Increased expression of interleukin 17 in inflammatory bowel disease

Abstract

Background and aim: Interleukin (IL) 17 is a cytokine which exerts strong proinflammatory activities. In this study we evaluated changes in IL-17 expression in the inflamed mucosa and in the serum of patients with inflammatory bowel disease (IBD).

Methods: Tissue samples were obtained endoscopically or surgically from patients with ulcerative colitis (UC) (n=20), Crohn's disease (CD) (n=20), infectious colitis (n=5), ischaemic colitis (n=8), and normal colorectal tissues (n=15). IL-17 expression was evaluated by a standard immunohistochemical procedure. Serum IL-17 levels were determined by ELISA. IL-17 mRNA expression was analysed by reverse transcriptase-polymerase chain reaction.

Results: IL-17 expression was not detected in samples from normal colonic mucosa, infectious colitis, or ischaemic colitis. In the inflamed mucosa of active UC and CD patients, IL-17 expression was clearly detectable in CD3(+) T cells or CD68(+) monocytes/macrophages. The average number of IL-17(+) cells was significantly increased in active UC and CD patients compared with inactive patients. IL-17 mRNA expression was not detected in normal mucosa but was detectable in the mucosa from active UC and CD patients. IL-17 was not detected in the sera from normal individuals, infectious colitis, or ischaemic colitis patients but IL-17 levels were significantly elevated in IBD patients.

Conclusions: IL-17 expression in the mucosa and serum was increased in IBD patients. It is likely that IL-17 expression in IBD may be associated with altered immune and inflammatory responses in the intestinal mucosa.

Figure 1

Immunohistochemical analysis of interleukin 17 (IL-17) protein expression in the colon. (A) Control normal mucosa (×200); (B) ischaemic colitis (×200); (C) and (D) ulcerative colitis (×200); (E) and (F) Crohn’s disease (×100 and ×200).

Figure 2

Number of interleukin 17 (IL-17) positive cells in the mucosa. Results are expressed as number of positive cells per field (×400). The lower and upper margins of the box represent the 25th and 75th percentiles, with the extended arms representing the 10th and 90th percentiles, respectively. The median is shown as a horizontal line within the box. UC, ulcerative colitis; CD, Crohn’s disease.

Figure 3

Cellular expression of interleukin 17 (IL-17) in Crohn’s disease (A–F) and ulcerative colitis (G–L) patients. Two colour immunofluorescence was used to determine IL-17 expression (rhodamine red, red fluorescence: B, E, H, and K), CD3 expression (fluorescein isothiocyanate (FITC), green fluorescence: A, G), and CD68 expression (FITC, green fluorescence: D, J). Cells showing coexpression of IL-17 and CD3 (C, I) or IL-17 and CD68 (F, L) were visualised by a yellow colour. The specificity of each antibody was confirmed by negative reactivity of subclass matched normal IgG for anti-CD3 (M), anti-IL-17 (N), and anti-CD68 (O).

Figure 4

Reverse transcription-polymerase chain reaction (RT-PCR) analysis of interleukin 17 (IL-17) mRNA expression. Purified T cells were stimulated by interleukin 2 for three hours, and purified monocytes/macrophages were stimulated by lipopolysaccharide for three hours. Total cellular RNA was extracted by the acid guanidium thiocyanate-phenol-chloroform (AGPC) method and IL-17 mRNA expression was evaluated by RT-PCR analysis. Similarly, IL-17 mRNA expression was investigated in mucosal samples from normal individuals and in active Crohn’s disease (CD) and ulcerative colitis (UC) patients.

Figure 5

Serum interleukin 17 (IL-17) levels in patients with inflammatory bowel disease. IL-17 level was determined by ELISA for human IL-17 purchased from Bio Source International (Camarillo, California, USA). The lower limit of ELISA was 9 pg/ml of IL-17. The lower and upper margins of the box represent the 25th and 75th percentiles, with the extended arms representing the 10th and 90th percentiles, respectively. The median is shown as a horizontal line within the box. UC, ulcerative colitis; CD, Crohn’s disease.