Multicolor flow cytometry for the identification and expression of CD64 on PB and bone marrow monocyte subsets. (A) Representative dot plots are shown to illustrate the gating strategy for the identification of total monocytes. Monocytes were identified by CD33⁺CX3CR⁺CD56^–CD14⁺ expression. (B) Representative histogram of CD64 expression on CD33⁺CX3CR⁺CD56^-CD14⁺ bone marrow monocytes/macrophages from a patient with MM pretreatment and posttreatment. The black histogram is the fluorescence minus one control (FMO). The gray filled histogram identifies the pretreatment bone marrow sample, and the dotted line represents the posttreatment bone marrow sample (left). Dot plots indicate the mean fluorescence intensity of CD64 expression pretreatment and posttreatment on CD33⁺CX3CR⁺CD56^–CD14⁺ monocytes/macrophages (n = 13) (right). (C) Representative histogram of CD64 expression on CD33⁺CX3CR⁺CD56^–CD14⁺ PB monocytes/macrophages from a patient with MM pretreatment and posttreatment. The black histogram is the FMO. The gray filled histogram identifies the pretreatment PB sample, and the dotted line represents the posttreatment PB sample (left). Dot plots indicate the mean fluorescence intensity of CD64 expression pretreatment and posttreatment on CD33⁺CX3CR⁺CD56^–CD14⁺ PB monocytes/macrophages (n = 13) (panel B, right). Lines between dots indicate paired samples. Wilcoxon matched pairs signed rank test and paired Student t tests were used to detect statistically significant differences between pretreatment and posttreatment samples. *P < .05, **P < .01. APC, allophycocyanin; FSC-H, forward scatter–height; MFI, mean fluorescence intensity; SSC, side scatter.