A modified IL-7 enhances the immune response to an inactivated GCRV-II vaccine in grass carp (Ctenopharyngodon idella).

Grass carp reovirus (GCRV) is a major pathogen causing hemorrhagic disease in grass carp (Ctenopharyngodon idella), posing a serious threat to aquaculture. However, the protective efficacy of current inactivated vaccines remains limited, underscoring the need for effective adjuvants. In this study, a modified grass carp interleukin-7 (mIL-7) was generated by mutating glutamine at position 130 to glutamic acid (Q130E), based on integrated structural and energetic analyses. Structural modeling suggested that Q130E mutation may improve local conformational stability and alter the predicted interface involved in receptor interaction. Functional characterization demonstrated enhanced immunomodulatory activity of mIL-7. mIL-7 promoted peripheral blood lymphocyte chemotaxis and enhanced phagocytic activity of head kidney macrophages. Further, combined mIL-7 with inactivated GCRV vaccine significantly elevated expression of immune-related genes in macrophages, including IgM, MHC II, IFN1, and IL-10, together with reduced expression of the viral gene VP56 following GCRV challenge, indicating enhanced antiviral responsiveness. Through in vivo experiments, immunization with the mIL-7-adjuvanted vaccine resulted in significantly increased serum innate immune enzyme activities (CAT, ACP, Gpx) and upregulated expression of antiviral and inflammatory genes (IFN1, Mx2, and TNF-α) and enhanced IgM levels. These responses were associated with decreased viral loads, alleviated histopathological damage after GCRV-II challenge, and improved survival compared with vaccination alone. Collectively, these findings suggest that targeted modification of IL-7 may enhance its immunomodulatory function and adjuvant efficacy, providing a rational strategy for cytokine engineering and highlighting the potential of modified IL-7 to improve vaccine performance in grass carp.