Markers and cytology of myeloid cells at sites of infection. (A) FCM analysis on medium (left), mck-mutant RM461-infected (middle), and mck-expressing RQ461 (right). Percentages of cells with each expression pattern are indicated in the Mac-1^-/Gr-1⁺, Mac-1⁺/Gr-1⁺, and Mac-1⁺/Gr-1^- quadrants. The Mac-1⁺/Gr-1^int population is indicated by a dashed box. FP leukocytes were prepared from groups of 3 BALB/c mice at 48 hours after inoculation (inoculum of 1 × 10⁶ PFUs). (B) May-Grunwald-Giemsa-stained FCM purified cells from pooled FPs (20 mice) at 48 hours after inoculation (inoculum of 1 × 10⁶ PFUs), comparing 4 examples from the Mac-1⁺/Gr-1^int population (left) and 4 examples from the Mac-1^-/Gr-1^- population (right) (× 1000). Mac-1⁺/Gr-1^int cells were prepared by MACS separation, followed by FACSvantage sorting, and Mac-1^-/Gr-1^- cells were from the initial MACS separation step. (C) Summary data for the frequency of Mac-1⁺/Gr-1^int cells of FP leukocytes. The mean (bars) with standard deviation (error bars) of 3 independent experiments is indicated.