Menus Subscribe Search

Genes Are Us

sick-man-healthy-woman

(Photo: Iakov Filimonov/Shutterstock)

Girls’ Immune Systems Rule, Boys Drool

• January 24, 2014 • 8:00 AM

(Photo: Iakov Filimonov/Shutterstock)

Why do women have such stronger immune systems than men?

What makes men and women different? Some differences are obviously biological, such as anatomy and the genetics of X and Y chromosomes. Other differences are social, the result of culture and history. And sometimes the reason men and women differ isn’t so clear. Disease often affects men and women differently, and in many cases it is difficult to know whether the cause is social, biological, or both—and this poses a challenge to medical researchers who struggle to account for the impact of gender on medical outcomes.

The reasons for differences between men and women in the incidence of some diseases are clear-cut. Lung cancer rates are higher among men for purely social reasons: until recently, men were more likely than women to smoke. On the other hand, the fact that the blood-clotting disorder hemophilia occurs almost exclusively in males is the result of genetics—the disease is caused by a mutation in a gene on the X chromosome. Women, with two X chromosomes, have a back-up version of this gene, while men, with only one X chromosome, don’t.

But other diseases pose more of a mystery. On average, men are affected more often and more severely by infectious diseases like viruses, bacteria, and other pathogenic microbes, and their immune systems respond less effectively to vaccines. While this observation could potentially be explained by social differences—maybe men are less likely to take simple precautions to avoid infection, or perhaps women are more likely to have their immune systems primed by exposure to sick children—researchers have long suspected that the immune systems of males and females are innately different.

In 1992, a pair of biologists at the University of Tromsø in Norway proposed the “immunocompetence handicap hypothesis,” which essentially says that males will perform dumb, dangerous stunts to impress females.

ONE KEY PIECE OF evidence for this idea is that women are more likely to suffer from autoimmune diseases like rheumatoid arthritis, when the immune system begins to attack things that it shouldn’t. That women are more susceptible to autoimmune diseases, while men have a higher incidence of infectious diseases suggests that women’s immune systems are much more active than men’s. It’s a neat hypothesis, but scientists have struggled to find any important differences in the detailed biology of the immune system that could explain why these diseases affect men and women so differently.

There is a set of obvious candidates that could be the cause of sex-based differences in immunity: hormones. Sex hormones, like estrogen and testosterone, are not only responsible for the characteristic physical differences between men and women, but they also have the ability to directly influence the many components of the immune system, like the white blood cells that produce antibodies and mount attacks against invading microbes and viruses. Intriguingly, some women experience a remission from some autoimmune diseases during pregnancy, when levels of sex hormones change dramatically. But it’s been difficult to establish any direct link between levels of sex hormones circulating in the blood and the performance of men’s and women’s immune systems.

Recent research is now beginning to firmly establish that link. This month, a team of scientists at Stanford University has reported some of the best evidence yet that testosterone directly influences immune system function in men. The researchers took blood samples from male and female volunteers who were given a flu shot. Women had higher levels of immune system molecules circulating in their blood than men, and they produced more effective antibodies against the flu virus. And there were not only differences between men and women, but there were differences among men—the men with the weakest response to the flu shot had high levels of both testosterone and testosterone-induced enzymes, suggesting that high levels of testosterone can suppress immunity.

This finding that testosterone may dial down the immune system in humans is consistent with the results of studies of other animals, ranging from fish to chimps. But why would an essential male hormone deliberately handicap the immune system?

THE ANSWER MIGHT BE that this is one of those odd outcomes that follow from the perverse incentives of evolutionary logic. In 1992, a pair of biologists at the University of Tromsø in Norway proposed the “immunocompetence handicap hypothesis,” which essentially says that males will perform dumb, dangerous stunts to impress females. The idea behind the immunocompetence handicap hypothesis is that, in order to prove their genetic fitness to potential mates, males make a trade-off between a robust immune system and a set of elaborate, testosterone-driven secondary sex characteristics, like brightly colored plumage in tropical birds. Those males with the best immune system genes will be healthy despite a big testosterone handicap. The males who can tolerate the highest testosterone levels will have the most exaggerated sex characteristics, and therefore, sex characteristics will be a reliable visual indicator of genetic fitness.

The immunocompetence handicap hypothesis has been provocative and controversial. The evidence for it is decidedly mixed, but the idea has spawned more extensive research into the question of what visual cues signal robust health in humans. Is men’s sexual attractiveness related to the performance of their immune systems? In a study published last year, an international team of scientists attempted to answer that question. The authors hypothesized that masculine features in young male volunteers would be rated more attractive by women and signal the possession of good immune system genes. It turns out that the body feature most closely linked to attractiveness and immune system performance is fat—as you might expect, having too much or too little is less attractive and less healthy.

Whether human males handicap their immune systems for the sake of sexual attractiveness is an unresolved question, but the consequences of sex-based differences in immunity are large, for both men and women. Medical researchers hope that a better understanding of the causes will help them tailor vaccines, drugs, and other treatments to the distinct needs of men and women.

Michael White
Michael White is a systems biologist at the Department of Genetics and the Center for Genome Sciences and Systems Biology at the Washington University School of Medicine in St. Louis, where he studies how DNA encodes information for gene regulation. He co-founded the online science pub The Finch and Pea. Follow him on Twitter @genologos.

