Physiological ecology of toxic molds in built environments

Background/Question/Methods

Common indoor and outdoor environmental fungi such as Aspergillus fumigatus produce asexual spores containing a collection of proteins that can bind IgE antibodies and trigger allergic reactions. It has been previously demonstrated that the environmental conditions in which a spore is produced may result in physiological changes and differential gene expression. We hypothesize that the temperature at which spores are produced will impact the per spore allergenicity of molds that are common in the indoor environment. To test this hypothesis, human IgE-binding was used to assess the relative allergenicity of A. fumigatus spores formed under sporulation temperatures ranging from 17 °C to 32 °C. The origin of variable allergenicity was studied by coupling these analyses with expression profiling of genes that encode for the 22 A. fumigatus allergenic proteins.

Results/Conclusions

Spores were significantly more allergenic on a per spore basis as sporulation temperatures decreased (p < 0.05, ANOVA). The allergenicity of spores cultivated at 17^oC was found to be approximately 12-fold higher than conidia that sporulated at 32^oC. Under gene expression, a total of 1,056 genes were found to be significantly differentially expressed between 17^oC and 32^oC sporulating cultures (p < 0.05). Of these, 501 were more highly expressed under sporulation at 17^oC, while 555 were more highly expressed under sporulation at 32^oC. Globally, genes associated with protein production were highly expressed at 17^oC. Among the 22 known allergens of Aspergillus fumigatus, genes encoding six of these allergens (the major allergens Asp f 1 and Asp f 3, along with Asp f 6, Asp f 10, Asp f 12 and Asp f 23), were found to have significantly higher mRNA levels in 17^oC sporulating cultures versus 32^oC sporulating cultures, while the three genes encoding minor allergens Asp f 15, Asp f 17 and Asp f 34 were found to have significantly higher transcript levels in cultures that sporulated under the higher temperature ( p < 0.05). Through Type I hypersensitivity and associated disorders like asthma, allergens affect the health of over 300 million people worldwide. The further development and application of methods that quantify allergenicity, rather than allergic organism presence, are necessary to strengthen the exposure science related to indoor mold.