Concepts of viral pathogenesis of multiple sclerosis.

Viral infections have long been suspected to cause or modulate the pathogenesis of multiple sclerosis. Recently, two viruses in particular have been associated with multiple sclerosis: human herpesvirus-6 and a retrovirus termed multiple sclerosis-associated retrovirus, which is a member of the human endogenous retrovirus-9 family. Reports on the detection of human herpesvirus-6-encoded proteins in and around multiple sclerosis lesions are intriguing. Serological and polymerase chain reaction analyses looking for signs of reactivation of human herpesvirus-6 in multiple sclerosis patients are ambiguous, however. If human herpesvirus-6 does play a role as an initiator or amplifier of inflammatory lesions in some multiple sclerosis patients, these individuals might benefit from antiviral therapy.