PSMB9 and rheumatoid arthritis: As for STAT1, GBP1, and PSMB9/LMP2, the validity of the rule ‘PLCG2 high in RA’ was emphasized by its appearance in three independently established rule sets (rule set ‘Berlin’, position 5; rule set ‘Jena’, position 14; rule set ‘Total’, position 4; see Table 5 and Additional file 4).