[Therapeutic effects of mucosal tolerance on inflammatory bowel disease: experiment with rats]

To evaluate the therapeutic effect of mucosal tolerance on inflammatory bowel disease (IBD).

Forty-two SD rats underwent enema of 2, 4, 6-trinitro-benzene-sulfonic acid (TNBS) so as to establish models of experimental colitis and then divided into 7 equal groups: colitis group (without treatment), oral ovalbumin (OVA) group (undergoing gastric perfusion of OVA as inducing antigen), nasal OVA group (undergoing OVA nose dropping), oral OVA plus adjuvant group [undergoing gastric perfusion OVA with lipopolysaccharide (LPS) as adjuvant], nasal OVA plus adjuvant group, adjuvant control group, and blank control group (administrated with PBS orally). Another 6 rats were used as blank control group. All of the rats were executed 21 days after enema with their spleens taken out. Splenic lymphocytes were isolated and co-cultured with OVA for 96 h. MTT method was used to calculate the proliferation index so as to detect the mucosal tolerance. Macroscopical and histolopathological scores of colon were estimated so as to evaluate the therapeutic effects.

Typical manifestations of colitis occurred 3-4 days after enema and persisted to the day 21 after enema. The macroscopical and histolopathological scores of colon of the colitis group (mean rank were 9.5 and 9.5) were both significantly higher than those of the normal control group (mean rank were 3.5 and 3.5 both P < 0.01). The splenic lymphocyte proliferation indexes of the oral OVA plus LPS, nasal OVA, and nasal OVA plus LPS groups were 0.11 +/- 0.05, 0.12 +/- 0.07, and 0.06 +/- 0.04 respectively, all significantly lower than that of the normal control group (0.30 +/- 0.13, all P < 0.05), however, without significant differences among these 3 groups (all P > 0.05). The splenic lymphocyte proliferation indexes of the oral OVA group was 0.25 +/- 0.10, not significantly different from that of the normal control group (P > 0.05). The macroscopical scores of the oral OVA plus LPS group, nasal OVA plus LPS group, and oral LPS alone group were 3.0 +/- 1.3, 2.0 +/- 0.6, and 4.3 +/- 1.0 respectively, all significantly lower than that of the colitis group (6.3 +/- 0.8, all P < 0.05); and the histological score of the oral OVA plus LPS group, nasal OVA plus LPS group, and oral LPS alone group were 3.0 +/- 1.1, 2.7 +/- 1.0, and 4.6 +/- 1.6 respectively, all significantly lower than that of the colitis group (7.5 +/- 1.0, all P < 0.05). The colonic score of the nasal OVA plus LPS group was most significantly decreased.

Colitis interferes with the induction of oral tolerance, but not the induction of nasal tolerance. Both oral tolerance combined with adjuvant and nasal tolerance combined with adjuvant have therapeutic effects on experimental colitis. Oral adjuvant alone also has therapeutic effect on colitis, and the therapeutic effect of nasal tolerance combined with adjuvant is the best.