Mice smell a mate’s immune system

A whiff of urine, sweat, or other body fluids may provide some mammals with a direct view into each other’s immune systems, giving them information that could prevent inbreeding, a new study suggests.

Researchers have long known that the major histocompatibility complex (MHC), a collection of immune system molecules that distinguishes tissues as self or nonself, plays an important role in mate choice.

Mammals, including people, tend to choose mates with MHC genes dissimilar from their own, and that has raised a vexing question: How do animals sense each other’s MHC makeup?

Frank Zufall of the University of Maryland at College Park and his colleagues suspected that the answer lies in the vomeronasal organ (VNO), a small pit inside the nose that, in many animals, detects pheromones and other molecules important in reproduction.

The researchers found that neurons in a mouse VNO section known as the basal zone fire when stimulated by MHC-produced molecules isolated from mouse urine. The VNO neurons’ unique response patterns to different molecules (SN: 10/9/04, p. 229: Available to subscribers at Nobel prizes: The sweet smell of success) may give mice a way to identify individuals through smell, Zufall and his team speculate in the Nov. 5 Science.