Abstract
This study established a type 1 diabetes (T1DM) mouse model via intraperitoneal injection of streptozotocin (STZ) and examined the effect of regulatory T (Treg) cells on the gut microbiota by comparing its composition and diversity across three groups: control, T1DM, and Treg-treated mice. Forty-one 8-week-old male C57BL/6 mice under specific pathogen-free conditions were divided into a healthy control group, an untreated T1DM group, and a Treg treatment group (receiving low, medium, or high doses). T1DM was induced by administering a low-dose STZ injection over five consecutive days, with diabetes confirmation defined as a blood glucose level ≥300 mg/dL. CD4+CD25+ Treg cells isolated from spleens of healthy mice were used for treatment. Fecal samples collected on days 0, 14, and 34 from three randomly selected mice per group were subjected to 16S rRNA gene sequencing targeting the V3-V4 regions. The results showed significant differences in both alpha and beta diversity among the groups. Dominant bacterial families varied: Ruminococcaceae and others were enriched in the Treg treatment group, Muribaculaceae in the control group, and Lactobacillaceae in the untreated T1DM group. Genus-level abundances also shifted over time. Firmicutes abundance positively correlated with Treg levels (r = 0.70, p = 0.0433) but negatively with IFN-γ, whereas Cyanobacteria exhibited the opposite correlation. The Firmicutes/Bacteroidetes ratio was higher in T1DM mice than in controls and lower in the Treg-treated group. Metabolic pathway analysis indicated that two-component systems and ABC transporters were more prevalent in T1DM mice. In summary, Treg cell treatment altered the diversity, composition, dominant taxa, and Firmicutes/Bacteroidetes ratio of the gut microbiota compared with untreated T1DM mice.