Degradation of Chlamydia trachomatis in human polymorphonuclear leukocytes: an ultrastructural study of peroxidase-positive phagolysosomes

Intracellular lifestyle of Chlamydia trachomatis and host-pathogen interactions

In recent years, substantial progress has been made in the understanding of the intracellular lifestyle of Chlamydia trachomatis and how the bacteria establish themselves in the human host. As an obligate intracellular pathogenic bacterium with a strongly reduced coding capacity, C. trachomatis depends on the provision of nutrients from the host cell. In this Review, we summarize the current understanding of how C. trachomatis establishes its intracellular replication niche, how its metabolism functions in the host cell, how it can defend itself against the cell autonomous and innate immune response and how it overcomes adverse situations through the transition to a persistent state. In particular, we focus on those processes for which a mechanistic understanding has been achieved.

The voltage-gated proton channel Hv1/VSOP inhibits neutrophil granule release

Neutrophil granule exocytosis is crucial for host defense and inflammation. Neutrophils contain 4 types of granules, the exocytotic release of which is differentially regulated. This exocytosis is known to be driven by diverse mediators, including calcium and nucleotides, but the precise molecular mechanism remains largely unknown. We show in the present study that voltage-gated proton (Hv) channels are necessary for the proper release of azurophilic granules in neutrophils. On activation of NADPH oxidase by PMA and IgG, neutrophils derived from Hvcn1 gene knockout mouse exhibited greater secretion of MPO and elastase than WT cells. In contrast, release of LTF enriched in specific granules was not enhanced in these cells. The excess release of azurophilic granules in Hv1/VSOP-deficient neutrophils was suppressed by inhibiting NADPH oxidase activity and, in part, by valinomycin, a potassium ionophore. In addition, Hv1/VSOP-deficient mice exhibited more severe lung inflammation after intranasal Candida albicans infection than WT mice. These findings suggest that the Hv channel acts to specifically dampen the release of azurophilic granules through, in part, the suppression of increased positive charges at the plasma membrane accompanied by the activation of NADPH oxidase in neutrophils.

The immunobiology of Chlamydia

Bacteria of the genus Chlamydia cause a wide variety of disorders in animals and people worldwide. The immune response to chlamydiae is poorly understood and, as Daniel Levitt shows here, there is recent evidence that these organisms induce perturbations in immune function that may assist their own survival in infected hosts and that of co-infecting microbes.

Regulation of chlamydial infection by host autophagy and vacuolar ATPase-bearing organelles

As arguably the most successful parasite, Chlamydia is an obligate intracellular bacterium replicating inside a vacuole of eukaryotic host cells. The chlamydial vacuole does not fuse with the defense cell organelle lysosome. We previously showed that chlamydial infection increases markers of autophagy, an innate antimicrobial activity requiring lysosomal function. However, the work presented here demonstrates that p62, an autophagy protein that is degraded in lysosomes, either remained unchanged or increased in chlamydia-infected human epithelial, mouse fibroblast, and mouse macrophage cell lines. In addition, the activities of three lysosomal enzymes analyzed were diminished in chlamydia-infected macrophages. Bafilomycin A1 (BafA), a specific inhibitor of vacuolar ATPase (vATPase) required for lysosomal function, increased the growth of the human pathogen Chlamydia trachomatis (L2) in wild-type murine fibroblasts and macrophages but inhibited growth in the autophagy-deficient ATG5(-/-) fibroblasts. BafA exhibited only slight inhibition or no effect on L2 growth in multiple human genital epithelial cell lines. In contrast to L2, the mouse pathogen Chlamydia muridarum (MoPn) was consistently inhibited by BafA in all cell lines examined, regardless of species origin and autophagy status. Finally, L2 but not MoPn grew more efficiently in the ATG5(-/-) cells than in wild-type cells. These results suggest that there are two types of vATPase-bearing organelles that regulate chlamydial infection: one supports chlamydial infection, while the other plays a defensive role through autophagy when cells are artificially infected with certain chlamydiae that have not been adapted to the host species.

