Shigella spp. are major enteric pathogens, causing acute diarrhea and bacillary dysentery leading to severe mortality and morbidity worldwide. Yet, there is no licensed vaccine to prevent shigellosis. Shigella virulence requires a T3SS and at least 30 secreted effectors that are often functionally redundant, yet required to invade host cells, maintain a replicative niche, minimize alarm signals, and promote colonization. We previously showed that S. flexneri T3SS activity is detected in macrophages by Caspase-1 inflammasomes, resulting in pyroptosis. In the recent mouse shigellosis model, the role of the inflammasome is only focused on gut intestinal epithelial cells (IECs). However, it is generally believed that Shigella initially infect macrophages and takes advantage of pyroptotic cell death to exit the cells and subsequently infect IECs. On the other hand, macrophage pyroptosis is known to generate pore-induced traps (PITs), trapping, and neutralizing intracellular bacterial pathogens. Since macrophages pyroptosis is considered to play dichotomous roles during Shigella infection, we propose to investigate the interaction between macrophages' inflammasomes and S. flexneri. We propose two specific Aims: In Aim1, we will investigate how pyroptotic macrophages from PITs trap intracellular bacteria. In Aim 2. We will define the role of pyroptotic macrophages and PITs during S. flexneri infection in vitro and in vivo. We hope that examining the role of macrophages pyroptosis against S. flexneri infection, will be highly significant and relevant for better understanding immunity and disease pathologies during Shigella infection and thereby providing the basis for developing novel safer, and more effective vaccines.

Shigella is a gastrointestinal pathogen that cause bloody diarrhea, resulting in mortality and morbidity worldwide, especially among children under ages of 5. Our study examines Shigella- host innate immune defenses to identify target (s) that will help to improve vaccines design.