Epitope mapping of human monoclonal antibodies to HLA-B27 by using natural and mutated antigenic variants

The epitopes defined by three human monoclonal antibodies (mAbs) (Tr3B6, TrCG10, TrBH12) against HLA-B27 have been mapped by flow cytometry. For this purpose we used murine transfected cells expressing at their surface hybrid antigens between HLA-B7 and -B27 and, in addition, Epstein-Barr virus cells lines expressing the six HLA-B27 alleles B^*2701 to B^*2706. The results indicated that the mAbs are domain specific. TrBH12 recognizes the first external (alpha-1) domain. Residues critical for the TrBH12 epitope are located in the alpha-1 helix and include the polypeptide stretch 63–76 plus a critical amino acid at position 77. Tr3B6 binds the second external (alpha-2) domain, and one mutation (VAL¹⁵²→GLU¹⁵²) destroyed its epitope. TrCG10 also binds the alpha-2 domain.