Predicted indirectly recognizable HLA epitopes presented by HLA-DR correlate with the de novo development of donor-specific HLA IgG antibodies after kidney transplantation.

BACKGROUND HLA class-I mismatches selectively induce antibody formation after kidney transplantation. The de novo development of donor-specific IgG HLA class-I antibodies may be dependent on the HLA class-II background of the patient by presenting T-helper epitopes within the recognized HLA class-I antigens. METHODS The correlation between antibody production against mismatched donor human leukocyte antigens (HLA) class I and the number of HLA class II-restricted predicted indirectly recognizable HLA epitopes (PIRCHE-II) in the respective HLA class-I mismatches was investigated. To this end, we analyzed sera taken after nephrectomy from a cohort of 21 non-immunized individuals that received a renal transplant. RESULTS Fourty-nine HLA class-I mismatches were found which all contained immunogenic eplets according to HLAMatchmaker. Donor specific HLA antibody responses were detected against 38 HLA class-I mismatches after nephrectomy. These mismatches were found to contain a larger number of PIRCHE-II when compared to mismatches which did not induce donor specific HLA antibodies. Most PIRCHE-II (68%) were not part of an eplet as defined by HLAMatchmaker. CONCLUSIONS Our data suggest that presentation of donor-derived HLA class-I peptides by recipient HLA class-II molecules plays a significant role in de novo development of donor-specific IgG HLA antibodies.