My favorite ones are those where women sniff the shirts of various men and pick out the ones that smell the best to them. The ones they like best are usually from men whose immune systems are most different from theirs.

This makes some sense if you think about it. The strongest immune system is a varied one. It can fight off lots of different kinds of bacteria, parasites, and viruses.

And since our immune system is programmed by our genes and our genes come from mom and dad, the more different mom and dad’s genes are, the more varied your immune system will be. So ideally you would choose a mate that would give your children the stronger immune system. That mate would have an immune system very different from yours.

One way you might be able to find that particular mate is if different immune systems have different odors. The stinky guys share your immune system; the pleasant smelling ones have a different one.

This seems to be what is happening in these armpit smelling experiments. So at least some amount of attraction between people is happening with the nose.

But what I found even more interesting was that oral contraceptives mess with this system. Women on the pill tend to prefer the smell of men with similar immune systems. Some scientists think this is because pregnant women prefer family around them and family tends to have a similar immune system.

When I first read this I thought, “Wow, this is going to really mess up future generations’ immune systems. Maybe it even helps to explain the recent rise in allergies and autoimmune diseases.”

But then I caught myself and thought a little harder. It is probably not that likely that the recent increases in allergies and autoimmune diseases would have happened so quickly if the pill were the main culprit. And besides, there is undoubtedly more to human mate selection than smell!

We are complicated. There are all sorts of cues that cause someone to fall in love. Pheromones may play a role but they are certainly not the whole story.

For example, some studies use photos and ask women which men are the most attractive. The women in these studies tend to pick men with more similar immune systems (apparently there is some correlation between facial symmetry and the immune system).

And when scientists look at couples who actually have children together, they get mixed results. An early study pointed to Europeans having children with partners with different immune system genes. But a deeper look at that data and looking at a larger group of couples showed that this didn’t seem to be the case. Differing immune systems had little impact on who women chose to have children with.

The most that could be said was that women tended to avoid men with really similar immune systems. A bit similar was OK.

Of course we could already be seeing the effects of the pill in these studies. Maybe if the women in these studies hadn’t been on the pill when they met their partners, they might have chosen someone with a more dissimilar immune system.

Scientists need to look at people who did not meet while women were on the pill. Then we will have a better idea of how big a role your nose plays in choosing your soul mate. And how worried we should be about the pill’s effect on that selection.

Nice PBS video about the t-shirt smelling experiments.

Marin County former astronaut Millie Hughes-Fulford was the first woman to travel into space as a working scientist, or "payload specialist," in 1991. Photo: Michael Goode

As NASA’s space shuttle program comes to an end, we profile Marin County former astronaut Millie Hughes-Fulford. In 1991, the molecular biologist was the first woman to travel into space as a working scientist. Since then, she has sent a string of experiments into space that could one day help space travelers on long voyages, and aging people here on Earth.

Hughes Fulford's career opens up a fascinating window onto the history of the shuttle program and of space science, which we were able to bring to life through a treasure trove of NASA footage. Associate producer Michael Goode and I sifted through dozens of hours of video of happy times and tragic moments. Hughes-Fulford clearly relishes her firefighting training before the flight, and is seen busy at work in the Spacelab on board the shuttle Columbia. But she also had the misfortune of sitting at Kennedy Space Center and watching in horror as the shuttle Challenger exploded soon after launching in January of 1986.

Hughes-Fulford made history in 1991, on board the shuttle Columbia, as the first woman “payload specialist.” Payload specialists are scientists who are experts on a particular mission’s experiments or “payload.” Although they undergo rigorous training, payload specialists aren’t career astronauts who expect to make space travel their life’s work. Instead, their goal is to carry out a group of experiments for other scientists who remain on Earth.

“You have the shuttle pilots, who are the commanders, and they get you there and they get you home,”
Hughes-Fulford said, explaining the different types of astronauts involved in space shuttle flights. “Then you have mission specialists, who are career astronauts, and they train for a specific mission. And then you have payload specialists who know the topic.”

Sally Ride, the Stanford-educated physicist who was the first American woman to fly into space, in 1983, was a career astronaut. The very first woman to travel into space was Soviet cosmonaut Valentina Tereshkova, in 1963.

One of the experiments that Hughes-Fulford carried out during her nine days on board shuttle Columbia had been designed by Switzerland-based researcher Augusto Cogoli to examine how the immune system fares in space. Cogoli’s experiment showed that the lack of gravity in space affected the immune system. Up until then, scientists had believed that perhaps hormones were to blame for space travelers’ weakened immune system. Cogoli’s experiment showed that zero gravity, not hormones, was to blame.

