Differences in resistance to herpes simplex virus type 1 (HSV-1) among oligodendroglia derived from different strains of mice are determined after viral adsorption but prior to the expression of immediate early (IE) genes

The effect of mouse strain on herpes simplex virus type 1 (HSV-1) infection of the central nervous system (CNS)

BACKGROUND

Mice infected with HSV-1 can develop lethal encephalitis or virus induced CNS demyelination. Multiple factors affect outcome including route of infection, virus and mouse strain. When infected with a sub-lethal dose of HSV-1 strain 2 via the oral mucosa, susceptible SJL/J, A/J, and PL/J mice develop demyelinating lesions throughout the brain. In contrast, lesions are restricted to the brainstem (BST) in moderately resistant BALB/c mice and are absent in resistant BL/6 mice. The reasons for the strain differences are unknown.

METHODS

In this study, we combine histology, immunohistochemistry, and in-situ hybridization to investigate the relationship between virus and the development of lesions during the early stage (< 24 days PI) of demyelination in different strains of mice.

RESULTS

Initially, viral DNA and antigen positive cells appear sequentially in non-contiguous areas throughout the brains of BALB/c, SJL/J, A/J, and PL/J mice but are restricted to an area of the BST of BL/6 mice. In SJL/J, A/J, and PL/J mice, this is followed by the development of 'focal' areas of virus infected neuronal and non-neuronal cells throughout the brain. The 'focal' areas follow a hierarchical order and co-localize with developing demyelinating lesions. When antigen is cleared, viral DNA positive cells can remain in areas of demyelination; consistent with a latent infection. In contrast, 'focal' areas are restricted to the BST of BALB/c mice and do not occur in BL/6 mice.

CONCLUSIONS

The results of this study indicate that susceptible mouse strains, infected with HSV-1 via the oral mucosa, develop CNS demyelination during the first 24 days PI in several stages. These include: the initial spread of virus and infection of cells in non-contiguous areas throughout the brain, the development of 'focal' areas of virus infected neuronal and non-neuronal cells, the co-localization of 'focal' areas with developing demyelinating lesions, and latent infection in a number of the lesions. In contrast, the limited demyelination that develops in BALB/c and the lack of demyelination in BL/6 mice correlates with the limited or lack of 'focal' areas of virus infected neuronal and non-neuronal cells in these two strains.

High susceptibility of a human oligodendroglial cell line to herpes simplex type 1 infection

More than 20 infectious agents, ranging from retroviruses to mycobacteria, have been associated with multiple sclerosis onset or relapses in which oligodendrocytes, the myelin-forming cells of the central nervous system, are the initial target of the pathogenic status. In this work, the nature of the susceptibility of the human precursor oligodendroglial KG-1C cell line to herpes simplex virus type 1 (HSV-1) was investigated. Infection of KG-1C cells was characterized by a high level of virus production and a notable progression of the cytopathic effect. After infection, there was a significant shut-off of host mRNA translation, which was correlated with evident synthesis of viral proteins. An examination by electron microscopy of the infected cells revealed the presence of large clusters of mitochondria located in the proximity of intracellular HSV-1 particle groups. In addition, transmission electron microscopy and nuclear fluorescence analysis showed neither signs of chromatin condensation nor of apoptotic bodies. Furthermore, procaspase-3 remained uncleaved, suggesting that apoptosis does not take place, at least in this system. Finally, expression and localization of MAL2, a subpopulation of detergent-insoluble lipid raft protein, was studied. Detection of MAL2 significantly increased after infection and it was colocalized with HSV-1 proteins. From these findings the authors conclude that human oligodendrocyte-like cells are highly susceptible to HSV-1 infection. The implications of this for central nervous system viral infection are discussed.

[Herpes and skin lesions: what's new?]

The spectrum of clinical lesions of herpes has grown, since the research of viruses by PCR permitted to bind to their etiology discrete or atypical lesions, and even, to display periods of asymptomatic viral excretion. These variable clinical aspects depend on the balance between, on the one hand, the qualitative and quantitative virulence of HSV and, on the other hand, the quality of the immunological defenses of the patient. So, "herpetic primary infection" and "herpetic recurrences" are serological definitions; the clinical aspects of the different stages can be interchangeable. Cultures or PCR and type-specific serologies also showed the increased frequency of HSV1 in genitals, explained by the increased oro-genital sex, since the beginning of AIDS.

Oligodendrocytes from human donors differ in resistance to herpes simplex virus 1 (HSV-1)

Primary cultures of human oligodendrocytes (HOLs) were established from six different donors. Differences in resistance to infection with herpes simplex virus 1 (HSV-1) were determined between the primary cultures of HOL in tissue culture infective dose 50 (TCID(50)), indirect immunofluoresence (IF), and serial electron microscopy (EM) studies. Virus production at different multiplicities of infection (MOIs) indicated that differences in HSV-1 replication were statistically significant and MOI-dependent. Overall, virus yield from the HOL cultures infected at an MOI of 1 increased up to 6 days postinfection (PI); no additional enhancement occurred at 7 days PI. However, differences in the replication capacity of the six HOL cultures observed at 5 days PI persisted at 6 and 7 days PI. When taken together, the results of these investigations indicate that, similar to experimental animals, resistance to HSV-1 differs between primary cultures of HOL and is donor-dependent. The results also raise the possibility that similar to experimental animals, resistance to HSV-1, mediated at the level of HOL, may be genetically determined. Furthermore, permissive infections of primary cultures of HOL were established with HSV-1 over a wide range of MOIs, similar to results obtained with viral infection of primary murine oligodendrocytes, but neither latent nor abortive infections of HOL were induced in vitro, even at very low MOIs. Resistance to HSV-1, mediated by glial cells, is a nonimmune mechanism that may influence the development of acute CNS infection in man as well as individual susceptibility to this virus.