Page 487 - Veterinary Immunology, 10th Edition

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FIG. 16.9 The gene structure of IgD differs greatly among
mammals. This diagram shows the exon structure of IgD heavy
chains in different species. No other immunoglobulin class shows
such variation, and its significance is unknown.

Box 16.1

IgD and the Microbiota

Recent studies on the role of IgD have determined that B cell class
switching from IgM to IgD in mice is initiated by the intestinal

microbiota! In mice, much IgD is produced by the B cells of the
intestinal mucosa-associated lymphoid tissues. However, it is not
produced in germ-free mice, nor is it produced in MyD88-deficient
mice, indicating that production is triggered through toll-like

receptors. The IgD produced in the intestine is active against the
intestinal bacteria. Microbiota-associated IgD class switching can
also be detected in the nasal mucosa. Thus IgD may play a role in
regulating the normal microbiota.

Choi JH, Wang KW, Zhang D, et al: IgD class switching is initiated by microbiota and
limited to mucosa-associated lymphoid tissue in mice, Proc Natl Acad Sci USA 114: E1196-
E1204, 2002.

The role of IgD has so far defied explanation, but it probably
regulates B cell responses. IgM to IgD class switching has been
described in the upper respiratory mucosa of humans. This

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