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Human sera IgE reacts with a Metarhizium anisopliae fungal catalase
Citation:
WARD, M. D., M. J. DONOHUE, Y. CHUNG, L. B. COPELAND, J. A. SHOEMAKER, S. J. VESPER, AND M. K. SELGRADE. Human sera IgE reacts with a Metarhizium anisopliae fungal catalase . INTERNATIONAL ARCHIVES OF ALLERGY AND APPLIED IMMUNOLOGY. Karger Libri AG, Basel, Switzerland, 150(4):343-351, (2009).
Impact/Purpose:
The objective of this study was to identify and characterize the extract proteins that induce IgE and determine if these same proteins were also found in other fungi or were reactive with human sera. This study identified a ubiquitous enzyme catalase as a possible allergen. Because the source of catalase was fungi the data suggest that functionally common proteins may be seen as immunologically foreign when the species are divergent (mold/fungi vs. man/mouse). Additionally, the similarities in the proteins identified by the mouse model and those detected with human sera suggest that the mouse model is a good model not only for hazard identification regarding allergenicity of extracts (mixtures) but also useful in the identification of the allergenic protein.
Description:
Background: Previous studies have demonstrated that Metarhzium anisopliae extract can induce immune responses in a mouse model that are characteristic of human allergic asthma. Objectives: The objective of this study was to identify and characterize the extract proteins that induce IgE and determine if these same proteins were also found in other fungi. Methods: Extracts of the proteinaceous material from the fungal mycelia were separated by 2-dimensional gel electrophoresis (2D gel). Seven proteins spots were found to bind IgE in hyperimmune serum from mice immunized with M. anisopliae crude antigen (MACA) extract. Matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) was used to obtain the peptide map of the IgE-reactive proteins and Nanoelectrospray tandem mass spectrometry (nano-ESI-MS/MS) provided de novo sequence information. Results: An IgE-reactive protein was identified as catalase. Subsequently, the presence of catalase in the mycelium extract was confirmed by a catalase activity assay and immunoblot of the extract with polyclonal antibodies raised against purified Aspergillus fumigatus catalase (CatB) and bovine liver catalase. Anti-bovine liver catalase was also shown to be reactive with Aspergillus niger catalase and a commercial mold mix used for skin prick testing. Furthermore, the anti-MACA serum was cross-reactive with two commercial mold mixes and A. niger catalase. Sensitization and challenge exposures of mice to A. niger or bovine liver catalase resulted in features characteristic of allergy. Western blot analysis also demonstrated that serum from six adult asthmatics was reactive with the mycelium extract and displayed a profile of reactivity similar to that of both anti-MACA mouse serum blots and anti-bovine liver catalase antibody. Conclusions: Our data suggest that 1) a M. anisopliae mycelium catalase can induce allergic responses in a mouse model; 2) a mouse model of allergic asthma may be useful in identifying the proteins within microbial extracts that may be human allergens; and 3) the potential allergenicity and cross-reactivity of fungal catalases deserve further study.
