 In humans, pDCs exhibit plasma cell morphology and express CD4, HLA-DR, CD123, blood-derived dendritic cell antigen-2 (BDCA-2), Toll-like receptor (TLR) 7 and TLR9 within endosomal compartments.Expression of TLR 7 and TLR 9 allows pDCs to interact with viral and host nucleic acids.TLR 7 and TLR 9 detect ssRNA and unmethylated CpG DNA sequences, respectively.