As there is evidence of early biochemical and histological changes in the normal-appearing white matter in MS, which appear to be independent of or precede demyelination, the formation of plaques may be incidental to a more primary lesion. The finding of persistently increased levels of IgG in the CSF of patients with MS points to an ongoing immune reaction in the CNS, possible against an infective agent; but virus-specific antibodies account for only a small proportion of IgG in the CSF. Furthermore, in vitro assays of T cell function suggest that there may be a regulator T cell defect in MS. Salk and colleagues (1980) have postulated that MS may be a disorder, attributable to multiple inducing agents, which is potentiated through deregulation of lymphocyte function.