Cleavage of the N-linked oligosaccharide from the surfaces of Chlamydia species affects infectivity in the mouse model of lung infection

Utilization of Galectins by Pathogens for Infection

Galectins are glycan-binding proteins which are expressed by many different cell types and secreted extracellularly. These molecules are well-known regulators of immune responses and involved in a broad range of cellular and pathophysiological functions. During infections, host galectins can either avoid or facilitate infections by interacting with host cells- and/or pathogen-derived glycoconjugates and less commonly, with proteins. Some pathogens also express self-produced galectins to interfere with host immune responses. This review summarizes pathogens which take advantage of host- or pathogen-produced galectins to establish the infection.

Pathogenic Puppetry: Manipulation of the Host Actin Cytoskeleton by Chlamydia trachomatis

The actin cytoskeleton is crucially important to maintenance of the cellular structure, cell motility, and endocytosis. Accordingly, bacterial pathogens often co-opt the actin-restructuring machinery of host cells to access or create a favorable environment for their own replication. The obligate intracellular organism Chlamydia trachomatis and related species exemplify this dynamic: by inducing actin polymerization at the site of pathogen-host attachment, Chlamydiae induce their own uptake by the typically non-phagocytic epithelium they infect. The interaction of chlamydial adhesins with host surface receptors has been implicated in this effect, as has the activity of the chlamydial effector TarP (translocated actin recruitment protein). Following invasion, C. trachomatis dynamically assembles and maintains an actin-rich cage around the pathogen’s membrane-bound replicative niche, known as the chlamydial inclusion. Through further induction of actin polymerization and modulation of the actin-crosslinking protein myosin II, C. trachomatis promotes egress from the host via extrusion of the inclusion. In this review, we present the experimental findings that can inform our understanding of actin-dependent chlamydial pathogenesis, discuss lingering questions, and identify potential avenues of future study.

Male genital tract immune response against Chlamydia trachomatis infection

Chlamydia trachomatis is the most commonly reported agent of sexually transmitted bacterial infections worldwide. This pathogen frequently leads to persistent, long-term, subclinical infections, which in turn may cause severe pathology in susceptible hosts. This is in part due to the strategies that Chlamydia trachomatis uses to survive within epithelial cells and to evade the host immune response, such as subverting intracellular trafficking, interfering signaling pathways and preventing apoptosis. Innate immune receptors such as toll-like receptors expressed on epithelial and immune cells in the genital tract mediate the recognition of chlamydial molecular patterns. After bacterial recognition, a subset of pro-inflammatory cytokines and chemokines are continuously released by epithelial cells. The innate immune response is followed by the initiation of the adaptive response against Chlamydia trachomatis, which in turn may result in T helper 1-mediated protection or in T helper 2-mediated immunopathology. Understanding the molecular mechanisms developed by Chlamydia trachomatis to avoid killing and host immune response would be crucial for designing new therapeutic approaches and developing protective vaccines. In this review, we focus on chlamydial survival strategies and the elicited immune responses in male genital tract infections.

Chlamydia pneumoniae induces expression of pro-atherogenic factors through activation of the lectin-like oxidized LDL receptor-1

Several lines of evidence have associated Chlamydia pneumoniae with cardiovascular disease including acceleration of atherosclerotic lesion progression in hyperlipidemic animal models by infection. Many of the pro-atherogenic effects of oxidized low-density lipoprotein (ox-LDL) occur through the activation of the lectin-like ox-LDL receptor-1 (LOX-1). Chlamydia pneumoniae upregulates the expression of the LOX-1 mRNA, promotes the uptake of ox-LDL, and utilizes the LOX-1 receptor for infectivity. The overall goal of this study was to determine whether C. pneumoniae organisms upregulated LOX-1 protein expression in vascular cells and whether upregulation of pro-atherogenic factors by C. pneumoniae occurred through LOX-1. Chlamydia pneumoniae induced LOX-1 protein expression in both endothelial cells and RAW macrophages. Upregulation was prevented by preincubation of cells with LOX-1 antibody prior to infection. Similarly, C. pneumoniae upregulated protein expression of adhesion molecules, MMP-1, and MMP-3, which was mitigated by anti-LOX-1 antibody. Prior treatment of organisms with PNGase, which removes the chlamydial glycan that is N-linked to the major outer membrane, abolished C. pneumoniae upregulation of LOX-1. These studies suggest that activation of LOX-1 expression occurs through binding of the chlamydial glycan and provides one mechanism by which C. pneumoniae infection could play a role in the pathogenesis of atherosclerosis.

Retinoic acid prevents Chlamydia pneumoniae-induced foam cell development in a mouse model of atherosclerosis

Chlamydia pneumoniae, a common respiratory pathogen, has been associated with cardiovascular disease. C. pneumoniae infection accelerates atherosclerotic lesion development in hyperlipidemic animals. Retinoic acid, an anti-oxidant, inhibits infection of endothelial cells by C. pneumoniae. The present study demonstrated that retinoic acid suppresses the acceleration of foam cell lesion development induced by C. pneumoniae in hyperlipidemic C57BL/6J mice. Retinoic acid treatment had no effect on foam cell lesion development in uninfected animals. Lung infection and duration was decreased in treated mice, suggesting one mechanism by which retinoic acid reduces C. pneumoniae-accelerated foam cell lesion formation in hyperlipidemic mice.

Efficacy of benzoxazinorifamycins in a mouse model of Chlamydia pneumoniae lung infection

The efficacy of rifalazil and other benzoxazinorifamycins was tested in a mouse model of lung infection against Chlamydia pneumoniae. Rifalazil and six related new chemical entities all showed efficacy after one dose per day for 3 days at either 3 or 1 mg/kg of body weight.

Retinoic acid inhibits the infectivity and growth of Chlamydia pneumoniae in epithelial and endothelial cells through different receptors

Chlamydia pneumoniae is a human respiratory pathogen that has also been associated with cardiovascular disease. C. pneumoniae infection accelerates atherosclerotic plaque development in hyperlipidemic animals and promotes oxidation of low density lipoprotein in vitro. All-trans-retinoic acid (ATRA), an antioxidant, has been shown to inhibit C. pneumoniae infectivity for endothelial cells by preventing binding of the organism to the M6P/IGF2 receptor on the cell surface. This current study investigates whether ATRA similarly affects C. pneumoniae infectivity of epithelial cells, which are the primary site of infection in the respiratory tract, and the effects on intracellular growth in both endothelial and epithelial cells. Because ATRA binds to both the nuclear retinoid acid receptor (RAR) and the M6P/IGF2 receptor, 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid (TTNPB), an ATRA analog, which binds to the RAR but not the M6P/IGF2 receptor was used to differentiate the receptor mediating the effects of ATRA. The results of this study showed two separate effects of ATRA. The first effect is through interaction with the M6P/IGF2 receptor on the cell surface preventing attachment of the organism (inhibition by ATRA but not TTNPB) in endothelial cells and the second is through the nuclear receptor (inhibition by both ATRA and TTNPB) which inhibits growth in both epithelial and endothelial cells.

Inoculation of Chlamydia pneumoniae or Chlamydia trachomatis with ligands that inhibit attachment to host cells reduces infectivity in the mouse model of lung infection: implication for anti-adhesive therapy

Previous studies have shown that the chlamydial glycan contains a high-mannose oligosaccharide, which mediates attachment and infectivity of the organism. Removal of the glycan decreases infectivity in vitro and in vivo. The present study demonstrates that simultaneous inoculation of chlamydial organisms and a ligand that prevents glycan binding reduces lung burden in infected animals.