Cyclooxygenase-2/prostaglandin E2 pathway regulates infectious bronchitis virus replication in avian macrophages

Infectious bronchitis virus (IBV) is a significant respiratory pathogen that affects chickens worldwide. As an avian coronavirus, IBV leads to productive infection in chicken macrophages. However, the effects of IBV infection in macrophages on cyclooxygenase- 2 (COX- 2) expression are still to be elucidated. Therefore, we investigated the role of IBV infection on the production of COX- 2, an enzyme involved in the synthesis of prostaglandin E2 (PGE2) in chicken macrophages. The chicken macrophage cells were infected with two IBV strains, and the cells and culture supernatants were harvested at predetermined time points to measure intracellular and extracellular IBV infection. IBV infection was quantified as has been the COX- 2 and PGE2 productions. We found that IBV infection enhances COX- 2 production at both mRNA and protein levels in chicken macrophages. When a selective COX- 2 antagonist was used to reduce the COX- 2 expression in macrophages, we observed that IBV replication decreased. When IBV- infected macrophages were treated with PGE2 receptor (EP2 and EP4) inhibitors, IBV replication was reduced. Upon utilizing a selective COX- 2 antagonist to diminish PGE2 expression in macrophages, a discernible decrease in IBV replication was observed. Treatment of IBV- infected macrophages with a PGE2 receptor (EP2) inhibitor resulted in a reduction in IBV replication, whereas the introduction of exogenous PGE2 heightened viral replication. Additionally, pretreatment with a Janus- kinase two antagonist attenuated the inhibitory effect of recombinant chicken interferon (IFN)-gamma on viral replication. The evaluation of immune mediators, such as inducible nitric oxide (NO) synthase (iNOS), NO, and interleukin (IL)-6, revealed enhanced expression following IBV infection of macrophages. In response to the inhibition of COX- 2 and PGE2 receptors, we observed a reduction in the expressions of iNOS and IL - 6 in macrophages, correlating with reduced IBV infection. Overall, IBV infection increased COX- 2 and PGE2 production in addition to iNOS, NO, and IL - 6 expression in chicken macrophages in a timedependent manner. Inhibition of the COX- 2/PGE2 pathway may lead to increased macrophage defence mechanisms against IBV infection, resulting in a reduction in viral replication and iNOS and IL - 6 expressions. Understanding the molecular mechanisms underlying these processes may shed light on potential antiviral targets for controlling IBV infection.