Table of Contents

m221 Asp f 4 Scientific Information Summary Epidemiology Environmental Characteristics Clinical Relevance Molecular Aspects Diagnostic Relevance Compiled By

Component

m221 Asp f 4

m221 Asp f 4 Scientific Information

Type:

Component

Name; WHO/IUIS:

Asp f 4

Biological function:

unknown

Allergen code:

m221

Molecular Weight:

30 kDa

Source Material:

Recombinant, CCD-free protein

Summary

Asp f 4 is a species-specific allergen of the ubiquitous environmental mold Aspergillus fumigatus (A. fumigatus), an agent of allergic fungal airway diseases (AFAD) affecting upper and lower airways, such as allergic fungal rhinosinusitis (AFRS), severe asthma with fungal sensitization (SAFS), and allergic bronchopulmonary aspergillosis (ABPA). Asp f 4 is a major allergen in ABPA, and a minor one in other AFAD, and therefore may contribute to the diagnosis of ABPA.

Epidemiology

Worldwide distribution

A. fumigatus is a cosmopolitan, thermotolerant airborne fungus affecting human health through multiple pathways: allergy, infection, direct toxicity [1].

The prevalence of Asp f 4 sensitization is highly variable depending on the study population in terms of geography, underlying lung condition, i.e. asthma, cystic fibrosis (CF), or chronic obstructive pulmonary disease (COPD), stage of AFAD, method of assessment (skin prick test, blood tests) and cut-off values. Despite wide variations, Asp f 4 sensitization presents with higher prevalence and higher levels in ABPA as compared to asthmatic patients and healthy individuals. Early reports in European asthmatic patients sensitized to A. fumigatus showed Asp f 4 sensitization in 92% of ABPA cases and in 25% of those without ABPA [2]. A similar figure of 84% for Asp f 4 sensitization was reported in 2020 in ABPA patients with asthmatic background, compared to 32% in A. fumigatus-sensitized asthmatic patients from India [3]. Conversely, the prevalence of Asp f 4 sensitization was only 33-36% in ABPA patients among two cohorts of Japanese asthmatics, compared to 6-20% of A. fumigatus-sensitized asthmatics without ABPA [4, 5]. In

Chinese asthmatic patients from Guangzhou, Asp f 4 sensitization was found in 61% of ABPA patients and in 33% of A. fumigatus-sensitized asthmatic patients without ABPA [6]. Considering CF patients with A. fumigatus-sensitization without ABPA, the prevalence of Asp f 4 sensitization varied from 0% in Swiss and British studies [7, 8] to 38% in a French one [9], increasing to 75% [8], 80% [7] or even 100% [9] in ABPA patients from the same cohorts. Similar figures were reported in a pediatric CF cohort from the US, with Asp f 4 sensitization present in 82% of ABPA patients and in 35% of A. fumigatus-sensitized patients without ABPA [10]. Among German and Polish self-reported asthmatic patients with A. fumigatus sensitization, 31% displayed Asp f 4 sensitization, but 17% of non-asthmatic subjects exposed to mold also displayed Asp f 4 sensitization [11].

Asp f 4 sensitization may be higher in atopic dermatitis (AD). In a Japanese cohorts, Asp f 4 sensitization was more frequent in AD patients without asthma (38%), followed by asthmatic patients with AD (20%) compared to asthmatic patients free of AD (6%) [4].

Asp f 4 sensitization was found in 10% of A. fumigatus sensitized German patients with allergic rhinitis, usually associated to sensitization to other molecular components [12]. In COPD patients, the prevalence of Asp f 4 sensitization was 1%, not different from 0% in controls [13].

Asp f 4 sensitization is usually absent in subjects (healthy, asthmatic, or CF) lacking detectable skin or blood A. fumigatus sensitization [3, 5, 14].

Environmental Characteristics

Source and tissue

Asp f 4 is a somatic protein of A. fumigatus [15], which is also expressed as a cell surface protein by hyphae and germinating conidia [16]. Its function is unknown [17]. It possesses low sequence identity with other fungal allergens [18] and is therefore considered as a species-specific allergen [19].

Risk factors

Sensitization and allergy to A. fumigatus occur mainly in subjects with pre-existent lung conditions, usually asthma or CF, with COPD increasingly recognized as another predisposing condition [1].

Clinical Relevance

Detailed information regarding A. fumigatus is available in the whole allergen section.

Clinical relevance of Asp f 4 IgE in ABPA

The diagnosis of ABPA is often complicated by symptoms due to underlying conditions and a complex pathophysiology combining IgE and IgG responses, sputum and systemic eosinophilia, and much debated fungal colonization [20, 21]. While Asp f 1 and Asp f 2 are major allergens and markers of genuine sensitization to A. fumigatus, Asp f 4 sensitization is a marker of a more complex sensitization pattern, associated with ABPA [20]. Detection of IgE to Asp f 4 had a 50-84% diagnostic sensitivity for ABPA in asthmatic patients and 67% in CF patients, with a specificity of 68-92% [22, 23].

