Dual dynamics of persistence and recruitment characterise the ACPA-expressing B cell response in rheumatoid arthritis

Rheumatoid arthritis, a prototypic autoimmune disease, is characterised by the presence of anticitrullinated protein antibodies (ACPAs). Unlike responses to recall antigens, ACPA-expressing B cells display a continuous phenotype of recent activation, even in patients with sustained clinical remission, indicating that these cells are continuously activated over long periods without 'dying out' or acquiring a resting or anergic phenotype. To elucidate whether this persistent activation reflects ongoing stimulation of the same B cell clones or recruitment of new cells, we longitudinally analysed ACPA B cell dynamics.

ACPA-expressing B cells were isolated using tetramer-based flow cytometry. One thousand five hundred eighty-one B cell receptor sequences were determined by Smart-Seq2-based immunoglobulin-gene amplification and paired heavy/light-chain Sanger sequencing. Antigen reactivity was validated by producing and testing 414 monoclonal antibodies.

The data obtained show that ACPA repertoires are polyclonal with oligoclonal expansions and skewed variable gene usage, increased lambda-to-kappa ratios, and extensive somatic mutations. Clonal phylogenetic analysis revealed the presence of highly mutated clones persisting over time, coexisting with newly appearing, lowly mutated expanded families. Remarkably, multiple clonal families could be traced over a period of 8 years.

These observations demonstrate that the ACPA-expressing B cell population includes persistent and newly recruited cells that together fuel this ongoing autoimmune response. These data provide insights into B cell autoreactivity and its seemingly exhaustless persistence in a prominent human autoimmune disease by indicating that human autoreactive B cell populations are not static but continuously reshape under chronic antigen stimulation.