CD4 and rheumatoid arthritis: Th1, Th2, Th17 and Treg are main subsets differentiate from naïve CD4+ T cells in chronic inflammatory bone disease such as RA and periodontitis.146 The differentiation of each Th subsets requires a series of signals during antigen presentation, and the complexity of the Th cell response depends on the immune states of DCs (Fig. 6).