Page 322 - Veterinary Immunology, 10th Edition

VetBooks.ir MHC and Body Odors

Mammals use odors to detect information about another
individual's gender, status, and individuality. The molecules that

carry this information are small volatile peptides found in urine.
These peptides can bind to the antigen-binding grooves of MHC
class I molecules. Thus, peptides known to bind to two mouse
MHC class I molecules of different haplotypes were shown to
induce responses (field potentials) in mouse vomeronasal organs.

The responses were not haplotype specific, but different peptides
induced different activation patterns. This finding may well explain
how mammals such as mice can recognize the MHC of other mice

by smell.
The class I region of mice, cattle, and pigs contains numerous
genes coding for pheromone olfactory receptors. As a result, the
MHC haplotype affects the recognition of peptide ligands causing
individual odors in an allele-specific fashion and thus influences the

mating preferences of mammals. Thus under controlled conditions,
mice prefer to mate with MHC-incompatible individuals. Such
matings preferentially generate heterozygote advantage, resulting

in optimized disease resistance (Box 11.1). However, this type of
mating could also prevent genome-wide inbreeding. Inbreeding
avoidance may be the most important function of MHC-based
mating preferences and therefore the fundamental selective force
diversifying MHC genes in species with such mating patterns.

Despite not having a vomeronasal organ, humans also have the
ability to sense MHC peptides in body odor, and this may influence
human mate choice.

Box 11.1

MHC and Sperm Counts in Horses

The MHC haplotype is closely linked to body odors. Mate choice
appears to be determined in some species by odor. For example, 12

stallions were exposed to a MHC-similar mare and then to a MHC-
dissimilar mare or vice versa for four weeks. Blood testosterone
levels were determined weekly. Ejaculates were collected at the

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