Human plasmacytoid dendritic cells regulate immune responses to Epstein-Barr virus (EBV) infection and delay EBV-related mortality in humanized NOD-SCID mice

Abstract

Epstein-Barr virus (EBV) is IntroductionEpstein-Barr virus (EBV) is a ubiquitous, potentially oncogenic human herpes virus affecting up to 95% of the adult population worldwide. Primary infection often occurs in childhood 1 as asymptomatic or mild self-limiting illness or as infectious mononucleosis in adults. 2 In immunocompromised patients with impaired cellmediated immunity, acute EBV infection is associated with the development of lymphoproliferative disease (LPD) with mortality rates between 10% and 100%. 3 In recipients of solid organ transplants, the incidence of posttransplant lymphoproliferative disease (PTLD) ranges from 1% to 15%, with the highest risk in EBV IgG-seronegative recipients receiving a graft from EBV IgG-seropositive donors. 4 Dendritic cells (DCs) are a rare, heterogenous population of antigen-presenting cells (APCs) that initiate and regulate both innate and adaptive immune responses against invading pathogens. [5][6][7] There are at least 2 circulating blood DC subsets including myeloid DC (MDCs) and plasmacytoid DC (PDCs). 8,9 Although both DC subsets are involved in the initial response against infectious agents, PDCs play a key role in antiviral immunity. PDC precursors (pre-PDCs) express distinct lymphoid markers including pre-T␣, 5, Ig1-like 14.1, and Spi-B; blood DC antigen 2 (BDCA-2) and BDCA-4 (neuropilin-1) 11 ; and toll-like receptor 7 (TLR-7) and TLR-9. 12,13 Viral stimulation of TLR-7 and TLR-9 expressed on PDCs results in production of type I interferons (IFNs), 12,13 key cytokines in antiviral response. 10,14,15 Humanized severe combined immunodeficiency (SCID) mice are a well-established model of spontaneous EBV-induced B-cell lymphoma. 16 Nonobese diabetic (NOD)-SCID mice possess additional immunologic defects (eg, decreased murine natural killer [NK] cell function) that permit greater engraftment of human cells following injection of human peripheral blood mononuclear cells (PBMCs). 17 In a previous study, we demonstrated that circulating pre-PDCs are severely reduced in the peripheral blood of renal transplant recipients resulting in impaired IFN-␣ production by PBMCs following viral stimulation. 18 We hypothesized that the reduction in circulating pre-PDCs observed in transplant recipients plays a crucial role in the risk of viral infection, and in particular EBV-related infection and the onset of LPD. In the present study, we address this hypothesis by assessing the impact of a reduction in the numbers of circulating PDCs in the development of EBVrelated infection and LPD using a humanized NOD-SCID mouse model as a surrogate model of human EBV infection. We demonstrate that reduction in PDCs enhances the development of EBV-related infection and LPD, whereas the supplementation of extra PDCs delays or even prevents the development of EBVrelated LPD in humanized NOD-SCID mice. We now show for the first time that PDCs are involved in anti-EBV immunity by the secretion of IFN-␣ and activation of T cells mediated by TLR-9 pathways. Thus, manipulating PDCs may provide no...

EBV Latent Membrane Protein 1 Is a Negative Regulator of TLR9

“…Several studies highlight the importance of the role played by TLR9 in anti-EBV immunity (25,26). We demonstrated that the inhibition of TLR9 expression by EBV is mainly mediated by its major oncoprotein LMP1, as EBV mutant lacking LMP1 is impaired in its ability to downregulate TLR9.…”

“…Yet, a third signal needs to be delivered coupled by BCR-TLR7 or -TLR9 in response to R848 or CpG, respectively, to produce optimal Ab responses to T celldependent Ags (23). In terms of viral recognition, it has been shown that TLR9 is required for the innate immune response to human DNA viruses including HSV-2 (21,24) and EBV (25), and the involvement of TLR9 in the antiviral immune response to the murine g-herpesvirus MHV-68 (a murine model of EBV infection) was demonstrated in a recent study (26). However, the direct effect of EBV infection in B cells on the TLR9-mediated innate immune response has not been elucidated.…”

Functional delivery of viral miRNAs via exosomes

“…We proposed that EBV-miRNAs may function outside infected B cells by exosome-mediated delivery into physiologically relevant recipient cells. Dendritic cells (DC) control T-cell-mediated immunity of EBV infection and control EBVdriven transformation (21,22). In addition, DC modulate adaptive immune responses by internalizing exosomes (23,24).…”

Animal models of Epstein Barr virus infection

“…Type I IFN secreting plasmacytoid DCs have been shown to restrict EBV infection in a PBMC transfer model (Lim et al, 2006), although IFN- might inhibit EBV infection only very early after viral encounter with B cells (Lotz et al, 1985). The role of other DC populations, which are required to prime protective EBV-specific T cells in vitro (Bickham et al, 2003), has not been investigated in an in vivo model of EBV infection so far.…”