Contrary to the common belief that pregnancy increases vulnerability to infections, researchers found that it strengthened an immune defense in mice, blocking the Influenza A virus from spreading to the lungs, where it can cause severe infection.

“Our results are surprising because of the current dogma, but it makes sense from an evolutionary perspective,” said co-lead author Dr. Maziar Divangahi, Professor in McGill’s Faculty of Medicine and Health Sciences and Senior Scientist at the Research Institute of the McGill University Health Centre (The Institute).

“A mother needs to stay healthy to protect her developing baby, so the immune system adapts to provide stronger defenses. This fascinating response in the nasal cavity is the body’s way of adding an extra layer of protection, which turns on during pregnancy.”

Exploring benefits for pregnancy and beyond

The researchers used a mouse model to observe how a certain type of immune cell activates in the nasal cavity of mice during pregnancy, producing a powerful molecule that boosts the body’s antiviral defenses, especially in the nose and upper airways.

“Influenza A virus remains among the deadliest threats to humanity,” said first author Julia Chronopoulos, who carried out the research while completing her PhD at McGill. “This natural immunity in pregnancy could change the way we think about flu protection for expectant mothers.”

The Public Health Agency of Canada recommends pregnant women and pregnant individuals get the flu vaccine, as they are at high risk of severe illness and complications like preterm birth. The new insights offer promise for more targeted vaccines for influenza, which is among the top 10 leading causes of death in Canada.

“The broader population could also benefit, as our findings suggest the immune response we observed could be replicated beyond pregnancy,” said co-lead author Dr. James Martin, Professor in McGill’s Faculty of Medicine and Health Sciences and Senior Scientist at the RI-MUHC. This could mean new nasal vaccines or treatments that increase protective molecules, known as Interleukin-17.

The team’s next focus is on finding ways to reduce lung damage during viral infections like the flu or COVID-19. Rather than targeting the virus, as previous research has done, they aim to prevent dysregulated immune systems from overreacting, an approach that could lower the risk of serious complications associated with flu infection.

The research was funded by the Canadian Institutes of Health Research.