Impaired gamma delta T cell-derived IL-17A and inflammasome activation during early respiratory syncytial virus infection in infants

Respiratory syncytial virus (RSV) infection remains a significant global health burden disproportionately affecting infants and leading to long-term lung disease. IL-17A has been shown to be involved in regulating viral and allergic lung inflammatory responses, which has led to a more recent interest in its role in RSV infection. Using a neonatal mouse model of RSV, we demonstrate that neonates fail to develop IL-17A responses compared to adult mice; the main immediate IL-17A contributor in adults were γδ T cells. Antibody neutralization of IL-17A in adult mice caused increased lung inflammation and airway mucus from RSV, while exogenous IL-17A administration to RSV-infected neonates caused decreased inflammation but no change in airway mucus. We also observed a lack of pro-inflammatory cytokine production (IL-1β, IL-6) from infected neonates. Using human cord blood mononuclear cells (CBMCs) and adult peripheral blood mononuclear cells (PBMCs), we compared inflammasome activation by direct retinoic acid-inducible gene I (RIG-I) agonism; CBMCs failed to induce pro-inflammatory cytokines or IL-17A(+) γδ T cells compared to PBMCs. Our results indicate that RSV disease severity is in part mediated by a lack of inflammasome activation and IL-17A production in neonates.