Serum IgA antibodies to Aspergillus fumigatus in various stages of allergic bronchopulmonary aspergillosis

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.

Immunopathogenesis of allergic bronchopulmonary aspergillosis in cystic fibrosis

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity lung disease mediated by an allergic late-phase inflammatory response to Aspergillus fumigatus antigens. ABPA is characterized by markedly elevated Aspergillus-specific and total IgE levels and eosinophilia, and manifested by wheezing, pulmonary infiltrates, and bronchiectasis and fibrosis, which afflict asthmatic and cystic fibrosis (CF) patients. We propose that ABPA develops in genetically susceptible CF patients due to HLA-DR2 and DR5 restriction, increased sensitivity to IL-4 stimulation, and increased A. fumigatus allergen-specific Th2 CD4+ T-cell-mediated responses. In addition, A. fumigatus proteases play a role in facilitation of antigen transport across the epithelial cell layer by damaging the epithelial integrity and by a direct interaction with epithelial cell surface receptors, resulting in pro-inflammatory cytokine production and corresponding inflammatory responses.

Cellular and humoral observations in a patient with allergic bronchopulmonary aspergillosis during a nonasthmatic exacerbation

A patient is described with an asymptomatic exacerbation of allergic bronchopulmonary aspergillosis (ABPA), clinically characterized by pulmonary infiltrates, with absence of obstructive reactions and a short period of hemoptysis 2 weeks before hospitalization. Cell counts and antibody concentrations were measured in serum, and bronchoalveolar fluid (BAF) samples and values were compared with data from previous periods of symptomatic exacerbations. During the asymptomatic exacerbation, concentrations of antibody to Aspergillus fumigatus, total IgE, and precipitating antibodies were elevated in peripheral blood. No quantitative differences in specific antibody concentrations (IgE, IgG, IgA, and IgM) against A. fumigatus were found between sera from symptomatic and asymptomatic periods of ABPA. In contrast to observations in the serum, protein concentrations in BAL fluid were normal during the asymptomatic period, whereas high concentrations were found during the symptomatic phases. Local antibody concentrations (in BAF) were characterized by high levels of IgA antibodies against A. fumigatus. During asymptomatic and symptomatic phases, eosinophils were elevated in peripheral blood, in sputum, in BAF, and highly elevated in tissue biopsy specimens. Activated eosinophils were found, as indicated by the presence of light-density cells in the circulation and monoclonal antieosinophil cationic protein binding to bronchoalveolar lavage eosinophils. In contrast to the symptomatic phase of ABPA in 1980, demonstrating aspecific airway reactivity to several pharmacologically active substances, no such hyperreactivity was found during the asymptomatic phase of ABPA in 1986. It is proposed that the asymptomatic infiltrative phase of ABPA is an intermediate stage that can develop into a symptomatic phase after prolonged and intensified infiltration of eosinophils. Mediators from the inflammatory cells may be involved in the induction of bronchial hyperresponsiveness. After induction of this hyperreactive stage of the airways, additional liberation of mediators from either eosinophils and/or mast cells will lead to a symptomatic (obstructive) phase of ABPA.