2.3 Haematoxylin-eosin (HE) staining
At necropsy, colonic tissues were collected, immersed in 4% paraformaldehyde (Solarbio, P110, USA), and stored for 48 h at 4 °C. Then, 5 μm sections were cut on a Leica RM2016 Microtome (Leica Biosystem) and stained with haematoxylin and eosin (H&E). The colon and spleen tissues were fixed at 40 g/L in polyformaldehyde for 12 h. After dehydration, the tissue was turned transparent with xylene and washed with PBS. The sample was embedded in paraffin, and the tissue slice was stained. Colon lesions and inflammatory infiltration of spleen tissue were observed under an optical microscope. Histological scoring was based on two parameters as indicated in Table 1 [9]. The total colon pathology score equalled the inflammatory cell score plus the tissue damage score.