CD4 and arthritic joint disease: In addition to inhibiting immunogenic CD4+ T cell populations, IL-10+ Bregs are also able to convert naïve CD4+ T cells into Tregs and IL-10-secreting type-1 regulatory CD4+ T cells (Tr1), as shown in experimental arthritis (11, 14, 197), lupus (34, 94), and EAE (104, 235).