Identification and characterisation of anti-citrullinated protein antibody (acpa)-producing b cells in patients with rheumatoid arthritis (ra)

This thesis describes the characterisation of citrullinated antigen-specific B cells in patients with rheumatoid arthritis (RA). These cells express and secrete anti-citrullinated protein antibodies (ACPA), which represent the most specific autoantibody system in RA. We started out by identifying ACPA-producing B cells in peripheral blood. FACS sort followed by culture showed that these cells are not confined to the memory B cell subpopulation, as circulating plasmablasts/cells were found that spontaneously produced ACPA in culture (chapter 2). Further characterisation showed an increased frequency of ACPA-secreting plasma cells in synovial fluid (SF), i.e. at the site of inflammation, which harbours the capacity to form a survival niche in culture that promotes sustained (auto-)antibody production (chapter 3). Next, ACPA-expressing B cells were identified directly after isolation using a streptavidin tetramer-based flow cytometry staining technique developed in chapter 4. Furthermore, we provided evidence for altered development of ACPA-producing B cells, as these cells were found to express lambda light chains (LC) more frequently than non-autoreactive B cells (chapter 5). Finally, we investigated CD28 expression on ACPA-expressing B cells and total B cells in RA patients as relevant molecule for an enhanced live span of long-lived plasma cells (chapter 6).