Endothelial cells are protected against phagocyte-transmitted Chlamydophila pneumoniae infections by laminar shear stress Gueinzius: Shear stress protects from C. pneumoniae infection

The respiratory pathogen Chlamydophila pneumoniae can be detected in atherosclerotic vessels, but the mechanism of dissemination from lung to vasculature remains unknown. Disturbance of vascular shear stress is a risk factor for atherosclerosis. We investigated whether polymorphonuclear neutrophils (PMN) might serve as carriers, transmitting C. pneumoniae to endothelial cells and how this is affected by shear stress. PMN were prepared from blood and incubated with C. pneumoniae. Real-time PCR and Pathfinder staining showed that after 1h, 20% of C. pneumoniae were ingested and started to form inclusions. When infected PMN were co-incubated with HUVEC for 96h, 10% of PMN-ingested C. pneumoniae were transmitted to HUVEC as shown by PCR and confocal microscopy. Infection of HEp-2 cells with C. pneumoniae harvested from HUVEC resulted in C. pneumoniae replication and confirmed that the bacteria remained infective. Exposure to laminar shear stress in a rotating cone-and-plate apparatus did not affect the transmission of C. pneumoniae from PMN to HUVEC, but led to a 75% reduction of inclusion formation. This can explain the focal distribution of C. pneumoniae in the vasculature and links two risk factors of atherosclerosis, i.e. the lack of laminar flow and infection.

Fc receptor regulation of protective immunity against Chlamydia trachomatis

The prevailing paradigm for designing potentially efficacious vaccines against the obligate intracellular bacterium, Chlamydia trachomatis, advocates regimens capable of inducing a mucosal antigen-specific T helper type 1 (Th1) response. However, recent reports indicate that rapid and efficient clearance of a secondary infection also requires certain B-cell functions. We investigated the hypothesis that Fc receptor (FcR)-mediated antibody effector mechanisms are important B-cell-related functions involved in controlling a chlamydial genital reinfection. Microbiological analysis of genital chlamydial infection in FcR knockout (FcRKO) mice lacking the activatory FcgammaRI (CD64) and FcRgammaIII (CD16), as well as the inhibitory FcgammaRIIB1 (CD32), revealed a greater intensity of secondary infection (i.e. bacterial shedding) in FcRminus sign/minus sign as compared to FcR+/+ mice; however, the course of the primary infection was indistinguishable in both animals. Pathologically, FcRKO mice suffered greater ascending infection than immunocompetent wild-type (WT) mice after a secondary infection. Immunological evaluation indicated that the presence of specific anti-chlamydial antibodies enhanced chlamydial antigen presentation for induction of a Th1 response by FcR+/+, but not FcRminus sign/minus sign, antigen-presenting cells. In addition, specific anti-chlamydial antibodies augmented both macrophage killing of infected epithelial cells by antibody-dependent cellular cytotoxicity (ADCC) and macrophage inhibition of productive growth of chlamydiae in co-cultures. These results indicate that B cells participate in anti-chlamydial immunity via FcR-mediated effector functions of antibodies, which are operative during reinfections. Such effector functions include ADCC, and possibly enhanced uptake, processing and presentation of chlamydial antigens for rapid induction of a Th1 response, all facilitating the early clearance of an infection. These findings suggest that a future anti-chlamydial vaccine should elicit both humoral and T-cell-mediated immune responses for optimal memory response and vaccine efficacy.

Role of polymorphonuclear neutrophils in a murine model of Chlamydia psittaci-induced abortion

To assess the role of polymorphonuclear neutrophils (PMNs) in Chlamydia psittaci infection in a pregnant mouse model, pregnant and nonpregnant Swiss OF1 mice were depleted of PMNs by treatment with the RB6-8C5 monoclonal antibody before intraperitoneal infection with C. psittaci serotype 1. Nondepleted mice served as infection controls. Depleted mice aborted earlier and had a much higher mortality rate than nondepleted mice. Bacteriological analysis showed that the number of chlamydiae isolated from the spleens of depleted mice at 5 and 7 days postinfection was 100 times greater than that isolated from nondepleted mice. Histopathological analysis of the placentas of depleted mice showed widespread necrosis of the uteroplacental units, with weak immunoreaction to chlamydial antigen, while the placentas of nondepleted mice showed substantial neutrophil infiltration but no large areas of necrosis, with moderate to strong immunoreaction to chlamydial antigen. The livers of depleted mice showed numerous chlamydial inclusions in the hepatocytes, delayed microgranuloma formation, and in the pregnant animals extensive coagulative periportal necrosis. The livers of nondepleted mice displayed multiple small foci of PMNs and mononuclear cells with microgranuloma formation. Among this group of mice, the pregnant animals always had more hepatic damage than nonpregnant animals. Our results suggest that PMNs play an essential role in the response to C. psittaci primary infection, preventing the uncontrolled multiplication of chlamydiae in the liver and spleen.

