Gateway to the gut : alterations in saliva in inflammatory bowel disease

Abstract

Inflammatory bowel disease (IBD), which consists of Crohn’s disease and ulcerative colitis, is a chronic immune-mediated disease thought to result from genetic and environmental interaction which influence the commensal flora to trigger an inappropriate mucosal immune response. IBD primarily affects the intestines but is not restricted to them. Extraintestinal manifestations are frequently observed within the oral cavity. This thesis aimed to investigate different mediators of inflammation within the intestines and oral cavity as a reflection of defective immune responses in IBD.

In our first study, we investigated the intestinal localization of macrophage growth factors IL-34 and CSF-1 and their involvement in IBD. IL-34 and CSF-1 demonstrated distinct expression patterns in the human intestine and were significantly elevated in human and experimental IBD. Infiltrating cells of the lamina propria and intestinal epithelial cells expressed IL-34, regulated by TNF-α through the NF-κB pathway. As a result, the newly discovered growth factor IL-34 was proposed as a new modulator of IBD.

The remaining part of this thesis investigated the expression of inflammatory proteins in saliva in relation to IBD. The second study aimed to analyze calprotectin, an established fecal marker of IBD, for the first time in saliva of IBD patients. We found that calprotectin was significantly elevated in saliva of IBD patients, particularly in CD and most prominently in newly diagnosed CD patients. This opened up for new hypotheses in the oral-gut connection in IBD and supported the notion that the oral cavity may contain early evidence of intestinal inflammation. In a third study, we compared the profile of 92 known inflammatory proteins in saliva and serum of IBD patients. The salivary and circulatory inflammatory profiles were similar but reflected different aspects of IBD activity. Several serum proteins were significantly altered in IBD patients compared to controls, whereas IL-6 and MMP-10 – proteins involved in the pathogenesis of IBD and its extraintestinal manifestations – were significantly elevated in stimulated saliva of IBD patients, providing additional proof of subclinical inflammatory mimicry of intestinal disease by the oral cavity. In the final study, we confirmed our previous findings related to elevated salivary calprotectin in IBD and showed that the concentrations were not significantly affected by oral disease. Moreover, we investigated potential sources of salivary calprotectin and showed that neutrophils isolated from saliva express calprotectin, demonstrate reduced CD11b expression in IBD patients, but share a similar ability to secrete calprotectin.

In conclusion, the work presented in this thesis highlights the aberrant immune responses associated to IBD and provides proof that such mechanisms can be reflected by the oral cavity.