High-Throughput Single-Cell Analysis of B Cell Receptor Usage among Autoantigen-Specific Plasma Cells in Celiac...

Characterization of Ag-specific BCR repertoires is essential for understanding disease mechanisms involving humoral immunity. This is optimally done by interrogation of paired H chain V region (V_H) and L chain V region (V_L) sequences of individual and Ag-specific B cells. By applying single-cell high-throughput sequencing on gut lesion plasma cells (PCs), we have analyzed the transglutaminase 2 (TG2)-specific V_H:V_L autoantibody repertoire of celiac disease (CD) patients. Autoantibodies against TG2 are a hallmark of CD, and anti-TG2 IgA-producing gut PCs accumulate in patients upon gluten ingestion. Altogether, we analyzed paired V_H and V_L sequences of 1482 TG2-specific and 1421 non-TG2-specific gut PCs from 10 CD patients. Among TG2-specific PCs, we observed a striking bias in IGHV and IGKV/IGLV gene usage, as well as pairing preferences with a particular presence of the IGHV5-51:IGKV1-5 pair. Selective and biased V_H:V_L pairing was particularly evident among expanded clones. In general, TG2-specific PCs had lower numbers of mutations both in V_H and V_L genes than in non-TG2-specific PCs. TG2-specific PCs using IGHV5-51 had particularly few mutations. Importantly, V_L segments paired with IGHV5-51 displayed proportionally low mutation numbers, suggesting that the low mutation rate among IGHV5-51 PCs is dictated by the BCR specificity. Finally, we observed selective amino acid changes in V_H and V_L and striking CDR3 length and J segment selection among TG2-specific IGHV5-51:IGKV1-5 pairs. Hence this study reveals features of a disease- and Ag-specific autoantibody repertoire with preferred V_H:V_L usage and pairings, limited mutations, clonal dominance, and selection of particular CDR3 sequences.