Wade A. Edris

Herpes simplex virus latent infection: reactivation and elimination of latency after neurectomy

Section of the sciatic nerve during the period of herpes simplex virus (HSV) latent infection was performed to evaluate residual latency in mouse dorsal root ganglion. In control mice without sciatic neurectomy, latency was present in 90-100%, while in those which underwent a neurectomy procedure, latent infection was surprisingly decreased to 28-50%. To investigate the hypothesis that the decrease of latency resulted from HSV reactivation and replication (with subsequent neuron destruction), groups of mice were treated with acyclovir to inhibit HSV reactivation, after having undergone a neurectomy procedure. Acyclovir treatment largely prevented the neurectomy-related elimination of latency and supported the hypothesized mechanism.

Thymidine kinase (TK) activity in herpes simplex virus type 1 recombinants that carry insertions affecting regulation of the TK gene

Determinations of the possible importance of herpes simplex virus type 1 (HSV) thymidine kinase (TK) expression in the pathogenesis of viral latency depend in part on the use of defined mutants. In a recent study by A. E. Sears, B. Meignier, and B. Roizman (J. Virol. 55, 410-416 (1985], in which they utilized genetically engineered viral recombinants considered to be TK-, the role of HSV TK expression in latency was reported to be minimal. To further investigate this conclusion we intensively studied the TK phenotypes of their M316-2 and M316-10 HSV-1 mutants. TK activity was investigated by phosphorylation of thymidine, by arabinosylthymine (ara-T) inhibition and by virus plaque autoradiography. TK activity of the M316-2 and M316-10 HSV mutants was not detected in 5-min assays (as performed by Sears et al.), but in longer assays substantial activity was apparent. In contrast, in assays of control TK- viruses, activity was minimal or absent at all time points. In ara-T inhibition assays the M316-2 and M316-10 viruses were inhibited more than 10-fold, consistent with viruses of intermediate TK activity. By plaque autoradiography both of these viruses produced plaques which incorporated significant amounts of thymidine. Based on these results we conclude that the M316-2 and M316-10 viruses should likely be considered to express intermediate levels of TK activity. HSV latency results using these mutants may need to be interpreted with this in mind.

Herpes simplex virus latency after direct ganglion virus inoculation

Herpes simplex virus (HSV) latent infection of ganglion neurons follows axoplasmic transport of HSV, probably in the form of nucleocapsid from peripheral sites of infection (e.g. footpad). This raises the possibility that latency is dependent on this particular means of presenting HSV to ganglion neurons. To investigate this, we directly infected ganglia of mice with HSV and evaluated latency. Initially, ganglia were surgically exposed in intact mice, infected with HSV and after 4 weeks evaluated for HSV latency-associated transcript (LAT) expression. LAT expression suggested latency. To more fully evaluate latency after direct ganglion inoculation, a transplant model was developed. In this model, ganglia were removed from mice, inoculated with HSV, transplanted into syngeneic recipients and evaluated for latency after several weeks. Latency was evident in transplanted ganglia by (1) the presence of LAT in neurons; (2) the lack of HSV ICP4 RNA or viral antigen, and (3) the isolation of HSV from explants of transplants but not from direct homogenates. The transplant model was then used to evaluate the effect of inhibition of HSV replication on latency. Antivirals which inhibited HSV replication markedly decreased the number of LAT-positive neurons in transplants, suggesting a role for HSV replication mechanisms and latency. It is thought that direct ganglion inoculation and ganglion transplant methods will permit unique investigations of mechanisms of latency.