Blocking IgG antibodies after rush immunotherapy with mites

The synthesis of blocking antibodies has been demonstrated in ten patients undergoing rush immunotherapy (R-IT) with mite extracts: basophil degranulation performed on washed cells (Allergolam* technique) did not differ significantly before and 10.8 (±6.8) months after R-IT. Preincubation of allergen (100, 25, 10, and 5 μg/mL) with individual serum collected before R-IT did not decrease degranulation, but degranulation was significantly decreased when the allergen was incubated 30 minutes at 37°C with individual serum collected after R-IT or with the IgG-fraction of a pool of sera collected in 22 treated patients. A linear correlation between the mean of degranulation and the log allergen concentration was observed in the two latter groups. The antigen neutralizing capacity of the IgG-fraction was studied on basophils of 11 'allergic donors'. Antigen neutralizing capacity clearly increased with time of incubation with the allergen (15, 30, and 60 min), but was also significant without preincubation, eg, for 10 and 5 μg/mL allergen concentrations. These results indicate that the improvement of asthma usually noticed 2 months after R-IT is probably due, essentially, to blocking antibodies, since the sensitivity of the basophils is not modified significantly.