DSS-Induced Colitis Model

Murine acute colitis was induced as previously described by Wirtz et al. (47), with the slightly modifications. Briefly, six-week-old C57BL/6 male mice was induced by giving 3% DSS (MW36 000–50 000; MP Biomedicals) dissolved in drinking water for seven consecutive days, and were euthanized by cervical dislocation under isoflurane anesthesia on day 8. To evaluate the severity of colitis, animals were monitored daily for loss of body weight, stool consistency and hematochezia. Individuals were also given a clinical score for the disease activity index (DAI), which ranged from 0 to 4. The entire colon was removed, gently flushed with saline and blotted on filter paper, cleaned of fat and mesentery, and longitudinally opened so as to exhaustively eliminate faucal residues. Each specimen was weighed and its length was measured under a constant load. A fraction of colon tissue was used for histological examination and scored, and remaining colon tissue were measured the expression level of inflammation factors, as well as the population of MDSC and Th subsets in lamina propria. Bacterial loading in the colon was tested as described previously (48–50). DNA samples were amplified using both 16S rRNA universal primers and 16S rRNA gene group-specific primers (UniF340 and UniR514). The primer sequences are presented in Supplementary Table 3.