Manganese improved Trachinotus ovatus immune against Cryptocaryon irritans infection

Abstract

Manganese is an essential trace mineral element that has been reported to promote mammalian immune systems. However, its role in fish immunity is not well understood. This study aimed to evaluate the function of Mn2+ in Trachinotus ovatus immune protection against Crytocaryon irritans. Monocyte phagocytosis was enhanced and increased expression levels of I-IFNs (IFNα3, IFNα4), cytokines (IL-6, TNFα), and immunoglobulin genes (IgM, IgT) were detected in ToHKLs treated with Mn2+. Additionally, we prepared colloidal manganese salt (Mn jelly, MnJ), a nano-material with dispersed manganese, which provided 21.0% immune protection against C. irritans when injected into pompano. Compared to traditional adjuvant Freund's adjuvant, no mortality or intense inflammation was observed in pompano after subcutaneous injection of MnJ. Immunization with MnJ plus Tetrahymena thermophila (MnJ + Tt) resulted in better immune protection against C. irritans challenge, and an increase in specific IgMs in serum and spleen culture medium as well as IgM positive signal were found in MnJ + Tt-vaccinated pompano. Furthermore, T. ovatus cGAS (TocGAS) was cloned and identified critical conserved residues that suggest manganese improves pompano immunity by activating the cGAS molecule. Our results indicate that manganese could improve pompano immunity against C. irritans infection and that MnJ may be a promising adjuvant candidate for C. irritans vaccine. However, further studies are needed to determine whether TocGAS is activated by manganese.