GB Virus C Envelope Protein E2 Inhibits TCR-Induced IL-2 Production and Alters IL-2–Signaling Pathways

Abstract

GB virus type C (GBV-C) viremia is associated with reduced CD4+ T cell expansion following Interleukin 2 (IL-2) therapy and with a reduction in T cell activation in HIV-infected individuals. Mechanism(s) by which GBV-C might alter T-cell activation or IL-2 signaling have not been studied. Here, we assess IL-2 release, IL-2 receptor (IL-2R) expression, IL-2 signaling, and cell proliferation in Tet-off Jurkat cells expressing the GBV-C envelope glycoprotein (E2) following activation through the T cell receptor (TCR). TCR activation was induced by incubation in anti-CD3/CD28 antibodies. IL-2 release was measured by ELISA, STAT5 phosphorylation was assessed by immunoblot, and IL-2Rα (CD25) expression and cell proliferation were determined by flow cytometry. IL-2 and IL-2Rα steady-state mRNA levels were measured by real-time PCR. GBV-C E2 expression significantly inhibited IL-2 release, CD25 expression, STAT5 phosphorylation and cellular proliferation in Jurkat cells following activation through the TCR compared to control cell lines. Reducing E2 expression by doxycycline reversed the inhibitory effects observed in the E2-expressing cells. The N-terminal 219 a.a of E2 was sufficient to inhibit IL-2 signaling. Addition of purified recombinant GBV-C E2 protein to primary human CD4+ and CD8+ T cells inhibited TCR activation-induced IL-2 release and upregulation of IL-2Rα expression. These data provide evidence that the GBV-C E2 protein may contribute to the block in CD4+ T cell expansion following IL-2 therapy in HIV-infected individuals. Furthermore, the effects of GBV-C on IL-2 and IL-2 signaling pathways may contribute to the reduction in chronic immune activation observed in GBV-C/HIV co-infected individuals.

GBV-C Infection and Risk of NHL among U.S. Adults

“…Briefly, recombinant E2-Fc fusion protein (29) (2 μg/ml in carbonate buffer) was used to coat ELISA plates, which were stored at 4°C until use. Following washing, patient samples (diluted 1:200) were added to the wells for 1 hour at 37°C.…”

GB virus C infection and B-cell, natural killer cell, and monocyte activation markers in HIV-infected individuals

“…Although these entry co-receptors are not typically considered markers of T cell activation, both receptors are upregulated following T cell activation. Furthermore, studies have demonstrated an association between GBV-C viremia and reduced levels of more typical markers of activated T cells including CD25, CD38, HLA-DR, and CD69 [5, 6, 8]. Finally, CD4+ and CD8+ T cell proliferation is reduced in GBV-C viremic subjects compared to those without GBV-C based on expression of the proliferation marker Ki67 [6].…”

“…A recent study found that the GBV-C envelope glycoprotein E2 interferes with both IL-2 receptor signaling and with T cell receptor-mediated activation [8]. GBV-C E2 protein did not interfere with the function of non-stimulated cells, but did reduce activation significantly in CD4+ and CD8+ T cells following stimulation through the T cell receptor.…”

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

“…Several clinical studies, including a meta-analysis of HIV-positive subjects found an association between persistent GBV-C infection and prolonged survival in HIV-infected individuals (6-10). Although several mechanisms have been proposed for this beneficial association between GBV-C coinfection and HIV-related survival(11), recent studies suggest that GBV-C reduces HIV-associated chronic immune activation, and that this contributes to better HIV clinical outcomes (5,12-17). …”