It’s a theory much discussed in the media – that animals and humans are able to smell certain genes linked to the immune system – which in turn influences their choice of mate. The genes in question are known as MHC (major histocompatibility complex) genes. Selecting a mate with very different MHC genes from one’s own makes sense, because your offspring will then have a greater variety of immunity genes – and a correspondingly greater resistance to disease. But until now, no scent offering information about MHC genes had been discovered among those scents emitted by humans and animals. Now researchers from the University of Tübingen’s Immunology department and the Proteome Center in Germany, working with their colleagues from the University of Saarland, also in Germany, have managed to do just that. Their results, published online on March 19, 2013 in Nature Communications, will lead scientists to review the “sniff out a mate” theory. It is well known that the MHC genes determine which MHC peptides a cell presents at its surface to the immune system’s killer cells. These peptides are usually composed of the body’s own proteins and therefore do not set off any reaction. But if the MHC peptides come from a virus, the immune system’s killer cells can recognize that and attack it. According to one current theory, the MHC peptides also communicate the smell which offers information about MHC genes – a theory tested in mice. Special sensor cells were found which are able to recognize and distinguish the various MHC peptides from one another. Experiments have shown that synthetic MHC peptides in high concentrations were able to influence the behavior of mice, and that mouse urine carries what is believed to be the smell of MHC genes. Until now, it was not known whether MHC peptides even occurred naturally in urine.
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