Omalizumab, an anti-immunoglobulin E (IgE) monoclonal antibody, inhibits the binding of circulating IgE to mast cells and basophils, resulting in fewer episodes of airway inflammation, asthma symptoms and exacerbations in patients with severe allergic asthma. Treatment of patients with asthma using omalizumab increases serum total IgE (tIgE) levels. However, little is known about the influence of omalizumab on allergen-specific IgE (sIgE).

tIgE and sIgE in 47 adult patients with severe asthma were measured with a fluorescent enzyme immunoassay (ImmunoCAP-FEIA) before and after omalizumab treatment.

Treatment with omalizumab increased tIgE and sIgE levels. The increases in sIgE by class category after omalizumab treatment were positively correlated with baseline sIgE positivity before treatment. The mean changes in sIgE levels after omalizumab treatment were also correlated with baseline sIgE levels before treatment. The mean changes in tIgE levels were positively correlated with the mean changes in IgE levels against Dermatophagoides pteronyssinus, crude house dust, Japanese cedar and moth. Omalizumab markedly influenced the negative-to-positive seroconversion rate for IgE against Japanese cedar (30.8%), Candida (29.0%) and moth (28.0%). Finally, all patients with negative-to-positive seroconversion for Japanese cedar-specific IgE had cedar pollinosis before beginning omalizumab treatment.

The changes in sIgE levels after omalizumab treatment may be dependent on the baseline sIgE levels. Our data may indicate the presence of undetectable but functional sIgE.