL-2R. To evaluate whether IL-15 is involved in the activation of granular lymphocytes (GL) in patient s with lymphoproliferative disease of granular lymphocytes (LDGL), we evaluated the ability of IL-15 to stimulate GL proliferation, cytotoxi c function, and the role of IL-2R beta and gamma molecules on relevant cells. Our results show that IL-15 stimulates cell proliferation and cytotoxic activity of GL in LDGL patients. Reverse-transcriptase polym erase chain reaction (RT-PCR) and phenotypic analyses using the anti-I L-2R gamma-chain-specific TUGh4 monoclonal antibody (MoAb) indicate th at both CD3(+) and CD3(-) GL express the p64 IL-2R, a result previousl y unknown. IL-15 activity was inhibited by antibodies against p75 and p64 IL-2R chains, while no inhibitory effects are detectable with anti -p55 IL-2R antibody. The association of anti-p75 and anti-p64 IL-2R Mo Abs resulted in a nearly complete (95%) inhibition of IL-15-induced GL proliferation Using RT-PCR analysis, we demonstrated that highly puri fied CD3(+) and CD3(-) GL did not express mRNA for IL-15 or IL-2. By c ontrast, a clear-cut IL-15 mRNA signal was detected by RT-PCR in patie nts' peripheral blood mononuclear cells, with monocytes likely account ing for the source of IL-15 in LDGL patients. However, even in concent rated supernatants from enriched monocyte populations, we could not de monstrate the presence of IL-15 protein. Using anti-IL-15 specific MoA bs, a membrane-bound form of this cytokine was demonstrated both on CD 3(+) and CD3(-) LDGL cells. By RT-PCR analysis, purified GL from these patients were found to express the message for IL-15 receptor alpha c hain. Taken together, these results indicate that both CD3(+) and CD3( -) GL are stimulated by IL-15 and that this cytokine mediates its acti vity through the beta and gamma chains of the IL-2R, providing further suggestions for the interpretation of the mechanisms that lead to cel l expansion in patients with LDGL. (C) 1997 by The American Society of Hematology.