Differential expression of TLR7 and iNOS in chicken experimentally infected with a nephropathogenic infectious bronchitis virus isolate from Kerala

Infectious bronchitis virus (IBV) is a major pathogen of poultry, with nephropathogenic variants causing persistent infection and economic losses. This study investigated the expression of Toll-like receptor 7 (TLR7) and inducible nitric oxide synthase (iNOS) in broiler chicken experimentally infected with a nephropathogenic IBV isolate from Kerala. Oneweek- old broilers were inoculated oculonasally with 1104 EID50 of the isolate, and trachea, lung and kidney tissues were collected at 3-, 7-, and 14- days post-infection (dpi). The relative gene expression was determined by quantitative real-time PCR (qPCR) using the 2ΔΔCt method. The TLR7 expression was significantly upregulated in the trachea at 3 dpi (7-fold) and in the kidneys at both 3 and 7 dpi (3-4 fold), before declining at 14 dpi. Pulmonary TLR7 expression was delayed, showing a two-fold rise at 7 dpi. The iNOS expression was markedly elevated in renal tissue (6-fold at 3 and 7 dpi) and in lungs (4-fold at 7 dpi), whereas tracheal expression was initially suppressed and recovered later. The findings of the study suggested that nephropathogenic IBV activates TLR7-mediated viral recognition and iNOS-driven inflammatory responses in a tissue and time-dependent manner. The results also pointed out that the viruss ability to evade or modulate the initial immune alarm system is a critical determinant of disease outcome.