Isolation of filamentous fungi from sputum in asthma is associated with reduced post-bronchodilator FEV1

Background

Fungal sensitization is common in severe asthma, but the clinical relevance of this and the relationship with airway colonization by fungi remain unclear. The range of fungi that may colonize the airways in asthma is unknown.

Objective

To provide a comprehensive analysis on the range of filamentous fungi isolated in sputum from people with asthma and report the relationship with their clinico-immunological features of their disease.

Methods

We recruited 126 subjects with a diagnosis of asthma, 94% with moderate-severe disease, and 18 healthy volunteers. At a single stable visit, subjects underwent spirometry; sputum fungal culture and a sputum cell differential count; skin prick testing to both common aeroallergens and an extended fungal panel; specific IgE to Aspergillus fumigatus. Fungi were identified by morphology and species identity was confirmed by sequencing. Four patients had allergic bronchopulmonary aspergillosis.

Results

Forty-eight percent of asthma subjects were IgE-sensitized to one fungal allergen and 22% to ≥ 2. Twenty-seven different taxa of filamentous fungi were isolated from 54% of their sputa, more than one species being detected in 17%. This compared with 3 (17%) healthy controls culturing any fungus (P < 0.01). Aspergillus species were most frequently cultured in isolation followed by Penicillium species. Post-bronchodilator FEV₁ (% predicted) in the subjects with asthma was 71(± 25) in those with a positive fungal culture vs. 83 (± 25) in those culture-negative, (P < 0.01).

Conclusion and Clinical Relevance

Numerous thermotolerant fungi other than A. fumigatus can be cultured from sputum of people with moderate-to-severe asthma; a positive culture is associated with an impaired post-bronchodilator FEV₁, which might be partly responsible for the development of fixed airflow obstruction in asthma. Sensitization to these fungi is also common.

CRTH2 expression on T cells in asthma

Mast cell-derived prostaglandin D2 (PGD2) is the major prostanoid found within the airway of asthmatics immediately following allergen challenge. PGD2 has been shown to have chemokinetic effects on eosinophils and T helper type 2 (Th2) cells in vitro. This occurs through the interaction of PGD2 with the G-protein-coupled chemokine receptor homologous molecule expressed on Th2 lymphocytes (CRTH2). The expression of CRTH2 has been shown to be highly selective for Th2 cells. Using flow cytometry we have studied the expression of CRTH2 on T cells in blood and bronchoalveolar lavage fluid in asthmatics and normal subjects. CRTH2 expression was confined to a small percentage of blood T cells in asthmatics (1.8%+/-0.2) and normal (1.6%+/-0.2) subjects. CRTH2 was enriched significantly on interleukin (IL)-4+/IL-13+ T cells compared to interferon (IFN)-gamma+ T cells (P<0.001). There was a small population of CRTH2+ T cells in the bronchoalveolar lavage (BAL) of asthmatics (2.3%+/-0.6) and normal subjects (0.3%+/-0.1), and there was a significant difference between the two groups (P<0.05). There were similar amounts of PGD2 in the BAL of asthma and normal subjects. Within paired blood-BAL samples from the same subject there was no increase in CRTH2+ T cells in the BAL compared to blood in asthmatics. Enrichment of CRTH2 on IL-4+ and IL-13+ T cells compared to IFN-gamma+ T cells was also seen in BAL from asthmatics (P<0.001). CRTH2 is expressed preferentially by IL-4+/IL-13+ T cells compared to IFN-gamma+ T cells. However, given their small numbers they are unlikely to have a significant involvement in the pathogenesis of asthma. CRTH2 antagonism may not diminish T cell accumulation in the asthmatic lung.

Expression of CCR8 is increased in asthma

Background

Chemokines and their receptors could play key roles in the recruitment of T cells to the asthmatic lung. CCR8 is preferentially expressed on T-helper type 2 cells, and is thought to play a role in the pathogenesis of human asthma.

Objective

Determine the expression of CCR8 on T cells in blood, bronchoalveolar lavage (BAL) and bronchial mucosa from asthmatics and normal subjects.

Methods

CCR8 expression in blood and BAL from asthma and normal subjects was studied using flow cytometry. CCR8 expression on IFN-γ⁺ and IL-4⁺/IL-13⁺ blood and BAL T cells was studied following stimulation with Phorbol–Myristate–Acetate and Calcium Ionophore. Paraffin-embedded bronchial biopsies were used to study CCR8 in bronchial epithelium.

Results

The percentage of CD3⁺ cells expressing CCR8 in the blood was higher in asthmatics (4.7±0.4%) compared with normal subjects (3.0±0.4%; P<0.01). There was an approximately sixfold enrichment of CCR8 on IL-4⁺/IL-13⁺ cells compared with IFN-γ⁺ T cells (P<0.001) in both asthmatic and normal subjects in both blood and BAL. Significantly more BAL T cells expressed CCR8 in asthmatic (8.6±0.8%) compared with normal subjects (3.9±0.7%) (P<0.01). In paired blood-BAL samples from asthmatics, significantly more CCR8+CD3⁺ T cells were present in BAL (9.0±0.9%) than in blood (5.6±0.9%; P<0.05). There were more CCR8-positive cells in bronchial biopsies from asthmatic (93±11 cells/mm²) compared with normal subjects (30±16 cells/mm²) (P<0.05). The ligand CCL1 was increased in the BAL of asthmatics compared with normal subjects (35±6 vs. 12.9±7 pg/mL; P<0.05).

Conclusion

There may be a role for CCR8 in the recruitment of T cells to the lung in asthmatics.

Cite this as: K. Mutalithas, C. Guillen, C. Raport, R. Kolbeck, D. Soler, C. E. Brightling, I. D. Pavord and A. J. Wardlaw, Clinical & Experimental Allergy, 2010 (40) 1175–1185.