Juxtacrine function of interleukin‐15/interleukin‐15 receptor system in tumour derived human B‐cell lines

Summary Interleukin‐15 (IL‐15) is a cytokine that induces proliferation and promotes cell survival of human T, B and NK cells. IL‐15 and interleukin‐2 (IL‐2) exhibit a similar spectrum of immune effects and share the IL‐2 receptor (IL‐2R) subunits IL‐2Rβ and IL‐2Rγ c for signalling in haematopoietic cells. Furthermore, each cytokine has a private α receptor, namely IL‐2Rα for IL‐2 and IL‐15Rα for IL‐15, that functions in ligand binding. Using reverse transcriptase‐polymerase chain reaction (RT‐PCR) and enzyme‐linked immunosorbent assay (ELISA) methods, the expression and secretion of IL‐15 and IL‐15Rα in tumour‐derived B‐cell lines were studied. The results as presented in this study identify that IL‐15 mRNA is predominantly expressed in EBV positive (EBV + ) B‐cell lines, although IL‐15Rα is ubiquitously and constitutively expressed in all these B‐cell lines. Although no detectable levels of IL‐15 protein secretion were observed in any of these cell lines, we were able to detect membrane‐bound expression of IL‐15 protein by FACS analysis in some cell lines. These data imply that the IL‐15/IL‐15R system requires complex regulatory mechanisms for protein secretion. Taken together, we speculate that these results suggest a juxtacrine, intracrine function for IL‐15/IL‐15R.