Four-color gating strategy for identification of presumptive pre-DC subsets in blood of rhesus monkeys. Rhesus DC subsets were identified on the basis of forward scatter (FSC) and side scatter (SSC) (A) within the Lin^- MHC class II⁺ fraction of total PBMCs after Ficoll gradient separation, indicated by the gated region (B). Isotype-matched control immunoglobulins were included as appropriate negative controls (C). Subsequently, monocytoid DC precursors (CD11c⁺ pre-DCs) were identified as CD11c⁺ CD123^-, and plasmacytoid DC precursors (CD123⁺⁺ pre-DCs) were identified as CD11c^- CD123⁺⁺ and comprised between 10% to 50% and 1% to 4% of the Lin^- MHC class II⁺ fraction, respectively (D).