Immunoglobulin D

Overview

IgD

IgD - B. Catchpole, RVC 2008

Shortened to IgD.

IgD is present in ruminants, pigs, dogs and rodents but has not been identified in horses, cats, rabbits and chickens. It is mainly expressed on the surface of B-cells i.e. it is never secreted.

Structure

IgD is Y-shaped. In rodents, it has two δ heavy chain constant regions, whereas other mammals have three. IgD has a long hinge region and no disulfide bonds.

Function

IgD is only expressed in association with IgM. It is thought to be important in B-cell development, although it has been shown in δ chain knockout mice (so they have no functional IgD) do not have any noticeable defects in immune function.

Interestingly IgD serum levels increase in allergic reactions, although it is not known why this is.