FAdV-4-induced secondary Pasteurella multocida infection potentiates bacterial adherence and aggravates pathological...

Fowl aviadenovirus (FAdV) is widely prevalent and often co-infects with other pathogens. During clinical sample testing in our laboratory, samples of FAdV and Pasteurella multocida（PM） co-infection were identified. Compared with single infections, co-infected chickens exhibited more severe clinical symptoms. However, the current epidemic situation of the two pathogens and whether there is synergistic pathogenic effect between them remains unclear. To address this, we established an in vivo model using specific-pathogen-free (SPF) chickens to study FAdV-4 secondary PM infection. The results demonstrated that FAdV-4 infection significantly promoted PM colonization in the host, leading to more severe clinical symptoms and hepatic pathological damage. Meanwhile, serum levels of inflammation-related cytokines, including TNF-α, CCL-4, IL-6 and IL-1β were markedly elevated. To further investigate the underlying mechanism, we performed transcriptome sequencing of liver tissues. Multiple genes closely associated with inflammatory responses (such as IL6) were significantly upregulated. Notably, TLR4, which is intimately linked to inflammatory reactions, was significantly upregulated after FAdV-4 infection. In an in vitro infection model established using leghorn male hepatocellular cells (LMH) cells, we also observed that FAdV-4 infection promoted PM adherence and invasion, accompanied by increased TLR4 expression. Furthermore, upregulation of TLR4 expression using the TLR4 agonist LPS enhanced PM adherence and invasion, whereas downregulation of TLR4 expression using the inhibitor Resatorvid (TAK-242) decreased PM adherence and invasion. In summary, this study confirms the synergistic pathogenic effect between FAdV-4 and PM and reveals that the TLR4 plays a critical role in this process.