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Updated: Aug 20, 2025
Dissecting Innate Immune Signaling in Viral Evasion of Cytokine Production
Published on: March 2, 2014
The ectromelia virus virulence factor C15 facilitates early viral spread by inhibiting NK cell contact
Elise M Peauroi1, Stephen D Carro1, Luxin Pei2
1Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Abstract:
The success of poxviruses as pathogens depends on their antagonism of host responses by multiple immunomodulatory proteins. The largest of these expressed by ectromelia virus (the agent of mousepox) is C15, one member of a well-conserved poxviral family previously shown to inhibit T cell activation. Here, we demonstrate by quantitative immunofluorescence imaging that C15 also limits contact between natural killer (NK) cells and infected cells in vivo. This corresponds to an inhibition in the number of total and degranulating NK cells, ex vivo and in vitro, with no detectable impact on NK cell cytokine production or the transcription of factors related to NK cell recruitment or activation. Thus, in addition to its previously identified capacity to antagonize CD4 T cell activation, C15 inhibits NK cell cytolytic function, which results in increased viral replication and dissemination in vivo. This work builds on a body of literature demonstrating the importance of early restriction of virus within the draining lymph node.
Insights
Ectromelia virus protein C15 hinders natural killer (NK) cell interactions with infected cells, impairing immune response and promoting viral spread. This study reveals a novel mechanism of poxvirus immune evasion.
Area of Science:
- Virology
- Immunology
- Cell Biology
Background:
- Poxviruses employ immunomodulatory proteins to evade host immune responses.
- Ectromelia virus protein C15 is a large viral protein known to inhibit T cell activation.
Purpose of the Study:
- To investigate the effect of ectromelia virus protein C15 on natural killer (NK) cell interactions and function.
- To understand the role of C15 in poxvirus immune evasion and viral dissemination.
Main Methods:
- Quantitative immunofluorescence imaging to assess NK cell contact with infected cells in vivo.
- Ex vivo and in vitro assays to evaluate NK cell numbers, degranulation, and cytokine production.
- Analysis of gene transcription related to NK cell recruitment and activation.
Main Results:
- Protein C15 limits the contact between NK cells and ectromelia virus-infected cells in vivo.
- C15 inhibits the total number and degranulating capacity of NK cells ex vivo and in vitro.
- No significant impact of C15 on NK cell cytokine production or key transcription factors was observed.
- C15's inhibition of NK cell function leads to increased viral replication and dissemination.
Conclusions:
- Ectromelia virus protein C15 antagonizes host immunity by inhibiting both T cell and NK cell functions.
- C15's dual action on T and NK cells contributes to viral pathogenesis and spread.
- Targeting C15 may represent a strategy to enhance antiviral immunity against poxviruses.
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