Fusion of Chlamydia trachomatis-containing inclusions is inhibited at low temperatures and requires bacterial protein synthesis

The human pathogen Chlamydia trachomatis is an obligate intracellular bacterium with a unique developmental cycle. Within the host cell cytoplasm, it resides within a membrane-bound compartment, the inclusion. A distinguishing characteristic of the C. trachomatis life cycle is the fusion of the chlamydia-containing inclusions with each other in the host cell cytoplasm. We report that fusion of inclusions does not occur at 32 degreesC in multiple mammalian cell lines and with three different serovars of C. trachomatis. The inhibition of fusion was inclusion specific; the fusion with sphingolipid-containing secretory vesicles and the interaction with early endosomes were unaffected by incubation at 32 degreesC. The inhibition of fusion of the inclusions was not primarily the result of delayed maturation of the inclusion, as infectious progeny was produced in host cells incubated at 32 degreesC, and the unfused inclusions remained competent to fuse up to 48 h postinfection. The ability to reverse the inhibition of fusion by shifting the infected cells from 32 to 37 degreesC allowed the measurement of the rate and the time of fusion of the inclusions after entry of the bacteria. Most significantly, we demonstrate that fusion of inclusions with each other requires bacterial protein synthesis and that the required bacterial protein(s) is present, but inactive or not secreted, at 32 degreesC.

Secretion of proinflammatory cytokines by epithelial cells in response to Chlamydia infection suggests a central role for epithelial cells in chlamydial pathogenesis

Chlamydia species infect epithelial cells at mucosal surfaces, and are major causes of sexually transmitted diseases. Infection is characterized by inflammation which is exacerbated upon reinfection, ultimately leading to tissue damage and scarring. Although central for the development of disease manifestations, little is known about the mechanisms that initiate and sustain the inflammatory response to Chlamydia. Infection of cervical and colonic epithelial cells with Chlamydia trachomatis and Chlamydia psittaci is shown in the present studies to upregulate mRNA expression and secretion of the proinflammatory cytokines IL-8, GRO alpha, GM-CSF, and IL-6. In contrast to the rapid, but transient, cytokine induction following infection with other invasive bacteria, the epithelial cytokine response to Chlamydia was delayed until 20-24 h after infection, persisted throughout the chlamydial growth cycle (2-4 d), and required bacterial protein synthesis. Moreover, epithelial cell lines and primary endocervical epithelial cells released IL-1alpha after Chlamydia infection, and increased secretion of the proinflammatory cytokines could be inhibited by anti-IL-1alpha. This suggests that IL-1alpha, released following lysis of infected epithelial cells, may amplify the inflammatory response by stimulating additional cytokine production by noninfected neighboring cells. These findings suggest a novel pathophysiologic concept wherein the acute host response to Chlamydia at mucosal surfaces is primarily initiated and sustained by epithelial cells, the first and major targets of chlamydial infection.

Role of neutrophils in controlling early stages of a Chlamydia trachomatis infection

Inoculation of mice with the granulocyte-depleting monoclonal antibody RB6-8C5 showed that neutrophils are critical protective effector cells during a Chlamydia trachomatis infection. In addition, administration of monoclonal antibody 2E6 demonstrated that extravasation of neutrophils into the peritoneal cavity in response to inoculation with the C. trachomatis MoPn biovar is dependent on the surface beta-2 integrin molecule CD18.

Alteration of Chlamydia trachomatis biologic behavior in synovial membranes. Suppression of surface antigen production in reactive arthritis and Reiter's syndrome

OBJECTIVE

To investigate the biologic state of Chlamydia and its surface antigen expression in the synovial membranes of patients with Chlamydia-associated reactive arthritis/Reiter's syndrome (ReA/RS).

