Modulatory effect of lipopolysaccharide on immune-related gene expression and serum protein fractionation in grey mullet, Mugil cephalus

Immunity occupies the top priority in aquaculture. Great efforts have been made to study fish immunity, but little is known about the immunity of grey mullet, Mugil cephalus despite of its importance. We evaluated the effect of different doses (0, 1, 10 and 100 µg/kg body weight) of lipopolysaccharide (LPS) on the expression of non-specific immune response genes (interleukin (il) 1β, il8, il10 and tumour necrosis factor alpha (tnfα)) in the liver, as well as its effect on the fractionation of serum protein in juvenile grey mullet along different times and concentrations. Analysis revealed that LPS initially caused an upregulation in the studied cytokines. After that, transcripts levels were switched sequentially between downregulation and upregulation, ending with an upregulation at 1 week post injection in il8, il10 and tnfα. Regarding il1β, its initial upregulation was followed by gradual decreases, which reached a marked downregulation at 1 week post injection. Protein fractionation exhibited many changes among doses and time. Nine fractions were discernable in protein electrophoresis of serum in all doses. The most pronounced changes were detected in fractions 7–9 (generally refer to γ globulins or immunoglobulins) using densitometric analysis. In addition, LPS suggested to modulate the levels of serum transferrin. It is known that LPS is a component of the cell wall of Gram negative bacteria, and this study sheds light on the molecular fitness mechanisms against bacterial infection, which could help in developing a strategy to improve resistance to bacterial diseases, or possibly to enhance immune response in grey mullet.