Characterization of IgD.

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Abstract
Human IgD present in the serum of normal individuals or of patients with Hodgkin's disease (having high IgD concentrations) was characterized and compared with five IgD myeloma proteins. IgD was isolated using a highly specific anti-δ insoluble immunoabsorbent from which the bound material was eluted with sodium dodecyl sulphate (SDS) or urea. The latter reagent could be removed by extensive dialysis, thus making possible the renaturation of the eluted molecules. The purity of the IgD thus isolated was confirmed by antigenic analysis. Both K and λ light chain determinants were present on serum IgD, although λ light chain was predominant with a ratio over the K chain of 2:1. SDS-polyacrylamide slab gel electrophoresis analysis revealed two different molecular forms of serum IgD, one (IgDI) migrating identically to monoclonal IgD, the other (IgD2) having a faster mobility. The difference between the two molecules was entirely, due to the different sizes of their constituent δ chains. Peptide mapping of the two chains (δ1 and δ2 respectively) and of the δ chain of an IgD myeloma protein was carried out using 125I-labelled material. The three molecules displayed a high degree of homology, the δ2 chain differing by the presence of three characteristic extra peptides. The significance of these extra peptides is discussed in the light of the peptide mapping technique employed.