Abstract
BackgroundThe rising incidence of pulmonary Mycobacterium avium-intracellulare complex (MAI) infection is unexplained but parallels the growing world-wide epidemic of allergic disease. We hypothesized an association between pulmonary MAI infection and Th2-type immune responses as seen in allergy.MethodsBiomarkers of patient Th2-type immune responses (peripheral blood eosinophil counts and serum IgE levels) were compared between patients with positive pulmonary samples for tuberculosis and non-tuberculous mycobacterial (NTM) infection. A further comparison of clinical characteristics, including respiratory co-morbidities, and biomarkers, was conducted between patients culturing MAI NTM and those culturing NTM other than MAI.ResultsPatients culturing NTM from pulmonary samples had significantly higher peripheral blood eosinophil levels than those culturing Mycobacterium tuberculosis. Furthermore, patients culturing MAI compared to those culturing NTM other than MAI had higher eosinophil counts (mean 0.29x109/L vs 0.15x109/L, p = 0.010) and IgE levels (geometric mean 138kU/L vs 47kU/L, p = 0.021). However there was no significant difference in the frequency of asthma between the two NTM groups.ConclusionsThere is an association between biomarkers of Th2-type immune responses and pulmonary MAI. Prospective and translational research could identify the direction of causation; and so determine whether our finding may be utilized within future management strategies for MAI.
Highlights
The rising incidence of pulmonary Mycobacterium avium-intracellulare complex (MAI) infection is unexplained but parallels the growing world-wide epidemic of allergic disease
Peripheral blood eosinophil counts are higher in patients with non-tuberculous mycobacterial (NTM) infection than in patients with tuberculosis Ninety-three patients cultured pulmonary NTM with at least two positive mycobacterial cultures over the fiveyear period. 19 were excluded from further analysis as they had known immunosuppressed states
Peripheral blood eosinophil counts were significantly higher in the NTM cohort than in patients with pulmonary TB. 13 (18%) of NTM patients had an eosinophilia of >0.4x109/L, with 19 (26%) a peripheral blood eosinophil count of ≥0.27x109/L
Summary
The rising incidence of pulmonary Mycobacterium avium-intracellulare complex (MAI) infection is unexplained but parallels the growing world-wide epidemic of allergic disease. The incidence of non-tuberculous mycobacterial (NTM) infection is rising [1], and this appears to be driven largely by an increase in pulmonary Mycobacterium avium-intracellulare complex (MAI) infection [2]. Pulmonary NTM disease is most often seen in patients with chronic respiratory illness but this is perhaps confounded by Pfeffer et al Respiratory Research (2017) 18:93 doctors most often testing for NTM in such populations. Research in patients with cystic fibrosis demonstrates a specific association between NTM infection and allergic-bronchopulmonary aspergillosis (ABPA) [9] - suggesting that the increased predilection for NTM infections in patients with chronic lung disease is more complex than mycobacteria thriving in damaged lungs [10, 11]
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