Rationale: Intrinsic asthma was described by Rackemann as asthma without allergy. Local IgE production has been documented in intrinsic asthma, but antigen specificity of this response remains elusive.
Objectives: We investigated (1) the presence of dust mite-specific IgE in sputum of patients with intrinsic asthma, (2) their clinical/immunological relevance, and (3) their functionality.
Methods: Specific IgE to Dermatophagoides pteronyssinus (Der p) and to recombinant major allergens (rDer p1 and rDer p2) were assayed by ELISA in sputum samples from patients with intrinsic versus atopic asthma and control subjects. Whole-lung challenge was performed with Der p for clinical and inflammatory readouts. Functionality of local IgE to trigger effector cells was assessed using basophil activation test (surface expression of CD203c).
Measurements and main results: Both total IgE and Der p-specific IgE levels are increased in patients with intrinsic asthma compared with healthy nonatopic patients. However, no immediate asthmatic responses were observed in patients with intrinsic asthma after Der p exposure. These sputum Der p-specific IgE do, however, recognize major allergens Der p1 and Der p2 and are able to trigger activation of blood basophils from atopic donors.
Conclusions: We confirm that IgE production occurs in intrinsic asthma and show that part of this IgE recognizes Der p antigens. However, this IgE reactivity does not translate into clinical responses to Der p exposure, despite specificity to major allergens and functionality to activate effector cells in vitro. We postulate that a second signal that promotes IgE-mediated asthmatic responses through FcεRI is lacking in intrinsic asthma.