Table 2. Summary and comparison of animal studies involving air pollutants and subsequent outcomes.

Study Name	Model Type	Age	Exposure Type	Exposure Frequency	Exposure Duration	Outcome
Exposure to ambient particulate matter alters the microbial composition and induces immune changes in rat lung72	Rat	7–9 weeks old	Control: Clean air Biomass fuel group (BMF): Smoke from smoldered China fir sawdust Motor vehicle exhaust group (MVE): PM from gasoline motorcycle engine	BMF group: Four 1 hour periods MVE group: Two 2 hour periods	5 days a week for 4 weeks	Bacteria phyla differed in abundance between controls and MVE group (p < 0.05), with increase in Proteobacteria in control group Macrophage levels increased in bronchoalveolar lavage fluid (BALF) in BMF group compared to controls (p = 0.045) Elevated IgA levels in BALF for both BMF group (p < 0.01) and MVE group (p = 0.02) compared to controls Reduced IgG levels in BALF for BMF group compared to controls (p = 0.031)
Inhalational exposure to particulate matter air pollution alters the composition of the gut microbiome96	Mice	8-12 weeks old	Control: Filtered air PM2.5: Concentrated PM from Chicago ambient air	8 hours	5 days a week for 3 weeks	Elevated richness (p = 0.019) and Shannon indices (p = 0.004) in intestinal samples of PM exposed mice compared to controls Decreased abundance of Firmicutes at all sites along gastrointestinal tract in PM exposed mice compared to controls (p < 0.05) Higher TNF-α expression in colon of PM exposed mice compared to controls (p < 0.05)
House dust exposure mediates gut microbiome Lactobacillus enrichment and airway immune defense against allergens and virus infection97	Mice	6-8 weeks old	Oral gavage of resuspended dust from pet homes or non-pet homes	NA	Daily for 1 week, followed by twice a week for 2 weeks	104 taxa with elevated abundances in mice exposed to dust from pet homes compared to non-pet homes (p ≤ 0.05) including Lactobacillus Reduced levels of IL-4 and IL-13 in lungs of mice exposed to dust from pet homes compared to non-pet homes (p < 0.05) Reduced levels of IgE in serum of mice exposed to dust from pet homes compared to non-pet homes (p < 0.05)
Environmental particulate matter induces murine intestinal inflammatory responses and alters the gut microbiome98	Mice	6-8 weeks old	Short treatment group: Vehicle or resuspended PM10 gavage Chronic treatment group: Feeding of mouse chow with addition of PM10	NA	Short term treatment: 7 or 14 days Chronic treatment: 35 days	Short term PM10 exposure for 7 days stimulated increased expression of IL-10, CXCL1 and IL-1β in the small intestine (p < 0.05) Short term PM10 exposure for 14 days led to increased gut permeability compared to controls (p < 0.05) Chronic PM10 exposure caused increased abundance of Verrucomicrobia in both wild-type and IL10-/- mice (p < 0.05), and decreased abundance of Bacteroidetes and increased abundance of Firmicutes in IL10-/- mice (p < 0.05) Chronic PM10 exposure resulted in increased expression of IL-17 and IL-13 in colon of wild type mice (p < 0.05), and increased expression of IL-17, IL-1β, TNF-α, IL-12, and IL-13 in IL-10−/− mice (p < 0.05) Chronic PM10 exposure led to reduced abundance of butyrate in both wild type and IL-10−/− mice (p < 0.05)
Exposure to concentrated ambient PM2.5 alters the composition of gut microbiota in a murine model99	Mice	4 weeks old	Control group: Filtered air Experimental group: Concentrated ambient PM2.5 (CAP)	8 hours per day, 6 days per week	Up to 48 weeks of exposure	Chronic exposure to CAP decreased faecal bacterial richness in ACE and Chao-1 indices (p < 0.05), associated with alteration in gut microbiota composition Helicobacter hepaticus and Clostridium sensu strito 1 were absent in CAP-exposed mice (p = 0.013) Chronic exposure to CAP did not influence faecal bacterial diversity and fungal communities (p > 0.05) Insulin resistance and impaired glucose tolerance were observed in mice exposed to CAP (p < 0.05)

Abbreviations: PM, particulate matter; BALF, bronchoalveolar lavage fluid; BMF, biomass fuel; MVE, motor vehicle exhaust; IL, interleukin; Ig, immunoglobin; TNF, tumor necrosis factor; CAP, concentrated ambient PM_2.5