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Evidence for a CD14+ population of monocytes in inflammatory bowel disease mucosa--implications for pathogenesis
M C Grimm1, P Pavli, E Van de Pol
1Division of Clinical Sciences, John Curtin School of Medical Research, Australian National University, Canberra.
Abstract:
Lipopolysaccharide (LPS) is abundant in the intestinal lumen. CD14 is the receptor for the LPS-LPS binding protein complex, and its presence on mononuclear phagocytes allows cell activation by pg/ml concentrations of LPS. We have shown that the recently recruited blood monocyte in inflammatory bowel disease mucosa is CD14+. This study examined the expression of CD14 on macrophages in inflamed (n = 13) and uninflamed (n = 7) intestine by immunohistochemistry, and on disaggregated lamina propria mononuclear cells (12 from inflamed, 17 from uninflamed intestine) and peripheral blood mononuclear cells (n = 26) by flow cytometry, using a panel of three MoAbs directed against CD14. Immunohistochemistry revealed that 3.7% of macrophages in uninflamed intestine were CD14+, while 25.1% of macrophages in active inflammatory bowel disease expressed CD14 (P < 0.02). Flow cytometry demonstrated that CD14 expression by macrophages from Crohn's disease and ulcerative colitis was augmented significantly (P = 0.02 and P = 0.01, respectively) compared with uninflamed intestine, with a discrete population of macrophages in inflammatory bowel disease, not present in normal intestine, which strongly expressed CD14. The characteristically high levels of CD14 on blood monocytes were unaffected by the presence of intestinal inflammation. Given the exposure of lamina propria cells to LPS present in the lumen of the terminal ileum and colon, the increased numbers of CD14+ macrophages in inflammatory bowel disease may result in greatly increased production of inflammatory mediators, thereby suggesting a mechanism for the perpetuation of mucosal inflammation.
Insights
Macrophages in inflammatory bowel disease (IBD) express significantly higher levels of CD14, a receptor for lipopolysaccharide (LPS). This increased CD14 expression on intestinal macrophages may drive inflammation in IBD.
Area of Science:
- Immunology
- Gastroenterology
- Cell Biology
Background:
- Lipopolysaccharide (LPS) is a key component of gram-negative bacteria found in the gut lumen.
- CD14 acts as a receptor for LPS, mediating its effects on immune cells like macrophages.
- Previous research indicated CD14+ monocytes are recruited to the inflamed mucosa in inflammatory bowel disease (IBD).
Purpose of the Study:
- To investigate the expression levels of CD14 on intestinal macrophages in active IBD compared to non-inflamed intestine.
- To determine if CD14 expression on lamina propria macrophages differs between inflamed and uninflamed intestinal tissues.
- To explore the potential role of CD14+ macrophages in the pathogenesis of IBD.
Main Methods:
- Immunohistochemistry was used to assess CD14 expression on macrophages in inflamed (n=13) and uninflamed (n=7) intestinal tissues.
- Flow cytometry analyzed CD14 expression on lamina propria mononuclear cells from inflamed (n=12) and uninflamed (n=17) intestines, and peripheral blood mononuclear cells (n=26).
- A panel of three anti-CD14 monoclonal antibodies (MoAbs) was employed for detection.
Main Results:
- Immunohistochemistry showed a significant increase in CD14+ macrophages in active IBD (25.1%) versus uninflamed intestine (3.7%; P < 0.02).
- Flow cytometry confirmed augmented CD14 expression on macrophages from Crohn's disease (P = 0.02) and ulcerative colitis (P = 0.01) compared to controls.
- A distinct population of strongly CD14-expressing macrophages was identified in IBD, absent in normal intestine; peripheral blood monocyte CD14 levels remained unchanged.
Conclusions:
- Macrophages in the inflamed intestinal mucosa of IBD patients exhibit significantly elevated CD14 expression.
- The increased presence of CD14+ macrophages in IBD may lead to heightened inflammatory mediator production due to luminal LPS exposure.
- This suggests a potential mechanism contributing to the chronic mucosal inflammation characteristic of inflammatory bowel disease.