Two types of TNFα in meagre (Argyrosomus regius): Discovery, distribution and expression modulation

TNFα is a key cytokine involved in systemic inflammation and regulation of immune cells and is important during development. In the present study, 2 isoforms of TNFα were discovered in meagre, an emerging species in aquaculture. Phylogenetic analysis suggests these isoforms represent the type I and type II TNFα classes previously described in other teleost species. This study is the first to compare how these 2 types of TNFα behave in meagre and aims to provide insights into their expression in teleost fish by interrogating expression in whole tissues and isolated cell populations in four immunologically important sites (gills, intestine, head kidney and spleen) following PAMP stimulation, as well as monitoring gene expression during meagre development. Differential expression was seen in head kidney and gills, where TNFα1 was more highly expressed. Both isoforms increased in head kidney of meagre following injection with LPS, but this was not seen in other tissues or after injection with other PAMPs. However, in vitro studies hinted at a possible mucosal bias for TNFα1, which was more highly induced in gill and intestinal cell suspensions by PAMPs. In contrast TNFα2 was more highly induced in cells from systemic tissues. Through early development expression of both types of TNFα decreased as the meagre matured, with the exception of a transient increase shortly after the move to a dry feed diet. However, during the later stages of development expression of both isoforms increased in the gills. This data demonstrates a degree of differential expression of TNFα1 and TNFα2 in meagre with regard to expression regulation, and highlights the importance of TNFα during early development of teleost fish.