Comparative study of the diversity of amino acids on human leucocyte antigen class II molecules in patients with acquired aplastic anaemia.

Human leucocyte antigen (HLA) class II molecules are critically involved in the pathology of acquired aplastic anaemia (AA) by regulating the immune response and autoreactive T cell-mediated haematopoietic cell death. In the study, amino acid residue variation and molecular structure of HLA class II have been initially investigated in 96 patients with AA. The frequencies of residues 9 and 57 in pocket 9 (P9) in DQB1, and amino acid positions 9, 11, 13, 16, 26, 38, 67 and 71 in the P4, P6 and P9 pockets in DRB1 were more prevalent among AA patients. By applying a multivariate recursive approach, the DRβ-Gln-16 (OR = 3.003, 95% CI = 1.468-6.145, p_c = 0.003), DRβ-Ala-71 (OR = 1.924, 95% CI = 1.233-3.002, p_c = 0.004) in P4/P7 and DQβ-Asp-57 (OR = 3.483, 95% CI = 1.079-11.242, p_c = 0.037) in P9, these critical residues were significantly discovered as risk amino acid residues on the onset of AA, as well as associated with PNH-type cells and pathological somatic or cytogenetic mutations. In silico structural model analysis showed that identified DRβ-Ala-71 and DQβ-Asp-57 within the antigen-binding groove interacting with a more variable antigenic segments, may impact the repertoire of peptides presented, influence the interface HLA-antigen-T-cell receptor β (TCR β). These findings provided light on the immunogenetic pathophysiology of AA aetiology and their potential impact on upcoming immunotherapies.