HLA-DRB1 and thrombotic thrombocytopenic purpura: Moreover, this cross-sectional study further reports a peripheral blood RGS, elevated expression of HLA-DRB1 and-DRB5 transcripts, and elevated expression of a discrete set of NK and T lymphocyte expressed immune genes as the first transcriptional correlates of relapse in ADAMTS13-deficient TTP.