Investigation of mammalian and viral Interleukin-10 family members during cytomegalovirus infection

Human cytomegalovirus (HCMV) infection in newborns and immunocompromised individuals with immature or deficient immune systems can cause life-threatening diseases. The clinical and subsequent economical burden of HCMV infection led the US Institute of Medicine designating a vaccine for HCMV as the highest level of priority. Complex virus-host interactions have developed over millions of years of co-evolution, making the understanding of the pathogenesis of HCMV disease particularly challenging. Consequently, a crucial factor in aiding the development of effective vaccinations and therapies to significantly reduce morbidity and mortality associated with HCMV infection is elucidating what immune mechanisms contribute to/impede protection against infection. For example, is the induction of immunomodulatory agents such as cytokines beneficial or harmful to the host during infection? Given the known immunosuppressive properties of one such cytokine, interleukin-10 (IL-10), in conjunction with the evolutionary acquisition by HCMV of its own IL-10 homologue, I hypothesised that mammalian- and viral-IL-10 suppress protective immunity during acute CMV infection. Utilising a mouse model of CMV infection, I revealed a surprising antiviral role for IL-10 during acute infection in vivo, which was achieved via limitation of activation-induced death of NK cells. The IL-10-related cytokine interleukin-22 (IL-22) provides critical protection against certain infectious agents and I therefore hypothesised that IL-22 provides protective immunity during acute CMV infection. Utilising the murine infection model once more, I discovered a tissue-specific antiviral role for IL-22 during acute infection in vivo and made the surprising finding that neutrophils play a protective role during infection. I also demonstrated that neutrophils can directly inhibit viral replication in vitro. Thus, novel insights into cytokine biology in the context of viral infections in vivo revealed by these studies highlighted important considerations for future research into herpesvirus infections, and has major implications for the treatment of this important infectious disease