Cross-reactivity between cockroach and ladybug using the radioallergosorbent test

Background: Home infestations from Harmonia axyridis (ladybug) occur throughout the United States. IgE-mediated sensitization with allergic disease has been reported. The prevalence of ladybug sensitization has been studied by questionnaire and allergy testing in patients diagnosed as having allergic disease. Cross-reactivity with cockroach exists. Objectives: To determine the prevalence of ladybug specific IgE in the general population by specific IgE immunoassay and to examine cross-reactivity to cockroach. Methods: An experimental solid phase for use in immunoassay was prepared using a ladybug extract, and performance characteristics were determined. Serum samples from 100 adult blood bank donors were tested using the ladybug specific I-E immunoassay. Known ladybug IgE-positive serum samples obtained from symptomatic patients were used to study cross-reactivity with German cockroach by specific IgE immunoassay inhibition. Results: The mean background response of the assay solid phase was 51 fluorescent units with an analytical cutoff of 59 fluorescent units. It was estimated that a response of 88 fluorescent units corresponds to a specific IgE concentration of 0.1 kUa/L. The extinction dilution curve was linear to 0.1 kUa/L. The assay cutoff was set at 0.1 kUa/L. Of the 100 blood donor serum samples, 10 were positive for ladybug specific IgE. Inhibition assays revealed partial cross-reactivity with German cockroach. Conclusion: Although an immunoassay solid phase prepared with ladybug whole body extract will identify persons in a general population sensitized to epitopes found in the extract, clinicians performing allergy testing using whole body ladybug extract should be aware that a positive result may or may not indicate that exposure to actual ladybug allergens is causing sensitization. Ann Allergy Asthma Immunol. 2009; 103:432-435.