Background: Some patients with allergic asthma treated with anti-IgE (Xolair®) do not become symptom free. Better criteria for response assessment than allergy skin tests or IgE determination are needed. The impact of the size of the disease relevant allergen-specific IgE antibody fraction, i.e. the percentage of IgE antibody of total IgE, was evaluated in cat allergic patients treated with the recommended doses of Xolair®. Results were measured as changes in basophil allergen threshold sensitivity (CD-sens).
Methods: In a double-blind placebo controlled trial 20 patients with a high (>3.8%) and 18 with a low (<1%) percentage of IgE antibodies to cat were given Xolair® for 16 weeks and the change in CD-sens was compared to 11 and 10 patients, respectively, in each group receiving placebo.
Results: The CD-sens dropped significantly in both the high (P < 0.001) and low (P < 0.001) group on Xolair® but did not change significantly after placebo. For Xolair®-treated patients, at the end of the trial there was a highly significant (P < 0.001) difference in CD-sens between the high group, where no patients, and the low group, where 13/18 patients, had become negative.
Conclusions: The currently recommended doses of Xolair® very efficiently eliminate IgE antibodies if the IgE antibody fraction is <1% of total IgE but has not enough effect on allergen sensitivity if the fraction is >3–4%. Further studies will show if increased doses of Xolair® would help also these patients, who seem to represent about 1/3 of the patient population.