Efficacy and specificity of immunotherapy with laboratory animal allergen extracts

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The clinical and immunologic response to immunotherapy with laboratory animal allergens was evaluated. There were 23 patients; 11 had received immunotherapy with 12 different extracts (five mouse, six rat, one rabbit), and 12 were matched untreated patients. As a group, nine of 23 had seasonal hay fever. Among the treated patients nine of 11 subjectively improved with immunotherapy. Blocking antibody titers were determined by serum inhibition of allergen-induced histamine release. Treated patients had mean blocking antibody levels of G 30 = 59.3 ± 38.7. In the untreated patients the antibody level was low (G 30 = 4.6 ± 3.6). The difference between the two groups was highly significant (t test p < 0.001). The blocking antibody level correlates with both the final weekly allergen dose and also the cumulative allergen dose received during immunotherapy. When pretreatment sera were available a temporal rise in blocking antibody was demonstrated during immunotherapy. In patients allergic to several laboratory animals and treated with one allergen, the blocking antibody response was predominantly specific to the allergen used in immunotherapy. This indicates a lack of cross-reactivity in the IgG response to the major animal allergens. When immunotherapy was discontinued in four patients there was a dramatic decrease in the blocking titer, and after 24 mo the levels were the same as those of untreated patients.