3.2 The lack of MPO expression inecreased greatly bacterial output and aggravated the shortening of the colon in mice with bacterial infection and hypoxia exposure.
The bacterial colonies on the faces of the mice were enumerated on the following day. (Figure 2a). An increase in excretion indicated an increase in the severity of inflammation (Figure 2b). Compared with that in the NI, HKI and KI groups, the number of bacteria excreted in the HI groups was significantly increased. Comparing the WT and MPO-/- groups, the number of bacteria excreted in the MPO-/- groups iecreased significantly. The total number of bacteria excreted in the HKI groups was the largest.We found that the colon lengths of the mice in the infected groups were significantly shorter (Figure 3a-b) after the mice were infected withC. rodentium , indicating that after the mice were infected, the colonic inflammation in the mice was aggravated as a result of colon shortening. There was a difference between the HI and NI groups (P= P <0.05), which indicated that the colon shortening of mice was more obvious under hypoxic conditions. Compared with that of the HKI group, the colon shortening of the KI group was more obvious, and there was a significant difference (P <0.05), indicating that the colon shortening of the MPO-/-mice in the hypoxic environment was not as obvious as that under normoxia. Comparing the NC with HC groups and the KC and HKC groups, we found that hypoxic exposure could significantly increase the colon length in mice (P <0.05). The average length of each group is NC 7.01cm,NI 6.05cm,HC 8.75cm,HI 6.43cm,KC 7.00cm,KI 5.78cm,HKC 8.35cm,HKI 6.45cm. There were significant differences between the KI and NI groups and the HKI and HI groups (P <0.05), which indicated that the deletion of the MPO gene could aggravate the shortening of the colon in mice.
3.3 Colitis and inflammatory cell infiltration in spleen was alleviative in MPO-/- mice.
The results of H&E staining of colon tissue showed (Figure 4a) that the structure of the small intestinal mucosa of the mice in each control group was clear and complete, the villus crypts were deep, and the villi were neatly arranged. We found that the pathological damage to colon tissue was more severe in the HI and KI groups as a result of colon oedema, thinning, disorganized and variable villi, inflammatory cell infiltration around crypts, and shallow crypts.
We evaluated the pathological changes in colon tissue in each group of mice. The results (Figure 4b) showed that the pathological changes of the mice in the HI group were the most serious,and the normal tissue structure of part of the mucosa was significantly damaged. Compared with the control group, the HI group had significant differences in colon pathological tissue scores after infection. However, comparing the pathological scores of the HKI group with the KI group and the HI group with the NI group, the scores were significantly lower (P <0.05), indicating that MPO could increase the inflammatory response in mice. Figure 4c shows that the spleens of mice in the NI and KI groups had a large amount of inflammatory cell infiltration.