Isolation of a herpes simplex virus type 2 that is retinovirulent in mice

Reduction of herpes simplex virus type-2 replication in cell cultures and in rodent models with peptide-conjugated morpholino oligomers

BACKGROUND

Genital herpes, caused by herpes simplex virus type-2 (HSV-2), is a recurrent, lifelong disease affecting tens of millions of people in the USA alone. HSV-2 can be treated therapeutically with acyclovir (ACV) and its derivatives; however, no treatment can prevent HSV reactivation. Novel topical anti-HSV microbicides are much needed to reduce HSV-2 transmission and to treat primary or reactivated infections, especially for ACV-resistant strains. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) are single-stranded DNA analogues that enter cells readily and can reduce target gene expression through steric blockage of complementary messenger RNA (mRNA).

METHODS

We investigated the antiviral activities of PPMOs targeted to the translation start-site regions of the mRNA for two HSV-2 immediate early genes, immediate early protein (ICP)0 and ICP27, and two early genes, unique long gene (UL)30 and UL39.

RESULTS

In cell cultures, PPMOs targeting ICP0 or ICP27 mRNA were found to be highly effective against two strains of HSV-2, one of which was ACV-resistant. In vivo, daily topical applications of up to 1 mM ICP27 PPMO caused no gross or microscopic damage to the genital tract of uninfected BALB/c mice or cotton rats. Cotton rats receiving topical application of ICP27 PPMO 24 h after HSV-2 inoculation showed a reduction in genital lesions and a 37.5% reduction in mortality at 14 days post-infection. Mice receiving topical application of 100 μM of an ICP27 and ICP0 PPMO combination before HSV-2 inoculation had no detectable viral replication in the genital tract at 3-5 days post-infection.

CONCLUSIONS

These results demonstrate that topically applied PPMOs hold promise as candidate antiviral microbicides against HSV-2 genital infection.

Role of nectin-1, HVEM, and PILR-alpha in HSV-2 entry into human retinal pigment epithelial cells

PURPOSE

Herpes simplex virus-type 2 (HSV-2) can cause acute retinal necrosis (ARN), which can lead to exudative and rhegmatogenous retinal detachment, yet little is known about the cellular and molecular mechanisms of HSV-2 entry into retinal pigment epithelial (RPE) cells. The goal of this study was to establish the identity of the critical receptors used by the virus for infection.

METHODS

A reporter HSV-2 virus, which expresses beta-galactosidase, was used to quantify entry into RPE cells, and viral replication was ascertained using a plaque assay. Flow cytometry and immunocytochemistry were used to determine cellular expression of entry receptors. Localization of these receptors to the apical or basal surface of RPE cells was determined with immunocytochemistry. The necessity of these receptors, individually and in combination, for viral entry was established using receptor-specific antibodies and siRNAs.

RESULTS

RPE cells are highly susceptible to HSV-2 entry and replication. Several assays demonstrated the expression of the entry receptors nectin-1, HVEM, and PILR-alpha and their localization primarily to the apical surfaces of RPE cells. Receptor-specific antibodies and siRNA knockdown of receptors significantly reduced viral entry and implicated nectin-1 as an important receptor, with HVEM and PILR-alpha potentially also contributing to entry.

CONCLUSIONS

HSV-2 is capable of developing a productive infection in RPE cells by using nectin-1 as an important entry receptor. To lesser degrees, HVEM and PILR-alpha may also contribute to HSV-2 entry into RPE cells.

Acute retinal necrosis caused by reactivation of herpes simplex virus type 2

Acute retinal necrosis is a severe form of necrotizing retinitis. Acute retinal necrosis has been demonstrated to be caused by varicella-zoster virus and herpes simplex virus type 1. We treated three patients with acute retinal necrosis apparently caused by recrudescence of latent herpes simplex virus type 2. Primary viral infection was probably congenital, with documented perinatal herpes simplex virus type 2 infection in two patients. Bilateral chorioretinal scars were present in two patients, neither of whom had a history of ocular herpetic infection, suggesting that earlier subclinical chorioretinitis had occurred. In each case, periocular trauma preceded the development of retinitis by two to three weeks. These cases are evidently caused by trauma-induced reactivation of latent virus rather than the onset of a primary infection.

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

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.

