Functional analysis of carp interferon-γ: Evolutionary conservation of classical phagocyte activation

In teleost fish two IFN-γ gene sequences were found for which two phylogenetic clusters can be distinguished. Our previous analysis of expression of these in carp led us to hypothesize that a classical IFN-γ function is associated with the IFN-γ2 cluster. We investigated the evolutionary conservation of the IFN-γ function, inducing classical activation of phagocytes, thus skewing towards a Th1-like profile of immune activation. Recombinant proteins for the carp IFN-γ sequences of both clusters were made and we studied their effects on expression of proinflammatory mediators. Carp IFN-γ2, in contrast to carp IFN-γ1, was powerful in inducing a proinflammatory reaction in phagocytes: a classical synergistic response with lipopolysaccharide was observed for the induction of iNOS expression and NO release, for expression of CXCL9-11-like chemokines and the expression of proinflammatory cytokines IL-1β, TNFα and the IL-12 subunits p35 and p40. In contrast, like in mammals, the CXCL8-like cytokines are LPS but not IFN-γ sensitive. These results corroborate an evolutionary conserved nature of IFN-γ function in lower vertebrates including classical activation of phagocytes.