Peptide-based molecular analyses of HLA class II-associated susceptibility to autoimmune diseases.

Recent advances in knowledge of crystal structures of MHC class II molecules has advanced understanding of the molecular basis for interactions between peptides and HLA class II molecules. Polymorphism of HLA class II molecules influences structures of peptides bound to HLA class II molecules. To better understand mechanisms related to particular HLA class II alleles and autoimmune diseases, it is important to identify self-peptides presented by disease-susceptible HLA class II molecules and triggering disease-causative autoreactive T cells. Autoimmune diseases occur in Caucasians, Blacks and Asians, albeit with a different incidence. In some autoimmune diseases, disease-susceptible HLA class II alleles are closely related but different, and clinical manifestations of diseases differ among ethnic groups. These phenomena strongly suggest that difference in autoimmune self-peptide(s) in the context of disease-susceptible HLA class II molecules may explain the different clinical manifestations of diseases. Therefore, a comparison among disease-susceptible HLA class II alleles, autoimmune self-peptides and clinical manifestations of autoimmune diseases in different ethnic groups would be instructive. We directed efforts to determining: (1) HLA-class II alleles specific to Asian populations and which are associated with susceptibility to autoimmune diseases, (2) binding-peptide motifs for these HLA class II molecules, and (3) self-peptides presented by susceptible HLA class II molecules to stimulate autoreactive T cells related to the development of autoimmune diseases in Asians. In this review, our related recent investigations are described and the uniqueness of HLA class II-associated autoimmune diseases in Asians is given emphasis.