Structure and properties of the major histocompatibility complex of the chicken. Speculations on the advantages and evolution of polymorphism.

Abstract

Our knowledge of the chicken MHC has greatly expanded since the last review article on the subject (Pazderka et al; 1975 a) through the great progress that has been made in the areas of genetic structure, biochemistry, disease resistance and serology of the chicken MHC. It is becoming increasingly apparent that the chicken MHC is very similar in most respects to mammalian MHC's. Most of the immunologically related phenomena or functions which are known for H-2 alleles are now known for the chicken MHC. These include the determination of serologically detectable antigens, histocompatibility antigens, immune responses, serum proteins, resistance to virus-induced malignancy and cell-cell interactions. The finding of all these immunological functions grouped together in close linkage disequilibrium in species as different as chickens, mice, and humans, as well as the striking homologies between MHC antigens of these species strongly favors the view that MHC's evolved and persisted in association with some functional advantages to the species. Apart from the interesting phylogenetic aspects one might naturally ask the question"why study the chicken MHC?" The answer to this question is quite simply that basic studies on the chicken MHC have given uniquely important clues to the functional advantage of MHC polymorphism as well as the survival value for the species of certain MHC alleles. The study of inbred mice has told us a great deal about the biochemistry of MHC antigens and the fine structure of the MHC but tells us little about natural selection. The herpes virus causing Marek's disease is an important agent of natural selection in the chicken and one MHC haplotype is strongly associated with resistance to this contagious lymphoma in several unrelated populations of chickens, including the progenitor of the species. Other MHC haplotypes of the chicken are associated with long life span and general fitness, or with high adult mortality. Other basic studies on the chicken MHC have revealed the widespread existence of natural antibodies against MHC as well as other polymorphic cell-surface antigens. These studies have also shown that the immune response of mice against