The invention provides methods of treating a mammal (e.g., a human) having or at risk of having an autoimmune disease by administering a composition that includes all or a portion of a viral polypeptide or a nucleic acid encoding a viral peptide (e.g., a live, killed, attenuated, or inactivated virus) or a composition that includes an immunosuppressive agent (e.g., an anti-CD3 antibody), and compositions for use in treating an autoimmune disease in the mammal.
