Modulation of the innate immune responses in the striped snakehead murrel, Channa striata upon experimental infection with live and heat killed Aeromonas hydrophila

It is well-known that the innate immune mechanisms in fish serve as the first line of defence against wide variety of pathogens. In most of the situations, innate responses get induced and enhanced after the pathogen invasion. It would be interesting to look into the inducibility of various innate immune mechanisms and the level of enhancement after infection with the pathogen. Hence, in the present investigation, modulation of the innate immune responses in the striped snakehead murrel, Channa striata on experimental challenge with either live virulent or heat killed Aeromonas hydrophila at a dose of 1x10(7) CFU (suspended in 0.2 mL PBS) were measured. Most of the non-specific (both humoral and cellular) immune responses tested were substantially induced or enhanced in both the experimental groups in comparison with the unchallenged control group. Significant increase in the lysozyme, total peroxidase, antiprotease and respiratory burst activities were observed after the pathogen challenge. Thus, most of the innate non-specific immune responses are inducible though they are constitutive of fish immune system exhibiting a basal level of activity even in the absence of pathogen challenge.