Page 305 - Veterinary Immunology, 10th Edition

Comparison of MHC Class I and Class II Structure
VetBooks.ir Class I Class II

Loci include Typically A, B, and C
Distribution Most nucleated cells DP, DQ, and DR
B cells, macrophages, and dendritic cells
Function Present antigen to cytotoxic T cells Present antigen to T helper cells
Result T-cell-mediated toxicity T-cell-mediated help
The collective name given to the proteins encoded by MHC genes
depends on the species. In humans, these molecules are called
human leukocyte antigens (HLA); in dogs, they are called DLA; in
rabbits, RLA; in cattle (bovines), BoLA; in horses, ELA; in swine,

SLA; and so forth. In some species, MHC molecules were identified
as transplantation antigens before their true function was
recognized, and their nomenclature is anomalous. Thus, in the
mouse the MHC is called H-2, and in chickens it is called B. The

complete set of alleles found within an individual animal's MHC is
called its MHC haplotype.
While the human and mouse MHC class I genes exhibit extreme
allelic polymorphism, this is not the case in other mammals. In

these, MHC diversity is generated by variations in the number of
MHC class I genes expressed. If some MHC genes are expressed in
some MHC haplotypes but not in others, the effect will be to
generate even more diversity than alternative combinations of

alleles of a fixed gene. Gene content variation and allelic
polymorphism can therefore be considered as two alternative
strategies to diversify MHC haplotypes. Nonhuman primates,
rodents, horses, pigs, and ruminants all rely on variations in MHC

gene content. In contrast, humans, mice, dogs, and cats have
relatively few functional MHC class I genes and rely on allelic
polymorphism.

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