HLA-DR antibody epitopes.

A single antigen (SA) Luminex beads assay was used to detect antibody specificities of allosera and monoclonal antibodies. Potential antibody epitopes were mapped by comparing the protein sequence differences of a group of HLA alleles that are either recognized or unrecognized by tested samples. A total of 61 epitopes, including 43 one amino acid (AA) epitopes, 11 two AA epitopes, and 7 epitopes with more than two residues involved, were identified. Among 38 residues constituting DR epitopes, 26 of them located in beta1 domain and 12 located in beta2 domain. Only 42% of beta1 domain epitopes are surface residues, while 83% of beta2 domain epitopes are on an antigen surface. These findings imply that some polymorphic AA residues, especially those on beta1 domain, may be indirectly involved in antibody-antigen interactions. In conclusion, sequence comparison following SA beads tests provides an ideal approach for epitope identification of HLA-specific antibody. Certainly, these identified potential epitopes need to be further proved or disproved by other approaches, such as absorption/elution from SA beads or cell lines, each of which contains unique epitope pattern.