Herpes simplex virus latency: adaptation to the peripheral nervous system. II

The role of viruses in idiopathic peripheral facial palsy and cellular immune response

PURPOSE

The purpose of this study is to investigate the role of viruses on the idiopathic peripheral facial palsy and show the interaction of immune system.

MATERIALS AND METHODS

The levels of immunoglobulin (Ig) G and IgM antibodies against to varicella-zoster virus (VZV), herpes simplex virus (HSV), cytomegalovirus (CMV), Ebstein-Barr virus (EBV), and mumps virus in venous blood taken from patients in the amount of 10 mL have been investigated by enzyme-linked immunosorbent assay method. Tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and transforming growth factor-beta (TGF-beta) were also examined. Of lymphocyte subpopulation, antibodies of CD3(+), CD4(+), CD8(+), CD19(+), and CD16(+) plus 56(+) were analyzed.

RESULTS

Ten of the patients had HSV-1 IgG; 1 of the patients IgM, 5 of the patients EBV IgG, 6 of the patients VZV IgG, 1 of the patients IgM, 9 of the patients mumps IgG, 1 of the patients IgM, and finally in 7 of the patients CMV IgG antibodies were obtained. It was found that CD4(+) cell and ratio of CD4(+)/CD8(+) lower and the percentage of the CD8(+) and CD16(+) plus 56(+) cells higher compared with the control group (P < .05). The levels of TNF-alpha were lower, whereas IFN-gamma and TGF-beta1 were higher.

CONCLUSION

It may be concluded from these results that VZV, HSV-1, CMV, EBV, and mumps virus play a significant role in the etiology of idiopathic peripheral facial palsy and activate the cellular immunity.

Localization of cis-acting sequence requirements in the promoter of the latency-associated transcript of herpes simplex virus type 1 required for cell-type-specific activity

We have previously demonstrated (A. H. Batchelor and P. O'Hare, J. Virol. 64:3269-3279, 1990) the selective activity in human neuroblastoma cells (IMR-32) of a promoter located upstream of the latency-associated transcript of herpes simplex virus type 1. In this work, we provide evidence for the basis of the selective activity of this latency-associated promoter (LAP). Recombinant constructs containing sequences up to -143 (relative to the LAP cap site) linked to the chloramphenicol acetyltransferase gene retain strong activity in HeLa cells but exhibit extremely weak activity in IMR-32 cells. Sequences mapping within the 108 bp upstream of -143 to position -251 enhance LAP activity by over 15-fold, restoring optimal levels of expression in IMR-32 cells, but have little or no effect (1.5-fold) in HeLa cells. This cell-type-specific enhancement of promoter activity took place in two major steps, with sequences between -143 and -158 conferring a four- to fivefold effect and sequences between -177 and -251 conferring a further threefold effect. Furthermore, sequences mapping from -40 to -258 could transfer the ability to be expressed in neuroblastoma cells to the normally inactive immediate-early 110K promoter (IE110K), increasing levels of expression by 35-fold. By comparison, this region had a relatively minor effect (twofold) on the activity of the IE110K promoter in HeLa cells, even though this promoter is open to activation by other mechanisms. However, neither of the overlapping subregions from -40 to -143 or -138 to -258 could confer efficient IMR-32 cell expression on the IE110K promoter, and we present alternative models for multiple element requirements or the requirement for a critical site around -140 which is not retained in either subfragment. We provide consistent evidence for a site around -140 and demonstrate the presence selectively in IMR-32 cells of a DNA-binding factor which binds a probe spanning this region. We propose that this element and the cognate factor (IC-1) may be involved in the selective activity of the LAP in neuroblastoma cells.

Regulation and cell-type-specific activity of a promoter located upstream of the latency-associated transcript of herpes simplex virus type 1

To identify promoter regions which control expression of the latency-associated transcript (LAT) of herpes simplex virus type 1 (HSV-1), we constructed a series of recombinant vectors in which various sequences upstream of LAT were linked to the chloramphenicol acetyltransferase gene and tested for expression efficiency by transfection into tissue culture cells. In HeLa cells no activity was observed from the region (-250 to +201) immediately surrounding the nominal 5' end of LAT, but high levels of activity were observed by using different fragments within the region -1267 to -594. This promoter activity was largely contained within the 140-base-pair region from -797 to -658 and was 20- to 50-fold stronger than typical HSV delayed-early promoters and at least as strong as the activity from the simian virus 40 (SV40) enhancer-promoter region or the HSV immediate-early 110,000-Mr (IE110K) promoter region. In human neuroblastoma cells (IMR-32), there was a dramatic switch in relative activities in favor of the LAT promoter, so that it was 45- and 200-fold stronger than the IE110K and SV40 constructs, respectively. Furthermore, optimal activity in the neuroblastoma cells required sequences within the region -1267 to -797. This region had little effect on activity in HeLa cells. We also show that the LAT promoter activity was very efficiently repressed by the IE175K protein. From internal deletion analysis, the site of repression was located within a 55-base-pair region just downstream of a potential TATA box. This region exhibited a high degree of homology with the IE175K cap site and may be a binding site for the IE175K protein.

