Trh positive strain of Vibrio parahaemolyticus induce immunity by modulating MAPK pathway: A molecular pathogenic insight in immune-related gene regulation

Vibrio parahaemolyticus is a zoonotic bacterium that causes infections in shellfish, fish and higher vertebrates as well as in humans. The Tdh and Trh positive strains of V. parahaemolyticus are generally considered as major virulent strains. The pathogenic mechanisms of Trh positive strain of V. parahaemolyticus are poorly understood. Therefore, in the present study Indian Major Carp, Labeo rohita was intraperitoneally challenged with a Trh positive strain of V. parahaemolyticus below lethal dose 50 (LD₅₀) to understand the innate immune response. A significant upregulation in the respiratory burst activity, myeloperoxidase activity and lysozyme activity of serum was observed in the challenged fishes. However, the serum alpha (α) 2-macro globulin activity and antiprotease activity remained unaltered in the infected fish. The relative expression study of some immune-related genes showed that after the experimental challenge the expression of immune-related genes viz., Toll-like receptor (TLR), Nucleotide-binding oligomerization domain (NOD), Interleukin-1β (IL-β), Interleukin-6 (IL-6), Tumor necrosis factor α (TNFα), Inducible nitric oxide synthase (iNOS), Complement factor 3a (C3a) and Heat shock proteins 70 (Hsp70) was upregulated during infection. Furthermore, overexpression of nuclear factor kappa light chain enhancer of activated B cells (NF-κβ), Myeloid differentiation primary response 88 (MyD88), Mitogen-activated protein kinases (MAPK) and cysteine-aspartic proteases (Casp 1) was also observed after post-infection which clearly indicated that Trh positive V. parahaemolyticus activates MAPK pathway. The present study strengthens the understanding of molecular pathogenesis and provides insights on gene regulation during infection with Trh positive V. parahaemolyticus.