Th2 and Th1 autoreactive anti-class II cell lines in the rat suppress or induce autoimmunity.

It is now currently thought that Th1 autoreactive cells may induce organ specific autoimmune disease and in these situations Th2 cells are considered as regulatory cells. However, in other situations Th2 cells may be pathogenic. Thus, some chemicals (HgCl2, gold salts or D-penicillamine) may induce Th2-mediated systemic autoimmune disorders in susceptible Brown-Norway (BN) rats. In contrast, HgCl2 induces non antigen specific immunosuppression in Lewis (LEW) rats and protects this strain against organ-specific autoimmune diseases such as experimental autoimmune encephalomyelitis (EAE). Anti-self MHC class II T cells have been detected in both susceptible and resistant strains upon exposure with these chemicals. Autoreactive T cell lines that recognize self MHC class II molecules have been derived from gold salt-injected BN rats (BNAu lines) and from HgCl2-injected LEW rats (LEWHg lines). BNAu T cell lines produced IL-4 and transferred antibody-mediated autoimmunity in BN rats deprived of CD8+ cells. In contrast, HgCl2 protects susceptible rats from Th1-mediated autoimmunity, (autoimmune uveoretinitis). LEWHg lines produced IL-2, IFN-gamma and TGF-beta and were able to protect LEW rats against cell-mediated autoimmunity (EAE) and (LEW x BN)F1 hybrids from antibody-mediated, HgCl2-induced autoimmunity. Several points will be discussed: the specificity of these autoreactive T cells, the mechanisms by which chemicals may induce these cells and the mechanisms by which the immune system maintains or reestablishes self tolerance in rats exposed to these agents.