BCR and juvenile idiopathic arthritis: We also found potential roles in pJIA and AU of BCR, TCR, RUNX3, Class I MHC, RANKL/RANK signaling pathway, macrophage activation, calcium-mediated signaling, etc. Previous studies found shared HLA class I and class II loci alleles between AU and JIA indicating that both B cell and T cell functions are important in the common mechanism.