Environmental and occupational respiratory disorders
Fungal fragments and undocumented conidia function as new aeroallergen sources

https://doi.org/10.1016/j.jaci.2005.02.009Get rights and content

Background

More than 100 genera of fungal conidia are currently recognized as sources of allergens. The contribution of other fungal genera plus airborne fungal hyphae and fragmented conidia to allergic diseases is poorly understood.

Objective

We sought to investigate the expression of allergens from airborne wild-type fungi using the Halogen immunoassay, which uses allergic serum IgE to immunostain immobilized allergens extracted from individual fungal particles.

Methods

Airborne fungi were collected onto mixed cellulose ester protein–binding membranes for 2.5 hours with volumetric air pumps. Collected fungi were incubated overnight in a humid chamber to promote the germination of conidia. The membranes were laminated with an adhesive cover slip and immunostained with an Alternaria species–sensitive serum IgE pool. The samples were examined by means of light microscopy, and positively immunostained fungal particles were classified and counted.

Results

All air samples contained fungal hyphae that expressed soluble allergens and were significantly higher in concentration than counts of conidia of individual well-characterized allergenic genera (P < .05). Resultant immunostaining of fungal hyphae was heterogeneous, and approximately 25% of all hyphae expressed detectable allergen compared with nonstained hyphae (P < .05). Fungal conidia of 10 genera that were previously uncharacterized as allergen sources were shown to demonstrate IgE binding to expressed antigens and accounted for 8% of the total airborne conidia count.

Conclusions

Our analysis of wild-type fungi collected indoors presents a new paradigm of natural fungal exposure, which, in addition to commonly recognized species, implicates airborne hyphae, fragmented conidia, and the conidia of a much more diverse range of genera as airborne allergens.

Section snippets

Personal air sampling

Personal volumetric air samplers (PASs), which are extensively used in occupational health settings, were used for the current study. The PASs consisted of an Institute of Occupational Medicine (IOM) sampling head (SKC Ltd, Dorset, United Kingdom)13 connected to a diaphragm pump providing a constant 2.0 L · min−1 air flow through a mixed cellulose ester protein–binding membrane (MPBM). The IOM sampling head was sterilized and fitted with a 0.8-μm pore size MPBM (Millipore Corp, Bedford, Mass)

Results

Airborne fungal spores, conidia, and hyphae expressed detectable levels of antigen in all personal air samples. Collected fungal hyphae varied markedly in size (5-100 μm), shape, color, and hyphal septation (Fig 1). Resultant immunostaining was heterogeneous and localized primarily to the outer margins of hyphal tips (Fig 1, A, B, D, and F), the septal junctions (Fig 1, C), and around the entire fragment (Fig 1, E) and restricted to the site of conidial fragmentation (Fig 1, G and H). The

Discussion

This study conclusively demonstrates that airborne fungal hyphae commonly function as sources of aeroallergen because positively immunostained hyphae were frequently observed on all indoor air samples. The resultant staining was heterogeneous and primarily localized around the entire length of the hyphae, outer margins of the tips, and septal junctions. It is suspected that allergen expression in the vicinity of these sites is attributable to the processes of separation and shear by

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Supported by a grant from The National Health and Medical Research Council (grant 253818), The Woolcock Institute of Medical Research, and the Department of Medicine, The University of Sydney, Australia.

Disclosure of potential conflict of interest: E. Tovey is inventor of the Halogen assay and is entitled to net proceeds from commercialization should the assay be licensed out by the University of Sydney (the owner of the patent).

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Copyright © 2005 American Academy of Allergy, Asthma and Immunology. Published by Mosby, Inc. All rights reserved.