Laboratory biomarkers in the diagnosis and follow-up of treatment of allergic bronchopulmonary aspergillosis in cystic fibrosis

Allergic bronchopulmonary aspergillosis (ABPA), a severe inflammatory respiratory disease, is caused by a hypersensitivity reaction to the colonization of the airways with Aspergillus fumigatus. It is most often described in patients with asthma or cystic fibrosis. The diagnosis of ABPA is based on a combination of clinical, radiological, and immunological findings that have been included in different diagnostic criteria over the years. In this paper, we review the biomarkers included in these diagnostic criteria and novel research biomarkers that may be used in the diagnosis and treatment follow-up of ABPA in cystic fibrosis.

Prospective Evaluation of Aspergillus fumigatus-Specific IgG in Patients With Cystic Fibrosis

Background

In Cystic Fibrosis (CF), the airways are often colonized by opportunistic fungi. The most frequently detected mold is Aspergillus fumigatus (Af). Af diseases are associated with significant morbidity and mortality. The most common clinical picture caused by Af is allergic bronchopulmonary aspergillosis (ABPA), triggered by an immunological reaction against Af. Af bronchitis and invasive aspergillosis rarely occur in CF as a result of spore colonization and germination. Since pulmonary mycoses and exacerbations by other pathogens overlap in clinical, radiological, and immunological characteristics, diagnosis still remains a challenge. The search for reliable, widely available biomarkers for Af diseases is therefore still an important task today.

Objectives

Af-specific IgG m3 is broadly available. Sensitivity and specificity data are contradictory and differ depending on the study population. In our prospective study on pulmonary Af diseases in CF, we determined specific IgG m3 in order to test its suitability as a biomarker for acute Af diseases and as a follow-up parameter.

Methods

In this prospective single center study, 109 patients with CF were screened from 2016 to 2019 for Af-associated diseases. According to diagnostic criteria, they were divided into four groups (control, bronchitis, ABPA, pneumonia). The groups were compared with respect to the level of Af-specific IgG (ImmunoCAP Gm3). We performed a receiver operating characteristic (ROC) curve analysis to determine cut-off, sensitivity and specificity. Twenty-one patients could be enrolled for a follow-up examination.

Results

Of the 109 patients, 36 were classified as acute Af-disease (Af bronchitis, ABPA, Af pneumonia). Of these, 21 patients completed follow up-screening. The median Af-specific Gm3 was higher in the acute Af-disease groups. There was a significant difference in Af-specific IgG m3 compared to the control group without acute Af-disease. Overall, there was a large interindividual distribution of Gm3. A cut-off value of 78.05 mg/L for Gm3 was calculated to discriminate controls and patients with ABPA/pneumonia with a specificity of 75% and a sensitivity of 74.6%. The follow up examination of 21 patients showed a decrease of Gm3 in most patients without statistical significance due to the small number of follow up patients.

Conclusion

Af specific IgG may be a useful biomarker for acute ABPA and Af pneumonia, but not for Af bronchitis in CF. However, due to the large interindividual variability of Gm3, it should only be interpreted alongside other biomarkers. Therefore, due to its broad availability, it could be suitable as a biomarker for ABPA and Af pneumonia in CF, if the results can be supported by a larger multicenter cohort.

The chemokine CCL18 characterises Pseudomonas infections in cystic fibrosis lung disease

Cystic fibrosis (CF) lung disease is characterised by chronic Pseudomonas aeruginosa infection and leukocyte infiltration. Chemokines recruit leukocytes to sites of infection. Gene expression analysis identified the chemokine CCL18 as upregulated in CF leukocytes. We hypothesised that CCL18 characterises infection and inflammation in patients with CF lung disease. Therefore, we quantified CCL18 protein levels in the serum and airway fluids of CF patients and healthy controls, and studied CCL18 protein production by airway cells ex vivo. These studies demonstrated that CCL18 levels were increased in the serum and airway fluids from CF patients compared with healthy controls. Within CF patients, CCL18 levels were increased in P. aeruginosa-infected CF patients. CCL18 levels in the airways, but not in serum, correlated with severity of pulmonary obstruction in CF. Airway cells isolated from P. aeruginosa-infected CF patients produced significantly higher amounts of CCL18 protein compared with airway cells from CF patients without P. aeruginosa infection or healthy controls. Collectively, these studies show that CCL18 levels characterise chronic P. aeruginosa infection and pulmonary obstruction in patients with CF. CCL18 may, thus, serve as a potential biomarker and therapeutic target in CF lung disease.

