Allergen content in German cockroach extracts and sensitization profiles to a new expanded set of cockroach allergens determine in vitro extract potency for IgE reactivity

Abstract

BACKGROUND: Cockroach allergens are an important cause of IgE-mediated sensitization in inner-city asthmatic patients. However, cockroach extracts used for diagnosis and immunotherapy are not standardized.

OBJECTIVE: We sought to determine the allergen content of nonstandardized German cockroach extracts and the levels of sensitization to an expanded set of cockroach allergens as determinants of in vitro extract potency for IgE reactivity.

METHODS: Twelve German cockroach extracts were compared for allergen content and potency of IgE reactivity. Bla g 1, Bla g 2, and Bla g 5 were measured by using immunoassays. IgE antibody levels to 8 purified recombinant allergens from groups 1, 2, 4, 5, 6, 7, 9, and 11 were measured by using ImmunoCAP. IgE antibody binding inhibition assays were performed to assess extract in vitro potencies (concentration inhibiting 30% of the total IgE antibody-binding inhibition) relative to an arbitrarily selected reference extract in 5 patients with cockroach allergy.

RESULTS: Allergen levels were highly variable. Three new major allergens (groups 6, 9, and 11), were identified among highly cockroach-sensitized subjects (CAP class ≥ 3). Sensitization profiles were unique per subject without immunodominant allergens. The sum of IgE to 8 allergen components showed a good correlation with cockroach-specific IgE levels (r = 0.88, P < .001). In vitro potencies varied among different extracts per subject and among subjects for each extract.

CONCLUSIONS: The in vitro potency of German cockroach extracts for IgE reactivity depends on allergen content and allergen-specific IgE titers of patients with cockroach allergy. These factors are relevant for selection of potent extracts to be used for immunotherapy and for the design and interpretation of data from immunotherapy trials.