Anti-HLA DP antibodies have been associated with renal allograft rejection and/or positive crossmatches. While the reactivity of anti-HLA DP Beta antibody (DPΒ-Ab) is described, less is known about the prevalence and patterns of anti-HLA DP Alpha antibodies (DPΑ-Ab).

Methods. We identified 186 consecutive renal transplant candidates or recipients tested between 2007–2012 for DPΑ- or DPΒ-Ab. The HLA-DP typing was performed by rSSO or SSP. Strong reactive/high-level antibodies were considered > 8000 mean fluorescence intensity (MFI) on Luminex single-antigen beads.

Results. One patient (0.5%) had DPΑ-Ab only, 139 (75%) had DPΒ-Ab only, and 46 (25%) exhibited both DPΑ- and DPΒ-Ab. The epitope distribution of DPΒ-Ab is summarized in table 1. Sixty-seven patients developed antibodies against a single DPΒ epitope, 67 towards two DPΒ epitopes, and 26 patients against more than two DPΒ epitopes.

High-level antibodies were detected in 72 cases (39%) and were associated with DPΑ reactivity: 77% (36/47) of cases with DPΑ-Ab + DPΒ-Ab were strong, versus only 25% (36/139) cases with DPΒ-Ab, p<0.0001. Furthermore, antibodies towards Α alleles DPA1*01:xx were associated with 84-87GGPM Β epitope, while antibodies towards Α alleles DPA1*02:xx were more prevalent in cases with 85-87EAV Β epitope (table 2).

Conclusions. One quarter of renal transplant candidates/recipients with anti-HLA DP alloantibody have shown reactivity towards the Α chain. Antibodies against Α alleles HLA-DPA*01:xx were associated with antibodies towards Β-84-87GGPM epitope, while antibodies against Α alleles HLA-DPA*02:xx correlated with antibodies towards Β 85-87EAV epitope. Furthermore, the presence of HLA-DPΑ reactivity was associated with high level of alloantibodies.

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