The pros and cons of cytokines for fowl adenovirus serotype 4 infection

Hepatitis-hydropericardium syndrome (HHS), caused by fowl adenovirus serotype 4 (FAdV-4), has spread on chicken farms worldwide, causing huge economic losses. Currently, the exact mechanism of pathogenesis of FAdV-4 remains unknown. Despite the severe inflammatory damage observed in chickens infected with pathogenic FAdV-4, few studies have focused on the host immune system-virus interactions and cytokine secretion. Host immunity acts as one of the most robust defense mechanisms against infection by pathogens, and cytokines are important in their elimination. However, excessive inflammatory cytokine secretion could contribute to the pathogenesis of FAdV-4. Understanding of the roles of cytokines produced during FAdV-4 infection is important for the study of pathogenicity and for developing strategies to control FAdV-4. Several previous studies have addressed the immune responses to FAdV-4 infection, but there has not been a systematic review of this work. The present review provides a detailed summary of the current findings on cytokine production induced by FAdV-4 infection to accelerate our understanding of FAdV-4 pathogenesis.