CXCL20a promotes the immune protection of an inactivated vaccine against grass carp reovirus infection in grass carp (Ctenopharyngodon idella).

Abstract

Grass carp (Ctenopharyngodon idella) is frequently threatened by hemorrhagic disease caused by grass carp reovirus (GCRV) infection in aquaculture. Vaccination represents a crucial strategy for preventing this infectious disease, where adjuvants play a pivotal role in enhancing vaccine efficacy. This study evaluated the chemokine CXCL20a as a molecular adjuvant to boost the immunogenicity of an inactivated GCRV vaccine. A CXCL20a fusion protein (rC20) was prepared and purified, and a tag-free form (Tf-rC20) was obtained after TrxA tag removal. Five experimental groups were established: PBS control, vaccine alone, rC20 alone, and vaccine combined with rC20 and Tf-rC20 in separate groups. The vaccine-alone group showed a 60 % survival rate, which increased to 74 % and 78 % in the Vac + rC20 and Vac + Tf-rC20 groups, respectively. Tf-rC20 showed slightly higher efficacy than rC20, although the difference was limited. Viral load quantification and splenic histopathology further confirmed that combined immunization suppressed viral replication and alleviated tissue damage. Serum immune parameters analyses revealed that combined immunization significantly enhanced the activities of lysozyme, total superoxide dismutase, and complement component C3, suggesting a potentiation of non-specific immunity. qRT-PCR results showed significant upregulation of immune-related genes, including IFN1, IL-6, Mx2, and IgM, in immune tissues, indicating that CXCL20a promoted both innate and adaptive immune responses. These results collectively demonstrate that the recombinant CXCL20a protein, functioning as a molecular adjuvant, can synergize with the inactivated vaccine to significantly enhance protective immunity against GCRV in grass carp, providing a promising candidate for the development of novel adjuvants in fish vaccines.