Influence of Immunological Maturity on Respiratory Syncytial Virus-Induced Morbidity in Young Children.

Respiratory syncytial virus (RSV) is a very frequent viral respiratory pathogen of the young (<5 years old) with a significant portion of young toddlers having been infected before 2 years of age. Although we understand that some of the morbidity associated with RSV in neonates is due to immunological maturation that favors immunosuppression over antiviral innate and/or adaptive immune responses, the rapid development of the immune system right after birth suggests that each age group (newborn, early infant, older infant, toddler, and older) may respond to the virus in different ways. In this study, we summarize the morbidity associated with infection in young children in the context of immunological maturation of monocytes/macrophages and the ramifications for poor innate control of viral pathogenesis. We also summarize key mechanisms that contribute to the diminished antiviral innate immune responses of these young children.