IgD: the comeback of a forgotten immunoglobulin

IgD was discovered more than 30 years ago in the serum obtain from a myelom a patient. Subsequently, the finding that it also exists as a membrane-boun d immunoglobulin stimulated a large number of studies during the seventies. Then, the interest on IgD shrank, largely because of the lack of known fun ction of secretory IgD. In the recent years, major development in the knowl edge of the physiology of the B cell receptor, of which IgD is the major co mponent, was followed by very significant advances on the role of secretory IgD in normal and diseased individuals. This paper, which is focused on hu man IgD but integrates mouse data when needed, reviews the present data on the structure, synthesis and functions of both membrane and secretory IgD, IgD receptors and the involvement of IgD in various diseases, especially th e hyperIgD syndrome.