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Differential effects of cytomegalovirus infection on complement synthesis by human mesangial cells
J J Timmerman1, M F Beersma, D J van Gijlswijk-Janssen
1Department of Nephrology, University Hospital Leiden, The Netherlands.
Abstract:
Viruses may be eliminated by the host immune system via complement-mediated lysis of infected cells. Previously, we have demonstrated that the synthesis of complement factor B by renal mesangial cells (MC) is enhanced by interferon-alpha (IFN-alpha), -beta and -gamma. In the present study we investigate the effect of human cytomegalovirus (HCMV) infection on the production of complement factors by MC. The production of factor B, C2, C4 and factor H by mock-infected MC was 0.2 +/- 0.4, 3.9 +/- 6.8, 1.7 +/- 0.8 and 149 +/- 36 ng/10(6) cells per 72 h, respectively. In HCMV-infected MC cultures an induction of both factor B and C2 protein synthesis was observed up to 2.2 +/- 1.1 and 156 +/- 74 ng/10(6) cells per 72 h, respectively. The synthesis of C4 and factor H of 2.9 +/- 2.0 and 146 +/- 31 ng/10(6) cells, respectively, was not altered significantly. By Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis it was demonstrated that factor B and C2 mRNA expression were up-regulated in HCMV-infected cell cultures, whereas the levels of C4 and factor H mRNA were not changed. When MC cultures were inoculated with heat- or UV-inactivated HCMV no enhancement of factor B mRNA expression was observed. The enhanced expression was not blocked by phosphono acetic acid (PAA), suggesting that expression of the HCMV immediate early or early genes is sufficient to induce complement synthesis. We conclude that infection of MC cultures with HCMV selectively induces complement C2 and factor B production, probably mediated by interferons.
Insights
Human cytomegalovirus (HCMV) infection selectively enhances the production of complement factors B and C2 in renal mesangial cells. This finding suggests a novel mechanism by which HCMV may modulate the host immune response and complement system.
Area of Science:
- Immunology
- Virology
- Cell Biology
Background:
- The host immune system eliminates viruses through complement-mediated lysis of infected cells.
- Renal mesangial cells (MC) synthesize complement factor B, which is enhanced by interferons (IFNs).
Purpose of the Study:
- To investigate the effect of human cytomegalovirus (HCMV) infection on complement factor production by MC.
- To determine the molecular mechanisms underlying HCMV-induced complement production.
Main Methods:
- MC cultures were infected with HCMV.
- Complement factor production was measured using ELISAs.
- mRNA expression of complement factors was analyzed by Northern blot and RT-PCR.
- The role of viral gene expression was assessed using inactivated HCMV and PAA treatment.
Main Results:
- HCMV infection significantly increased the synthesis and mRNA expression of complement factors B and C2 in MC.
- Production and mRNA levels of complement factors C4 and H remained unchanged.
- The induction of factor B mRNA was dependent on infectious HCMV and not blocked by PAA, indicating early viral gene involvement.
- Interferons likely mediate the enhanced complement production.
Conclusions:
- HCMV infection selectively induces the production of complement factors B and C2 in MC.
- This induction is mediated at the transcriptional level and likely involves early HCMV gene expression.
- The findings suggest a role for HCMV in modulating the host complement system.