CD4 and rheumatoid arthritis: Moreover, Kavousanaki et al. suggested that mature plasmacytoid dendritic cells (DCs) from RA patients with low disease activity, but not those from healthy controls, expressed high levels of indoleamine 2,3-dioxygenase and promoted the differentiation of allogeneic naive CD4+CD25− T cells into interleukin-10-secreting Treg cells, or Tr1 cells, which showed poor proliferation in vitro.