Page 1472 - Veterinary Immunology, 10th Edition
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FIG. 43.9 The evolutionary relationships among the major
vertebrate immunoglobulin heavy chains. This is a distance tree
constructed by aligning the amino acid sequences of representative
vertebrate IgH-chain constant regions. (From Warr GW, Magor KE, Higgins
DA: IgY: clues to the origins of modern antibodies, Immunol Today 16:392-398,
1995.)
IgD: The gene for the IgD heavy chain (δ) has been identified in
the toad Xenopus tropicalis. It is expressed on mature B cells. As in
mammals, the Cδ heavy chain gene is located immediately 3′ to the
IgM gene. Xenopus IgD is orthologous to IgW found in
cartilaginous fish and lungfish. This implies that IgD/W was
present in these ancestors of all living jawed vertebrates. This IgD is
structurally variable. Its gene shows many duplications, deletions
of domains, the presence of multiple splice forms, or even the loss
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