Hughes-Fulford has since sent up her own experiments to space —some in collaboration with Cogoli— to further investigate the mechanisms by which a lack of gravity weakens the immune system. Her findings could one day translate into treatments for diseases brought on by the immuno-suppression associated with aging, as well as HIV infection, which hurts the immune system, and rheumatoid arthritis, in which the immune system is too active. And if we’re ever going to send astronauts to Mars —a trip that could take six months with today’s technology— we’ll need to figure out how to keep them healthy.

She and her lab members at the San Francisco VA Medical Center just sent up a group of research mice (known as “astromice”) on the shuttle Atlantis, the very last shuttle flight. Hughes-Fulford and colleagues Esmeralda Aguayo and Joe Meissler were in Florida to watch the Atlantis take off and land. Hughes-Fulford wrote the following for QUEST as she flew back to the Bay Area from Florida three days after the July 21 landing:

“As I fly back from Kennedy Space Center to the Bay Area, I reflect back on the last fantastic and final launch and landing of the space shuttle Atlantis. Upon return to Earth, most astronauts and cosmonauts remark about seeing no borders when they looked at our planet. While in orbit, we see one world. The shuttle program speaks to the one-world concept. This era of spaceflight saw a time where international scientific cooperation from Europe, Japan, Canada and many other countries was at its best and most rewarding in scientific discovery.”

The invitation for Hughes-Fulford to send her latest experiment up on the Atlantis came at the very last moment, she told QUEST. In fact, she received a phone call at the end of June, just weeks before the July launch.

In our TV story, which we finished back in May, we reported that Hughes-Fulford had sent eight experiments into space and was preparing to send her ninth one up in 2012. That was before she was invited to send her research up on the Atlantis. With the successful completion of the Atlantis flight, she’s now preparing her tenth experiment.

Since the shuttle is no longer available, Hughes-Fulford plans to send her next experiment up with a private company, Los Angeles-based SpaceX. If all goes well, her tenth experiment will travel into space in April 2012 and might actually be the very first experiment to go up to the International Space Station on a SpaceX vehicle.

CORRECTION: In the TV story, we say that 40 women have flown into space. The correct number, according to NASA, is 54. We regret the error.

Exercise prevents the shortening of telomeres caused by psychological stress. Image courtesy of mikebaird.

New research by Nobel Prize winning UCSF researcher, Elizabeth Blackburn, provides a possible mechanism by which exercise protects against stress-related chromosome aging.

The findings, presented this month at the American Association for Cancer Research 102nd Annual Meeting, were based on earlier research showing that stress accelerates telomere shortening. Telomeres are protective strands of DNA found on the end of chromosomes that protect them from degradation during cell division. Telomere length is associated with cellular health, and is a known marker of cell aging.

Shorter telomeres are associated with cell death and chromosome instability, which can lead to inflammation. In immune cells, short telomeres can predict poorer prognosis in patients with heart disease and cancer.

In a previous study by Blackburn, psychological stress was associated with shorter telomeres in the lymphocytes of caregivers of chronically ill children. This was the first demonstration that telomere length is correlated to perceived stress. In the current study, co-authored by biochemist Jue Lin, telomere length was again associated with stress levels, this time in primary caregivers looking after a family member with dementia. However when the researchers looked at the immune cells in those who exercised, there was no association between stress and telomere length.

Another study, led by Eli Puterman, examined the impact of exercise on the telomeres of healthy women who had been victims of child abuse. In this study those who exercised were protected against the effects of stress on telomere length.

“We saw a relationship between childhood trauma and short telomere length but the relationship seems to go away in people who exercise vigorously at least three times a week,” said Lin in a press release.

Exercise is known to beneficially impact immune function and several other aspects of health. This new research illuminates on one possible mechanism by which physical activity exerts its helpful effects.

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Love is in the air

We've known for awhile that animals find their "true love" partly through smells. One of the things they are sensing is whether the potential mate has a different set of MHC genes.

MHC genes are a big part of our immune system. These genes are used to create the huge number of antibodies that we each make to battle bacteria, viruses, etc. Everyone has a different set of these antibodies.

The more varied your MHC genes are, the more invaders your immune system can recognize and defeat. So two parents with very different MHC genes will have kids with immune systems that can recognize (and so defeat) lots of different kinds of bacteria and viruses. Parents with similar MHC genes will have kids with less varied immune systems. (This is a big reason why inbred animals are so sickly.)

Animals can tell about a potential mate's MHC genes through smell. And people might be able to do this as well.

Lots of experiments have been done where men or women sniff the sweaty t-shirts of members of the opposite sex to see which t-shirt smells better. If the potential mates are of the same ethnic group, the sniffers tend to prefer mates with very dissimilar MHC genes. If the potential mates were of different ethnic groups, the sniffers preferred mates with somewhat but not wildly dissimilar MHC genes.

