Work

Identification of the central tolerance checkpoint for autoreactive proteinase 3+ B cells in human bone marrow

Year: 2024

Type: article

Abstract: Major target antigens of ANCA-associated vasculitis (AAV) are myeloperoxidase (MPO) and proteinase 3 (PR3). High-affinity MPO- and PR3-ANCA immunoglobulins are produced by antigen-experienced, class-switched autoreactive B cells. To prevent autoreactivity, B cells are subjected to several self-tolerance checkpoints, from the early immature stages in the bone marrow (BM), collectively called “central tolerance”, to late mature stages, collectively called “peripheral tolerance”; the latter was recently elucidated for autoreactive PR3 + B cells. Here we investigated central tolerance controlling immature PR3 + B cells in the BM before their migration into the periphery as transitional B cells. We applied an established flow cytometry-based method using labeled recombinant PR3 (rPR3) to identify the PR3 + B cells to compare the phenotype of PR3 + B cells in paired samples of BM mononuclear cells (BMMC) and peripheral blood mononuclear cells (PBMC) of non-vasculitis controls (No-AAV), and PBMC of patients with PR3-ANCA-associated vasculitis (PR3-AAV). We observed that the proportion of PR3 + B cells within BMMC was higher (median [IQR]; 1.98 % [1.77–2.75]) than within PBMC of No-AAV (0.9 % [0.63–1.44], p < 0.01 by paired comparison) and similar to their proportion within PBMC of patients with PR3-AAV (1.82 % [1.66–3.21]; p > 0.05). Within CD24 ++ CD38 ++ B cells, the subset of B cell migrating from BM to the periphery, BMMC contained a greater proportion of PR3 + B cells as compared to PBMC in No-AAV (3.35 % [1.99–4.92] versus 1.23 % [0.62–1.55], p < 0.01), showing different surface markers of maturation (i.e. higher proportion of CD27 − CD10 + and lower expression of CD21, IgD, IgM). Importantly, we observed a significant decline of the PR3 + fraction from the immature subset (IgD − IgM + ; 2.80 % [1.23–4.02]) to the early transitional subset (IgD + IgM + ; 1.76 % [0.96–2.68], p < 0.01) in BMMC, while no significant reduction was observed between the early transitional of BMMC and the transitional compartment of PBMC in No-AAV (1.26 % [0.62–1.56], p > 0.05). In conclusion, to prevent PR3-related autoimmunity, autoreactive PR3 + B cells pass a stringent selection in the BM, and their removal by central tolerance checkpoint activity occurs mainly between T1-like/immature to T2-like/early transitional B cells of BMMC. • The proportion of proteinase 3 (PR3 + ) B cells within bone marrow mononuclear cells (BMMC) is higher than within peripheral blood MC (PBMC) of non-vasculitis controls (No-AAV), and similar to that one within PBMC of PR3-ANCA associated-vasculitis patients (PR3-AAV). • Within CD24 ++ CD38 ++ B cells, BMMC contains the greatest proportion of PR3 + B cells as compared to PBMC in No-AAV. • There is a significant decline of the PR3 + fraction from immature subset to early transitional subset within BMMC, representing the tolerance checkpoint contributing the most to PR3 + B cell removal in No-AAV.

Source: Journal of Autoimmunity

DOI: 10.1016/j.jaut.2024.103330