Immunohistochemical characterization of gastrointestinal macrophages/phagocytes in dogs with inflammatory bowel disease (IBD) and non-IBD dogs.

Intestinal Mϕ play a pivotal role in the maintenance of gut homeostasis, but can also contribute to inflammation such as inflammatory bowel disease (IBD). In contrast to human tissues, little is known about phenotypes of Mϕ in the canine gastrointestinal tract. Therefore, an immunohistochemical study was performed using Abs against Mϕ-associated molecules (Cluster of differentiation (CD)64, CD163, CD204, ionized calcium-binding adaptor molecule 1, L1 Ag, and MHC II) on stomach, duodenum, jejunum, ileum and colon from non-IBD dogs. In addition, marker-expression in the stomach, duodenum and colon of the non-IBD dogs was compared to that in dogs with IBD. Results revealed predominance of resident Mϕ displaying an anti-inflammatory phenotype represented by expression of CD163 as well as CD204 in the gut of non-IBD dogs with high Mϕ numbers especially present in the small intestinal villus area. Compared to non-IBD tissue counterparts, stomach, duodenum, and colon from dogs with IBD showed reduced Mϕ numbers with the exception of slightly increased numbers of CD64+ Mϕ. Correlation analyses between marker-expression of Mϕ and the Canine Inflammatory Bowel Disease Activity Index as well as histological scores failed to reveal relevant relationships. The present study provides evidence of the canine steady state gastrointestinal tract being dominated by Mϕ with anti-inflammatory properties maintaining gut homeostasis. A significant reduction in these resident Mϕ may reflect disturbances in homeostatic capacity that could contribute to the development of canine IBD. In contrast to human IBD and murine disease models, infiltration of pro-inflammatory Mϕ does not significantly contribute to the inflammatory process of canine IBD, which may illustrate possible species-specific differences in IBD pathogenesis.

Canine gut dendritic cells in the steady state and in inflammatory bowel disease.

Alongside the intestinal border, dendritic cells (DCs) sample large amounts of endogenous and potentially pathogenic antigens followed by initiation of protective immune responses or induction of tolerance. Breakdown of oral tolerance towards commensal bacteria is suggested to be crucial for the development of both human and canine inflammatory bowel disease (IBD). The aim of this study was to investigate canine intestinal DCs in the steady state and in dogs with IBD using multicolour immunofluorescence. In the healthy gut, DC-like cells expressed MHC II, CD1a8.2 and CD11c, and, in lower amounts, CD11b, within lamina propria, Peyer's patches (PPs) and mesenteric lymph nodes (MLNs), whereas those expressing CD80 and CD86 were only present in PPs and MLNs. Occasionally, DC-like cells were in contact with the intestinal lumen through transepithelial projections. In canine IBD, CD1a8.2+, CD11b+ and CD11c+ DC-like cells were decreased within the stomach, duodenum and colon, whereas the colonic mucosa revealed elevation of CD86+ DC-like cells. The complex network of DC-like cells in the gut indicates their important role in canine mucosal immunity, including active sampling of luminal antigens. Furthermore, their shift in diseased dogs suggests a pathogenetic significance for canine IBD.

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 µm2) to crypts (median: 1.89/62 500 µm2). Tregs were further increased in the villi of middle-aged dogs (median: 18.92/62 500 µm2) in contrast to juvenile (median: 3.50/62 500 µm2) and old (median: 9.56/62 500 µm2) individuals. Compared to healthy controls, animals suffering from IBD revealed reduced numbers of Tregs in duodenal villi (median: 4.13/62 500 µm2). Dogs with intestinal nematode infection displayed increased numbers of Tregs (median: 21.06/62 500 µm2) 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.