Immunomodulatory effect of saponin treatment and microbial infections provoke the expression of Mx gene in catla (Labeo catla)

Diseases due to microbial infection had been a great hindrance towards sustainable growth in the aquaculture sector across the globe. The present study identified an alternative stimulatory Mx gene product in catla (Labeo catla) and demonstrated its tissue-specific expression kinetics through semi-quantitative real-time polymerase chain reaction (semi-q-PCR). Mx genes were quantified in catla infected with Flavobacterium columnare and Aeromonas veronii and myxosporean parasites, Myxobolus sp. The ratio of Mx/beta-actin (housekeeping gene) expression in all organs of catla has been determined continuously for 14 days. The results showed the highest expression of Mx in the spleen (p < 0.05), followed by the brain, liver, intestine, heart, kidney, and gill. Mx expression was observed to be highest on day 2 in all the organs except in the spleen, where its upregulation was noticed on day 3 with a gradual decrease in expression level over the study period. It has been evident that the ratio of Mx/beta-actin ratio was significantly (p < 0 .05) upregulated in all tissues irrespective of types of infections and saponin administration. Noticeably, maximum heterologous expression of Mx due to bacteria and parasites challenge was observed on the 3rd day, while in the case of saponin administration, it showed at 30 min. The present study revealed the prospects of microbial infection and saponin treatment as potent immuno-stimulatory agents. Thus, the present finding provides an insight into the inherent origin of the Mx gene in the early stages of fish that provide protection against microbial infection as a natural gatekeeper, which could advocate the safe valorization of saponins at <= 40 mg. L-1 as an immune booster in fish as well as a future source for fish vaccination.

Automated summary

This study identified the expression of Mx gene in different organs of catla fish and found that the spleen had the highest expression. The expression of Mx gene was significantly upregulated in all tissues regardless of the type of infection or saponin administration. The study also revealed the potential of microbial infection and saponin treatment as immune-stimulatory agents.