Immune dysregulation in MS is likely to be an early event [18, 22, 25, 41] preceding the onset of MS disease by many years or a decade [18, 22, 25] . It should thus be emphasized that the epidemiologic observations on the possible infectious background of MS partly, if not predominantly, reflect the earliest stage in the natural history of MS. A situation similar to that postulated here has been described in malignant melanoma in which, as discussed above, cross-reactive protective immune responses are induced by homologous epitopes in BCG, vaccinia and yellow fever vaccines given at least 10 years before the onset of disease [8] [9] [10] [11] . It was suggested that melanocytes in the early stages of malignant transformation, may be eliminated or repaired by CD8 ? T-cells which recognise cells expressing a HERV peptide. This immune reaction seems to suppress the genetic activity of HERV proviruses (env genes) associated with malignant transformation [10, 54, 55] . The HERV env proteins probably impair the redox Table 2 Homologies in proteins of sero-epidemiologic MS-associated pathogens to MS associated EBV-epitopes [34, 35] 