Pathophysiology of experimental Aeromonas hydrophila infection in Puntius sarana: Early changes in blood and aspects of the innate immune-related gene expression in survivors

A decline in production of Puntius sarana worldwide and subsequent intensification of its culture as a measure for conservation and increase food fish production have led to emergence of diseases. Investigations on innate immunological changes in fish that survives an acute bacterial infection are a few or lacking. An attempt was made to study the detailed changes in innate immune responses in P. sarana following an intraperitoneal challenge with Aeromonas hydrophila at 2.24 × 107 colony-forming unit (CFU)/fish. Sequential changes in transcription of immune related genes in liver and kidney, innate immune status, haematological profile and histopathology of major organs were studied after different time intervals post-challenge in the survivors. A significant increase in serum myeloperoxidase, ceruloplasmin activities and total leucocyte count, and decline in alternative complement activity were observed at early infection periods. A significant decline in plasma glucose level, total erythrocyte count, haemoglobin content and packed cell volume in blood was noticed after challenge. Superoxide radical production and serum antiprotease activity increased significantly at later period of challenge. In addition, few immune related genes pertinent to acute phase reactants and inflammatory response viz., complement component 3 (C3), lysozyme G, lysozyme C, β2-microglobulin (B2M), transferrin, interleukin 1β, interleukin 8, manganese superoxide dismutase (MnSOD), natural killer cell enhancing factor-B and chemokine CXCa were modulated after bacterial challenge. In liver, a significant up-regulation of C3 and transferrin, and down-regulation of lysozyme G, interleukin 8, MnSOD and B2M were noticed in survivors. On the contrary, lysozyme G, lysozyme C, interleukin 1β, interleukin 8, CXCa, and MnSOD were found to be significantly up-regulated and C3 was down-regulated in the kidney. All these data suggest that the innate immune factors were highly modulated during infection process to render protection of P. sarana to this bacterium. This study also generated the primary information on many innate immune molecules/genes for this important medium carp species for the first time.