Incidence and specificity of anti HLA-DP antibodies in kidney retransplants patients

Not only HLA-DR and -DQ but also -DP antigen are constitutively expressed on endothelial cells . Thus, HLA.DP molecules may play the role of alloantigens in kidney transplantation and consequently induce humoral response. We evalueted the presence of anti HLA-DP antibodies in sera from 81 patients who re-entered the waiting list after kidney graft loss and were anti HLA class II antibody-positive using flow cytometric technique. We characterized DR, DQ and DP specificities of detected antibodies using microbeads coated with single HLA alleles. In particular, a panel of 8 DPB1allele coated-beads (0101, 0201, 0301, 0401, 0501, 1101,1301 and 1701) was used. Anti HLA-DP antibodies were detected in sera from 38 (46,9%) patients. Six subjects produced only anti HLA-DP antibodies while 32 also produced anti HLA-DR and/or anti HLA-DQ antibodies. Anti HLA-DP antibody specificities has been correlated to particular motifs of the six hypervariable regions within exon 2 of DP gene. Forty-five patterns of antibody specificities were identified. In all but 7 cases, a "single motifs" was sufficient to account for all anti HLA-DP specificities present in the serum. The 84-87 DEAV motif was involved in development of 23 (51%) antibody patterns.This event determined the production of antibodies specific for multiple DPB1 alleles sharing the same motif (0101,0301,0501,1101, 1301 and 1701). The remaining antibody patterns were due to 55-57DED (16%), 65-69I-E (16%), 33-36E-FV (7%), 84-87GGPM (4%), 76V (4%) AND 194Q(2%). This study shows a high incidence of HLA-DP sensitization in retransplant patients. The anti-HLA antibody patterns result specific for motifs shared between multiple alleles. All these findings demonstrate an important role of HLA-DP compatibility in kidney transplantation.