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Dissecting Innate Immune Signaling in Viral Evasion of Cytokine Production
Published on: March 2, 2014
Complement Regulation and Immune Evasion by Hepatitis C Virus
Young-Chan Kwon1,2,3, Ranjit Ray4,5
1Department of Internal Medicine, Saint Louis University, St. Louis, MO, USA.
Insights
Hepatitis C virus (HCV) infection specifically reduces complement C9 mRNA in the liver, impacting immune responses. This impairment in complement synthesis is not linked to liver damage severity in HCV patients.
Area of Science:
- Immunology
- Hepatology
- Virology
Background:
- The complement system links innate and adaptive immunity.
- Hepatocytes in the liver are the primary sites for complement component synthesis.
- Complement deficiencies can increase susceptibility to infections.
Purpose of the Study:
- To investigate the effect of Hepatitis C Virus (HCV) on complement synthesis in hepatocytes.
- To determine if liver damage correlates with altered complement levels in HCV patients.
- To identify specific complement components affected by chronic HCV infection.
Main Methods:
- Analysis of complement component synthesis (C4, C3) in relation to HCV infection.
- Correlation analysis between complement levels and markers of liver fibrosis, rheumatoid factor, albumin, and alkaline phosphatase.
- Quantitative analysis of complement component mRNA levels (C9, C6, C8, Factor B, MASP1, MBL) in HCV-infected liver biopsies.
Main Results:
- HCV infection was found to impair the synthesis of complement components C4 and C3.
- Changes in complement component levels in HCV patients did not correlate with liver fibrosis or other clinical markers.
- A significant reduction in C9 mRNA was observed in HCV-infected liver tissue, while other complement genes remained largely unaffected, suggesting a virus-specific effect.
Conclusions:
- HCV specifically interferes with complement component synthesis, particularly C9, at the mRNA level in hepatocytes.
- The observed complement dysregulation is likely a direct effect of HCV, not solely a consequence of liver disease.
- Impaired complement function due to HCV may affect immune responses and increase infection risk.
Abstract:
A prominent role for complement has been identified in the linkage of innate and adaptive immunity. The liver is the main source of complement and hepatocytes are the primary sites for synthesis of complement components in vivo. We have discovered that hepatitis C virus (HCV) impairs C4 and C3 synthesis. Liver damage may diminish capacity of complement synthesis in patients. However, we observed that the changes in measured complement components in chronically HCV infected patients do not correlate with liver fibrosis or rheumatoid factor present in the blood, serum albumin, or alkaline phosphatase levels. Complement component C3 is of critical importance in B cell activation and T cell-dependent antibody responses. C3 activity is required for optimal expansion of CD8+T cells during a systemic viral infection. Deficiencies in complement may predispose patients to infections via ineffective opsonization, and defects in lytic activity via membrane attack complex. Interestingly, C9 is significantly reduced at the mRNA level in chronically HCV infected liver biopsy specimens, while many hepatocyte derived complement components (C6, C8, Factor B, MASP1, and MBL) and unrelated genes remain mostly unaffected. This implies an HCV specific effect, not a global effect from liver disease.
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