XBP1 and juvenile idiopathic arthritis: For B cells of JIA and cHC, three subtypes had been identified by evaluating the expression of CD38, MZB1, XBP1, TNFRSF13B, CD79A, CD79B, CD19, MS4A1, IGHD, TCL1A (Figures 1D, E), these included Naïve B (Naïve B cells), Memory B (Memory B cells) and Plasma B (Plasma B cells) (Figures 1D, E).