Immunohistochemical investigation of Foxp3 expression in the intestine in healthy and diseased dogs

Intestinal immune regulation including development of oral tolerance is of great importance for the maintenance of intestinal homeostasis. Concerning this, regulatory T cells (Tregs) occupy a pivotal role in cell-mediated immunosuppression. Dysregulation of mucosal immunology leading to an abnormal interaction with commensal bacteria is suggested to play a key role in the pathogenesis of Inflammatory Bowel Disease (IBD) in men and dogs. The aim of this study was to characterise the expression of Foxp3 in the normal canine gut of 18 dogs (mean age: 6.03 years), in 16 dogs suffering from IBD (mean age: 5.05 years), and of 6 dogs with intestinal nematode infection (mean age: 0.87 years) using immunohistochemistry. In the duodenum, Tregs in healthy dogs declined from villi (median: 10.67/62 500 μm(2)) to crypts (median: 1.89/62 500 μm(2)). Tregs were further increased in the villi of middle-aged dogs (median: 18.92/62 500 μm(2)) in contrast to juvenile (median: 3.50/62 500 μm(2)) and old (median: 9.56/62 500 μm(2)) individuals. Compared to healthy controls, animals suffering from IBD revealed reduced numbers of Tregs in duodenal villi (median: 4.13/62 500 μm(2)). Dogs with intestinal nematode infection displayed increased numbers of Tregs (median: 21.06/62 500 μm(2)) compared to healthy animals. Age-related changes indicate a progressive establishment of oral tolerance and immunosenescence in the canine elderly. The results further suggest that a defect in Treg homeostasis may be involved in the pathogenesis of canine IBD. In contrast, increased numbers of Tregs in the duodenum may be due to nematode infection.