[Immune-mediated thrombotic thrombocytopenic purpura and susceptible HLA alleles]

Thrombotic thrombocytopenic purpura (TTP) is an extremely rare and fatal thrombotic disorder characterized by impaired enzyme activity of von Willebrand factor cleaving protease, also known as ADAMTS13. Immune-mediated TTP (iTTP) is an acquired form of TTP caused by the production of auto-antibodies against ADAMTS13. The pathophysiology of autoimmune disorders is multifactorial, with several human leukocyte antigen (HLA) alleles identified as a genetic risk factor for autoimmune diseases known as susceptible HLA. In the early 2010s, three distinct European groups revealed that DRB1^*11 is one of the most susceptible alleles in acquiring iTTP among Caucasians based on HLA typing data. Several in silico predictions for allele-restricted ADAMTS13 epitopes against T cells are made in this context, followed by an in vitro validation employing mass spectrometry using eluted peptides and T-cell assays. However, similar analyses in a genetically distinct Japanese population have not yet been conducted. We used next-generation sequencing to perform HLA typing for 52 Japanese patients with iTTP from 19 institutes. Our detailed analysis revealed that the specific allele DRB1^*08:03 was identified as a genetic risk factor for iTTP in Japanese patients, but there were no statistically significant differences in the allele frequency of DRB1^*11 between iTTP and healthy controls.