Abstract
Epstein-Barr virus (EBV) infection of primary B cells causes B-cell activation and proliferation. Activation of B cells requires binding of antigen to the B-cell receptor and a survival signal from ligand-bound CD40, signals that are provided by the EBV LMP1 and LMP2A latency proteins. Recently, Toll-like receptor (TLR) signaling has been reported to provide a third B-cell activation stimulus. The interaction between the EBV and TLR pathways was therefore investigated. Both UV-inactivated and untreated EBV upregulated the expression of TLR7 and downregulated the expression of TLR9 in naive B cells. UV-inactivated virus transiently stimulated naive B-cell proliferation in the presence of the TLR7 ligand R837, while addition of the TLR7 antagonist IRS 661 impaired cell growth induced by untreated EBV. Interferon regulatory factor 5 (IRF-5) is a downstream mediator of TLR7 signaling. IRF-5 was induced following EBV infection, and IRF-5 was expressed in B-cell lines with type III latency. Expression of IRF-5 in this setting is surprising since IRF-5 has tumor suppressor and antiviral properties. B-cell proliferation assays provided evidence that EBV modulates TLR7 signaling responses. Examination of IRF-5 transcripts identified a novel splice variant, V12, that was induced by EBV infection, was constitutively nuclear, and acted as a dominant negative form in IRF-5 reporter assays. IRF-4 negatively regulates IRF-5 activation, and IRF-4 was also present in type III latently infected cells. EBV therefore initially uses TLR7 signaling to enhance B-cell proliferation and subsequently modifies the pathway to regulate IRF-5 activity.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Adjuvants, Immunologic / pharmacology
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Alternative Splicing / drug effects
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Alternative Splicing / genetics
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Alternative Splicing / physiology
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Aminoquinolines / pharmacology
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B-Lymphocytes / metabolism*
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B-Lymphocytes / virology
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CD40 Antigens / genetics
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CD40 Antigens / metabolism
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CD40 Ligand / genetics
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CD40 Ligand / metabolism
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Cell Line, Transformed
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Cell Proliferation / radiation effects
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Cell Survival / drug effects
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Cell Survival / genetics
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Cell Survival / radiation effects
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Epstein-Barr Virus Infections / genetics
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Epstein-Barr Virus Infections / metabolism*
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Gene Expression Regulation / drug effects
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Gene Expression Regulation / genetics
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Gene Expression Regulation / radiation effects
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HeLa Cells
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Herpesvirus 4, Human / genetics
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Herpesvirus 4, Human / metabolism*
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Humans
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Imiquimod
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Interferon Regulatory Factors / genetics
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Interferon Regulatory Factors / metabolism
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Lymphocyte Activation* / drug effects
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Lymphocyte Activation* / genetics
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Lymphocyte Activation* / radiation effects
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Signal Transduction* / drug effects
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Signal Transduction* / genetics
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Signal Transduction* / radiation effects
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Toll-Like Receptor 7 / agonists
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Toll-Like Receptor 7 / metabolism*
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Toll-Like Receptor 9 / genetics
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Toll-Like Receptor 9 / metabolism
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Ultraviolet Rays
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Viral Matrix Proteins / genetics
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Viral Matrix Proteins / metabolism
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Virus Latency / drug effects
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Virus Latency / genetics
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Virus Latency / radiation effects
Substances
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Adjuvants, Immunologic
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Aminoquinolines
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CD40 Antigens
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EBV-associated membrane antigen, Epstein-Barr virus
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IRF5 protein, human
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Interferon Regulatory Factors
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TLR7 protein, human
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TLR9 protein, human
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Toll-Like Receptor 7
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Toll-Like Receptor 9
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Viral Matrix Proteins
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interferon regulatory factor-4
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CD40 Ligand
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Imiquimod