Use of thiocyanate elution to estimate relative avidity of allergen specific IgE antibodies

Although several methods for estimating avidity of antigen-antibody reactions are available, most are impractical for the study of human IgE antibodies because of a requirement for pure allergen and antibody in relatively large amounts. To determine the relative avidity of specific IgE antibodies for Dermatophagoides pteronyssinus allergens, seven concentrations of the chaotropic thiocyanate ion were used to disrupt epitope-antibody binding in a specific IgE immunoassay system, using sera from 16 allergic patients with marked skin test reactivity to a standardized D. pteronyssinus extract. Relative avidity, the molarity of thiocyanate required to produce a 50% decrement in binding, ranged from 0.29-3.1. Within assay coefficient of variation (CV) was 9.9% and between assay CV was 13%. D. pteronyssinus specific IgE levels ranged from 0.66-141 kUa/L, not correlating with relative avidity (rho = -0.12). Thiocyanate elution appears to be a useful method for estimating relative avidity of specific IgE antibodies for the myriad epitopes of the allergenic proteins in an allergen extract. It could be used to study the immunochemistry of specific IgE assays; avidity maturation in allergen immunotherapy and in asymptomatic but sensitized patients; and preseasonal versus postseasonal changes in avidity within individuals. With a suitable solid phase, it could be modified to examine avidity at the epitope level.