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CD14 expression and production by human hepatocytes
1Department of Medicine, University of Michigan, Ann Arbor 48109-0666, USA. gsu@umich-edu
Background/Aims:
CD14 has been identified as a receptor for LPS and is present both in a membrane-bound and a soluble form. Membrane CD14 (mCD14) is predominantly expressed on monocytes, macrophages and granulocytes. The source of soluble CD14 (sCD14) is as yet unclear. Previous investigation using monocytes has shown that sCD14 can be derived either from the shedding of mCD14 or from direct secretion by monocytes. Whether the monocyte is the sole or even the major source of sCD14 is as yet uncertain. Clearance of LPS from the bloodstream is thought to be primarily mediated by the liver. Production of CD14 by hepatocytes would potentially provide a powerful mechanism by which the liver could clear LPS, and therefore we examined the ability of human hepatocytes to produce CD14.
Methods:
Human hepatocytes were isolated using collagenase perfusion.
Results:
Human hepatocytes were found to have CD14 mRNA by Northern blot analysis. Western blot analysis and immunohistochemical staining confirmed CD14 protein in primary hepatocyte cultures. Further studies showed that a liver epithelial-like cell line AKN-1 is capable of producing CD14. Comparisons of the size of hepatocyte-derived CD14 protein with the sCD14 protein from the human monocytic leukemia cell line HL60 suggested that a slightly larger form of CD14 is expressed by human liver cells.
Conclusion:
This is the first study to demonstrate production of CD14 by human hepatocytes.
Insights
Human hepatocytes produce CD14, a receptor for lipopolysaccharide (LPS). This finding suggests a novel role for the liver in LPS clearance, potentially impacting immune responses and sepsis treatment.
Area of Science:
- Immunology
- Hepatology
- Molecular Biology
Background:
- CD14 acts as a lipopolysaccharide (LPS) receptor, existing in membrane-bound (mCD14) and soluble (sCD14) forms.
- Monocytes are known producers of sCD14, but the liver's role remains uncertain.
- The liver is crucial for clearing LPS from circulation.
Purpose of the Study:
- To investigate the capacity of human hepatocytes to produce CD14.
- To determine if hepatocytes contribute to the circulating pool of sCD14.
- To explore a potential mechanism for hepatic LPS clearance.
Main Methods:
- Isolation of primary human hepatocytes via collagenase perfusion.
- Detection of CD14 mRNA using Northern blot analysis.
- Confirmation of CD14 protein expression through Western blot and immunohistochemistry.
Main Results:
- Human hepatocytes express CD14 mRNA and protein.
- A liver epithelial cell line (AKN-1) also demonstrated CD14 production.
- Hepatocyte-derived CD14 appears slightly larger than that from monocytic cell lines.
Conclusions:
- This study provides the first evidence of CD14 production by human hepatocytes.
- Hepatocytes represent a potential source of sCD14.
- Hepatic CD14 production may contribute to LPS clearance and immune regulation.