Human leukocyte antigen class I epitopes: Update to 103 total epitopes, including the C locus

Background. Epitopes of human leukocyte antigen (HLA) are the sites to which the antibodies bind. We identify here 103 HLA class I epitopes shared by groups of class I antigens. In particular, our emphasis was on identifying epitopes exclusive to the C-locus antigens or interlocus epitopes among A, B, and C antigens. The use of monoclonal antibodies or alloantibodies eluted from HLA recombinant single antigen cell lines tested with a panel of single antigen beads have proved very useful in the identification of the epitopes. Methods. Alloantibodies absorbed onto then eluted from HLA single antigen cell lines and monoclonal antibodies were tested with a panel of 95 A, B-, and C- single antigen beads and the HLA specificities determined. Each epitope was defined by amino acids shared exclusively by the positive antigens for each antibody. Results. In addition to the 58 A and B class I epitopes identified in an earlier study, we add 45 more new A, B, C epitopes including, for the first time, epitopes found on C locus antigens. Conclusion. Beads bearing single antigens tested with monoclonal or eluted alloantibodies proved very powerful in identifying epitopes shared among HLA antigens. These epitopes are the targets of the antibodies. Antibody specificities to nondonor-specific antigens, often found in sera of transplant patients, can now be understood as reactions to epitopes shared with the donor specific antigens. The importance of identifying these epitopes is that they may be the "transplantation antigens" responsible for antibody-mediated transplant rejection.