LBP30: THE SPECIFICITY OF HLA-DP ANTIBODIES ARE DEFINED BY TWO DIMORPHIC EPITOPES

Abstract

Aim The presence of HLA-DP antibodies may cause AMR. It has been reported that serologic epitopes of HLA-DP are defined by two sequence dimorphisms based on a small cohort of patients. Our aim was to determine whether the specificity of DP antibodies we identified in a much larger study were explained by these two serologic epitopes, and to characterize their reactivity patterns. Methods Among 2821 renal patients who were analyzed by SAB class II testing, 486 patients displayed HLA-DP antibodies. The association between DP antibody specificities was analyzed by hierarchical clustering to identify potential epitope patterns. 4 Sera displaying strong DP antibodies were then adsorbed by cells carrying the related epitope, the bound antibodies were eluted with acid, placed in a buffered solution and reanalyzed by SAB testing to identify which antigens remained reactive. Results Based on hierarchical clustering analysis, HLA-DP antibodies were categorized into 4 clusters (Fig. 1). These 4 clusters are largely consistent with the serologic groups as described by Cano et al. dependent on the presence of epitopes GPM or EAV at positions 85–87 or the presence of A or E at position 56. Antibodies against cluster 3 (DP6, 3, 14, 9, 17) are most common and were found in 160 patients. In contrast, antibodies against cluster 2 (DP401, 402, 2, 18, 28) are least common. Only 44 patients developed antibodies against cluster 2. This is likely due to the high frequency of this cluster (>60%) in the population. To confirm whether antibodies within each group recognize the same epitope, we performed the cell adsorption-elution assay. For example, we found cells carrying homologous HLA-DP2 can bind antibodies that are against cluster 2 and 4 antigens which share the epitope GPM 85–87 with HLA-DP2. Conclusion DP antibodies recognize two major dimorphic epitopes. HLA-DP epitope matching between the donor and recipient at these two critical epitopes should reduce post-transplant sensitization and improve transplant outcome.