GB Virus C Particles Inhibit T Cell Activation via Envelope E2 Protein-Mediated Inhibition of TCR Signaling

Abstract

Viruses enter into complex interactions within human hosts leading to facilitation or suppression of each other's replication. Upon coinfection, GB virus C (GBV-C) suppresses HIV-1 replication in vivo and in vitro, and GBV-C coinfection is associated with prolonged survival in HIV-infected people. GBV-C is a lymphotropic virus capable of persistent infection. GBV-C infection is associated with reduced T cell activation in HIV-infected humans, and immune activation is a critical component of HIV disease pathogenesis. We demonstrate that serum GBV-C particles inhibited activation of primary human T cells. T cell activation inhibition was mediated by the envelope glycoprotein E2, as expression of E2 inhibited T cell receptor (TCR)-mediated activation of tyrosine kinase (Lck). The region on the E2 protein was characterized and revealed a highly conserved peptide motif sufficient to inhibit TCR-mediated signaling. The E2 region contained a predicted Lck substrate site, and substitution of an alanine or histidine for the tyrosine reversed TCR signaling inhibition. GBV-C E2 protein and a synthetic peptide representing the inhibitory amino acid sequence were phosphorylated by Lck in vitro. The synthetic peptide also inhibited TCR-mediated activation of primary human CD4+ and CD8+ T cells. Extracellular microvesicles from GBV-C E2-expressing cells contained E2 protein and inhibited TCR signaling in bystander T cells not expressing E2. Thus, GBV-C reduced global T cell activation via competition between its envelope protein E2 and Lck following TCR engagement. This novel inhibitory mechanism of T cell activation may provide new approaches for HIV and immunoactivation therapy.

Human Pegivirus (HPgV; formerly known as GBV-C) inhibits IL-12 dependent natural killer cell function

“…HPgV envelope protein (E2) modulates TCR and IL-2 receptor signaling pathways (Bhattarai et al, 2013. Since HPgVmediated inhibition of IL-12 signaling in NK cells did not require viral replication (Fig.…”

“…In HIV-infected humans, persistent HPgV coinfection is associated with reduced T cell activation, proliferation and function (Maidana-Giret et al, 2009;Schwarze-Zander et al, 2010;Stapleton et al, , 2009 suggesting that HPgV-mediated immune modulation may contribute to viral persistence. In vitro, HPgV envelope glycoprotein (E2) inhibits T cell activation by reducing signaling through the IL-2 receptor and the T cell receptor (TCR), with resultant reduction in activation of the lymphocyte specific tyrosine kinase (Lck) (Bhattarai et al, 2013). The effects of HPgV on T cell activation may contribute to the observed protective effect of HPgV coinfection on survival of HIV-and Ebola-infected individuals (Nunnari et al, 2003;Tillmann et al, 2001;Vahidnia et al, 2012;Xiang et al, 2001;Lauck et al, 2015).…”

“…The proportion of cells infected with HPgV is low (approximately 1-10 genome copies per 100 NK cells) (Chivero et al, 2014). The majority of serum-derived HPgV RNA is present in gradient fractions containing extracellular vesicles (EV) that have properties of exosomes (Bhattarai et al, 2013;Chivero et al, 2014). It is difficult if not impossible to exclude the presence of virions from EV preparations; however, HPgV RNA-containing particles prepared from gradients enriched for EVs deliver viral RNA to peripheral blood mononuclear cells, including NK cells (Bhattarai et al, 2013;Chivero et al, 2014).…”

Antigenic composition of single nano-sized extracellular blood vesicles

“…EVs play an important role in cell-to-cell communication because different proteins, lipids and RNAs are specifically incorporated into these vesicles, which can be targeted to remote cells through receptor-ligand interactions 1,3 . Release of EVs was reported to change in pathologies (reviewed in 4,5 ) including cancer 6-9 , neurological, hematological 9 , cardiovascular 10,11 , autoimmune and rheumatologic 12 diseases, and viral infection 13-15 .…”

GB Virus C Coinfections in West African Ebola Patients

“…If GBV-C infection attenuates EBOV pathogenesis, it is possible that this occurs through modulation of the host immune response. In the context of HIV infection, GBV-C has been associated with a reduced production of proinflammatory cytokines and a reduction in T-cell activation in vivo and in vitro (34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44). Conversely, robust production of proinflammatory cytokines and lymphocyte activation followed by massive T-cell death are thought to play a major role in EBOV pathogenesis and have been associated with poor clinical outcome in retrospective studies (21)(22)(23)(24)(25)(26)(27).…”