Page 307 - Veterinary Immunology, 10th Edition

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FIG. 11.3 The structure of a class Ia MHC molecule on a cell
membrane. Its antigen-binding site is formed by the folding of both
its α and α domains.
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Gene Arrangement

The size of the MHC class I region varies. Humans and rodents
have the largest, and pigs have the smallest. Each MHC class I

region has a common framework of non-MHC genes, and size
differences are mainly due to variations in these framework genes.
The number of class Ia genes also varies between mammals
ranging from rats with more than 60 to pigs with 11. Not all these

genes are functional. In mice, only two or three class I genes are
expressed. The remainder are pseudogenes (defective genes that
cannot be expressed). In humans the functional polymorphic genes
are called A, B, and C. In mice they are called K and D (and in some

strains, L). In other mammals they are usually numbered (Fig. 11.4).

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