Plaque-associated expression of human herpesvirus 6 in multiple sclerosis

Schizophrenia, the heteromodal association neocortex and development: potential for a neurogenetic approach

The heteromodal association neocortex is believed to be a major site of involvement in schizophrenia. This system includes the prefrontal cortex and portions of the superior temporal and inferior parietal cortices, which are linked in cognitive networks observing complex executive functions. The heteromodal cortex is highly elaborated in humans and is believed to continue to develop past birth. The neuropathology of schizophrenia is likely to be heterogeneous and appears to involve developmental abnormalities, with a prominent genetic component. However, the genes involved in the development of the neocortex, and particularly the heteromodal cortex, are not well understood. A candidate-gene approach to schizophrenia using techniques of differential expression might now be feasible and could illuminate the basic neurobiology of the heteromodal cortical network.

Novel human herpesviruses (human herpesviruses 6, 7 and 8)

The number of members in the family Herpesviridae has increased in the last 10 years due to the description of three novel human herpesviruses: human herpesvirus 6 (HHV-6) in 1986, human herpesvirus 7 (HHV-7) in 1990, and human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), in 1994. HHV-6 and HHV-7 were first isolated from blood lymphocyte cultures, while HHV-8 was identified following a specific molecular biology approach in the search for the etiologic agent of Kaposi's sarcoma. The three viruses are lymphotropic, T-cells being the targets of HHV-6 and HHV-7, and B-cells being probably those of HHV-8. The ability to be propagated in cell cultures in vitro differs according to the virus concerned: this can be done readily with HHV-6, with more difficulties in the case of HHV-7, and has not yet been achieved in the case of HHV-8. Human infection with HHV-6 and HHV-7 is ubiquitous, widespread and acquired early in life. HHV-8 epidemiology is still unclear, and there are two hypotheses: a restricted dissemination in the general population like herpes simplex virus type 2, or a widespread infection like all other human herpesviruses. The polymerase chain reaction is the common method for the detection of infection using specific primers and probes for HHV-6, HHV-7 and HHV-8 respectively. Serologic assays are only available for HHV-6 and HHV-7, with limitations being due, in particular, to possible cross-reactions with cytomegalovirus. HHV-6 is the causative agent of exanthem subitum (sixth disease). Its role as an opportunistic agent and immune dysfunction inducer is debated and currently under investigation. The pathogenic role of HHV-7 seems to be modest, with one case of exanthem subitum reported so far. HHV-8 is strongly associated with three diseases: Kaposi's sarcoma, Castleman's disease and body-cavity-based lymphomas. The therapy against these novel viruses has to be considered in the future.

Infection of primary human fetal astrocytes by human herpesvirus 6

Human herpesvirus 6 (HHV-6) is a lymphotropic betaherpesvirus which productively infects human CD4+ T cells and monocytes. HHV-6 is the etiologic agent for exanthem subitum (roseola), and it is well-known that central nervous system complications occur frequently during the course of HHV-6-associated disease. In addition, HHV-6 has been associated with encephalitis or encephalopathy. However, very little is known about its tropism for neural cells. There are reports that HHV-6 may infect some glial cell lines, but whether it can infect any primary neural cells is not known. Our studies show that both HHV-6A (GS) and HHV-6B (Z-29) can infect highly purified primary fetal astrocytes in vitro. Infected cells showed cytopathic effects, forming giant syncytia. In dual immunofluorescence assays, the infected cells were detected by antibodies against the HHV-6 p41 nuclear antigen and glial fibrillary acidic protein, indicating that the infected cells are indeed astrocytes. PCR and Northern (RNA) blot analyses also confirmed that the astrocytes are infected by HHV-6. The progeny virus did not alter its host range and could reinfect T cells as well as primary astrocytes. These findings suggest that infection of primary human astrocytes may play a role in the neuropathogenesis of HHV-6.

Molecular approaches to the identification of unculturable infectious agents

New molecular biologic techniques, particularly representational difference analysis, consensus sequence-based polymerase chain reaction, and complementary DNA library screening, have led to the identification of several previously unculturable infectious agents. New agents have been found in tissues from patients with Kaposi's sarcoma, non-A, non-B hepatitis, hantavirus pulmonary syndrome, bacillary angiomatosis, and Whipple's disease by using these techniques without direct culture. The new methods rely on identifying subgenomic fragments from the suspected agent. After a unique nucleic acid fragment belonging to an agent is isolated from diseased tissues, the fragment can be sequenced and used as a probe to identify additional infected tissues or obtain extended portions of the agent's genome. For agents that cannot be cultured by standard techniques, these approaches have proved invaluable for identification and characterization studies. Applying these techniques to other human diseases of suspected infectious etiology may rapidly elucidate novel candidate pathogens.