The ectromelia virus virulence factor C15 facilitates early viral spread by inhibiting NK cell contact
The success of poxviruses as pathogens depends upon 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 nor 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.
iScience; November 5, 2022
HIV-1–specific CD4+ T cells (TCD4+s) play a critical role in controlling HIV-1 infection. Canonically, TCD4+s are activated by peptides derived from extracellular (“exogenous”) Ags displayed in complex with MHC class II (MHC II) molecules on the surfaces of “professional” APCs such as dendritic cells (DCs). In contrast, activated human TCD4+s, which express MHC II, are not typically considered for their APC potential because of their low endocytic capacity and the exogenous Ag systems historically used for assessment. Using primary TCD4+s and monocyte-derived DCs from healthy donors, we show that activated human TCD4+s are highly effective at MHC II–restricted presentation of an immunodominant HIV-1–derived epitope postinfection and subsequent noncanonical processing and presentation of endogenously produced Ag. Our results indicate that, in addition to marshalling HIV-1–specific immune responses during infection, TCD4+s also act as APCs, leading to the activation of HIV-1–specific TCD4+s.
Journal of Immunology; August 5, 2022
Type II alveolar cell MHCII improves respiratory viral disease outcomes while exhibiting limited antigen presentation
Type II alveolar cells (AT2s) are critical for basic respiratory homeostasis and tissue repair after lung injury. Prior studies indicate that AT2s also express major histocompatibility complex class II (MHCII) molecules, but how MHCII expression by AT2s is regulated and how it contributes to host defense remain unclear. Here we show that AT2s express high levels of MHCII independent of conventional inflammatory stimuli, and that selective loss of MHCII from AT2s in mice results in modest worsening of respiratory virus disease following influenza and Sendai virus infections. We also find that AT2s exhibit MHCII presentation capacity that is substantially limited compared to professional antigen presenting cells. The combination of constitutive MHCII expression and restrained antigen presentation may position AT2s to contribute to lung adaptive immune responses in a measured fashion, without over-amplifying damaging inflammation.
Nature Communications; June 28, 2021
Ectromelia-encoded virulence factor C15 specifically inhibits antigen presentation to CD4+ T cells post peptide loading
Smallpox and monkeypox pose severe threats to human health. Other orthopoxviruses are comparably virulent in their natural hosts, including ectromelia, the cause of mousepox. Disease severity is linked to an array of immunomodulatory proteins including the B22 family, which has homologs in all pathogenic orthopoxviruses but not attenuated vaccine strains. We demonstrate that the ectromelia B22 member, C15, is necessary and sufficient for selective inhibition of CD4+ but not CD8+ T cell activation by immunogenic peptide and superantigen. Inhibition is achieved not by down-regulation of surface MHC- II or co-stimulatory protein surface expression but rather by interference with antigen presentation. The appreciable outcome is interference with CD4+ T cell synapse formation as determined by imaging studies and lipid raft disruption. Consequently, CD4+ T cell activating stimulus shifts to uninfected antigen-presenting cells that have received antigen from infected cells. This work provides insight into the immunomodulatory strategies of orthopoxviruses by elucidating a mechanism for specific targeting of CD4+ T cell activation, reflecting the importance of this cell type in control of the virus.
PLoS Pathogens; August 3, 2020
Kinetically distinct processing pathways diversify the CD8 + T cell response to a single viral epitope
The source proteins from which CD8+ T cell-activating peptides are derived remain enigmatic. Glycoproteins are particularly challenging in this regard owing to several potential trafficking routes within the cell. By engineering a glycoprotein-derived epitope to contain an N-linked glycosylation site, we determined that optimal CD8+ T cell expansion and function were induced by the peptides that are rapidly produced from the exceedingly minor fraction of protein mislocalized to the cytosol. In contrast, peptides derived from the much larger fraction that undergoes translocation and quality control are produced with delayed kinetics and induce suboptimal CD8+ T cell responses. This dual system of peptide generation enhances CD8+ T cell participation in diversifying both antigenicity and the kinetics of peptide display.
Proceedings of the National Academy of Sciences USA; August 11, 2020
By convention, CD4+ T lymphocytes recognize foreign and self peptides derived from internalized antigens in combination with major histocompatibility complex class II molecules. Alternative pathways of epitope production have been identified, but their contributions to host defense have not been established. We show here in a mouse infection model that the CD4+ T cell response to influenza, critical for durable protection from the virus, is driven principally by unconventional processing of antigen synthesized within the infected antigen-presenting cell, not by classical processing of endocytosed virions or material from infected cells. Investigation of the cellular components involved, including the H2-M molecular chaperone, the proteasome and γ-interferon-inducible lysosomal thiol reductase revealed considerable heterogeneity in the generation of individual epitopes, an arrangement that ensures peptide diversity and broad CD4+ T cell engagement. These results could fundamentally revise strategies for rational vaccine design and may lead to key insights into the induction of autoimmune and anti-tumor responses.
Nature Medicine; October 2015