Does a retrovirally encoded superantigen cause multiple sclerosis?

Retroviruses are commonly associated with neurological disease in animals, for example, inflammatory encephalomyelopathies of sheep (visna virus),' horses (equine infectious anaemia virus), goats (caprine encephalitis/arthritis virus)2 and mice (murine leukaemia virus).3 The first retrovirus shown to be pathogenic in humans was discovered by Gallo's group4 who demonstrated that human lymphotrophic virus type-i (HTLV1) was the cause of adult T-cell leukaemia (ATL). Subsequently this virus was associated with a myelopathy endemic in the Caribbean56 and Japan,' a condition now called tropical spastic paraparesis (TSP) or HTLV-1 myelopathy (HAM). TSP is an inflammatory demyelinating and degenerative myelopathy predominantly affecting the thoracic and lumbar regions causing a progressive paraparesis with sphincter involvement.89 Immune mechanisms probably play an important part in the pathogenesis of this condition.'0 The discovery of the association of HTLV-1 with TSP and the similarities between TSP and the primary progressive form of multiple sclerosis (MS) led to an intensive search for retroviruses in the latter condition. Two groups of workers" 12 claimed that an HTLV-1 like agent was indeed associated with MS and considerable excitement engendered by the observation that using DNA amplification techniques (polymerase chain reaction, PCR) sequences of DNA homologous with parts of the HTLV1