FAdV-4 induces more severe inflammatory responses compared to FAdV-8b.

Multiple infections, either single or mixed, involving pathogens such as serotype 4 fowl adenovirus (FAdV-4) and serotype 8b fowl adenovirus (FAdV-8b), have been observed in numerous laying hens in China, leading to severe liver damage. Thus, fowl adenovirus (FAdVs) is speculated to cause and inflammatory response. In this study, single infections with FAdV-4 and FAdV-8b were confirmed through RT-PCR and Enzyme-linked Immunosorbent Assay (ELISA) in specific pathogen-free (SPF) chickens exhibiting severe liver damage. Following this, the two reference strains, FAdV-4 and FAdV-8b, were inoculated into cardiomyocytes (CM) and cardiac fibroblasts (CF) to assess their immune responses. Additionally, the replication dynamics of FAdV-4 and FAdV-8b, as well as the expression levels of immune-related cytokines, were evaluated. The results demonstrated that FAdV-4 significantly enhanced viral replication in the heart, CM, and CF cells. The transcriptional levels of IL-1β, TNFα, IL-6, and IL-8 were markedly increased in cells infected with either FAdV-4 or FAdV-8b. These findings confirmed the in vitro and in vivo infection of FAdV-4 and FAdV-8b, elucidating their pathogenic mechanisms and providing new insights into the viral interactions and immune responses.