Fig. 3. In vitro exposure to a particulate pollutant induces trained immunity in human circulating monocytes.Schematic representation of a standard protocol for induction of trained immunity in monocytes (A). The levels of TNF, IL-6, and IL-8 were compared in supernatants collected from monocytes under training with SRM 1648a pollutant (red), or vehicle (blue) after stimulation with medium, LPS, or HDM. Training of monocytes with SRM1648a pollutant induced a robust increase in LPS or HDM-mediated elevation of TNF, IL-6, and IL-8 levels. (N=10 subjects including 7 healthy and 3 asthmatic children per group) (B). The role of environmental exposure to PM2.5 on induction of trained immunity was studied by comparing these mediators in subjects exposed to low (pink) versus high (purple) levels of ambient PM2.5 (N=5 subjects including 4 healthy and 1 asthmatic children per group) (C). The impact of re-exposure to pollutant on trained immunity was determined by measuring the levels of TNF, IL-6, and IL-8 in supernatants (D). The graphs represent a single set of measurements from one of 2 independent cytokine experiments. Statistical significance was determined using non-parametric Wilcoxon sum test.