BACKGROUND
Inflammatory bowel disease (IBD) is caused by an abnormal immune response. Programmed cell death 1 (PD-1) is an immunostimulatory molecule, which interacts with PD ligand (PD-L1) playing a prime important role among autoimmune diseases.
Bifidobacterium infantis
(
B. infantis
) can promote the differentiation of CD (cluster of differentiation) 4
+
T cells into regulatory T cells (Tregs). Tregs participate in the development of IBD and may be related to disease activity.
B. infantis
amplify the expression level of PD-1, PD-L1 and Tregs’ nuclear transcription factor forkhead box protein 3 (Foxp3). But the mechanism of
B. infantis
on PD-1/PD-L1 signaling remains unclear.
AIM
To explore the mechanism of
B. infantis
regulating the immune response in IBD.
METHODS
Forty-eight-week-old BALB/c mice were randomly divided into five groups: The control group, dextran sulphate sodium (DSS) model group, DSS +
B. infantis
group, DSS +
B. infantis
+ anti-PD-L1 group, and DSS + anti-PD-L1 group. The control group mice were given drinking water freely, the other four groups were given drinking water containing 5% DSS freely. The control group, DSS model group, and DSS + anti-PD-L1 group were given normal saline (NS) 400 μL daily by gastric lavage, and the DSS +
B. infantis
group and DSS +
B. infantis
+ anti-PD-L1 group were given NS and 1 × 10
9
colony-forming unit of
B. infantis
daily by gastric lavage. The DSS +
B. infantis
+ anti-PD-L1 group and DSS + anti-PD-L1 group were given 200 μg of PD-L1 blocker intraperitoneally at days 0, 3, 5, and 7; the control group, DSS + anti-PD-L1 group, and DSS +
B. infantis
group were given an intraperitoneal injection of an equal volume of phosphate buffered saline (PBS). Changes in PD-L1, PD-1, Foxp3, interleukin (IL)-10, and transforming growth factor β (TGF-β) 1 protein and gene expression were observed. Flow cytometry was used to observe changes in CD4
+
, CD25
+
, Foxp3
+
cell numbers in the blood and spleen.
RESULTS
Compared to the control group, the expression of PD-1, Foxp3, IL-10, and TGF-β1 was significantly decreased in the intestinal tract of the DSS mice (
P
< 0.05). Compared to the control group, the proportion of CD4
+
, CD25
+
, Foxp3
+
cells in spleen and blood of DSS group was visibly katabatic (
P
< 0.05).
B. infantis
upgraded the express of PD-L1, PD-1...