## 3 Results  
### Jurkat and THP-1 Cells Differ in Their Sensitivity to H\({}_{2}\)O\({}_{2}\) and HOCl Exposure  
Besides their roles in inflammation and involvement in the pathology of several diseases, H\({}_{2}\)O\({}_{2}\) and HOCl can be generated by gas plasmas for therapeutic purposes which are investigated and applied in dermatological and oncological treatment regimes. Plasmas generate a variety of short-lived species, including hydroxyl radicals or singlet oxygen, in the gas phase. Their high reactivity leads to quick deterioration and formation of secondary long-lived species in liquids. The profile of species generated in the liquid can partially be influenced by providing different feed gases. As such, the liquid chemistry can be tuned between an H\({}_{2}\)O\({}_{2}\)- or HOCl-rich regime, which are considered as main biological effectors, if bulk liquids surround cells. Exposure of sodium chloride solutions to an argon gas plasma (Figure 1a) resulted in the deposition of 200 \(\upmu\)M H\({}_{2}\)O\({}_{2}\) in sodium chloride solutions (Figure 1b). In contrast, the usage of helium-oxygen as feed gas (Figure 1c) generated HOCl in treated liquids (Figure 1d). The present study investigated differences in the responses to isolated H\({}_{2}\)O\({}_{2}\) and HOCl-induced oxidative stress in Jurkat and THP-1 cells using various methods (Figure 1e). To assess the difference in metabolic activity, a resazurin-based assay was used (Figure 2a) and employed to calculate the IC20 to compare the toxicity of both oxidants investigated. Jurkat cells showed relatively high sensitivity to H\({}_{2}\)O\({}_{2}\) and relatively low sensitivity to HOCl (Figure 2b). In contrast, THP-1 cells were somewhat less sensitive to H\({}_{2}\)O\({}_{2}\) but more susceptible to HOCl than Jurkat cells (Figure 2c). Interestingly, the cell lines differed in their absolute and relational sensitivity to H\({}_{2}\)O\({}_{2}\) or HOCl. This was shown by calculating the ratios of H\({}_{2}\)O\({}_{2}\) to HOCl IC20 values (Figure 2d) and the ratios of IC20 values identified in Jurkat to THP-1 cells, respectively (Figure 2e). To verify that the reduced metabolic activity came with a certain degree of cytotoxicity, flow cytometry was employed using DAPI to discriminate viable from dead cells (Figure 2f). In both cell lines, the number of viable cells was reduced one day after treatment with respective IC20 concentrations of H\({}_{2}\)O\({}_{2}\) or HOCl (Figure 2g,h).  
Figure 1: **Gas plasma-derived H\({}_{2}\)O\({}_{2}\) and HOCI and study scheme.** (**a**) Schematic overview of argon gas plasma treatment; (**b**) formation of H\({}_{2}\)O\({}_{2}\) in argon gas plasma-treated liquids; (**c**) schematic overview of helium–oxygen gas plasma treatment; (**d**) formation of HOCI in helium–oxygen gas plasma-treated liquids; (**e**) Jurkat and THP-1 cells were seeded under similar conditions, and their IC20 was determined for H\({}_{2}\)O\({}_{2}\) and HOCI by analyzing metabolic activity. Cell death was verified using flow cytometry, and GSH and GSSG levels were measured. Time-lapse fluorescence microscopy was performed to identify the time point of the maximal slope of caspase 3/7 activation in both cell types.  
Figure 2: **Metabolic activity and viability.** (**a**) Representative photograph of the resazurin-based metabolic activity assay in Jurkat cells; **(b)** IC20 calculations for H\({}_{2}\)O\({}_{2}\) and HOCl in Jurkat cells; **(c)** IC20 calculations for H\({}_{2}\)O\({}_{2}\) and HOCl in THP-1 cells; **(d)** IC20 ratio of HOCl over H\({}_{2}\)O\({}_{2}\) for Jurkat and THP-1 cells; **(e)** IC20 ratio of Jurkat over THP-1 cells for H\({}_{2}\)O\({}_{2}\) and HOCl; **(f)** representative flow cytometry dot plots of untreated, H\({}_{2}\)O\({}_{2}\)-treated (IC20), and HOCl-treated (IC20) THP-1 cells; **(g.h)** number of viable Jurkat (**g**) and THP-1 (**h**) cells as determined via flow cytometry. Results are representative of three experiments.