The new study looked at a group of 30 European American couples from Utah and 30 Yoruba couples from Nigeria. Thankfully there was no sweat smelling involved. Instead the researchers compared the DNA between the spouses of each couple in many different places throughout their genome.

What they found was that for the Utah couples, the DNA around the MHC genes was much less alike than the DNA almost everywhere else. This did not appear to be the case for the Yoruba couples. This suggests that at least for these 30 couples from Utah, having a very different set of MHC genes may have been part of picking a spouse.

Why the difference between the Utahans and the Yorubans? It is hard to say without more data but one possibility has to do with how much of a role social factors play in picking a spouse in each society. Perhaps the European Americans are freer to choose a mate. If this is the case, then they might be more likely to follow some sort of biological imperative.

Another possibility is that this smell test is only a big deal if the potential mates are all very similar to start with. The Utah couples all had pretty similar DNA to each other to begin with. The Yoruba couples' DNA was less alike.

Of course, this is a total of 60 couples and so is in no way exhaustive and may be proven wrong tomorrow. But it adds to a growing pile of evidence that suggests how mate selection works at the biological level. And it shows the wide range of things we can learn about ourselves by studying our DNA in great detail. Maybe it even gives perfume companies some ideas too.

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You're as likely to be struck by lightning
as to have a severe reaction to a vaccine.

I was reading an article in Time last week about parents not vaccinating their children. The story was about how this phenomenon is becoming more widespread.

These kinds of stories are weird to me because vaccines are pretty safe. The risk of an adverse side effect is incredibly small. For example, the risk for anaphylaxis from the Hepatitis B Virus vaccination is around 1 in 600,000. This is about the same risk as being struck by lightning (1 in 700,000).

Of course, the article wasn't talking about known risks. Instead, it was referring to a hypothesized link between vaccines and autism.

People proposed this link when they noticed that cases of autism and the number of vaccinations were rising at the same time. Of course, just because two things happen to occur at the same time, this does not mean they are causally linked. For example, the increase in global temperature is not related to the decrease in the world's populations of pirates (despite what the Pastafarians say).

So how could an increased number of vaccinations cause an increase in the number of cases of autism? I have seen two ideas put forth. The first is that thimerosal is to blame. The second is that there are so many vaccinations now that we are stressing out the body's immune system. Most likely neither idea is valid.

Thimerosal is a mercury-based preservative that used to be used in vaccines. Even though there haven't been any good studies on the effects of thimerosal on brain development, everyone knows mercury is bad for the brain. So the idea behind thimerosal makes some sense.

Back in 2001, vaccine manufacturers decided to eliminate thimerosal from their vaccines. We would predict, then, that cases of autism should go down significantly if thimerosal was linked to autism. They haven't. In fact, in one California study, cases have continued to climb. So thimerosal is most likely not to blame.

Another point that has been made is that there are so many vaccines now that we are stressing out our bodies' immune systems. Again, this concern is unfounded.

Vaccines are injections of viral proteins. Our bodies see the proteins and raise antibodies to them. Then when a virus invades, we have antibodies that recognize the virus and target it for destruction.

It is the number of viral proteins that matter in terms of taxing the body's immune system and not the number of vaccinations. All of the current vaccines put together do not have as many viral proteins as the old smallpox vaccine (150 vs. 200). So the number of vaccines is unlikely to be the issue.

What all of this means is that vaccines are probably not responsible for the significant increase in the number of cases of autism. What is responsible? No one knows for sure.

It may be that the rise just comes from all of us recognizing the symptoms more. Or it could be due to some cause we don't know about or understand.

What we do know is that vaccines save many lives. I assume no one wants to go back to the early 20th century when polio epidemics swept the country. For example, 2,500 cases of polio ended up at one Los Angeles hospital between May and November of 1934. And in 1952, the U.S. had 21,000 cases of paralytic polio.

We can prevent this sort of thing from happening by making sure everyone is vaccinated. And yet there are people who choose to hide behind the people who take the miniscule risk of getting vaccinated.

Is this a matter of free choice? Should parents be allowed to opt out of vaccinating their children even if it risks society at large?

One idea, I suppose, is to have people who choose not to be vaccinated to sign a waiver saying they accept full responsibility for their actions. In practice this would mean that health insurance and the government would not be responsible for their children's health care bills if they become ill with one of the diseases they refused to be vaccinated against.

And if your infant, grandma, or immuno-suppressed cousin came down with a disease these folks refused to be vaccinated against, then you could sue the un-vaccinated for damages. The common good isn't enough to encourage these folks. Perhaps threats to their pocketbook will be.

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