Pregnancy enhances antiviral immunity independent of type I IFN but dependent on IL-17-producing γδ T cells in the nasal mucosa.

Pregnancy is associated with profound changes in immunity. However, pregnancy-related respiratory immune adaptations in response to influenza infection and their impact on disease severity remain unclear. Here, we describe, in a preclinical model of mid-gestation pregnancy, a mechanism of enhanced host defense against influenza A virus (IAV) localized to the nasal cavity that limits viral replication and reduces the magnitude of intrapulmonary immune responses. Consequently, the pregnant mice show reduced pulmonary pathology and preserved airway function after IAV infection. The early restriction of viral replication is independent of type I interferon (IFN) but dependent on increased antimicrobial peptides (AMPs) driven by interleukin-17 (IL-17) γδ T cells within the nasal passages. This pathway of host defense against IAV infection in the upper airways during pregnancy restricts early viral infection and prevents virus dissemination into the lung supporting maternal fitness.