Which HLA antigen would be expected to elicit an HLA antibody response in a kidney transplant recipient with the following HLA type: A*01,03; B*07,14; C*01,04N; DRB1*16,07?

• A. HLA-A*01
• B. HLA-B*14
• C. HLA-C*04
• D. HLA-DRB1*16

Answer: (C)

Antibody formation after transplantation happens when the recipient’s immune system encounters donor HLA antigens that are not expressed by the recipient. In this case, the recipient’s HLA-C type includes C01 and C04N, where C04N is a null allele that is not expressed on the cell surface. If the donor kidney carries C04, this C locus antigen would be a mismatch relative to the recipient. The recipient’s immune system would recognize C04 as foreign and could produce antibodies against it. The other antigens listed (A01, B14, DRB116) are already represented in the recipient’s own HLA type, so they are less likely to provoke a new antibody response in this transplantation scenario. Therefore, HLA-C*04 is the antigen most likely to elicit an HLA antibody response.