Vitamin C supplementation attenuates IBV-induced histopathological lesions and modulates innate immune-related gene expression in SPF chickens.

Vitamin C (VC) supplementation has been reported to benefit poultry health and performance; however, the antiviral effects of VC have remained largely unknown. This study evaluated the effects of oral VC supplementation on viral RNA load, histopathology, and immune-related gene expression in specific-pathogen-free (SPF) chickens challenged with IBV. Eighty one-day-old SPF chicks were randomly allocated to control group or VC group and orally administered VC every other day at doses equivalent to 0 or 400 mg/kg diet for 21 days. All birds were challenged with 0.1 mL of 10⁷ 50% embryo infectious dose of IBV strain CK/CH/I0317/22 via the intraocular and intranasal routes. Results showed that VC supplementation did not affect growth performance, clinical signs, gross lesions, or IBV-specific antibody titers. However, VC alleviated IBV-induced histopathological damage in the trachea and kidney and reduced viral RNA load in the bursa of Fabricius (P < 0.05). In addition, VC supplementation modulated the expression of genes involved in Toll-like receptor signaling, avian β-defensin responses, antioxidant defense, and inflammatory regulation in a tissue-specific and time-dependent manner. In particular, the expression of several TLR signaling- and inflammation-related genes was decreased in selected tissues, whereas avian β-defensin-1 (AvBD1), AvBD2, SOD1, GSH-Px2, and IL-10 expression was increased in selected tissues and at specific time points (P < 0.05). Collectively, these findings indicated that VC supplementation was associated with attenuated IBV-induced histopathological lesions, lower viral RNA load in the bursa of Fabricius, and tissue-specific modulation of innate immune-, inflammatory-, and antioxidant-related gene expression following IBV challenge.