It is likely that a diverse range of MS-associated infectious agents other than EBV and, possibly, CP, is involved in the generation and maintainance of the postulated immune responses associated, beneficially or detrimentally, with MS. By generating populations of T reg s or of competing T-helper cells, such infectious agents would play a role in the generation of various immunological networks based on T reg s which, in turn, would facilitate the expansion or suppression of populations of effector T cells including epitope-specific CD8 ? T-cells. The epitope recognised by these T-cells should be common to the MS-associated infectious pathogens and to one or more cellular gene products. The latter was preferentially sought in HERVs since patients with MS expressed HERV-W env at higher copy numbers as compared with controls (P = 0.00003) [32, 45] and a HERV-K18 env genotype was described as a risk factor for MS [46] .