ERVW-1 and rheumatoid arthritis: A few recent examples include i) the possible association of Rec (HERV-K) with germ-cell tumors [31], ii) the immunosuppressive abilities of HERV-H Env in a murine cancer model resulting in disturbed tumor clearance [32] and iii) the possible superantigenic (SAg) properties of envelopes from HERV-K and HERV-W [33,34] and the increased activity of such proviruses in multiple sclerosis [34], rheumatoid arthritis [35], schizophrenia [36] and type-1 diabetes [33].