HSPD1 and rheumatoid arthritis: Baseline HSPD1 gene expression was significantly higher in the B cell–rich subset of patients with RA and was associated with good clinical responders, as defined by the R4RA trial’s clinical primary endpoint, the Clinical Disease Activity Index (CDAI), and by the secondary endpoint, the Disease Activity Score 28–C-reactive protein (DAS28-CRP) (Figure 6, B and C).