A thymidine kinase deficient HSV‐2 strain causes acute keratitis and establishes trigeminal ganglionic latency, but poorly reactivates in vivo

Abstract

The incidence of herpetic keratitis following intranasal or direct ocular infection with thymidine kinase-negative (TK-) strains of herpes simplex virus (HSV)-2 has not been well studied, and the role of the TK gene in the establishment of latency and virus reactivation is controversial. To determine whether a TK- strain of HSV-2 could establish trigeminal ganglionic latency and be reactivated in vivo to produce recurrent keratitis or nervous system infection, an animal model of acute and recurrent infection was utilized. Rabbits were infected by the intranasal or ocular routes, and latency was reactivated by immunosuppression. Virus shedding in nasal and ocular secretions was monitored, and the eyes were examined for the presence of corneal epithelial lesions during acute and reactivated infections. Central nervous system (CNS) and trigeminal ganglionic tissues were assayed by histologic, virologic, and in situ hybridization techniques. All rabbits intranasally infected shed virus in both ocular and nasal secretions, whereas only 30% of rabbits infected in the eyes shed virus in nasal secretions. Virus was recovered from cocultivation cultures, but not from cell-free homogenates, of trigeminal ganglionic and CNS tissues from animals inoculated by both routes. The incidence of keratitis was much greater after direct ocular inoculation, although both routes of inoculation produced CNS and ganglionic inflammatory lesions. Keratitis healed in 92% of the animals infected by the ocular route by 26 days post infection. Of rabbits initially infected in the eyes and then subjected to drug-induced reactivation, only 30% shed virus, which was limited to a 24 hour period; there was no reappearance of epithelial keratitis, no animal became blind, and none died. In contrast, latently infected control rabbits uniformly reactivated. These studies show that this TK-HSV-2 strain (i) replicates in the eye, (ii) is neuroinvasive but non-neurovirulent following intranasal and direct ocular infection; (iii) sheds in the eye more frequently and for longer periods after ocular than after intranasal inoculation; (iv) induces epithelial keratitis that usually heals spontaneously; (v) establishes latency in trigeminal ganglionic neurons, but no other ganglionic cells; and, (vi) reactivates in a small proportion of animals, but does not produce recurrent ocular lesions following drug-induced immunosuppression. Thus, the TK gene appears directly involved in HSV latency and reactivation in vivo.

Mucosal delivery of CpG oligodeoxynucleotides expands functional dendritic cells and macrophages in the vagina

“…However, TKmutant virus is pathogenic in humans, causing acute keratitis and establishing latency in trigeminal ganglion, and hence cannot be used clinically. 43 Interestingly, HSV-2 DNA has recently been shown to directly stimulate TLR9, suggesting that both TK -HSV-2 and IVAG CpG-ODN alone may mediate the up-regulation of vaginal DC through a common TLR9-mediated pathway. To this end, CpG-ODN delivery may well be a viable means of expanding mucosal tissue APC in immuno-compromised individuals in a clinical setting.…”

A novel, cell-specific attenuation of a herpes simplex virus type 1 infection in vivo

“…After euthanasia, using 100 mg/kg sodium nembutal and transcardial perfusion with PBS, brains were removed and fixed in formalin or 1 mM sodium m-periodate, 75 mM lysine, 2% paraformaldehyde in 37 mM phosphate buffer, pH 7.4 for 24 h [46,48,49,50]. The brains were then cut into 11-12 blocks, processed for paraffin embedding, and sectioned [48].…”

Antiviral therapy of herpes simplex virus infection: recent developments

“…Many studies; have shown that TK~ deletion mutants establish latent infections in mouse trigemina! ganglia which fail to reactivate or reactivate poorly when ganglia are cocultivated with susceptible indicaior cells [87][88][89]. TK"" mutants cause much concern because of their maintained pathogenecity in animal studies since the TK phenotype does not necessarily attenuate the ability to induee disease in different animal models [81,89].…”

“…ganglia which fail to reactivate or reactivate poorly when ganglia are cocultivated with susceptible indicaior cells [87][88][89]. TK"" mutants cause much concern because of their maintained pathogenecity in animal studies since the TK phenotype does not necessarily attenuate the ability to induee disease in different animal models [81,89]. Concerning the neurovirulence, PFU/LD^,, ratios resulting from intracerebra] inocu]ation indicate that differences in the pathogcnicities of viruses with different TK phenotypes are greater in this model than in the skin infeetion model.…”