More From Michael White

A weekly roundup of the best of Pacific Standard and PSmag.com, delivered straight to your inbox.

Recent Posts

August 21 • 2:37 PM

How the Brains of Risk-Taking Teens Work

There’s heightened functional connectivity between the brain’s emotion regulator and reason center, according to a recent neuroscience paper.


August 21 • 2:00 PM

Cracking Down on the Use of Restraints in Schools

Federal investigators found that children at two Virginia schools were being regularly pinned down or isolated and that their education was suffering as a result.


August 21 • 12:00 PM

What Makes You So Smart, School Principal?

Noah Davis talks to Evan Glazer about why kids aren’t getting smarter and what his school’s doing in order to change that.



August 21 • 10:00 AM

Why My Neighbors Still Use Dial-Up Internet

It’s not because they want to. It’s because they have no other choice.


August 21 • 8:15 AM

When Mothers Sing, Premature Babies Thrive

Moms willing to serenade pre-term infants help their babies—and themselves.


August 21 • 8:00 AM

To Fight the Obesity Epidemic Americans Will Have to First Recognize That They’re Obese

There is a void in the medical community’s understanding of how families see themselves and understand their weight.


August 21 • 6:33 AM

One Toxic Boss Can Poison the Whole Workplace

Office leaders who bully even just one member of their team harm everyone.


August 21 • 6:00 AM

The Fox News Effect

Whatever you think of its approach, Fox News has created a more conservative Congress and a more polarized electorate, according to a series of recent studies.


August 21 • 4:00 AM

Do Children Help Care for the Family Pet?

Or does mom do it all?


August 20 • 4:00 PM

Why Can’t Conservatives See the Benefits of Affordable Child Care?

Private programs might do a better job of watching our kids than state-run programs, but they’re not accessible to everyone.


August 20 • 2:00 PM

Oil and Gas Companies Are Illegally Using Diesel Fuel in Hundreds of Fracking Operations

An analysis by an environmental group finds hundreds of cases in which drillers used diesel fuel without obtaining permits and sometimes altered records disclosing they had done so.


August 20 • 12:00 PM

The Mystery of Britain’s Alien Big Cats

In a nation where the biggest carnivorous predator is a badger, why are there so many reported sightings of large cats?


August 20 • 10:00 AM

Death Row in Arizona: Where Human Experimentation Is the Rule, Not the Exception

Recent reports show that chemical roulette is the state’s M.O.


August 20 • 9:51 AM

Diversity Is in the Eye of the Beholder

Perception of group diversity depends on the race of the observer and the extent to which they worry about discrimination.


August 20 • 8:40 AM

Psychopathic or Just Antisocial? A Key Brain Difference Tells the Tale

Though psychopaths and antisocial people may seem similar, what occurs in their brains isn’t.


August 20 • 8:00 AM

What the Cost of Raising a Child in America Tells Us About Income Inequality

You’ll spend nearly a quarter of a million dollars to raise a kid in the United States, or about five times the annual median income.


August 20 • 6:00 AM

In Praise of ‘American Greed’

While it remains semi-hidden on CNBC and can’t claim the car chases of Cops, American Greed—now with eight seasons in the books—has proven itself a worthy endeavor.


August 20 • 4:00 AM

Of Course I Behaved Like a Jerk, I Was Just Watching ‘Jersey Shore’

Researchers find watching certain types of reality TV can make viewers more aggressive.


August 20 • 2:00 AM

Concluding Remarks About Housing Affordability and Supply Restricitions

Demand, not supply, plays the dominant role in explaining the housing affordability crisis. The wages are just too damn low.


August 19 • 4:00 PM

Can Lawmakers Only Make Laws That Corporations Allow?

There’s a telling detail in a recent story about efforts to close loopholes in corporate tax laws.




August 19 • 12:00 PM

How ‘Contagion’ Became Contagious

Do ideas and emotions really spread like a virus?


August 19 • 10:00 AM

Child Refugees: The New Barbarians

The disturbing rhetoric around the recent rise in child refugees into the United States from Central America may be shaping popular opinion on upcoming immigration reform.


Follow us


How the Brains of Risk-Taking Teens Work

There's heightened functional connectivity between the brain's emotion regulator and reason center, according to a recent neuroscience paper.

When Mothers Sing, Premature Babies Thrive

Moms willing to serenade pre-term infants help their babies—and themselves.

One Toxic Boss Can Poison the Whole Workplace

Office leaders who bully even just one member of their team harm everyone.

Diversity Is in the Eye of the Beholder

Perception of group diversity depends on the race of the observer and the extent to which they worry about discrimination.

Psychopathic or Just Antisocial? A Key Brain Difference Tells the Tale

Though psychopaths and antisocial people may seem similar, what occurs in their brains isn’t.

The Big One

One in two full-time American fast-food workers' families are enrolled in public assistance programs, at a cost of $7 billion per year. July/August 2014 fast-food-big-one
Subscribe Now

Copyright © 2014 by Pacific Standard and The Miller-McCune Center for Research, Media, and Public Policy. All Rights Reserved.