Gram-negative microbiota is related to acute exacerbation in children with asthma

Abstract

Background: The upper-airway microbiota may be associated with the pathogenesis of asthma and useful for predicting acute exacerbation. However, the relationship between the lower-airway microbiota and acute exacerbation in children with asthma is not well understood. We evaluated the characteristics of the airway microbiome using induced sputum from children with asthma exacerbation and compared the microbiota-related differences of inflammatory cytokines with those in children with asthma.

Methods: We analysed the microbiome using induced sputum during acute exacerbation of asthma in children. We identified microbial candidates that were prominent in children with asthma exacerbation and compared them with those in children with stable asthma using various analytical methods. The microbial candidates were analysed to determine their association with inflammatory cytokines. We also developed a predictive functional profile using PICRUSt.

Results: A total of 95 children with allergic sensitisation including 22 with asthma exacerbation, 67 with stable asthma, and 6 controls were evaluated. We selected 26 microbial candidates whose abundances were significantly increased, decreased, or correlated during acute exacerbation in children with asthma. Among the microbial candidates, Campylobacter, Capnocytophaga, Haemophilus, and Porphyromonas were associated with inflammatory cytokines including macrophage inflammatory protein (MIP)-1β, programmed death-ligand 1, and granzyme B. Both Campylobacter and MIP-1β levels were correlated with sputum eosinophils. Increased lipopolysaccharide biosynthesis and decreased glycan degradation were observed in children with asthma exacerbation.

Conclusion: Gram-negative microbes in the lower airway were related to acute exacerbation in children with asthma. These microbes and associated cytokines may play a role in exacerbating asthma in children.

Keywords: asthma; children; induced sputum; lipopolysaccharide; microbiome.

FIGURE 1

Heatmap plotted from linear discriminant analysis effect size (LEfSe) analysis at the genus level between groups. Capnocytophaga was increased in children with asthma exacerbation compared to in those with stable asthma and controls, whereas Saccharominas, Rothia, Gemella, Bulleidia, and Eubacterium_g10 were decreased

FIGURE 2

Relative abundance (operational taxonomic unit abundance) of discriminant microbiota plotted from SIMPER analysis at the genus level between groups. The 19 microbial candidates listed in the heatmap explained the difference between asthma exacerbation and stable asthma with up to 80% cumulative dissimilarity (Dis.)

FIGURE 3

Network analysis of microbiota in asthma exacerbation. Node size is proportional to the mean relative abundance. Node colour (red represents increased microbiota and grey represents decreased microbiota in asthma exacerbation) and node hue is proportional to the difference in microbiota relative abundance between asthma exacerbation and stable asthma. Each edge: a significant correlation coloured to indicate either positivity (red) or negativity (grey). Edge width and transparency are proportional to the absolute value of the correlation coefficient. Correlations were determined with SparCC with a correlation cut‐off R value of greater than 0.25 or less than −0.25

FIGURE 4

Correlation between microbial candidates distinct in asthma exacerbation from LEfSe, SIMPER, and network analysis using SparCC and prominently increased inflammatory cytokines in asthma exacerbation. Node size is proportional to Spearman's rank correlation coefficient. Red bar: positive correlation; blue bar: negative correlation; dark coloured node: false discovery rate (FDR) p < 0.05; light coloured node: FDR p ≥ 0.05

FIGURE 5

Heatmap plotted from linear discriminant analysis effect size analysis of predicted functional profiles using PICRUSt between groups. Lipopolysaccharide biosynthesis was increased and glycan degradation was decreased in children with asthma exacerbation compared to in children with stable asthma and controls

FIGURE 6

Gram‐negative microbes in the lower airway that increase lipopolysaccharide biosynthesis and decrease glycan degradation may promote acute exacerbation of allergic asthma in children via inflammatory cytokines including programmed death‐ligand 1, macrophage inflammatory proteins (MIP)‐1β, and granzyme B. Among the increased gram‐negative microbes, Campylobacter was associated with increased MIP‐1β and sputum eosinophils, indicating that this genus plays a role in asthma exacerbation in children