The human bone marrow plasma cell compartment in rheumatoid arthritis - Clonal relationships and anti-citrulline autoantibody producing cells
Aase Hensvold, Begum Horuluoglu, Peter Sahlström, Radha Thyagarajan, Juan Sebastian Diaz Boada, Monika Hansson, Linda Mathsson‐Alm, Christina Gerstner, Natalie Sippl, Lena Israelsson, Rikard Wedin, Johanna Stéen, Lars Klareskog, Bence Réthi, Anca I. Catrina, Lina-Marcela Díaz-Gallo, Vivianne Malmström, Caroline Grönwall
Abstract
A majority of circulating IgG is produced by plasma cells residing in the bone marrow (BM). Long-lived BM plasma cells constitute our humoral immune memory and are essential for infection-specific immunity. They may also provide a reservoir of potentially pathogenic autoantibodies, including rheumatoid arthritis (RA)-associated anti-citrullinated protein autoantibodies (ACPA). Here we investigated paired human BM plasma cell and peripheral blood (PB) B-cell repertoires in seropositive RA, four ACPA+ RA patients and one ACPA- using two different single-cell approaches, flow cytometry sorting, and transcriptomics, followed by recombinant antibody generation. Immunoglobulin (Ig) analysis of >900 paired heavy-light chains from BM plasma cells identified by either surface CD138 expression or transcriptome profiles (including gene expression of MZB1, JCHAIN and XBP1) demonstrated differences in IgG/A repertoires and N-linked glycosylation between patients. For three patients, we identified clonotypes shared between BM plasma cells and PB memory B cells. Notably, four individuals displayed plasma cells with identical heavy chains but different light chains, which may indicate receptor revision or clonal convergence. ACPA-producing BM plasma cells were identified in two ACPA+ patients. Three of 44 recombinantly expressed monoclonal antibodies from ACPA+ RA BM plasma cells were CCP2+, specifically binding to citrullinated peptides. Out of these, two clones reacted with citrullinated histone-4 and activated neutrophils. In conclusion, single-cell investigation of B-cell repertoires in RA bone marrow provided new understanding of human plasma cells clonal relationships and demonstrated pathogenically relevant disease-associated autoantibody expression in long-lived plasma cells.