Sex hormone may protect women from worst effects of the flu

Progesterone, a female sex hormone, found in most forms of hormone-based birth control pills, appears to stave off the worst effects of influenza infection and help damaged lung cells to heal more quickly, suggests a new study.
In mouse studies, researchers from the Johns Hopkins Bloomberg School of Public Health, in the US, suggest that sex hormones have an effect far beyond the reproductive system and that progesterone may one day be a viable flu treatment for women.
The World Health Organisation reports that more than 100 million young adult women around the world are on progesterone-based contraception. And women of reproductive age are twice as likely as men to suffer from complications related to the influenza virus.

"Despite the staggering number of women who take this kind of birth control, very few studies are out there that evaluate the impact of contraceptives on how the body responds to infections beyond sexually transmitted diseases," said lead author Sabra L. Klein, associate professor in the Bloomberg School.
"Understanding the role that progesterone appears to play in repairing lung cells could really be important for women's health. When women go on birth control, they don't generally think about the health implications beyond stopping ovulation, and it's important to consider them," she added.
For their research, Klein and her colleagues placed progesterone implants in female mice and left other mice, also female, without. The mice were then infected with influenza A virus. Both sets of mice became ill, but those with implants had less pulmonary inflammation and better lung function and saw the damage to their lung cells repaired more quickly.

The researchers found that progesterone was protective against the more serious effects of the flu by increasing the production of a protein called amphiregulin by the cells lining the lungs. When the researchers bred mice that were depleted of amphiregulin, the protective effects of progesterone disappeared as well.

Klein said she was not surprised that progesterone lessened the inflammation and damage associated with the flu. What she did not expect was to find that progesterone also helped induce repair.
Klein said there is no scientific data to date showing whether progesterone in humans has any relationship to flu severity, since no researchers have asked those questions.

The mice in the original study were given actual progesterone and not a synthetic form of the hormone, which is what is in contraception. More recently, as part of their ongoing research, Klein and her team gave synthetic progesterone to mice and found a similar effect.
The findings appears in the journal PLOS Pathogens.