Evolutionary and Immunological Implications of the Role of the MHC in Olfactory Signalling
Amongst its many odour signals, urine emits an odour, unique to each individual, which is directly related to the MHC type (Yamazaki et al., 1976, Singh et al., 1987, Brown et al., 1989). Extreme polymorphism of the class I MHC loci provides sufficient variation within a species to confer uniqueness on individuals at this molecular level (Klein, 1982). However, the way in which this protein polymorphism is expressed as odour polymorphism in the urine is not known. Since the MHC class I molecules are themselves excreted in the urine, they could be thought to provide individually unique signals except that they are non-volatile proteins and therefore not detectable by smell. Because the excreted class I molecules are extensively degraded in the urine (Singh et al., 1987), it is possible that aromatic amino acids, characteristic of the variable sequences in the heavy chain contribute the aromatic signals. However, since most amino acids have no smell, this explanation seems unlikely.
KeywordsHeavy Chain Volatile Odorant Urine Odour Bacterial Volatile Congenic Pair
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