New research suggests men with high circulating levels of testosterone didn't reap as much benefit from the flu shot as those with lower levels.
Researchers found that women had a stronger response to the flu shot than men, a Stanford University Medical Center news release reported.
Men tend to be more susceptible to "bacterial, viral, fungal and parasitic infection" than women; and they do not respond as well to vaccines for "influenza, yellow fever, measles, hepatitis and many other diseases."
Women have been known to possess more signaling proteins that immune cells use to "jump-start" inflammation, which is an indicator that the immune system has been activated. Testosterone has also been shown to have anti-inflammatory properties. Because of these findings researchers believed there was a link between testosterone and immune responses.
The recent study did not find a link between "pro-inflammatory proteins and responsiveness to the flu vaccine," or a direct link between testosterone and the immune system. Instead the team found testosterone interacts with certain genes in a way that suppresses immune responses.
"This is the first study to show an explicit correlation between testosterone levels, gene expression and immune responsiveness in humans," ark Davis, PhD, professor of microbiology and immunology and director of Stanford's Institute for Immunity, Transplantation and Infection, said in the news release. "It could be food for thought to all the testosterone-supplement takers out there."
The team used sophisticated tools to take into account factors such as "numerous" immune-signaling proteins and a number of blood-cell subtypes, and how large of a role about 22,000 genes played in circulating played in circulating immune cells.
"Most studies don't report on sex differences, a major determinant of variation in immune response," said the study's lead author, David Furman, PhD, a research associate in Davis' group. The Stanford team, in collaboration with researchers at the French governmental research organization INSERM, aimed at probing those differences.
The researchers looked at blood samples from 53 women and 34 men, and found women had a stronger "antibody responses to the influenza vaccine."
This was not surprising," David Furman, PhD, a research associate in Davis' group said.
The team pinpointed a certain set of male genes (module 52) that usually turned off and on at the same time and were related to a weakened antibody response to the flu vaccine.
The research team separated the 34 men into two groups: "those whose circulating levels of testosterone in its bioactive form were above the median level, and those with below-median levels of the hormone."
The researchers found that in men with high testosterone levels showed a significant correlation between "high-activation levels of Module 52" and lower antibody levels after receiving a flu shot. Women and men with lower testosterone levels did not show a significant correlation.
Getting the flu is unpleasant; but researchers believe the weakened immunes response may have an evolutionary background.
Women are more susceptible to sepsis than men, which is caused by an "inflammatory overdrive."
"Ask yourself which sex is more likely to clash violently with, and do grievous bodily harm to, others of their own sex," Davis said.
