TLR9 and neoplasm: Although most studies have focusedon the role of pDCs in antiviral immunity, several new lines of evidence havesuggested that pDCs are also involved in tumor immunity, as well as inpromoting peripheral tolerance [42–47].Interestingly, pDCs can synthesize large amount of functional indoleamine 2,3-dioxygenase(IDO), which requires autocrine release of type I IFN, upon Toll-like receptor-9(TLR9) and CD200R ligands stimulation.