Different groups have observed retrovirus particle (RVP) production in cell cultures from patients with multiple sclerosis (MS). This in vitro production appeared relatively specific for MS versus healthy controls, but was likely to be enhanced or activated by infectious triggers such as Herpesviruses (e.g. HSV, EBV). Independent molecular analysis of retroviral RNA associated with RVP revealed two different genetic families of endogenous retroviral elements (HERV): MSRV/HERV-W and RGH/HERV-H. Interestingly, these sequences were detected by mutually exclusive primers in RT - PCR amplifications. Surprisingly, these two HERV families both contain an ancestral proviral copy inserted in chromosome 7q21-22 region at about 1 kb of distance of each other. Another HERV-W proviral sequence is located within a T-cell alpha-delta receptor (TCR) gene in chromosome 14q11.2 region. Interestingly, these two regions correspond to genetic loci previously identified as potentially associated with 'multigenic' susceptibility to MS and TCR alpha chain genetic determinants have been reported to be statistically associated with MS. A plausible role for infectious agents triggering a co-activation of the chromosome 7q HERV tandem (replicative retrovirus and/or other virus and/or intracellular bacteria) and, eventually, other HERV copies, is discussed. The role of particular HERV polymorphism and the production of pathogenic molecules (gliotoxin and superantigen) possibly associated with retroviral expression are also evoked. An integrative concept of pathogenic 'chain-reaction' in MS involving several step-specific pathogenic 'agents' and 'products' somewhat interacting with particular genetic elements would federate most partial data obtained on MS, including retroviral expression.