Apoptosis (programmed cell death). Apoptosis is usually a mechanism of defense to infection, given that apoptotic cells eventually attract immune cells to remove them and the pathogen. Many pathogenic bacteria have developed mechanisms to prevent apoptosis, not the least to maintain their host environment. For instance, the EPEC/EHEC effectors NleH and NleF block apoptosis. Similarly, the Shigella effectors IpgD and OspG (a homolog of NleH) block apoptosis, the former by phosphorylating and stabilizing the double minute 2 protein (MDM2) which in turn leads to a block of NF-kB-induced apoptosis. Salmonella inhibits apoptosis and activates pro-survival signals, dependent on the effectors AvrA and SopB, respectively.
