Antibody response following prolonged hyposensitization with Dermatophagoides pteronyssinus extract

An antigen-binding radioimmunoassay was used to measure IgG, IgA and IgE antibody (ab) to Dermatophagoides pteronyssinus in sera from patients who had been hyposensitized with either aqueous D. pteronyssinus extract or placebo. An allergen, F4P1, was obtained from D. pteronyssinus culture and 125I-labelled for use in the assay. The radioallergosorbent test was also used to measure IgE ab to D. pteronyssinus and IgE ab to Dermatophagoides farinae. The radioimmunoassay results showed a selective rise in IgG ab in sera from D. pteronyssinus-treated (DP) patients. An increase of greater than twofold in IgG ab in post-treatment sera was found in 27 of 29 DP patients compared to 1 of 29 placebo-treated ('placebo') patients (p less than 0.001). The mean rise in IgG ab in DP patients was sixfold, and the maximum rise was 50-fold. There was little change in the levels of IgA ab or IgE ab in either DP or 'placebo' patients during treatment. The DP patients showed significant clinical improvement compared with the 'placebo' patients (p less than 0.01). However, no correlation was found between post-treatment IgG ab and post-treatment symptom scores, or between the changes in IgG ab and the changes in symptom scores during treatment. The time course of the antigen-binding assay was investigated using very low concentrations of F4P1. The results showed that antigen-binding was slow, even in the presence of an excess of IgG ab. The role of IgG ab in hyposensitization is discussed.