The "trigger" of an autoimmune disease could be linked to environmental insults, such as viruses. A T cell co-expressing TCRs specific for a self-antigen and a foreign antigen could potentially allow for autoreactive T cells to be activated if the host is exposed to that foreign antigen. The activation of a subset of T cells could than lead to tolerance being broken and the initiation of an autoimmune disease if these T cells experienced a particular organ or tissue that expressed the self-antigen for the other TCR expressed at the surface of the T cell. In support of a role for dual TCRs in autoimmune diseases, work performed in our laboratory characterized autoreactive CD8 + T cells isolated from the spleens of Theiler's murine encephalomyelitis virus (TMEV)infected SJL/J mice [65] . In vitro assays testing CD8 + T cell killing activity found a population of CD8 + T cells that killed uninfected syngeneic cells [65] . Adoptively transferring these TMEV-specific autoreactive CD8 + T cells into non-infected SJL/J mice caused CNS pathology [65] . Further support for the importance of the mechanism by which viral infection could induce an autoimmune disease through dual TCR-expressing T cells was performed by Ji et al.