The strategies utilized by pathogens to exit host cells are an area of pathogenesis which has received surprisingly little attention, considering the necessity of this step for infections to propagate. Even less is known about how exit through these pathways affects downstream host-pathogen interactions and the generation of an immune response. Chlamydia trachomatis exits host epithelial cells through two equally active mechanisms: lysis and extrusion. Studies have characterized the outcome of interactions between host innate immune cells, such as dendritic cells and macrophages, and free, extracellular Chlamydia bacteria, such as those resulting from lysis. Exit via extrusion generates a distinct, host-membranebound compartment of Chlamydia separate from the original infected cell. In this study, we assessed the effect of containment within extrusions upon the interaction between Chlamydia and host dendritic cells. Extrusion dramatically affected the outcome of Chlamydia-dendritic cell interactions for both the bacterium and the host cell. Dendritic cells rapidly underwent apoptosis in response to engulfment of an extrusion, while uptake of an equivalent dose of free Chlamydia had no such effect. Containment within an extrusion also prolonged bacterial survival within dendritic cells and altered the initial innate immune signaling by the dendritic cell.KEYWORDS Chlamydia, apoptosis, dendritic cell, extrusion C hlamydia trachomatis is a highly successful Gram-negative bacterial pathogen, being the leading bacterial cause of sexually transmitted infections and the leading cause of infectious blindness globally (1-3). In the absence of diagnosis and treatment, Chlamydia infections can lead to severe long-term outcomes, such as chronic pelvic pain, infertility, and ectopic pregnancy (4, 5). During infection, innate and adaptive immune responses are mounted against Chlamydia; however, approximately 50% of infections last for a year or more (6). Even after the resolution of infection, only partial protective immunity is achieved and reinfection is common (7-9). This suggests that Chlamydia is adept at establishing and sustaining infection in the face of immune recognition.Due to Chlamydia's obligate intracellular nature and a historically limited genetic toolbox, key attributes of the host-Chlamydia interaction are still unknown. Chlamydia infection is initiated by the uptake of metabolically inactive elementary bodies (EB) into mucosal epithelial cells, which transition into reticulate bodies (RB) within a vacuole called an inclusion. Here, the metabolically active RB replicates robustly to generate hundreds of Chlamydia bacteria that undergo transition back to EB (10). Chlamydia inhibits apoptosis of the host epithelial cell, ensuring its ability to complete this replication cycle before exit from the cell (11-13). Bacterial exit from host cells is a crucial but underscrutinized stage of the life cycle of this and other intracellular pathogens. Chlamydia possesses two distinct, equally prevalent exit mechan...