Analysis of human IL-21 expression

Interleukin 21 (IL-21) regulates the functions of T cells, B cells, natural killer (NK) cells and dendritic cells. Activated-CD4(+) T cells was reported to produce IL-21, however, there are conflicting data on IL-21 producing cells. To identify the IL-21 secreting cell populations in human, we established a hybridoma cell line producing an anti-human IL-21 (hIL-21) mAb. Intracellular hIL-21 staining showed that hIL-21 was mainly expressed in activated-CD4(+) central memory T cells (T-CM). In vitro differentiation experiments of naive CD4(+) T cells demonstrated that only a small population of T(H)1 cells, but not T(H)2 cells produced IL-21 after activation of these cells. Furthermore, we assessed the functional role of IL-21 in proliferation of CD4(+) T cells. IL-21 could strongly enhance the cytokine-driven proliferation of both CD4(+) TCM and effector memory T cells (T-EM) synergistically with IL-7 and IL-15.