Detection of ROS production in human neutrophils and MDMs. The luminescence was measured over a 30-min (A, C, neutrophils) or 60-min (B, D, MDMs) time period in these human phagocytes, and the baseline ROS luminescence was determined by measuring the luminescence of control cells treated with medium only. A and B, F. novicida (FN; ◊), ΔacpA (▲), ΔABCH (■), formalin-killed F. novicida (FKFN; X), and F. novicida followed by serum-opsonized zymosan (FN+OPZ; ○), serum-opsonized zymosan (OPZ; □), or 200 nM PMA (●). C and D, F. tularensis subspecies tularensis SchuS4 (Schu S4; ◆), formalin-killed F. tularensis subspecies tularensis (FKFT; X), and F. tularensis subspecies tularensis followed by serum-opsonized zymosan (Schu S4 + OPZ; ○), serum-opsonized zymosan (OPZ; □), or 200 nM PMA (●). Data are the mean ± SD of triplicate samples from a representative experiment (n = 7).