IRF5 and rheumatoid arthritis: Instead, it has been suggested that HLADRB3 and interferon regulatory factor 5 (IRF5) may predispose to seronegative RA.13–15 It is also unclear as to whether seronegative RA is one or several disease entities.3 Finally, we recently reported quantitative differences in the composition of synovial tissue-resident memory T cells between patients with established RA versus PsA.5