T cells recognize peptide antigen bound in the groove of MHC molecules by means of the their T cell receptor (TCR). Variable regions on both the a and b chains(Va and Vb) are involved in the binding of the MHC/peptide complex. However, there exists a class of antigens, called superantigens, which binds a different region of MHC class II molecules and activates T cells depending solely on the family of Vb that the TCR utilizes. Superantigens are encoded endogenously by mouse mammary tumor viruses (mtv) in the mouse genome, and are synthesized exogenously by bacterial enterotoxins as well as some viruses. Encounter of these superantigens in the peripheral immune system leads to first T cell activation, followed by tolerance induction. Autoimmune diseases are often attributed to activation of self-reactive T cells specific for a restricted epitope on a self antigen. In cases such as these, it would be useful to be able to induce tolerance in a specific group of T cells. Therefore, experiments have been initiated to create a hybrid superantigen that maintains the tolerance-inducing activity of a superantigen yet can be directed towards any desired T cell. The initial construct was created by joining the nonpolymorphic region of the gene encoding mtv 7 to a nucleotide sequence encoding the peptide antigen 91-104 of moth cytochrome C. This construct will be expressed in a baculovirus expression system, purified, then characterized for its ability to bind MHC molecules. Finally, the molecule will be analyze for its ability to induce tolerance in mice expressing a transgenic T cell receptor specific for the cytochrome C peptide. Experiments will also be conducted in normal mice. The ultimate goal is to extend these experiments to a model autoimmune disease in which the construct will be altered to express the epitope of a self peptide involved in the disease.
