Specific amino acid patterns define split specificities of HLA-B15 antigens enabling conversion from DNA-based typing to serological equivalents

Abstract

The HLA-B15 typing by serological approaches defined the serological subgroups (or splits) B62, B63, B75, B76, B77 and B70 (B71 and B72). The scarcity of sera with specific anti-HLA antibodies makes the serological typing method difficult to discriminate a high variety of HLA antigens, especially between the B15 antigen subgroups. Advancements in DNA-based technologies have led to a switch from serological typing to high-resolution DNA typing methods. DNA sequencing techniques assign B15 specificity to all alleles in the HLA-B*15 allele group, without distinction of the serological split equivalents. However, the presence of antibodies in the patient defined as split B15 antigens urges the identification of HLA-B*15 allele subtypes of the donor, since the presence of donor-specific antibodies is an important contraindication for organ transplantation. Although the HLA dictionary comprises information regarding the serological subtypes of HLA alleles, there are currently 394 B15 antigens out of 516 in the IPD-IMGT/HLA database (3.38.0) without any assigned serological subtype. In this regard, we aimed to identify specific amino acid patterns for each B*15 serological split, in order to facilitate the assignment of B*15 alleles to serological equivalents after high-resolution molecular typing. As a result, serological specificities of 372/394 not yet assigned alleles could be predicted based on amino acid motifs. Furthermore, two new serological types were identified and added, B62-Bw4 and B71-Bw4.

A new strategy for systematically classifying HLA alleles into serological specificities

“…The other differences were observed in outlier alleles. For example, the alleles HLA-B*15:46, -B*15:53, -B*15:106, -B*15:212, and -B*15:525 were not previously assigned to any broad HLA-B15 serotypes, 74 on the other hand, these alleles were assigned as B4005 in the present study. The allele HLA-B*15:46 was assigned as HLA-B72 in the HLA Dictionary 2008, but carries a mismatch at residue 45 K compared with the serotype HLA-B72 (45E).…”

“…A comprehensive evaluation of the splits corresponding to the HLA-B*15 alleles was performed in the present study; the results were concordant with those reported in a recent publication from Duygu and collaborators. 74 In both studies, similar sets of residues were used to define the broad HLA-B15 and -B70 serotypes except for residues 24 and 77 that were used for HLA-C serotypes in the present study, and residue 163 that was not used by Duygu and collaborators (Table 3C). Supplemental Table 11 contains 41 HLA-B*15 alleles that were discussed by Duygu and collaborators 74 and the serotype assignments in this study.…”

“…Only a few studies correlating serologic testing with molecular typing have been performed to present. 68,74 In addition, a small number of the serologic typing reagents have been characterized with novel and refined antibody screening technologies that include testing cells expressing a single expressed HLA antigen 107 or solid phase assays with single antigen preparations. 108 Therefore, the currently recognized HLA antigens do not identify the full extent of possible serotypes that can be defined by reagents detecting the most common immunogenic HLA epitopes, and do not include all specificities corresponding to some loci.…”

“…In both studies, similar sets of residues were used to define the broad HLA‐B15 and ‐B70 serotypes except for residues 24 and 77 that were used for HLA‐C serotypes in the present study, and residue 163 that was not used by Duygu and collaborators (Table 3C). Supplemental Table 11 contains 41 HLA‐B*15 alleles that were discussed by Duygu and collaborators 74 and the serotype assignments in this study. The minor differences were because of the differences in these residues (Supplemental Table 11).…”

“…Recently, serological specificities were predicted for HLA‐B*15 alleles based on amino acid sequence patterns 74 . Using the information of the key AA residues that define serotypes, a computational tool that performs virtual serotype assignments for the HLA‐A, ‐B, ‐C, ‐DRB1, ‐DRB3/4/5 and ‐DQB1 alleles that have little or no information about their serological specificities is designed in this study.…”