Expression of Toll-like receptor 2 (TLR2), TLR4, and CD14 in biopsy samples of patients with inflammatory bowel diseases: upregulated expression of TLR2 in terminal ileum of patients with ulcerative colitis

Abstract

Dysregulation of innate and adaptive intestinal immune responses to bacterial microbiota is supposed to be involved in pathogenetic mechanisms of inflammatory bowel diseases (IBDs). We investigated expression of Toll-like receptor 2 (TLR2), TLR4, and their transmembrane coreceptor CD14 in biopsy samples from patients with IBD and in non-inflamed gut mucosa from controls. Small intestine and colon samples were obtained by colonoscopy from patients with Crohn's disease (CD), ulcerative colitis (UC), and controls. Immunohistochemical analysis of cryostat sections using polyclonal and monoclonal antibodies specific for TLR2, TLR4, and CD14 showed a significant increase in TLR2 expression in the terminal ileum of patients with inactive and active UC against controls. Significant upregulation of TLR4 expression relative to controls was found in the terminal ileum and rectum of UC patients in remission and in the terminal ileum of CD patients with active disease. CD14 expression was upregulated in the terminal ileum of CD patients in remission and with active disease, in the cecum of UC patients in remission and with active disease, and in rectum of UC patients with active disease. Hence, dysregulation of TLR2, TLR4, and CD14 expression in different parts of the intestinal mucosa may be crucial in IBD pathogenesis.

Figure 1

(A–L) Expression of TLR2 and TLR4 in inflammatory bowel disease (IBD) and in normal gut. (A) Strong expression of TLR2 in the superficial epithelial layer of ileal villi and weaker positivity in the epithelium of crypts in a patient with ulcerative colitis (UC) (grade 2). Scattered mononuclear cells in the lamina propria (LP) express endogenous peroxidase (Epx). (B) Negativity of epithelium in the control test; Epx in the LP as in A. (C) Negative reaction of epithelium in a control patient (grade 0). (D) Strong positivity of TLR4 in both surface and cryptic epithelium in a patient with CD (grade 2). Rare single cells with Epx in the LP. Absence of villi. (E) Negativity of epithelia in the control test; Epx in the LP as in D. (F) Negative epithelia in a control patient (grade 0). (G) Medium positivity of TLR4 in ileal crypts in a patient with UC (grade 1.5). Scattered Epx cells in the LP. (H) Negativity of crypts in the control test; similar scatter of Epx. (I) Negative result of TLR4 in a healthy control. (J) Strong expression of TLR4 in the crypts of rectal mucosa in a patient with UC (grade 2.5). (K) Negative crypts in the control test; single Epx cells are seen in the LP. (L) Faint reaction of TLR4 in the rectal crypts in a control patient (grade 0.5).

Figure 2

(A–M) Expression of CD14 in IBD and in normal gut; fluorescence detection of CD14 and CD68 in the cecum of a CD patient. (A) Infiltration of LP of an ileal villus by CD14-positive cells (membranous expression, grade 2.5) in a CD patient. Coarse brown–black cytoplasmic product in several elements represents Epx. (B) Absence of membranous expression in the control test; Epx comparable to A. (C) Scarce CD14-positive cells in ileal villus of a control patient (grade 1). Coarse dark masses of Epx are seen in scattered cells. (D) Multiple CD14-positive cells in the LP of cecum in a patient with UC (grade 2.5). Single cells express coarse cytoplasmic product of Epx. (E) Epx are displayed only in the control sections. (F) Rare single elements and minute clusters of cells expressing CD14 in control patients (grade 1). (G) Well-pronounced scatter of both CD14-positive cells with membranous positivity and Epx elements in the LP of rectum in a patient with UC (grade 2.5). (H) Persistence of Epx cells; no cell-membrane expression in the control reaction. (I) Discrete scatter of CD14-positive cells in the rectal LP of a control patient (grade 1). Rare single cells expressing cytoplasmic Epx. (J) Nuclei counterstained with DAPI. (K) Scattered CD14-positive cells in the LP. (L) Similar though less intensive scatter of cells expressing CD68. (M) Merged staining in about one half of the elements. Cells with green fluorescence (CD14) are more numerous.