Dietary ferulic acid boosts the immunity and antioxidant activity of T lymphocytes in Nile tilapia (Oreochromis niloticus) challenged with Aeromonas hydrophila

Functional feed additives are increasingly incorporated into aquafeeds to improve growth performance, metabolic status, and overall health of farmed fish. However, their regulatory effects on adaptive immunity, particularly T cell–mediated immune responses, remain poorly characterized. In this study, we evaluated the effects of dietary ferulic acid supplementation on T cell immunity and antioxidant capacity in Nile tilapia (Oreochromis niloticus). Fish were fed diets supplemented with 0, 200, or 400 mg/kg ferulic acid and subsequently challenged with Aeromonas hydrophila. Compared with the basal diet group, supplementation with 200 mg/kg ferulic acid significantly enhanced T cell proliferation and survival during infection, accompanied by increased proportions and absolute numbers of CD4-1⁺ T cells. In parallel, ferulic acid supplementation elevated expression of key T cell functional molecules, including interferon-γ (IFN-γ), perforin A, tumor necrosis factor α (TNF-α), and Fas ligand (Fas-L), together with reduced bacterial burden, alleviated hepatic inflammatory infiltration and lesions, and improved survival. In addition, ferulic acid markedly enhanced antioxidant capacity in lymphocytes, as evidenced by increased activities of total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-Px), elevated total antioxidant capacity (T-AOC), and reduced malondialdehyde (MDA) levels. Consistently, intracellular reactive oxygen species (ROS) accumulation in T cells and the expression of pro-inflammatory genes were significantly reduced following 200 mg/kg ferulic acid supplementation. Taken together, we demonstrate that dietary ferulic acid supplementation functionally enhances T cell–mediated immune responses and antioxidant capacity in tilapia during bacterial infection, with 200 mg/kg identified as the optimal concentration, supporting its potential application as a functional feed additive in aquaculture.