Interaction between interleukin-12 (IL-12) and its receptor (IL-12Rβ2) mediates CD4⁺ T cell subsets activation in flounder (Paralichthys olivaceus)

Interleukin-12 (IL-12) regulates the differentiation of CD4⁺ T lymphocytes into Th1 cells by binding to its receptor, thereby promoting cellular immunity. This study characterized IL-12 and its receptor β2 (IL-12Rβ2) in flounder (Paralichthys olivaceus) and investigated their interaction, effects on T cell proliferation and differentiation, and the adjuvant effects of IL-12. The recombinant IL-12 was successfully expressed, and the IL-12Rβ2 antibody was confirmed to specifically recognize IL-12Rβ2. IL-12 bound to IL-12Rβ2 at the cellular level. IL-12 stimulation increased leukocyte proliferation and the proportion of CD4⁺/IL-12Rβ2⁺ cells. Moreover, blocking IL-12Rβ2 with antibody reduced Th1 markers (STAT4, T-bet, IFN-γ) and increased Th2 markers (JAK3, STAT6, GATA3). Immunization with rOmpV+IL-12 significantly upregulated CD4⁺/IFN-γ⁺ cells on day seven, peaked the sIgM⁺ B lymphocyte response in the fourth week, and enhanced survival after Edwardsiella tarda challenge. In conclusion, IL-12 signaling effectively facilitates the differentiation of Th1 cells and negatively impacts the function of Th2 cells in flounder. This study provides new insights into the immune regulation of CD4⁺ T cells in teleosts and lays the foundation for understanding the cellular immune mechanisms of vaccines in aquaculture.