Seven protein levels were significantly increased in RA compared to OA and/or CPPA (Figure 1B): cytosol aminopeptidase (LAP3), DnaJ homolog subfamily B member 11 (DNAJB11), mesencephalic astrocyte-derived neurotrophic factor (MANF), plastin-2 (LCP1), cathepsin Z (CTSZ), receptor-type tyrosine-protein phosphatase C (PTPRC) and echinoderm microtubule-associated protein-like 4 (EML4). Here, PTPRC is linked to rheumatoid arthritis.