Along with the prevalence of Asp f 4 sensitization, Asp f 4 IgE levels are higher in ABPA [2, 9, 22, 23]. Median levels of IgE to Asp f 4 in ABPA patients vary among cohorts, and may reach 15 kUA/L [6, 8, 9, 23, 24], supporting the observation that statistically determined cut-off levels in a given population perform better than fixed cut-offs [23]. Using population-based cut-offs, the reported area under the receiver operating curve of Asp f 4 was 0.740 to 0.970 in different populations [9, 22, 23].

Diagnostic performance of Asp f 4 is improved when used in conjunction with other A. fumigatus molecular allergens [23-25]. As an example, a meta-analysis revealed that the presence of either Asp f 4 or Asp f 6 sensitization detected ABPA with a pooled specificity of 99% in asthmatic patients, and 93.9% in CF patients [22].

Disease severity and prediction

Asp f 4 sensitization and increasing levels of Asp f 4 IgE in asthmatic or CF patients are statistically associated to an increased risk of ABPA, as explained above. In CF patients with ABPA, a strong correlation (r = 0.89, p<0.01) was reported between levels of Asp f 4 IgE and the levels of thymus and activation-regulated chemokine (TARC), a marker of clinically active ABPA in CF patients, involved in Th2 responses through recruitment of CCR4+ and CCR8+ Th2 cells [26].

Asp f 4 sensitization is associated with bronchiectasis in patients with AFAD, but not in COPD patients [13, 27]. Asp f 4 sensitization has not been described as associated with poorer lung function [27].

Cross-reactive molecules

Asp f 4 sequence exhibits an identity of 80% or higher with only 6 other proteins from the Aspergillus genus [28].

Molecular Aspects

Biochemistry

Asp f 4 is an acidic protein of 30 kDa, as yet of unknown function, but with confirmed allergenic activity [20, 29, 30]. Asp f 4 is among the ten most upregulated RNA transcripts after 16 hours of A. fumigatus culture [31].

Isoforms, epitopes, antibodies

As of November 7th, 2021, Asp f 4 comprises only one isoallergen officially published by the World Health Organization (WHO) and the International Union of Immunological Societies (IUIS) Allergen Nomenclature: Asp f 4.0101 [17].

Cross-reactivity due to structural similarity

Asp f 4 is considered as a species-specific A. fumigatus allergen, not known to engage in clinically relevant cross-reactivity, in line with the absence of known structural homologues at the genomic and protein levels [18].

Diagnostic Relevance

Disease Severity

Asp f 4 sensitization, especially at high levels, is a specific marker of ABPA in A. fumigatus-sensitized asthmatic and CF patients [22]. Asp f 4 sensitization is associated with bronchiectasis in AFAD [27].

Cross-Reactivity

Asp f 4 is considered as a species-specific A. fumigatus allergen [19].

Exposure

Asp f 4 sensitization occurs through inhalation upon exposure to A. fumigatus [15].

