Alteration of Gut Immunity and Microbiome in Mixed Granulocytic Asthma

Abstract

Growing evidence suggests that there is an essential link between the gut and lungs. Asthma is a common chronic inflammatory disease and is considered a heterogeneous disease. While it has been documented that eosinophilic asthma affects gut immunity and the microbiome, the effect of other types of asthma on the gut environment has not been examined. In this study, we utilized an OVA/poly I:C-induced mixed granulocytic asthma model and found increased Tregs without significant changes in other inflammatory cells in the colon. Interestingly, an altered gut microbiome has been observed in a mixed granulocytic asthma model. We observed an increase in the relative abundance of the Faecalibaculum genus and Erysipelotrichaceae family, with a concomitant decrease in the relative abundance of the genera Candidatus arthromitus and Streptococcus. The altered gut microbiome leads to changes in the abundance of genes associated with microbial metabolism, such as glycolysis. We found that mixed granulocytic asthma mainly affects the gut microbial composition and metabolism, which may have important implications in the severity and development of asthma and gut immune homeostasis. This suggests that altered gut microbial metabolism may be a potential therapeutic target for patients with mixed granulocytic asthma.

Keywords: gut microbiota; intestinal immune cells; microbial metabolism; mixed granulocytic asthma.

Figure 1

Establishment of the OVA/poly I:C model of mixed granulocytic asthma. (A) Schematics diagram of the OVA/poly I:C model. Mice were sensitized with OVA and poly I:C and then challenged with OVA as shown. (B) Representative images of hematoxylin and eosin stained lung section (original magnification: X200). (C) Differential cell counts in BAL fluid showing total cells, macrophages (Mac), eosinophils (Eos), neutrophils (Neu), and lymphocytes (Lym). (D) Levels of cytokine in whole lung homogenates of mice. Data shown are represented as mean ± SEM and representative of 3 independent experiments with 5 to 7 mice in each group. * p < 0.05, *** p < 0.001, and **** p < 0.0001, as determined by Student’s t test.

Figure 2

Increased regulatory T cells in the gut of mixed granulocytic asthma. Representative and cumulative flow cytometric analyses of (A) CD11b⁺ SiglecF⁺ eosinophils after neutrophil exclusion and (B) CD11b⁺ Ly6G⁺ neutrophils in the colon of the indicated group of mice. (C) Representative and cumulative flow cytometry analyses of Foxp3, RORγt, T-bet, or GATA3 expressing CD4⁺ T cell subsets gated on CD3 in the colon of the indicated group of mice. (D) Relative IL-10 expression in the colon. (E) Representative and cumulative flow cytometry analyses of IgA⁺B220⁻ and IgM⁺B220⁺ B cells in the colon of mice in the indicated groups. Data are represented as mean ± SEM and are representative of three independent experiments with 5 to 7 mice in each group. ** p < 0.01 as determined by Student’s t test.

Figure 3

Altered gut microbiome in mixed granulocytic asthma. (A) Chao1 and Shanon index for alpha diversity. (B) PCoA plot by Brady-Cutis distance. (C) Taxanomic cladogram generated by LEfSe showing control enriched taxa (green) and mixed granulocytic asthma enriched taxa (red). (D).

Figure 4

Functional changes within the gut microbiome in mixed granulocytic asthma. Functional pathways enriched in each groups based on PICRUSt prediction. LEfSe analysis (LDA > 2, p < 0.05).