While our understanding of the immunology of pregnancy has considerably improved, many questions remain unanswered. These questions include how the immune system changes throughout pregnancy and how these changes might influence susceptibility to and severity of infectious diseases. In a new study, researchers from McGill University show that pregnancy protects mice from influenza A virus (IAV) infection by enhancing antiviral immunity in the nasal cavity.

To date, most of the studies exploring immune changes during pregnancy and their impact on host defence have relied on BALB/c mice, a mouse strain quite sensitive to IAV infection. BALB/c mice develop severe disease and have been useful to study maternal morbidity after influenza infection. Here, the researchers infected pregnant and nonpregnant female C57BL/6 mice intranasally with sublethal doses of H1N1 virus and monitored the animals for several days. Their results revealed that IAV-infected pregnant mice lost less weight than the nonpregnant females compared to their respective uninfected controls.

Further analysis showed that pregnancy reduced the pulmonary viral burden at 10 h and day 1 (D1) post-IAV infection, with limited lung IAV-induced immunopathology at D9 post-infection, confirming that pregnancy in C57BL/6 mice enhanced host resistance to IAV infection. Additional experiments demonstrated that resistance to IAV infection was independent of type I interferon response in the lung, but dependent on enhanced immunity mediated by antimicrobial peptides (AMPs) within the nasal passages.

Future studies are necessary to elucidate if AMPs in the nasal mucosa directly restrict IAV replication and/or promote the recruitment of inflammatory cells to clear infection. However, this study introduces a new pregnancy model of resistance to infection in C57BL/6 mice, as an important step to further understand pregnancy-related immune changes and their influence on host defence.

Original reference: Chronopoulos, J. et. al. Sci. Adv. 10, eado7087 (2024)