MHCgenes

This Week

Love is in the air
18 Aug 01

Smell your partner if you want to know whether the romance will
last

FORGET love horoscopes. If you want to know what the future holds
for you and a partner, sniff yourselves with an "e-nose".

                                Researchers in Germany have developed an electronic nose that can
                                detect the smells that mice use to choose mates with compatible
                                genes. The device should make it easier to test the controversial idea
                                that people also rely on smells, and that having the wrong ones may
                                sometimes sow the seeds of divorce.

                                Rodents sniff their suitors to see whether they have the same major
                                histocompatibility complex genes as their own. MHC genes code for
                                proteins in the immune system, and the more diverse they are, the
                                better your chances of coping with new infections. So rats and mice,
                                at least, follow their noses and choose mates with different MHC
                                genes, to endow their offspring with a varied portfolio.

                                Until now, researchers have not been able to directly measure
                                differences in smells associated with MHC genes. They have relied on
                                rodents to do this for them in behavioural experiments. But
                                Hans-Georg Rammensee and his colleagues at the University of
                                TÜbingen have built an electronic nose that does the job.

                                The e-nose has two components. The first contains a series of eight
                                tiny quartz crystals coated with different polymers. Odour molecules
                                stick to particular coatings, and just a few molecules will change the
                                frequency at which the crystal vibrates. The second part uses a
                                series of semiconducting metal-oxide gas sensors. Gases react with
                                oxygen on the sensor surfaces and change their conductivity. Both
                                components are hooked up to a computer that can recognise the
                                patterns of each smell. "It's very sensitive-it can distinguish different
                                brands of coffee, for example," says Rammensee.

                                The e-nose has already singled out mice with different MHC genes by
                                sniffing their urine. And, as the team will report in Proceedings of the
                                National Academy of Sciences, it can also distinguish the smell of
                                blood serum from people with different MHC genes.

                                The jury is still out on whether MHC smells affect our choice of
                                partners (New Scientist, 10 February, p 36). We probably mask MHC
                                smells with perfumes and deodorants. So a partner might only
                                subconsciously register them after a long exposure. Rather than being
                                involved in the dating game, MHC incompatibility may manifest itself in
                                today's high divorce rate.

                                Rammensee suggests that sociologists could use the e-nose to test
                                this idea, sniffing divorced couples to see if they have a higher
                                incidence of MHC incompatibility than those celebrating their silver
                                wedding anniversary, for example. "It is speculation," he cautions. But
                                if the idea is confirmed, courting couples could one day be
                                surreptitiously sniffing each other with e-noses to find out if they
                                make a good match.

Jon Copley
From New Scientist magazine, vol 171 issue 2304, 18/08/2001, page 15