Comparison of Murine Cervicovaginal Infection by Chlamydial Strains: Identification of Extrusions Shed In vivo

Abstract

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infections (STIs) and preventable blindness. Untreated, asymptomatic infection as well as frequent re-infection are common and may drive pelvic inflammatory disease, ectopic pregnancy, and infertility. In vivo models of chlamydial infection continue to be instrumental in progress toward a vaccine and further elucidating the pathogenesis of this intracellular bacterium, however significant gaps in our understanding remain. Chlamydial host cell exit occurs via two mechanisms, lysis and extrusion, although the latter has yet to be reported in vivo and its biological role is unclear. The objective of this study was to investigate whether chlamydial extrusions are shed in vivo following infection with multiple strains of Chlamydia. We utilized an established C3H/HeJ murine cervicovaginal infection model with C. trachomatis serovars D and L2 and the Chlamydia muridarum strain MoPn to monitor the (i) time course of infection and mode of host cell exit, (ii) mucosal and systemic immune response to infection, and (iii) gross and histopathology following clearance of active infection. The key finding herein is the first identification of chlamydial extrusions shed from host cells in an in vivo model. Extrusions, a recently appreciated mode of host cell exit and potential means of dissemination, had been previously observed solely in vitro. The results of this study demonstrate that chlamydial extrusions exist in vivo and thus warrant further investigation to determine their role in chlamydial pathogenesis.

Genetic Inactivation of Chlamydia trachomatis Inclusion Membrane Protein CT228 Alters MYPT1 Recruitment, Extrusion Production, and Longevity of Infection

“…Therefore, recruitment of host MYPT1 to the inclusion by CT228 serves to regulate the manner and degree of host cell egress. Although the extrusion process has been observed in vitro for many years (Todd and Caldwell, 1985 ; Hybiske and Stephens, 2007 , 2008 ), it was only recently documented to occur in vivo across multiple serovars (Shaw et al, 2017 ).…”

Chlamydia trachomatis inclusion membrane protein MrcA interacts with the inositol 1,4,5-trisphosphate receptor type 3 (ITPR3) to regulate extrusion formation

“…It has recently been shown that extrusions are readily phagocytosed by macrophages where they show enhanced survival and may contribute to dissemination [ 44 ]. In vivo evidence of extrusions have also been detected using a cervicovaginal infection model suggesting relevance to active infections [ 45 ]. Recognition of the signaling pathways influencing the different exit strategies should provide insights into the regulation of chlamydial dissemination during disease.…”

Impact of Active Metabolism on Chlamydia trachomatis Elementary Body Transcript Profile and Infectivity

“…The EB cell type is wholly responsible for initiating new rounds of infection, mediating cell entry and initiating the creation of the intracellular replication niche, while the RB cell type replicates and initiates differentiation to the EB cell type to prepare for release and reinfection. The production of the EB cell type is asynchronous, leading to EBs of vastly different ages present in the inclusion until released by host cell lysis or extrusion of the inclusion (32). The release of chlamydial EBs at the end of the intracellular developmental cycle by the aforemen- tioned mechanisms has been the focus of research for several decades.…”

“…Maintenance of chlamydial infectivity within both the inclusion and extracellular environments has only received minimal attention, likely in part due to the long-held view that the chlamydial EB is metabolically inert. Indeed, the more recently introduced concept of the extrusion of intact inclusions (32,36), in addition to the release of EBs from the host by lysis, has been presented as a potential mechanism for chlamydiae to survive for longer periods of time following release from the host cell.…”

“…The exosome could be considered a hybrid environment maintaining some of the environmental conditions of the intracellular inclusion in combination with access to the extracellular environment. Extrusion of the chlamydial inclusion from cells occurs in roughly half of infected cells in culture, and the extruded chlamydial exosomes have been detected during in vivo infections of mice (32). The environmental and nutritional conditions within these exosomes has not yet been described, but it is conceivable that the exosome represents a nutritionally favorable environment for the maintenance of EB infectivity to increase the transmission and spread of the infection.…”