Transcriptional investigation of immune gene expression dynamics in Rohu (Labeo rohita) in response to killed Flavobacterium columnare vaccine.

BACKGROUND: The study investigated the transcriptional level expression dynamics of nonspecific (iNOS and TLR22) and specific (IgM, IgD, and IgZ) immune genes in rohu (Labeo rohita) following challenge with formalin-inactivated and virulent Flavobacterium columnare in the specific tissues, such as gill, kidney, liver, gut, and skin. METHODS AND RESULTS: Fish were immunized on days 0 and 14 with 7.98 × 107 CFU/mL F. columnare and challenged with live bacteria on day 35 (7.98 × 108 CFU/mL). Immune gene expression was analyzed at multiple time points. Samples for long-term monitoring were taken at 0, 7, 14, 21, 28, 35, and 42 days post-vaccination (dpv), while immediate responses were evaluated at 0, 12, 24, 36, 48, and 60 h post-vaccination (hpv) for the instantaneous responsive genes. Significant (p ≤ 0.05) iNOS expression was observed on 7 dpv, peaking in the kidney (7–24 dpv), with skin showing the lowermost response. TLR22 was upregulated on 7 dpv in all tissues except the liver, which further increased post-challenge. The booster (day 14) had no significant effect on nonspecific immune responsive genes, but the virulent bacterial challenge enhanced the expression of iNOS and TLR22. Early post-vaccination transcript analysis of iNOS and TLR22 showed significant (p ≤ 0.05) upregulation from 12 to 60 h, with the highest modulation in the gill, skin, and gut for TLR22 and liver, kidney, and gill for iNOS. Specific immune genes showed tissue-specific responses: IgM peaked in the kidney, gill, gut, and skin; IgD in the skin, gill, kidney, and gut; and IgZ in the gut, skin, and gill. Spiked expression of all specific genes was observed at seven days post-booster challenge, indicating a classical immune response. CONCLUSION: This study examines the immune gene expression dynamics in rohu fish following vaccination and bacterial challenge, providing insights into tissue-specific immune responses and implications for disease control strategies using vaccination. This study contributes to understanding immune gene expression dynamics post-vaccination, advancing knowledge of host-vaccine-pathogen interactions and key foundations of disease control tactics in fish.