Toxoplasma gondii Inactivates Human Plasmacytoid Dendritic Cells by Functional Mimicry of IL-10 [INFECTIOUS DISEASE AND HOST RESPONSE]

Abstract

Plasmacytoid dendritic cells (pDCs) are the major producers of IFN-α, an antiviral cytokine involved in immunomodulation and control of HIV type 1 replication, whereas Toxoplasma gondii is a life-threatening opportunistic infection in AIDS patients. During infection with HIV type 1, human pDCs decrease in circulation and remaining pDC produce lower amounts of IFN-α in response to viral stimulation. In this study, we investigated the impact of coinfection with T. gondii on the innate virus-directed responses of human pDCs. Using intracellular flow cytometry and fluorescence microscopy, we determined that T. gondii invaded but did not induce IFN-α or TNF-α in human pDC. However, T. gondii inhibited IFN-α and TNF-α produced in response to HSV and HIV, thus functionally inactivating pDC. IFN-α production was inhibited only in cells infected by T. gondii, which inhibited neither uptake of GFP-HSV nor localization of TLR9 in CD71+ endosomes, directing us to investigate downstream events. Using imaging flow cytometry, we found that both T. gondii and IL-10 inhibited virus-induced nuclear translocation, but not phosphorylation, of IFN response factor 7. Blockade of IFN response factor 7 nuclear translocation and inhibition of the IFN-α response was partially reversed by a deficiency in the T. gondii–derived ROP16 kinase, known to directly phosphorylate STAT3, a critical mediator of IL-10’s anti-inflammatory effects. Taken together, our results indicate that T. gondii suppresses pDC activation by mimicking IL-10’s regulatory effects through an ROP16 kinase-dependent mechanism. Our findings further imply a convergent mechanism of inhibition of TLR signaling by T. gondii and IL-10 and suggest potential negative consequences of HIV/T. gondii coinfection.

Footnotes

  • This work was supported by grants from the National Institute of Allergy and Infectious Diseases, National Institutes of Health (R01AI062806 and R01AI106125 to P.F.-B. and R56AI124691 and R01AI083405 to G.S.Y.) and National Institute for Research Resources Grant S10ODO18103 to P.F.-B. P.L.P. was supported by a predoctoral fellowship from the New Jersey Commission on Cancer Research.

  • Abbreviations used in this article:

    HIV-1
    HIV type 1
    HSV-1
    HSV type 1
    IRF
    IFN response factor
    MOI
    multiplicity of infection
    OI
    opportunistic infection
    pDC
    plasmacytoid dendritic cell
    PFA
    paraformaldehyde
    PVM
    parasitophorous vacuole membrane.
  • Received July 19, 2017.
  • Accepted October 20, 2017.

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