The Ebola Interferon Inhibiting Domains Attenuate and Dysregulate Cell-Mediated Immune Responses

Abstract

Ebola virus (EBOV) infections are characterized by deficient T-lymphocyte responses, T-lymphocyte apoptosis and lymphopenia. We previously showed that disabling of interferon-inhibiting domains (IIDs) in the VP24 and VP35 proteins effectively unblocks maturation of dendritic cells (DCs) and increases the secretion of cytokines and chemokines. Here, we investigated the role of IIDs in adaptive and innate cell-mediated responses using recombinant viruses carrying point mutations, which disabled IIDs in VP24 (EBOV/VP24m), VP35 (EBOV/VP35m) or both (EBOV/VP35m/VP24m). Peripheral blood mononuclear cells (PBMCs) from cytomegalovirus (CMV)-seropositive donors were inoculated with the panel of viruses and stimulated with CMV pp65 peptides. Disabling of the VP35 IID resulted in increased proliferation and higher percentages of CD4+ T cells secreting IFNγ and/or TNFα. To address the role of aberrant DC maturation in the IID-mediated suppression of T cell responses, CMV-stimulated DCs were infected with the panel of viruses and co-cultured with autologous T-lymphocytes. Infection with EBOV/VP35m infection resulted in a significant increase, as compared to wt EBOV, in proliferating CD4+ cells secreting IFNγ, TNFα and IL-2. Experiments with expanded CMV-specific T cells demonstrated their increased activation following co-cultivation with CMV-pulsed DCs pre-infected with EBOV/VP24m, EBOV/VP35m and EBOV/VP35m/VP24m, as compared to wt EBOV. Both IIDs were found to block phosphorylation of TCR complex-associated adaptors and downstream signaling molecules. Next, we examined the effects of IIDs on the function of B cells in infected PBMC. Infection with EBOV/VP35m and EBOV/VP35m/VP24m resulted in significant increases in the percentages of phenotypically distinct B-cell subsets and plasma cells, as compared to wt EBOV, suggesting inhibition of B cell function and differentiation by VP35 IID. Finally, infection with EBOV/VP35m increased activation of NK cells, as compared to wt EBOV. These results demonstrate a global suppression of cell-mediated responses by EBOV IIDs and identify the role of DCs in suppression of T-cell responses.

Inhibiting pyrimidine biosynthesis impairs Ebola virus replication through depletion of nucleoside pools and activation of innate immune responses

“…EBOV and MARV have been demonstrated to inhibit interferon-α/β (IFN) responses by several mechanisms (Basler et al, 2003; Basler et al, 2000; Kaletsky et al, 2009; Leung et al, 2010; Mateo et al, 2010; Prins et al, 2010; Reid et al, 2006; Reid et al, 2007; Valmas and Basler, 2011; Xu et al, 2014). These include inhibition of the RIG-I-like receptor (RLR) signaling pathways by VP35 proteins which results in inhibition of IFN production, a block to induction of interferon stimulated gene (ISG) expression and impaired maturation of dendritic cells (Cardenas et al, 2006; Lubaki et al, 2016; Yen et al, 2014; Yen and Basler, 2016). Further, EBOV VP24 and MARV VP40 inhibit IFN-triggered signaling such that IFN-induced ISG expression is blocked (Reid et al, 2006; Reid et al, 2007; Valmas and Basler, 2011; Xu et al, 2014).…”

The Host E3-Ubiquitin Ligase TRIM6 Ubiquitinates the Ebola Virus VP35 Protein and Promotes Virus Replication

“…In addition to VP35's critical role in virus replication as a cofactor of the viral polymerase, it has also been extensively studied for its function in inhibition of innate signaling pathways and expression of antiviral type I interferons (IFN-I) (10,11,(14)(15)(16)(17)(18)(19)(20). VP35 also inhibits the maturation of dendritic cells (DCs) and prevents efficient adaptive immune responses (21)(22)(23)(24)(25).…”

Innate Immune Responses of Bat and Human Cells to Filoviruses: Commonalities and Distinctions

“…Point mutations in VP35 IID resulted in an increase of a type I IFN response, the maturation of human dendritic cells that is normally blocked by EBOV infection, and the consequential activation of T lymphocytes, B lymphocytes, and NK cells. This increased immune response leads to an attenuation of the EBOV VP35 mutant in vitro and in animal models of filovirus infection (15)(16)(17)(18)(19)(20).…”