Thymidine kinase-negative herpes simplex virus mutants establish latency in mouse trigeminal ganglia but do not reactivate

Herpes simplex virus infection of mammalian hosts involves lytic replication at a primary site, such as the cornea, translocation by axonal transport to sensory ganglia and replication, and latent infection at a secondary site, ganglionic neurons. The virus-encoded thymidine kinase, which is a target for antiviral drugs such as acyclovir, is not essential for lytic replication yet evidently is required at the secondary site for replication and some phase of latent infection. To determine the specific stage in viral pathogenesis at which this enzyme is required, we constructed virus deletion mutants that were acyclovir resistant and exhibited no detectable thymidine kinase activity. After corneal inoculation of mice, the mutants replicated to high titers in the eye but were severely impaired for acute replication in trigeminal ganglia and failed to reactivate from ganglia upon cocultivation with permissive cells. Nevertheless, latency-associated transcripts were expressed in neuronal nuclei of ganglia from mutant-infected mice and superinfection of the ganglia with a second virus rescued the latent mutant virus. Thus, contrary to a widely accepted hypothesis, the thymidine kinase-negative mutants established latent infections, implying that neither thymidine kinase activity nor ganglionic replication is necessary for establishment of latency. Rather, thymidine kinase appears to be necessary for reactivation from latency. These results suggest that acyclovir-resistant viruses could establish latent infections in clinical settings and have implications for the use of genetically engineered herpesviruses to deliver foreign genes to neurons.

A conserved open reading frame that overlaps the herpes simplex virus thymidine kinase gene is important for viral growth in cell culture

Of 18 mutants containing clustered point mutations within UL24 (an open reading frame that overlaps the herpes simplex virus thymidine kinase gene on the opposite strand), 15 formed small plaques and were substantially impaired for virus growth in cell culture. Mutations conferring the small plaque phenotype disrupt regions of UL24 that share considerable sequence similarity with open reading frames common to herpesviruses of mammals and birds. We infer that UL24 is expressed and important for virus growth in cell culture and suggest that possible effects on UL24 should be considered in studies of thymidine kinase-deficient mutants.

Low levels of herpes simplex virus thymidine- thymidylate kinase are not limiting for sensitivity to certain antiviral drugs or for latency in a mouse model

Herpes simplex virus mutant KG111 contains a nonsense mutation at codon 44 of the viral thymidine kinase (tk) gene and produces low amounts of a truncated tk polypeptide. We tested mutant KG111 and related viruses that specify varying amounts of similar truncated tk polypeptides for their sensitivities to antiviral nucleoside analogs at different temperatures using plaque reduction assays. The results of these assays showed that the nonsense mutation confers high resistance to bromovinyldeoxyuridine (BVdU) at any temperature and temperature-dependent resistance to acyclovir (ACV), buciclovir (BCV), ganciclovir (DHPG), and fluoroiodoarabinouracil (FIAU). Above relatively low threshold levels of tk that varied depending on the drug tested, viruses exhibited full sensitivity to ACV, BCV, DHPG, and FIAU at 34 degrees. Below these threshold levels, however, decreases in drug sensitivity were linear with decreases in tk levels, forming the basis of a pharmacological assay for tk gene expression. Studies of thymidine (TdR) anabolism in infected 143 tk-cells showed that when high TdR concentrations were added to the medium, KG111 directed thymidine monophosphate (TMP) formation at rates consonant with the amount of tk polypeptide produced by the mutant. When low concentrations to TdR were added to the medium, however, KG111 directed TMP formation at a rate similar to that directed by wild-type virus, indicating that the truncation of the tk polypeptide had little or no effect on tk activity at 34 degrees. Subsequent anabolism to thymidine diphosphate and thymidine triphosphate was reduced in KG111-infected cells, indicating a defect in TMP kinase activity that explains this mutant's resistance to BVdU. Despite the low levels of tk and TMP kinase activity expressed by KG111, this mutant established reactivatable latent infections as efficiently as wild-type virus in a mouse model.

An improved method for detection of ganglionic latency in herpes simplex virus type-1 infected guinea pigs

A simple method was developed which increased the sensitivity and reliability of detecting latent herpes simplex virus type-1 (HSV-1) in trigeminal ganglia of guinea pigs. Animals were infected with the Shealey strain of HSV-1 immediately following scarification of the cornea and maintained for 30-40 days to ensure that true latency was established. Viral latency was defined as the appearance of infectious virus in ganglia only upon cultivation in vitro. Thus, ganglia from similarly infected animals, homogenized immediately upon removal, did not contain infectious virus. Excised ganglia were incubated intact in high glucose medium and yielded maximal positive results (90-100%) by the twelfth day of incubation. This method was compared with the standard cocultivation technique in which minced fragments of ganglionic tissue were explanted onto Vero cell cultures. Cocultivation yielded a considerably lower latency rate and was more variable (29-57%) than the whole ganglion culture method.