A unique MHCII-binding register correlates with HLA-associated immunogenicity of the major K blood group antigen

Abstract

Abstract Kell is a glycoprotein expressed on red blood cells (RBCs). Its K and k isoforms contain either Met (K antigen) or Thr (k antigen) at position 193. Development of anti-K antibodies following K-mismatched blood transfusions can destroy RBCs, while cross-placental transfer of anti-K antibodies can destroy RBC precursors, resulting in Hemolytic Disease of the Newborn. HLA-DR11, DR13 and DR15 are over-represented among K-immunized patient populations. The immunogenicity of overlapping 15-mer Kell peptides with M193 or T193 at every possible position was investigated by Stephen et al (Blood. 2012;119(23):5563-5574). Surprisingly, peptide W179-M193, with the polymorphic M193T site at the peptide’s C-terminus, was the most effective at stimulating CD4 T cells from K-immunized women. The present study utilized MHCII binding prediction algorithms and quantitative peptide-MHCII binding assays to determine the binding registers, anchor residues and affinities of wild-type, truncated, and sequence-modified Kell peptides. Predictions were generated using IEDB and Propred algorithms. Competitive peptide-MHCII binding assays utilized 13 recombinant HLA-DRB1 monomers, Kell peptides and high-affinity reference peptides. Interestingly, the assays identified a unique binding register (W179-S187) restricted to HLA-DR11 and DR15, in addition to the polymorphic site, suggesting stronger MHCII avidity may explain the increased disease susceptibility associated with these alleles.