PRTN3 and rheumatoid arthritis: The mechanisms operating in the UPR response of RA cells are similar to those described above for cancer cells [14]; however, during the progress of RA, B cells differentiate into plasma cells and infiltrate the synovial membrane where they synthesize autoantibodies such as immunoglobulin M rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (ACPA) [42,43].