METHODS

Expression of chlamydial lipopolysaccharide (LPS), major outer membrane protein (MOMP), and elementary body (EB) antigens was studied by gold labeling immunoelectron microscopy on 6 synovial membrane and 2 synovial fluid (SF) pellet samples from 6 patients with Chlamydia-associated arthritis. The study findings were compared with 24-hour cultures of HeLa cells infected with Chlamydia trachomatis EB.

RESULTS

Persistent C trachomatis infection was found in all 6 synovial membrane samples from patients who had either early or chronic arthritis. The infection persisted despite antibiotic treatment, including a 1-month course of doxycycline therapy. Most persistent organisms were atypical reticulate bodies (RBs) found in both fibroblasts and macrophages. Specific, but weak, immunogold staining for all 3 antibodies was found on both intracellular RBs and extracellular EBs. In the SF samples, Chlamydia surface antigens were detected only in phagosomes containing degraded electron-dense materials.

CONCLUSION

The synovial membrane biopsies conducted in this study of Chlamydia-associated ReA/RS revealed atypical RBs with diminished MOMP and LPS expression. Such altered organisms may escape immune surveillance and contribute to disease chronicity; moreover, these organisms may be difficult to detect and treat in some ReA/RS patients.

Chlamydia psittaci infections: a review with emphasis on avian chlamydiosis

In the first part of this article the general characteristics of Chlamydia psittaci namely the history, taxonomy, morphology, reproductive cycle, metabolism and genetics are reviewed. For the taxonomy in particular, a considerable amount of new information has become available in recent years, following the application of monoclonal antibodies and restriction enzymes. Using these techniques isolates of Chlamydia psittaci from birds have been subdivided in different serovars, a number of isolates have been classified in a new species (Chlamydia pecorum) and isolates from animals have been classified as Chlamydia trachomatis. In the second part of the article, the current knowledge on avian chlamydiosis is summarized. Emphasis is put on clinical signs, lesions, pathogenesis, epizootiology, immunity, diagnosis, prevention and treatment. Also the public health considerations are reviewed. It is concluded that the diagnosis of avian chlamydiosis is laborious and that there is still a need for more accurate, simple and rapid diagnostic tools, both for antigen and antibody detection in various species of birds.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Implications for persistent chlamydial infections of phagocyte-microorganism interplay

In vitro models of Chlamydia trachomatis inhibition by cytokines, human-monocyte derived macrophages (HMDM) and human polymorphonuclear leukocytes (HPMN) are discussed in an attempt to delineate the molecular basis of parasite-host cell interplay in persistent and chronic chlamydial infection. Interferon gamma (IFN) has been found to reversibly inhibit chlamydial growth at an early stage in the replicative cycle, while tumor necrosis factor (TNF) has a more profound effect on chlamydial growth resulting in production of aberrant reticulate bodies and enhancement of production of prostaglandin E2 (PGE2). Chlamydia trachomatis (serovar L2) replicate in HMDM while serovar K has been found to be restricted in these cells. Chlamydiae are killed by HPMN but the cell walls persist undegraded, inducing production of oxygen radicals which can be demonstrated to induce DNA strand scissions in HeLa target cells. Evidence is accumulating that chlamydia specific serum IgA antibodies may serve as a noninvasive serological marker for diagnosis of a number of acute and persistent Chlamydia trachomatis infections.

Characterization of the cytochalasin D-resistant (pinocytic) mechanisms of endocytosis utilized by chlamydiae

