Diagnosis and immunotherapy of mould allergy VII. IgG subclass response and relation to the clinical efficacy of immunotherapy with Cladosporium.

The IgG subclass response was evaulated by a sensitive allergen- and stibclass-specific solid phase immunoradiometric assay during a 1-year placebo-controlled, double-blind study of immunotherapy with Cladosporium herbarum in 22 adult asthmatics. The IgG response was mainly restricted to subclasses 1 and 4 but a few patients were IgG₂ and IgG₃ responders. An intense and early IgG, response was observed during the first clusters of injection followed by a levelling down of the titer. The IgG₄ response had a later onset and showed slowly increasing levels during the 12 months of immunotherapy. The graded clinical efficacy estimated by symptom-medication score was significantly correlated to the preseasonal IgG₁ value, with high values indicating a deleterious response of immunotherapy (deterioration of disease activity). Likewise, the fold increase of IgG₁ and IgG₄ after two clusters of immunotherapy (i.e. after 4 weeks) was significantly related to the clinical outcome. Little or no increase of IgG₁ and IgG₄ was associated with improvement, i.e. decrease in symptom-medication score. The magnitude of the IgG, response during the dose-increase phase was directly correlated to the number of systemic side effects. No relation of IgG₁, IgG₄ or IgG₄/IgG₄ ratio to changes in the IgE-mediated parameters (skin prick test, bronchial challenge and circulating specific IgE) was observed. Our data, which are based on few patients and only one allergen system, do not support the hypothesis of IgG acting as blocking antibody being the immunologic mechanism of immunotherapy. The association between high IgG₄ values and a deleterious efficacy of immunotherapy might be caused by IgG₄ acting as sensitizing antibodies. This explanation, however, is opposed by the lack of relation to systemic side effects. [ABSTRACT FROM AUTHOR]