Elevated human beta-defensin-2 levels indicate an activation of the innate immune system in patients with irritable bowel syndrome.

Objectives: Irritable bowel syndrome (IBS) is a highly prevalent functional disorder. According to the Rome criteria, macroscopic and histological inflammation is a crucial exclusion criterion for IBS. Human defensins appear to be part of the innate immune system in the gastrointestinal tract. Human beta-defensin-2 (HBD-2) was the first inducible human antimicrobial protein discovered. The expression is induced by probiotic microorganisms and proinflammatory cytokines. Recent results imply that HBD-2 is expressed in active intestinal inflammation, especially in ulcerative colitis (UC). Our aim was to evaluate fecal measurements of HBD-2 in patients with active UC and IBS, and in healthy controls (HCs).

Methods: Fecal specimens were collected from a total of 100 participants (30 with active UC, 46 IBS, and 24 HCs). Exclusion criteria were the current use of probiotics and antibiotics. Furthermore, IBS patients with elevated C-reactive protein or leukocytes, a history of bacterial overgrowth or infectious gastrointestinal disease over the last 6 month were excluded. Disease status was addressed in all participating subjects by medical history and current symptoms. In addition, each IBS and UC patient underwent ileocolonoscopy with histopathology. Fecal inflammation markers lactoferrin (Lf) and calprotectin (Cal) were measured by enzyme-linked immunosorbent assay (ELISA) and reported as microg/g. Fecal HBD-2 was measured by ELISA and reported as ng/g feces. In addition, immunoblots were performed for fecal HBD-2. Paraffin-embedded tissue from colonic biopsies was tested for HBD-2 peptides by immunohistochemistry.

Results: Lf as well as Cal was elevated in active UC (mean: 152.1+/-s.d. 374.7 microg/g; 103.5+/-87.1 microg/g), compared with IBS (8.3+/-19.4 microg/g; 18.6+/-23.3 microg/g), and HCs (0.4+/-0.5 microg/g; 7.1+/-7.9 microg/g). Scheffe post hoc tests revealed significant differences (P=0.006; P<0.001) between active UC vs. IBS and HC. In contrast, HBD-2 levels were highest in active UC (mean: 106.9+/-s.d. 91.5 ng/g), almost as high in IBS (pts 76.0+/-67.9 ng/g), and lowest for HCs (29.9+/-16.1 ng/g). Scheffe post hoc tests revealed significant differences (P<0.001) between the groups of patients (UC and IBS) vs. HCs. Immunohistochemical investigation was consistent with fecal secretion data and demonstrated the presence of beta-defensin 2 peptides in colonic epithelial enterocytes in UC as well as IBS patients with elevated fecal HBD-2.

Conclusions: The results indicate significantly elevated levels of HBD-2 in patients with IBS compared with HCs and similar to those with active UC. The results support an activation of the mucosal innate defense system toward a proinflammatory response in IBS patients in the absence of macroscopic signs of inflammation.