Expression of Interleukin-2 receptor subunit gamma (IL-2R?) and its binding with IL-2 induced activation of CD4 T lymphocytes in flounder (Paralichthys olivaceus)

Interleukin-2 receptor (IL-2R), as the specific ligand of interleukin-2 (IL-2), binds to IL-2 and transmits signals and then can induce the proliferation of T lymphocytes in mammals. In this paper, the subunit of IL-2R in flounder (Paralichthys olivaceus), interleukin-2 receptor subunit gamma (IL-2R gamma) was cloned, and polyclonal antibodies (Abs) against its extracellular region were produced, then the expression of flounder IL-2R gamma (fIL-2R gamma) at transcriptional and cellular levels were characterized. Moreover, the interaction of flounder IL-2 (fIL-2) with fIL-2R gamma was investigated, and the variations on CD4+/IL-2R gamma+ cells in flounder after treatment with recombinant IL-2 (rIL-2), anti-IL-2R gamma Abs were detected, respectively. The results showed that fIL-2R gamma protein had a typical fibronectin type III (FN3) domain. The Abs could specifically recognize native fIL-2R gamma molecules at 39.9 kDa. FIL-2R gamma was localized on both T and B lymphocytes, and the percentages of CD4+/IL-2R gamma+ and IgM+/IL-2R gamma+ lymphocytes were high in spleen. In addition, pBiFC-VN173-IL-2R gamma plasmids could bind to pBiFC-VC155-IL-2 plasmids. The percentage of CD4+/IL-2R gamma+ lymphocytes was significantly decreased after blocking with anti-IL-2R gamma Abs both in vivo and in vitro. In the meantime, four T cell markers genes and six IL-2-IL-2R pathway genes were down-regulated in anti-IL-2R gamma Abs group. These results first demonstrated that fIL-2R gamma molecules were expressed on both T and B lymphocytes in flounder, and the bond between fIL-2R gamma and fIL-2 activated the CD4 T lymphocytes. This study gave a new sight into the exploration of IL-2R function on T lymphocytes proliferation in fish.