Development of dextran sulphate sodium-induced experimental colitis is suppressed in genetically mast cell-deficient Ws/Ws rats

Abstract

Ws/Ws rats have a small deletion of the c-kit gene, and are deficient in both mucosal-type mast cells (MMC) and connective tissue-type mast cells (CTMC). In the present study we investigated the role of intestinal MMC in the development of dextran sulphate sodium (DSS)-induced experimental colitis using Ws/Ws rats. Ws/Ws and control (+/+) rats were given a 3% DSS aqueous solution orally for 10 days, and the subsequent mucosal damage was evaluated macroscopically and histologically. The mucosal myeloperoxidase (MPO) activities and histamine levels were also measured. (i) DSS induced severe oedema and hyperaemia with sporadic erosions in the control (+/+) rats, but these changes were significantly attenuated in the Ws/Ws rats (P < 0.01). (ii) The microscopic mucosal damage score was lower in the Ws/Ws rats than in the control (+/+) rats (P = 0.06). (iii) There were no significant differences in mucosal MPO activity between the Ws/Ws and control (+/+) rats (P = 0.46). (iv) The mucosal histamine levels in the colon were significantly reduced in the Ws/Ws rats compared with the control (+/+) rats (P < 0.05). (v) Significant positive correlations were observed between mucosal histamine levels and the degree of mucosal oedema (calculated as colonic wet weight/protein content) (r = 0.778, P < 0.01), and between histamine levels and the macroscopic damage (r = 0.623, P < 0.05), respectively. (vi) DSS induced a local recruitment of MMC in the colonic mucosa of Ws/Ws rats, and mucosal damage gradually increased in accordance with this MMC recruitment. These results indicate that MMC play an important role in the development of DSS colitis.

Fig. 1

Dextran sulphate sodium (DSS)-induced colitis in Ws/Ws and control (+/+) rats. The rats were treated with a 3% DSS solution for 10 days. (A) Ws/Ws rats. (B) Control rats. The mucosal damage in the control rats extended further towards the oral side than the Ws/Ws rats.

Fig. 2

Microscopic findings of dextran sulphate sodium (DSS)-induced colitis in the Ws/Ws and control (+/+) rat. Rectal specimens taken at 1 cm from the anal margin were preserved in Carnoy's fixative, sectioned, and stained with H–E. (A) Ws/Ws rat, and (B) control (+/+) rat (× 100).

Fig. 3

Microscopic findings of dextran sulphate sodium (DSS)-induced colitis in the Ws/Ws and control (+/+) rat. Toluidine blue staining was performed as described in Materials and Methods. (A) Ws/Ws rat. (B) Control (+%+) rat. Some mast cells (open triangle) and macrophages (arrow) containing ingested DSS particles, with metachromasia, were detected in the mucosa and submucosa (× 400).

Fig. 4

Rat mast cell protease II (RMCP II)-immunopositive cells in the mucosa. (A) Ws/Ws rat. (B) Control (+/+) rat. The RMCP II-immunopositive cells were scattered in the mucosa of Ws/Ws and (+/+) rats. Sporadic globule leucocytes, which are regarded as mast cells, infiltrating the epithelial layer, were also observed (arrow) (× 200).

Fig. 5

Relationship between mucosal histamine levels and mucosal damage markers. (a) Correlation between mucosal histamine levels and the degree of mucosal oedema (the ratio of the wet weight to the protein content in the colonic mucosa). The line represents the regression line for data from both Ws/Ws and control rats (Y = 0.038X − 0.011, R = 0.778, P < 0.01). (b) Correlation between mucosal histamine levels and the ratio of the macroscopically damaged area to the entire colonic surface (Y = 0.9074X + 0.4916, R = 0.623, P < 0.05).