Purified <i>Astragalus</i> Polysaccharide\nCombined with Inactivated Vaccine Markedly Prevents Infectious Haematopoietic\nNecrosis Virus Infection in Rainbow Trout (Oncorhynchus\nmykiss)

Rainbow trout (Oncorhynchus mykiss) is experiencing a catastrophic pandemic. In recent years, infectious\nhematopoietic necrosis virus (IHNV) has spread nationwide, resulting\nin significant mortality. Currently, there are no available treatments\nor vaccines for IHNV in China. Here, the <i>Astragalus</i> extract was purified and characterized. Then, we developed an inactivated\nIHNV vaccine with purified <i>Astragalus</i> polysaccharide\n(P-APS) as an adjuvant. Safety assays showed that IHNV was successfully\ninactivated. After a serious IHNV challenge, the cumulative mortality\nrates were 76.0, 38.0, and 22.1% in control, vaccine, and P-APS +\nvaccine groups, respectively. P-APS + vaccine was effective at reducing\nhead kidney damage and apoptosis after IHNV challenge by histopathological\nand terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)\nanalyses. The P-APS + vaccine group showed better results in enhancing\nspecific antibodies (IgM) and immune enzyme activities (C3, LZM, GOT,\nand GPT). RNA-seq revealed that many immune-related pathways were\nsignificantly enriched. <i>TLR2</i>, <i>TLR7</i>, <i>C3</i>, <i>IFN-γ</i>, <i>IgM</i>, <i>MHC1</i>, <i>MHC2</i>, <i>MX1</i>, and <i>VIG1</i> were identified as core genes based on\nRNA-seq and PPI networks. Mechanistic investigations showed that P-APS\n+ vaccine activates the immune pathway by upregulating the expression\nof these genes. P-ASP+vaccine induced effective innate and adaptive\nimmune responses that were stronger than single vaccines after vaccination\nand IHNV challenged. Our findings will provide a promising vaccine\ncandidate against IHNV.