Identification and functional characterization of multiple interleukin 12 in amberjack (Seriola dumerili)

Interleukin (IL) -12 is a heterodimeric cytokine mainly produced by monocytes, macrophages, and dendritic cells in mammals. IL-12p70 composed of IL-12p35 and IL-12p40, is known to play a crucial role in promoting cell-mediated immunity (CMI) through Th1 differentiation and IFN-γ production. Although two types of IL-12p35 (p35a, p35b) and three types of IL-12p40 (p40a, p40b and p40c) have been identified in several fish species, the knowledge on functional characteristics of teleost IL-12 is still limited. In the present study, we cloned two types of IL-12p35 and three types of IL-12p40 genes in amberjack and yellowtail, and analyzed their expressions in response to stimulation with Nocardia seriolae in amberjack. As a result, four types of IL-12 (IL-12p35a, p35b, p40a and p40b) and IFN-γ mRNA were increased by live-N. seriolae stimulation but not by formalin-killed N. seriolae, suggesting that four types of IL-12 (p35, p35b, p40a and p40c) participate in promoting CMI. Subsequently, we produced six types of recombinant IL-12p70 (rIL12p70) protein in insect cells. Head kidney leukocytes were cultured with formalin-killed N. seriolae and six types of rIL-12p70 to elucidate the role of amberjack IL-12p70 in induction of CMI. After stimulation, IFN-γ expression was elevated whereas IL-10 expression was suppressed in Head kidney leukocytes stimulated with four types of rIL-12 (p40a/p35a, p40c/p35a, p40a/p35b, p40a/p35b). On the other hand, two types of rIL-12 (p40b/p35a, p40b/p35b) only elicited down regulation of IL-10 expression. These results indicate that all amberjack IL-12p70 isoforms are involved in Th1 -differentiation and promotion of CMI with different manners. Fish IL-12 has a potential for the promising vaccine adjuvant.