Systemic autoimmune diseases are an important cause of morbidity and mortality in the human population (Borchers et al., 2000). The use of experimental models has increased the knowledge of autoimmune disease mechanisms (Bigazzi, 1998). Heavy metals, especially mercury (Hg), generate autoimmune responses which are relevant with regard to human diseases (Bigazzi, 1999), creating an opportunity to investigate the effects of immunomodulating agents on autoimmunity. The administration of subtoxic doses of heavy metals like mercury into the genetically susceptible mice, leads to systemic autoimmune diseases which are induced to develop antinucleolar antibodies (ANoA) and systemic immune complex (IC) deposits. (Havarinasab and Hultman, 2006). Rodents susceptibility to mercury induced autoimmunity is MHC dependent (Layland and Wulferink. 2004).

 CD4⁺CD25⁺ regulatory T (Treg) cells that express Forkhead box P3 (FoxP3) are the main factors for controlling autoimmune responses. Certain strains of mice develop Treg cells which suppress development of unspecified ANA autoantibodies induced by heavy metals like Hg. Susceptible mice pretreated with Hg showed resistance to induce systemic autoimmunity in the later stage.

 CD4⁺CD25⁺ Ts cells, can suppress the development of different autoimmune diseases, immunopathological conditions and responses to foreign antigens.(Layland and Wulferink. 2004).