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BACKGROUND:The house dust mite (HDM) allergen Der p 18 belongs to the glycoside hydrolase family 18 chitinases. The relevance of Der p 18 for house dust mite allergic patients has only been partly investigated. OBJECTIVE:To perform a detailed characterization of Der p 18 on a molecular, structural and immunological level. METHODS:Der p 18 was expressed in E. coli, purified to homogeneity, tested for chitin-binding activity and its secondary structure was analyzed by circular dichroism. Der p 18-specific IgG antibodies were produced in rabbits to localize the allergen in mites using immunogold electron microscopy and to search for cross-reactive allergens in other allergen sources (i.e. mites, crustacea, mollusca and insects). IgE reactivity of rDer p 18 was tested with sera from clinically well characterized HDM-allergic patients (n = 98) and its allergenic activity was analyzed in basophil activation experiments. RESULTS:Recombinant Der p 18 was expressed and purified as a folded, biologically active protein. It shows weak chitin-binding activity and partial cross-reactivity with Der f 18 from D. farinae but not with proteins from the other tested allergen sources. The allergen was mainly localized in the peritrophic matrix of the HDM gut and to a lower extent in fecal pellets. Der p 18 reacted with IgE from 10% of mite allergic patients from Austria and showed allergenic activity when tested for basophil activation in Der p 18-sensitized patients. CONCLUSION:Der p 18 is a rather genus-specific minor allergen with weak chitin-binding activity but exhibits allergenic activity and therefore should be included in diagnostic test panels for HDM allergy.

Background: IgE-associated allergic sensitization to house dust mite (HDM) allergens is associated with a variety of allergic symptoms such as rhinitis, conjunctivitis, dermatitis and asthma. Allergen exposure chambers allow the precise assessment of clinical symptoms specifically induced with HDMs. Objective: To investigate if an association between serologic IgE and HDM-induced symptoms such as asthma, rhinitis and conjunctivitis can be established. Methods: The clinical symptoms of 91 HDM allergic patients were assessed in the Vienna Challenge Chamber during a controlled 6-hour exposure to HDM allergens. The symptoms assessed were total nasal symptom score, total ocular symptom score and asthma symptom score. Sera from the 91 patients were tested for IgE reactivity to 13 Dermatophagoides pteronyssinus allergens using allergen microarray technology (ImmunoCAP ISAC chip technology) and allergen-specific IgE levels to Dermatophagoides pteronyssinus (Der p) allergen extract were quantified by ImmunoCAP measurements. Results: Patients with high Der p-specific IgE levels measured by ImmunoCAP (> 10 kU/L) had higher IgE-levels to all important HDM allergens than patients with low IgE levels ( 6, mean value of four hours) also had higher asthma symptom score and total ocular symptom score, as well as higher IgE-levels to micro-arrayed Der p: 2, 5, 7, 21 and 23 compared to patients with low total nasal symptom score ( 4) and in patients with high Total Ocular Symptom Score (> 2) compared to those with low symptom scores. Conclusions: Our study indicates that IgE-reactivity profiles to micro-arrayed HDM allergens but not allergen-specific IgE levels to HDM extracts are associated with allergic symptoms to HDM exposure.