Spontaneous molecular reactivation of herpes simplex virus type 1 latency in mice

Abstract

Infection of the mouse trigeminal ganglia (TG) is the most commonly used model for the study of herpes simplex virus type 1 (HSV-1) latency. Its popularity is caused, at least in part, by the perception that latent infection can be studied in this system in the absence of spontaneous viral reactivation. However, this perception has never been rigorously tested. To carefully study this issue, the eyes of Swiss-Webster mice were inoculated with HSV-1 (KOS), and 37-47 days later the TG were dissected, serial-sectioned, and probed for HSV-1 ICP4, thymidine kinase, glycoprotein C, and latency-associated transcript RNA by in situ hybridization. Serial sections of additional latently infected TG were probed with HSV-1-specific polyclonal antisera. Analysis of thousands of probed sections revealed abundant expression of viral transcripts, viral protein, and viral DNA replication in about 1 neuron per 10 TG tested. These same neurons were surrounded by a focal white cell infiltrate, indicating the presence of an antigenic stimulus. We conclude that productive cycle viral genes are abundantly expressed in rare neurons of latently infected murine TG and that these events are promptly recognized by an active local immune response. In the absence of detectable infectious virus in these ganglia, we propose the term ''spontaneous molecular reactivation'' to describe this ongoing process.H erpes simplex virus type 1 (HSV-1) infections of the skin or eye lead to invasion of the trigeminal ganglia (TG), where the virus follows one of two pathways (1-3). In some infected neurons, the virus replicates and destroys the cell. This lytic cycle path involves regulated viral gene expression in which immediate-early genes are required for the efficient expression of early and late genes. In other neurons, a latent infection is established in which lytic cycle genes are not expressed and infectious virus is not produced. Latent infection of neurons is characterized by the expression of the latency-associated transcripts (LAT), which are encoded in a single region of the HSV-1 genome and which accumulate to high levels in the nucleus of the host cell (4-10). In situ hybridization (ISH) studies of latently infected sensory ganglia have revealed numerous neurons expressing LAT but no other viral RNAs (4, 5, 7, 9-15). Thus, for many years a latent neuron has been defined in molecular terms as a neuron that is positive for LAT and negative for other viral RNAs.In humans, HSV-1 intermittently reactivates from the latent state, with peripheral shedding of infectious virus. Shedding of infectious virus is similarly observed in rabbit ocular models of HSV infection, both spontaneously and in response to local or systemic stimuli (16,17). In contrast, latent HSV-1 infection in the mouse seems to be more tightly regulated, and attempts to identify infectious virus or viral antigen in murine sensory ganglia after resolution of primary infection (indicative of a spontaneous reactivation localized to the sensory ganglion) have been unsuccessful (2,7,9,...

CXCL10/CXCR3-Dependent Mobilization of Herpes Simplex Virus-Specific CD8 + T EM and CD8 + T RM Cells within Infected Tissues Allows Efficient Protection against Recurrent Herpesvirus Infection and Disease

“…A critical question remains as to which animal model would be the most appropriate to mimic the immunoprotective versus immunopathological aspect of recurrent herpes as occurs in humans? Unlike humans, spontaneous HSV-1 reactivation in latently infected mice and virus shedding in tears either does not occur at all or occurs at very low levels in mice (57). Only a handful of studies have employed the mouse model of UV-B light-induced recurrent herpetic corneal disease, mostly using C57BL/6 and BALB/c mice (54,55,58).…”

Selective retention of herpes simplex virus-specific T cells in latently infected human trigeminal ganglia

“…These results support the recent diversion from the old dogma that HSV-1 latency is an antigenic silent infection (1). Several studies have now demonstrated the expression of viral immediate early, early, and even late gene transcripts in human and mouse HSV-1 latently infected ganglia (7,8,12,(30)(31)(32). The collective data argue that the neuron-interacting T cells are most likely HSV-1 specific and recognize those latently infected neurons that intermittently express low amounts of viral proteins below levels detectable by using biochemical means or a particular subset of neurons in which HSV-1 has reactivated from latency (32).…”

Effect of human apolipoprotein E genotype on the pathogenesis of experimental ocular HSV-1

“…In most cases, only one eye shed infectious HSV-1 once on many continuous days of swabbing. Feldman et al (2002) described abundant expression of select viral transcripts and proteins and noted viral DNA synthesis in about 1 neuron per 10 TGs at 37--47 days P.I. This process was termed "spontaneous molecular reactivation"; however, no evidence of infectious virus was reported in that study (Feldman et al, 2002).…”

“…Feldman et al (2002) described abundant expression of select viral transcripts and proteins and noted viral DNA synthesis in about 1 neuron per 10 TGs at 37--47 days P.I. This process was termed "spontaneous molecular reactivation"; however, no evidence of infectious virus was reported in that study (Feldman et al, 2002). In a recent report, Margolis et al, 2007, reported that spontaneous reactivation of infectious HSV-1 indeed occurs in a limited percentage (~6%) of mouse TG at 37 days P.I.…”