Experimental viral evolution to specific host MHC genotypes reveals fitness and virulence trade-offs in alternative MHC types

This study tests the requirements of the antagonistic coevolution hypothesis for MHC variability. If frequency-dependent selection on MHC alleles is occurring, then the pathogens must be more fit in "familiar" (ie more common) MHC host types, verses unfamiliar (ie rare) host types, and this fitness must be correlated with virulence. The researchers test this hypothesis by infecting mice of various MHC profiles with a mouse-specific retrovirus. The study presents positive results: the more common the MHC type, the more fit and virulent the pathogen. They conclude that this study is unique in confirming the necessary conditions for the antagonistic coevolution model of MHC evolution.