Karger Publishers, Journal of Innate Immunity, 3(14), p. 192-206, 2021
DOI: 10.1159/000517855
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Epithelial cells play a crucial role in detection of the pathogens as well as in initiation of the host immune response<i>. Streptococcus pneumoniae</i> (pneumococcus) is a typical colonizer of the human nasopharynx, which can disseminate to the lower respiratory tract and subsequently cause severe invasive diseases such as pneumonia, sepsis, and meningitis. Hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) is produced by pneumococci as a product of the pyruvate oxidase SpxB. However, its role as a virulence determinant in pneumococcal infections of the lower respiratory tract is not well understood. In this study, we investigated the role of pneumococcal-derived H<sub>2</sub>O<sub>2</sub> in initiating epithelial cell death by analyzing the interplay between 2 key cell death pathways, namely, apoptosis and pyroptosis. We demonstrate that H<sub>2</sub>O<sub>2</sub> primes as well as activates the NLRP3 inflammasome and thereby mediates IL-1β production and release. Furthermore, we show that pneumococcal H<sub>2</sub>O<sub>2</sub> causes cell death via the activation of both apoptotic as well as pyroptotic pathways which are mediated by the activation of caspase-3/7 and caspase-1, respectively. However, H<sub>2</sub>O<sub>2</sub>-mediated IL-1β release itself occurs mainly via apoptosis.