Dietary ursodeoxycholic acid supplementation enhanced nonspecific immunity, antioxidant capacity, and anti-inflammatory-related gene expression in juvenile large yellow croaker (Larimichthys crocea)

Bile acids (BAs) are known to confer health benefits across various fish species; nevertheless, the beneficial effects of ursodeoxycholic acid (UDCA) on immunity are largely unknown. This research investigated the impact of UDCA supplementation on nonspecific immunity, antioxidant capacity, and immune-related gene expression in juvenile large yellow croaker ( Larimichthys crocea ). The experimental diets were formulated with different UDCA supplement levels: 0 mg/kg (CON), 50 mg/kg (UL), 100 mg/kg (UM), and 500 mg/kg (UH). A total of four hundred fish were randomly distributed into 16 tanks with 25 fish per tank. Each diet was fed to four replicate groups twice daily. After a 70-day feeding trial, the results indicated that the UM diet significantly increased the percentage of nitroblue tetrazolium (NBT)-positive cells, serum lysozyme (LZM) activity, alternative complement pathway (ACP) activity, liver antioxidant capacity, and survival rate postcatch stress ( P < 0.05). To elucidate the mechanisms underlying the immunomodulatory effects of UDCA, we conducted RNA sequencing of liver, intestinal, olfactory, and brain tissues from the CON and UM groups. Results indicated that UDCA upregulated genes associated with nonspecific immune responses, particularly those related to complement pathways ( c3 , c4a , and cfh ), antioxidants ( sod1 , sod2 , and gpx7 ), and lysozyme production ( lyg ). Conversely, the expression of chemokine genes ( mrc1 , ccl21 , and ccr9 ) in the intestine significantly decreased ( P < 0.05). Weighted gene coexpression network analysis (WGCNA) identified gene clusters linked to immunity primarily through the NF-κB pathway ( chuk , nfkb1 , traf2 , and ikbkb ). In vitro experiments with primary hepatocytes demonstrated that incubation with 10 μM UDCA markedly downregulated cytokine production genes ( il1b and nfkb1 ) but upregulated antioxidant genes ( gpx7 , cat , sod1 , and nrf2 ) following 1 mg/mL LPS challenge. In summary, the present study indicated that UDCA supplementation positively influences nonspecific immunity, enhances antioxidant responses, and reduces proinflammatory signaling in juvenile large yellow croaker. • Dietary 100 mg/kg UDCA promotes non-specific immunity and resistance to catching stress. • UDCA increases antioxidant enzyme activities and antioxidant-related gene expression. • UDCA notably reduces the overall proinflammatory response in primary hepatocytes.