The association among allelic differences in HLA expression levels and disease were reported for single HLA alleles/loci such as HLA-B expression and immunoglobulin A (IgA) deficiency (17); HLA-C expression and HIV control (18–20); Crohn disease (21), and acute graft-vs.-host disease (GVHD) (22); HLA-DQ and HLA-DR expression and cystic fibrosis (23); HLA-DP expression and hepatitis B virus infection (24) and acute GVHD (25); and HLA-DRB5 and interstitial lung disease (26). The gene discussed is HLA-DPB1; the disease is acute graft versus host disease.