Herpes simplex virus type 2 induced retinal necrosis in BALB/c mice

We injected herpes simplex virus type 2 of MS- or G-strain into the anterior chamber of BALB/c mice. In the contralateral eye inflammatory cell infiltration began in the ciliary body; focal retinitis, detected by day 8, led to total destruction of the retina by day 10. Contralateral disease was observed in 75% of mice inoculated with 8 x 10(3) pfu herpes simplex virus type 2, but in only 20% of mice receiving 80 pfu herpes simplex virus type 2. Still this low concentration, however, produced a suppressed delayed-type hypersensitivity response. Anti-herpes simplex virus type 2 antibody, first detected on day 8, reached high titers on day 10; by then, most of the mice had died of encephalitis. The G-strain of herpes simplex virus type 2 was more neurotoxic than the MS-strain, but produced the same incidence of contralateral retinitis. Herpes simplex virus type 2 products contralateral necrotizing retinitis comparable to that produced by herpes simplex virus type 1. These findings, like those of other authors, suggest a role for herpes simplex virus type 2 in some cases of acute retinal necrosis in humans.

MS strain of type 2 herpes simplex virus produces necrotizing retinitis in mice

Intracerebral inoculation of mice with the MS strain of type 2 herpes simplex virus (HSV-2) causes a brief encephalitis associated with multifocal central nervous system demyelination. Many of the mice develop unilateral or bilateral impairment of the pupillary light reflex. We have examined the development of ocular disease in inbred NIH mice inoculated intracerebrally with a low dose (10 pfu) of HSV-2 (MS). The resulting acute encephalitis was fatal in 30-50% of the mice. By 1 month after inoculation, the pupillary response to light was absent or impaired in approximately 80% of the surviving mice. Infectious virus could be isolated from the trigeminal ganglia and optic nerves from day 2 and from the eyes by day 4. Viral antigen was first immunohistochemically detectable in the optic nerves on day 5 and in the retinae on day 6. During the second week after inoculation up to half of the mice developed unilateral or bilateral necrotising retinitis associated with high titres of virus in the eyes and abundant viral antigen in the retinae. Electron microscopy confirmed the presence of viral particles in the retinae, in glia and degenerating neurons. No viral antigen was detected in the corneas and only rarely was antigen found in the ciliary body or iris. Infectious virus persisted longer in the eyes than in the trigeminal ganglia or optic nerves and could still be isolated from a few of the animals 2 weeks after inoculation. By 1 month the titres of virus within the eyes had fallen to undetectable levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of bilateral retinal necrosis in mice by unilateral intracameral inoculation of a glycoprotein-C deficient clinical isolate of herpes simplex virus type 1

Herpes simplex virus can cause acute retinal necrosis, a blinding retinal disease in man. A unilateral intracameral inoculation of herpes simplex virus type 1 (HSV-1) in mice induces retinal necrosis primarily in the contralateral eye and provides an experimental model for the disease. Previous studies suggested that a major envelope glycoprotein of HSV-1, glycoprotein C (gC), is required for retinal necrosis. We studied HSV-1 strain TN-1, a gC-deficient clinical isolated from a lesion of herpetic keratitis, for its pathogenicity in mice with an intracameral inoculation of the virus and found that TN-1 could induce severe necrotizing retinitis in both inoculated and uninoculated eyes of BALB/c mice. Inoculation with a lower dose of TN-1 resulted in a unilateral necrotizing retinitis in the uninoculated eyes. Tissue virus titration of infected mice killed at various times after inoculation detected an infectious virus in various organs including the eyeballs, trigeminal ganglia, brain and adrenal glands. Anterior chamber-associated immune deviation (ACAID) was observed in TN-1-inoculated mice as well as in mice inoculated with gC-positive laboratory strain KOS 7 days postinoculation. Our findings suggested that gC of HSV-1 is not necessary for either the induction of retinal necrosis, neural spread of the virus, or ACAID.

Cytopathogenicity, drug susceptibility, and thymidine kinase activity of a retinovirulent herpes simplex virus type 2

We investigated some of the biological and biochemical characteristics of a neuroinvasive, retinovirulent herpes simplex virus type 2 strain SL (HSV-2[SL]) and compared them with those of a neurovirulent, nonretinovirulent HSV-2 (186). HSV-2(SL) was shown to spread rapidly and produce large syncytium in vitro. HSV-2(SL) and HSV-2(186) were equally susceptible to acyclovir (ACV) and thymine arabinoside (Ara-T). However, HSV-2(SL) was fourfold and 44-fold more susceptible than HSV-2(186) to iododeoxyuridine (IUdR) and bromovinyldeoxyuridine (BVDU), respectively. In addition, cytosolic TK from HSV-2(SL)-infected cells phosphorylated 4, 20, and 23,000 times more IUdR, iododeoxycytidine (IdCyD), and Ara-T than the TK of HSV-2(186), respectively. Further, HSV-2(186) TK did not phosphorylate Ara-T, but HSV-2(186) replication was inhibited by Ara-T. These studies indicate that the retinovirulent HSV-2(SL) has a syn phenotype and a TK with broad substrate activity.