Page 503 - Veterinary Immunology, 10th Edition

Primates
VetBooks.ir Humans have four IGHG genes coding for IgG1 to IgG4.

Chimpanzees and rhesus macaques possess three IGHG genes

coding for IgG1, IgG2, and IgG3. The chimpanzee IgG2 molecule
contains epitopes also found on both human IgG2 and IgG4,
suggesting that the IGHG2 and IGHG4 genes split after humans
separated from chimpanzees. Baboons (Papio cynocephalus) have

four IGHG genes, but they differ significantly from human IgG in
their hinge region. Rhesus macaques may have two IgM subclasses.
All the great apes, with the exception of the orangutan, have two
IgA subclasses.

Other Mammals

Rats and mice have four or five functional IGHG genes. In contrast,
rabbits have only one IGHG gene despite having 13 IGHA genes, at
least 12 of which are functional! They appear to lack IgD. The

expression of these IgA subclasses varies among tissues.

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