Compiled By

Author: Joana Vitte

Reviewer: Dr. Christian Fischer

Last reviewed: February 2022

References

Wardlaw, A.J., et al., New Perspectives in the Diagnosis and Management of Allergic Fungal Airway Disease. J Asthma Allergy, 2021. 14: p. 557-573.
Hemmann, S., et al., Skin test reactivity to 2 recombinant Aspergillus fumigatus allergens in A fumigatus-sensitized asthmatic subjects allows diagnostic separation of allergic bronchopulmonary aspergillosis from fungal sensitization. J Allergy Clin Immunol, 1999. 104(3 Pt 1): p. 601-7.
Muthu, V., et al., Role of recombinant Aspergillus fumigatus antigens in diagnosing Aspergillus sensitisation among asthmatics. Mycoses, 2020. 63(9): p. 928-936.
Tanimoto, H., et al., Molecular-based allergy diagnosis of allergic bronchopulmonary aspergillosis in Aspergillus fumigatus-sensitized Japanese patients. Clin Exp Allergy, 2015. 45(12): p. 1790-800.
Kuwabara, K., et al., Serological analysis of sensitization in allergic bronchopulmonary aspergillosis: a study on allergen components and interspecies relationships. J Asthma, 2020. 57(6): p. 610-617.
Luo, W., et al., Molecular allergen sensitization of Aspergillus fumigatus between allergic bronchopulmonary aspergillosis and A fumigatus-sensitized asthma in Guangzhou, Southern China. J Clin Lab Anal, 2020. 34(10): p. e23448.
Hemmann, S., et al., Differential IgE recognition of recombinant Aspergillus fumigatus allergens by cystic fibrosis patients with allergic bronchopulmonary aspergillosis or Aspergillus allergy. Eur J Immunol, 1998. 28(4): p. 1155-60.
Alghamdi, N.S., et al., Serum IgE and IgG reactivity to Aspergillus recombinant antigens in patients with cystic fibrosis. J Med Microbiol, 2019. 68(6): p. 924-929.
Vitte, J., et al., Aspergillus fumigatus components distinguish IgE but not IgG4 profiles between fungal sensitization and allergic broncho-pulmonary aspergillosis. Allergy, 2016. 71(11): p. 1640-1643.
Knutsen, A.P., et al., IgE antibody to Aspergillus fumigatus recombinant allergens in cystic fibrosis patients with allergic bronchopulmonary aspergillosis. Allergy, 2004. 59(2): p. 198-203.
Kespohl, S. and M. Raulf, Mold Sensitization in Asthmatic and Non-asthmatic Subjects Diagnosed with Extract-Based Versus Component-Based Allergens. Adv Exp Med Biol, 2019. 1153: p. 79-89.
Volgger, V., et al., Value of Component Resolved Diagnostics to Aspergillus fumigatus in Patients with Upper Airway Complaints. Int Arch Allergy Immunol, 2021. 182(2): p. 120-130.
Everaerts, S., et al., Sensitization to Aspergillus fumigatus as a risk factor for bronchiectasis in COPD. Int J Chron Obstruct Pulmon Dis, 2017. 12: p. 2629-2638.
Kurup, V.P., et al., Specific antibodies to recombinant allergens of Aspergillus fumigatus in cystic fibrosis patients with ABPA. Clin Mol Allergy, 2006. 4: p. 11.
Matricardi, P.M., et al., EAACI Molecular Allergology User's Guide. Pediatr Allergy Immunol, 2016. 27 Suppl 23: p. 1-250.
Jia, L.J., et al., Biotinylated Surfome Profiling Identifies Potential Biomarkers for Diagnosis and Therapy of Aspergillus fumigatus Infection. mSphere, 2020. 5(4).
IUIS/WHO. IUIS/WHO Aspergillus fumigatus. November 7 2021]; Available from: http://allergen.org/search.php?allergenname=&allergensource=Aspergillus+fumigatus&TaxSource=&TaxOrder=&foodallerg=all&bioname=.
Bowyer, P., M. Fraczek, and D.W. Denning, Comparative genomics of fungal allergens and epitopes shows widespread distribution of closely related allergen and epitope orthologues. BMC Genomics, 2006. 7: p. 251.
Fukutomi, Y. and M. Taniguchi, Sensitization to fungal allergens: Resolved and unresolved issues. Allergol Int, 2015. 64(4): p. 321-31.
Carsin, A., et al., Aspergillus fumigatus in cystic fibrosis: An update on immune interactions and molecular diagnostics in allergic bronchopulmonary aspergillosis. Allergy, 2017. 72(11): p. 1632-1642.
Asano, K., et al., New clinical diagnostic criteria for allergic bronchopulmonary aspergillosis/mycosis and its validation. J Allergy Clin Immunol, 2021. 147(4): p. 1261-1268 e5.
Muthu, V., et al., Utility of recombinant Aspergillus fumigatus antigens in the diagnosis of allergic bronchopulmonary aspergillosis: A systematic review and diagnostic test accuracy meta-analysis. Clin Exp Allergy, 2018. 48(9): p. 1107-1136.
Muthu, V., et al., Diagnostic Cutoffs and Clinical Utility of Recombinant Aspergillus fumigatus Antigens in the Diagnosis of Allergic Bronchopulmonary Aspergillosis. J Allergy Clin Immunol Pract, 2020. 8(2): p. 579-587.
Fricker-Hidalgo, H., et al., Recombinant allergens combined with biological markers in the diagnosis of allergic bronchopulmonary aspergillosis in cystic fibrosis patients. Clin Vaccine Immunol, 2010. 17(9): p. 1330-6.
Lukaszewicz, R., et al., Medical algorithm: Aspergillus fumigatus components in the diagnosis of Allergic Bronchopulmonary Aspergillosis. Allergy, 2021.
Hartl, D., et al., Chemokines indicate allergic bronchopulmonary aspergillosis in patients with cystic fibrosis. Am J Respir Crit Care Med, 2006. 173(12): p. 1370-6.
Woolnough, K., et al., rAsp f3 and rAsp f4 are associated with bronchiectasis in allergic fungal airways disease. Ann Allergy Asthma Immunol, 2018. 120(3): p. 325-326.
BLAST, U. BLAST from UniProtKB - O60024 (ALL4_ASPFU) Asp f 4. 2021 November 22 2021]; Available from: https://www.uniprot.org/blast/uniprot/B2021112292C7BAECDB1C5C413EE0E0348724B6820205FFX.
Crameri, R., Recombinant Aspergillus fumigatus allergens: from the nucleotide sequences to clinical applications. Int Arch Allergy Immunol, 1998. 115(2): p. 99-114.
Caraballo, L., et al., The allergenic activity and clinical impact of individual IgE-antibody binding molecules from indoor allergen sources. World Allergy Organ J, 2020. 13(5): p. 100118.
Cagas, S.E., et al., The proteomic signature of Aspergillus fumigatus during early development. Mol Cell Proteomics, 2011. 10(11): p. M111 010108.