Interplay of LAT and HVEM affect HSV-1 Latency and CD8+ T Cell Exhaustion

Abstract

Purpose: : The herpesvirus entry mediator (HVEM; TNFRSF14) plays a significant role regulating immune responses, yet appears to have only a minor role as an viral entry route during primary infection in mucosal and neural tissues. The immune regulatory role for HVEM suggested the possibility of its involvement in latency. Latency associated transcript (LAT) of HSV-1 plays a major role in the level of HSV-1 latency and virus reactivation. Whether there is a synergy between LAT and HVEM in the establishment of latency and reactivation in trigeminal ganglia (TG) of infected mice is unknown. To address this issue, we used both an in vitro model looking at the effect of LAT on HVEM in Neuro2A and C1300 cells and LAT(+) and LAT(-) viruses to evaluate the effect of LAT in HVEM-deficient mice.

Methods: : WT (C57BL/6) and HVEM^-/- mice were infected ocularly with 2 X 10⁵ PFU/eye of WT (LAT-plus) HSV-1 strain McKrae or dLAT2903, dLAT-CD80 and dLATgK³ (LAT-minus viruses). Individual TG from surviving mice were isolated on day 30 post-infection (PI) and used for detection of viral DNA. Isolated TG were also tested for the presence of viral antigens and exhaustion markers by FACS, RT-PCR, and immunostaining. In addition, the effect of LAT on up-regulation of HVEM in Neuro2A cells stably expressing or transiently transfected with various LAT regions were evaluated.

Results: : The increase of latency in TG of WT mice infected with LAT(+) virus compared to LAT(-) virus correlated with an increase in the level of HVEM, but not nectin-1, nectin-2, PILR-α, or 3-O sulfated heparin sulfate. LAT also upregulated HVEM expression in Neuro2A cells stable expressing LAT, and in cells transfected with LAT sRNA1 or sRNA2. In contrast to WT mice, the level of latency in HVEM^-/- mice infected with LAT(+) was three fold lower, similar to that of LAT(-) virus. Decrease of latency in HVEM^-/- mice or WT mice infected with LAT(-) viruses correlated with a significant decline in the level of CD8 and PD-1. However, the absence of HVEM did not alter primary virus replication in the eye of HVEM^-/- mice compare with HVEM^+/+.

Conclusions: : These results demonstrate for the first time a link between LAT and HVEM suggesting a molecular basis for selective advantage of this entry route for the pathogen during latency-reactivation.

Keywords: herpes simplex virus • inflammation • microscopy: light/fluorescence/immunohistochemistry