Further studies revealed that HERV-W/MSRV Env pro-inflammatory properties depend on the stimulation of toll-like receptor 4 (TLR4) (Perron et al., 2001; Rolland et al., 2006; Saresella et al., 2009), evoking the same proinflammatory cytokines prevalent in MS, such as interleukins (IL-1, IL-6) and tumor necrosis factor α (Rolland et al., 2005, 2006; Mameli et al., 2007b). Here, TLR4 is linked to myeloid sarcoma.