CD33 and viral infectious disease: Myeloid/classical DCs (mDCs) express typical myeloid antigens (CD11c, CD13, CD33, CD11b) with the majority of them expressing CD1c/BDCA1, while plasmacytoid DCs (pDCs) express CD123, CD303/BDCA2, CD304/BDCA4, and produces IFNα after activation with CpG or viral infection (12–16).