Sensitive ELISA for human immunoglobulin D measurement in neonate, infant, and adult sera

Secreted immunoglobulin D (IgD) is present in small amounts in human serum, and membrane-bound IgD is a major component of the B-cell antigen receptor (1)(2). The role of secreted IgD is largely unknown (3). Results from a recent study of IgM-deficient mice suggest that IgD is able to substitute for IgM in most of its functions (4). However, the phenotype of IgD-deficient mice is virtually normal, except for an impairment of antibody (Ab) affinity maturation (5)(6). Reported IgD concentrations in sera of healthy subjects are widely dispersed (0.15–300 mg/L), with a nongaussian distribution (7)(8), which was described as trimodal by Dunnette et al. (9). The placenta is an effective barrier for IgD (10), and IgD concentrations are low or undetectable in newborns (8)(11)(12). IgD concentrations progressively increase during childhood. The serum IgD half-life is known to be short, which is probably attributable to its high sensitivity to proteolysis (13). IgD Abs specific for viruses, bacteria, allergens, and autoantigens have been detected (14). Serum polyclonal IgD concentrations are increased in various diseases, including the hyper IgD syndrome and allergic disorders, which raises the question of a possible role of IgD in such disorders (15)(16). Conversely, some recent studies aimed at measuring IgD in patients with immunodeficiency or Henoch-Schonberg purpura reported undetectable serum IgD. However, the detection threshold of the assay used in the latter studies was relatively high (17)(18). We considered it useful to develop a sensitive assay able to measure IgD in all normal sera, whatever the age of the subjects. Such an assay could allow laboratories to provide and compare values below the detection limits of previous assays. We hence developed an ELISA that permits the measurement of low concentrations of human IgD in …