Studies on Fungal Allergies in Relation to Asthma with Special Emphasis on IgE and Antigenic Determinants

Abstract

The significance of fungal allergy to the morbidity of asthma in Wellington is largely unknown. Factors that contribute to this include inadequate standardization of fungal allergen extracts and allergenic cross-reactivity between fungi. In addition, many different fungi have been implicated as allergens. A single commercial preparation containing extracts of many fungi is used to detect fungal allergy at Wellington Hospital. However, the efficacy of this preparation has not been studied and it may contain allergens that are inappropriate for the detection of allergy to fungi present in the local air spora. The aims of this project were first, to isolate and identify fungi present in the local air spora. Second, to prepare extracts of representatives of the major allergenic fungal groups. Third, to determine the sensitivity of a group of asthmatic patients to extracts of fungi isolated from the local air spora. And fourth, to study the allergenic determinants in these extracts. More than 61 distinct fungi were isolated from the air in the homes of two asthmatic patients. The identity of many of these, including all of those that were subsequently used for allergen preparation, was confirmed by the International Mycological Institute, Kew, England. Allergen extracts were prepared from representatives of the major allergenic groups. Asthmatic patients and a group of controls were tested for allergy to these, and other allergen extracts, by the skin prick test and an enzyme immunoassay for the detection of allergen-specific serum immunoglobulin E (IgE). Positive skin prick tests to extracts of local fungi were found in six of 13 asthmatic patients, but only two of 40 asthmatic patients were positive when tested with the commercial preparation routinely used. However, skin prick tests with other inhalent allergens including house dust mite, cat dander, and grass pollen, were more frequently positive in this larger group of asthmatic patients. In addition, there was a significant association between these latter skin prick test results and total serum IgE, but no association between total serum IgE and the fungal allergen skin prick test results. These results suggest that the commercial fungal allergen preparation routinely used at Wellington hospital probably underestimates the number of patients with cutaneous hypersensitivity to fungi. They also suggest that the fungi tested are less important allergens than dust mite, cat dander, or grass pollen, in this group of asthmatic patients. Total serum Immunoglobulin E (IgE) and allergen-specific serum IgE were measured in 36 asthmatic patients and 125 blood donors. Total serum IgE and Cladosporium-specific serum IgE were significantly higher in the sera of asthmatic patients than in blood donors, but Alternaria and house dust mite-specific IgE levels were similar in both groups. These results suggest that there was significant allergy to Cladosporium among the asthmatic patients tested. However, the lack of association between any of the fungal allergen or dust mite specific IgE results and total IgE suggests that the reaction to Cladosporium formed only a small part of the total IgE response and was therefore a relatively unimportant allegen in this group of asthmatic patients. Allergenic determinants in the extracts were studied using enzyme immunoassay inhibition, isoelectric focussing and Western blotting. In vitro cross-reactivity was demonstrated between extracts of 12 Penicillium species, 4 basidiomycete extracts, Cladosporium herbarum and C. cladosporioides extracts, and between extracts of Alternaria alternate, Ulocladium atrum and Epicoccum nigrum. Confirmation of cross-reactivity between extracts of C. herbarum and C. cladosporioides was demonstrated by the presence of significant rank correlations for serum specific IgE levels, while confirmation of the cross-reactivity between A. alternata and U. atrum was obtained by demonstration of a single IgE reactive band in the U. atrum extract that corresponded with the isoelectric point of the major allergen in the A. alternata extract. These results indicate that fungal specific IgE cross-reacts with allergens that are shared between species and sometimes between genera of fungi.