Critical roles of CD4-1+ T cells and their secreted IL-21 in vaccine-induced humoral immunity in grass carp
- Fish Shellfish Immunol. 2026 Aug:175:111421. doi: 10.1016/j.fsi.2026.111421.
- 1. National Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Engineering Research Center of Green Development for Conventional Aquatic Biological Industry in the Yangtze River Economic Belt, Ministry of Education, College of Fisheries, Huazhong Agricultural University, Wuhan, 430070, China.
- 2. National Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Engineering Research Center of Green Development for Conventional Aquatic Biological Industry in the Yangtze River Economic Belt, Ministry of Education, College of Fisheries, Huazhong Agricultural University, Wuhan, 430070, China; Hubei Jiangxia Laboratory, Wuhan, 430200, China; Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Wuhan, 430070, China; Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen, 518124, China. Electronic address: [email protected].
- 3. National Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Engineering Research Center of Green Development for Conventional Aquatic Biological Industry in the Yangtze River Economic Belt, Ministry of Education, College of Fisheries, Huazhong Agricultural University, Wuhan, 430070, China; Hubei Jiangxia Laboratory, Wuhan, 430200, China; Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Wuhan, 430070, China; Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen, 518124, China. Electronic address: [email protected].
Although CD4+ T cells are known to play a crucial helper role in mammalian humoral immunity, the function of early-evolved CD4-1+ T cells in teleost fish for assisting B cell-mediated antibody production remain to be elucidated. Using grass carp (Ctenopharyngodon idella) as a model, this study demonstrated that CD4-1+ T cells play a critical role in vaccine-induced antibody production and Antibacterial immunity. We confirmed that inactivated Aeromonas hydrophila vaccine significantly induced interleukin-21 (IL-21) expression in grass carp head kidney leukocytes (HKLs), and identified CD4-1+ T cells as the primary cellular source of IL-21. In vitro experiments showed that IL-21 effectively promoted B cell differentiation into plasma cells and enhanced IgM secretion, which synergized with A. hydrophila to exert a more pronounced effect. Meanwhile, our in vivo studies demonstrated that IL-21 possess molecular Adjuvant function when co-immunized with A. hydrophila. Depletion of CD4-1+ T cells reduced A. hydrophila-elicited specific IgM levels and Antibacterial immune protection, confirming their essential helper function. Injection of IL-21 into CD4-1+ T cell depletion fish can partially improve the survival rate but could not restore antibody levels, indicating that while IL-21 has direct immunoenhancing effects, CD4-1+ T cells are essential for a full antibody response. In conclusion, these results demonstrated the critical roles of CD4-1+ T cells and their secreted IL-21 in vaccine-induced humoral immunity in grass carp, providing a foundation for identifying Tfh-like cells in teleost fish and supporting the potential application of IL-21 as molecular Adjuvant in fish vaccines.