Figure 4.

Activated monocytes directly induce reactive oxygen species (ROS) production by neutrophils. (A) Graphical summary of flow cytometry analyses showing the fraction of ROS⁺ neutrophils out of CD66b⁺ neutrophils following 2 h culture with lipopolysaccharide (LPS)-activated human CD14⁺ monocyte cells or with their cell-free supernatants; Polymyxin B (PMB) was added to all cultures in order to avoid direct activation of neutrophils by LPS remnants. (B) Left, representative histogram plot showing the expression level of the neutrophil activation marker CD66b following different treatments. Right, Summarizing graph showing the geometric mean fluorescence intensity (Geo MFI) of CD66b protein following different treatments. (C) Left, representative flow cytometry image showing the identification of AnnexinV⁺FSC^lo apoptotic cells among CD66b⁺ neutrophils. Right, Summarizing graph showing the fraction (%) of these cells among total CD66b⁺ neutrophils. (D) The fraction of ROS⁺ neutrophils out of CD66b⁺ neutrophils following 2 h culture with human CD14⁺ monocyte cells pre-activated with HepG2 apoptotic bodies. Data were analyzed by unpaired, two-tailed t-test and are presented as mean ± SEM with significance: *p < 0.05, **p < 0.01, ***p < 0.001 (n ≥ 3 human donors/group for each monocyte group, the same pool of neutrophils was used).