FIGURE 1: Possible sources of pro-death signals acting on Chlamydia-infected cells.

(A) Inside the host, Chlamydia-infected cells are exposed to cytotoxic cytokines and death-inducing immune cells, but have evolved to block induction of cell death by these stimuli.

(B) The ability of Chlamydia spp. to block apoptosis induced by cellular stress inducers suggests that the bacteria actually need to protect host cells from infection-induced lethal stress.

(C) Cell death may be induced by activation of immune sensors that regulate cell-autonomous defense mechanisms. Our recent study demonstrated that the C. trachomatis inclusion membrane protein CpoS counteracts the activation of the PAMP sensor STING and prevents emission of pro-death signals from the inclusion.