Immunomodulation of experimental allergic encephalomyelitis by antibodies to the antigen-Ia complex

Autoimmune diseases occur when T lymphocytes become activated on recognizing self antigen linked to the autologous class II molecule of the major histocompatibility complex (MHC). The resulting complex of antigen MHC T-cell receptor could be a target for treatment of autoimmune diseases. Studies in which each component is blocked separately might be limited by interference in non-relevant immune responses that either use the same set of T-cell-receptor V gene segments or are linked to the same MHC. We report here an attack by a specific antibody on the unique antigenic site formed by the binding of two components of the trimolecular complex, the autoantigen bound to the self MHC. We tested its effect in experimental allergic encephalomyelitis, an acute neurological autoimmune disease which is widely regarded as a model for autoimmune disorders and which is mediated by CD4+ T cells recognizing myelin basic protein (BP), or its peptides, in association with self Ia. We made monoclonal antibodies which bound only the complex of BP and I-As. These antibodies blocked the proliferative response in vitro to the encephalitogenic determinant of BP and reduced the response to intact BP, without affecting the response to a nonrelevant antigen-purified protein derivative of tuberculin presented on syngeneic macrophages. They also inhibited experimental allergic encephalomyelitis in H-2s mice. Hence, antibodies directed specifically to the autoantigen-Ia complex, may offer a highly selective and effective treatment in autoimmune diseases.