Evaluation of Immune-Related Gene Expression in the Common Carp After Immunization with an Autogenous Vaccine Derived from a Local Isolate of Aeromonas hydrophila

In the absence of commercial vaccines, autogenous vaccines derived from local pathogen isolates represent a practical and cost-effective approach to disease prevention in aquaculture. We evaluated anti-inflammatory and humoral responses following vaccination with a formalin-killed Aeromonas hydrophila (FKAH) vaccine delivered either by intraperitoneal injection (VI) or spray (VS), followed by an experimental challenge. FKAHCs were prepared by treating a local A. hydrophila isolate with 0.5% neutral-buffered formalin. Common carp received doses on days 0, 14, and 28. On day 46, a subset was challenged intramuscularly with LPAH (0.1mL; 2.3×10⁶ CFU/mL). Liver, gill, and blood were collected for mRNA expression of IL10, IgT, and IgM genes in affected groups were analyzed using the Kruskal–Wallis test with post-hoc comparisons; temporal and organ patterns were assessed across days 14, 28, and 42. Infection alone strongly suppressed IL-10 and showed route-dependent polarization (P 0.038): VS drove additional suppression post-challenge, while VI shifted to IL-10 upregulation after challenge, indicating anti-inflammatory recall. IgM increased with both routes (P= 0.037), maximally with VS pre-challenge, but VS responses contracted after challenge; VI sustained or increased IgM post-challenge. IgT amplification was robust and largely route-independent (P= 0.558 overall), with stable post-challenge levels, especially high in the gills, suggesting conserved mucosal protection. These results indicate that the delivery route shapes distinct immune architectures: VS biases toward pro-inflammatory recall with transient IgM, while VI favors IL-10-linked anti-inflammatory control with sustained antibodies. IgT provides a stable, route-independent mucosal response.