Functional characterization of group Ⅱ interferon, IFNf in the acipenseriform fish, Chinese sturgeon (Acipenser sinensis)

Teleost fish possess a diversity of type Ⅰ interferons (IFNs) repertoire, which play a crucial role in antiviral and antimicrobial immune responses. In our previous study, IFNe1-3 and IFNb were identified and cloned from Chinese sturgeon (Acipenser sinensis), an acipenseriform fish. However, the absence of Chinese sturgeon genome data has left the question of whether there are other type Ⅰ IFN members in this species unresolved. In this study, we have identified and characterized a novel IFN, IFNf in Chinese sturgeon (AsIFNf). Bioinformatics analysis revealed that the AsIFNf contains a unique disulfide bond (2 cysteines) located in the second exon and fifth exon region, distinguishing it from other reported teleost type I IFNs. Meanwhile, qPCR results showed that AsIFNf mRNA was detectable in all examined tissues and up-regulated in the spleen or kidney in response to poly I: C, Citrobacter freundii, and Spring Viremia of Carp Virus (SVCV), but not by LPS. Furthermore, compared to recombinant AsIFNe2 protein (rAsIFNe2), rAsIFNf exhibited a stronger protective effect on Chinese sturgeon fin cells against SVCV and also induced higher expression of antiviral genes Mx and viperin. Importantly, AsIFNf displayed characteristics similar to antimicrobial peptides (AMPs) with a positive charge and demonstrated a broad spectrum of antimicrobial activity in vitro. These findings provide a theoretical foundation for understanding the primitive structure and function of interferon, as well as deepening our comprehension of the innate immune system and disease defense in the endangered Chinese sturgeon.