The cytochalasin D-resistant (pinocytic) portion of the entry of two chlamydia strains (Chlamydia trachomatis L2/434/Bu and Chlamydia psittaci GPIC [guinea pig inclusion conjunctivitis]) was examined. By ultrastructural criteria, few organisms of either strain were observed in association with coated host-cell plasma membrane during entry into McCoy cells; this argues against a coated-pit mechanism of entry. When association with a coated membrane was seen, coat material appeared to pinch off ahead of internalizing chlamydiae. However, entry of both strains was substantially reduced by cytosol acidification, a procedure shown to prevent coated-pit vesiculation (K. Sandvig, S. Olsnes, O. W. Petersen, and B. van Deurs, J. Cell Biol. 105:679-689, 1987). No conclusive evidence of displacement of the fluid-phase marker [3H]sucrose from constitutively forming endocytic vesicles was found. Indeed the entry of strain 434 (but not strain GPIC) was accompanied by the influx of a large volume of fluid, suggesting an inducible mechanism. Additionally, entry of strain 434 (but not strain GPIC) was partially inhibitable by amiloride, yet the drug had no effect on the entry of transferrin, a ligand known to enter solely via coated pits. Our findings endorse the view that chlamydial entry can occur via a pathway involving coated pits. However, the unusual morphology of entry and lack of fluid exclusion are consistent with a process whereby although chlamydiae are not fully enclosed by coat material, their entry is dependent on the vesiculation of coated pits. Furthermore, the data support the proposition that a significant proportion of the entry of strain 434 occurs via an inducible pathway independent of coated-pit uptake.

Inhibition of human neutrophil NADPH oxidase by Chlamydia serovars E, K, and L2

The effects of Chlamydia trachomatis (serovars E, K, and L2) on human neutrophil activation were examined with respect to the organisms both as primary agonists and as agents that modulate cell responses to a second stimulus. Unopsonized chlamydiae alone, at ratios of 1.5 to 100 organisms per cell, failed to elicit changes in intracellular calcium or membrane depolarization or to stimulate the respiratory burst or degranulation during 60 min of incubation. Each of these functions except the respiratory burst was also normally activated when chlamydia-infected neutrophils were subsequently stimulated with formylmethionyl leucine phenylalanine or phorbol myristate acetate; the respiratory burst was inhibited 30 to 65%. Inhibition was dependent on live organisms and was maximal within 5 min of incubation. The organisms had no effect on the superoxide (O2-) assay, and the site of chlamydial inhibition was determined at the level of the NADPH oxidase itself, not at an intermediate step in the activation cascade. The mechanism of enzyme inactivation could not be determined. These results show that unopsonized chlamydiae do not elicit responses from infected neutrophils and suggest that microbicidal mechanisms other than those dependent on elaboration of toxic oxygen-derived species are required to inactivate chlamydiae.

Management and prevention of ocular viral and chlamydial infections

A majority of cases of preventable and/or curable ocular morbidity and blindness are caused by ocular infections. They may account for 70 to 90% of all ocular morbidity seen by family doctors, general practitioners, health centers, and local ophthalmologists in both developed and developing countries. Unfortunately, most health authorities and doctors, including ophthalmologists, consider these diseases to be of little or no importance because they are not fully aware of the high prevalence of these infections and the blinding sequelae which may occur following incorrect diagnosis and treatment. Also, they are not aware of the social and economic impact of these infections in the absence of proper management and implementation of preventive measures. In this review, we examine present knowledge of chlamydial and common viral ocular infections. We discuss the problems of diagnosis, management, and prevention and propose solutions relevant to developed and developing countries.

Nonoxidative antimicrobial effects of human polymorphonuclear leukocyte granule proteins on Chlamydia spp. in vitro

Proteins from isolated granules of human polymorphonuclear leukocytes were assessed for their nonoxidative microbicidal effect on chlamydiae by two different methods: a radioisotope assay for elementary body integrity and a biological assay for inclusion development. Crude granule extract, which consisted of a mixture of all granule proteins, caused a 20 to 30% decrease in infectivity and a 52% decrease in infectivity when incubated with Chlamydia psittaci CAL-10 and Chlamydia trachomatis serovar E, respectively. To define more specifically the components that were damaging to chlamydiae, crude granule extract was subjected to Sephadex G-75 column chromatography and isolated granule fractions were obtained. Only fractions containing lysozyme as the major component consistently caused reductions in infectivity of C. trachomatis elementary bodies. In contrast, fractions collected after the lysozyme fraction, containing proteins with molecular masses of 13,000 daltons or less, had detrimental effects on C. psittaci infectivity. Additional experiments using highly purified human polymorphonuclear leukocyte lysozyme confirmed its infectivity-reducing action upon C. trachomatis but not upon C. psittaci.