Fungi: the neglected allergenic sources

Allergic diseases are considered the epidemics of the twentieth century estimated to affect more than 30% of the population in industrialized countries with a still increasing incidence. During the past two decades, the application of molecular biology allowed cloning, production and characterization of hundreds of recombinant allergens. In turn, knowledge about molecular, chemical and biologically relevant allergens contributed to increase our understanding of the mechanisms underlying IgE-mediated type I hypersensitivity reactions. It has been largely demonstrated that fungi are potent sources of allergenic molecules covering a vast variety of molecular structures including enzymes, toxins, cell wall components and phylogenetically highly conserved cross-reactive proteins. Despite the large knowledge accumulated and the compelling evidence for an involvement of fungal allergens in the pathophysiology of allergic diseases, fungi as a prominent source of allergens are still largely neglected in basic research as well as in clinical practice. This review aims to highlight the impact of fungal allergens with focus on asthma and atopic dermatitis.

Innate immunity in cystic fibrosis lung disease

Chronic lung disease determines the morbidity and mortality of cystic fibrosis (CF) patients. The pulmonary immune response in CF is characterized by an early and non-resolving activation of the innate immune system, which is dysregulated at several levels. Here we provide a comprehensive overview of innate immunity in CF lung disease, involving (i) epithelial dysfunction, (ii) pathogen sensing, (iii) leukocyte recruitment, (iv) phagocyte impairment, (v) mechanisms linking innate and adaptive immunity and (iv) the potential clinical relevance. Dissecting the complex network of innate immune regulation and associated pro-inflammatory cascades in CF lung disease may pave the way for novel immune-targeted therapies in CF and other chronic infective lung diseases.

Serum markers for allergic bronchopulmonary aspergillosis in cystic fibrosis: State of the art and further challenges

Allergic bronchopulmonary aspergillosis (ABPA), which results from hypersensitivity, primarily to Aspergillus, represents a severe complication in patients suffering from asthma or cystic fibrosis (CF). Since early treatment of ABPA is supposed to prevent long-term damages, ABPA has to be diagnosed promptly. However, this diagnosis is not straightforward due to clinical and radiological features of ABPA overlapping with those of CF. Despite ABPA specific diagnosis criteria proposed by the Cystic Fibrosis Foundation in 2003, making a definitive ABPA diagnosis in CF patients remains a challenge. Recent advances in the immunopathogenesis of ABPA have initiated the development of new serological tests, such as the recently reported detection of specific IgE to recombinant A. fumigatus allergens, or Thymus- and activation-regulated chemokine (TARC / CCL17), both of which are of value in the diagnosis of APBA. We review in this paper the serum markers that can advance ABPA diagnosis in CF patients, ranging from the well known criteria (anti-A. fumigatus IgE, IgG, and precipitins) to the recent biomarkers (IgE towards recombinant A. fumigatus allergens or TARC detection). Taking into account the up-dated physiopathology of ABPA, we discuss their place and their usefulness, especially TARC, to improve early ABPA detection and monitoring in CF patients.

Characteristics of pathogenic fungi and antifungal therapy in cystic fibrosis

A defective mucociliary clearance facilitates colonization with bacteria and fungal spores in cystic fibrosis patients. Yeasts and molds are cultured from the cystic fibrosis respiratory tract and often their clinical relevance is unknown. Candida spp. are the most commonly isolated yeasts, whereas Aspergillus spp., Scedosporium apiospermum, as well as Exophiala dermatitidis in some countries, are the most frequent molds recovered from respiratory specimens. Molecular biotyping studies have revealed that some fungal genotypes are capable of chronically colonizing the airways. Persistent Aspergillus fumigatus infection is associated with an increased risk of pulmonary exacerbations requiring hospitalization. The prevalence of non-Aspergillus molds may be underestimated due to overgrowth of Pseudomonas and Aspergillus spp. on routine media. Allergic bronchopulmonary aspergillosis is usually treated by oral steroids and an antifungal azole drug. Interactions with the co-medication have to be considered. A small number of antifungal pharmacokinetic studies indicate a high inter-subject variability for itraconazole, voriconazole and posaconazole, and therefore therapeutic drug monitoring is recommended.

Cystic fibrosis, atopy, asthma and ABPA

The role of atopy on cystic fibrosis (CF) progression remains unclear but evidence suggests that it may influence the appearance of co-morbid conditions such as CF asthma or allergic bronchopulmonary aspergillosis (ABPA). Recognising asthma in patients with CF is not always easy but the identification of atopic markers favours the diagnosis. Physicians should be aware of this fact in order to achieve a better control of respiratory symptoms in patients with CF. Bronchial mucosa inflammation and abnormal mucus predispose to mould colonisation. These patients are at higher risk of allergic sensitisation, especially when atopic susceptibility is present. In the particular case of A. fumigatus, allergic sensitisation precedes ABPA development, which occurs in up to 10% of CF patients. Progression of lung function deterioration is most strikingly pronounced in patients with ABPA. Therefore, sensitisation with A. fumigatus should be regularly tested in patients with CF, especially those at higher risk. Recombinant allergens constitute an important advance in differentiating Aspergillus sensitisation from ABPA itself.