HLA D (-P,-Q,-R) genes are members of the Major histocompatibility complex (MHC) gene family and have analogs in other mammalian species. In mice the MHC locus known as IA is homologous to human HLA DQ. Several autoimmune diseases that occur in humans that are mediated by DQ also can be induced in mice and are mediated through IA. Myasthenia gravis is an example of one such disease. Linking specific sites on autoantigens is more difficult in humans due to the complex variation of heterologous humans, but subtle differences in T-cell stimulation associated with DQ-types has been observed. These studies indicate that potentially a small change or increase in the presentation of a potential self-antigen can result in autoimmunity. This may explain