Figure 20.

The principle of bystander signaling. Primary singlet oxygen (¹O₂) generated through the interaction of long-lived species in CAP-treated medium or directly derived from the gaseous phase of CAP (red dots) (A) causes local inactivation of membrane-associated catalase on very few tumor cells (B). Subsequent generation of secondary ¹O₂ (green dots) causes spreading of the catalase inactivation on the cell membrane of the initially triggered cells and their neighbours (C,D). Finally, the majority of cells in the population show substantial inactivation of their protective catalase and thus can foster intercellular apoptosis-inducing ROS signaling, but also can transmit bystander signaling to previously untreated cells, as shown in the next Figures.