Vol1-2Art2

The dual roles of fungi: allergens and pathogens

Xin Zhou1,2, Yu Quan1,3,4, Sarah A. Ahmed1,4, Macit Ilkit5, Wentao Liu2, Xiaoya Zhang2, Peiying Feng2#

1RadboudUMC/CWZ Center of Expertise for Mycology, Nijmegen, The Netherlands; 2Department of Dermatology and Allergy, the Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China; 3Respiratory and Critical Care Center, Affiliated Hospital of Guangdong Medical University, Zhanjiang, China; 4Foundation Atlas of Clinical Fungi, Hilversum, The Netherlands; 5Division of Mycology, Department of Microbiology, Faculty of Medicine, Çukurova University, Adana, Türkiye

Abstract

Fungal infections and hypersensitivity represent two distinct yet interconnected host immune responses. While infection primarily activates innate immune pathways to combat pathogens and opportunists, hypersensitivity arises from exaggerated immune responses to fungal allergens. This duality highlights the complex balance between immune defence against infection and the risk of an inappropriate hypersensitivity response to fungal antigens. Allergens elicit allergic reactions in the respiratory system, skin, and gastrointestinal tract. Inhalation of airborne propagules from e.g., Aspergillus, Alternaria, and Penicillium species frequently leads to respiratory disorders like allergic rhinitis, allergic fungal rhinosinusitis, allergic asthma, or allergic bronchopulmonary aspergillosis / mycosis. Cutaneous exposure to allergens such as Trichophyton may provoke Id reactions, and Malassezia and Candida exacerbate atopic dermatitis or induce urticaria. Furthermore, fungal antigens may interact with the gut-associated immune system, potentially triggering or aggravating food allergies. Antibody- and T-cell-mediated hypersensitivity responses are central to these pathophysiological processes, with environmental influences and genetic predispositions modulating the intensity of allergic manifestations, especially in predisposed individuals. Despite the high prevalence of fungus-induced allergic diseases, precise diagnosis remains challenging due to the vast heterogeneity of extant species and antigenic cross-reactivity. Conventional diagnostic tools, such as skin prick tests and serum total or specific IgE assays are limited by the lack of standardized extracts and variability in antigenic specificity. The dual role of fungal exposure in infection and hypersensitivity underscores the need to deepen our understanding of the immunopathological mechanisms underlying microbial sensitization, identify specific allergens, and elucidate the molecular pathways involved. These areas are essential for enhancing diagnostic accuracy and developing standardized allergen extracts, thereby facilitating the management and treatment of allergic conditions.

Open Access

Cite this article :
Zhou X, Quan Y, Ahmed SA, Ilkit M, Liu W, Zhang X, Feng PS 2024 The dual roles of fungi: allergens and pathogens One Health Mycology 1(2), 54-71

ISSN: 3050-4627
doi.org/10.63049/OHM.24.12.2

Keywords: Fungal allergy; hypersensitivity; Fungal allergens; host immune response; allergic cross-reactivity; diagnosis

Article highlights:

  • Dual roles of fungi: The article underscores fungi’s dual nature as allergens causing hypersensitivity and pathogens inducing infections, reflecting the complex interplay between immune defense and hypersensitivity risks.
  • Fungal allergens and cross-reactivity: Over 30 fungal genera, including Ascomycota, Basidiomycota, and Mucorales, are identified as allergen producers. Significant cross-reactivity among fungal species, due to structural similarities in allergen epitopes, complicates accurate allergen identification.
  • Immune response to fungal allergens: The article explores innate and adaptive immune mechanisms underlying fungal sensitization, influenced by environmental and genetic factors that modulate allergic intensity.
  • Fungal allergens and clinical conditions: It links fungal allergens to clinical conditions such as respiratory diseases (allergic rhinitis, asthma, allergic bronchopulmonary aspergillosis/mycosis, and hypersensitivity pneumonitis), skin diseases (atopic dermatitis, cutaneous Id reaction, and urticaria), and cross-reactivity between fungi and foods.
  • Molecular allergy diagnostics: The article discusses the advances in molecular allergy diagnostics, including the use of purified natural or recombinant allergenic molecules for more accurate diagnosis, which is a significant update from traditional crude allergen extracts.

#Correspondence: fengpeiying77@163.com

Article info:
Received 23 October 2024
Revised 11 November 2024
Accepted 17 November 2024
Appeared online 26 November 2024
One Health Mycology 1(2): 54−71, 2024