Accumulation of chlamydial lipopolysaccharide antigen in the plasma membranes of infected cells

TargeTron Inactivation of Chlamydia trachomatis gseA Results in a Lipopolysaccharide 3-Deoxy-d-Manno-Oct-2-Ulosonic Acid-Deficient Strain That Is Cytotoxic for Cells

All members of the family Chlamydiaceae have lipopolysaccharides (LPS) that possess a shared carbohydrate trisaccharide antigen, 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) that is functionally uncharacterized. A single gene, genus-specific epitope (gseA), is responsible for attaching the tri-Kdo to lipid IVA. To investigate the function of Kdo in chlamydial host cell interactions, we made a gseA-null strain (L2ΔgseA) by using TargeTron mutagenesis. Immunofluorescence microscopy and immunoblotting with a Kdo-specific monoclonal antibody demonstrated that L2ΔgseA lacked Kdo. L2ΔgseA reacted by immunoblotting with a monoclonal antibody specific for a conserved LPS glucosamine-PO4 epitope, indicating that core lipid A was retained by the mutant. The mutant strain produced a similar number of inclusions as the parental strain but yielded lower numbers of infectious elementary bodies. Transmission electron microscopy of L2ΔgseA-infected cells showed atypical developmental forms and a reduction in the number of elementary bodies. Immunoblotting of dithiothreitol-treated L2ΔgseA-infected cells lysates revealed a marked reduction in outer membrane OmcB disulfide cross-linking, suggesting that the elementary body outer membrane structure was affected by the lack of Kdo. Notably, lactic acid dehydrogenase release by infected cells demonstrated that L2ΔgseA was significantly more cytotoxic to host cells than the wild type. The cytotoxic phenotype may result from an altered outer membrane biogenesis structure and/or function or, conversely, from a direct pathobiological effect of Kdo on an unknown host cell target. These findings implicate a previously unrecognized role for Kdo in host cell interactions that facilitates postinfection host cell survival.

Chlamydia Lipooligosaccharide Has Varied Direct and Indirect Roles in Evading both Innate and Adaptive Host Immune Responses

Chlamydia bacteria are obligate intracellular pathogens which can cause a variety of disease in humans and other vertebrate animals. To successfully complete its life cycle, Chlamydia must evade both intracellular innate immune responses and adaptive cytotoxic T cell responses. Here, we report on the role of the chlamydial lipooligosaccharide (LOS) in evading the immune response. Chlamydia infection is known to block the induction of apoptosis. However, when LOS synthesis was inhibited during Chlamydia trachomatis infection, HeLa cells regained susceptibility to apoptosis induction following staurosporine treatment. Additionally, the delivery of purified LOS to the cytosol of cells increased the levels of the antiapoptotic protein survivin. An increase in survivin levels was also detected following C. trachomatis infection, which was reversed by blocking LOS synthesis. Interestingly, while intracellular delivery of lipopolysaccharide (LPS) derived from Escherichia coli was toxic to cells, LOS from C. trachomatis did not induce any appreciable cell death, suggesting that it does not activate pyroptosis. Chlamydial LOS was also a poor stimulator of maturation of bone marrow-derived dendritic cells compared to E. coli LPS. Previous work from our group indicated that LOS synthesis during infection was necessary to alter host cell antigen presentation. However, direct delivery of LOS to cells in the absence of infection did not alter antigenic peptide presentation. Taken together, these data suggest that chlamydial LOS, which is remarkably conserved across the genus Chlamydia, may act both directly and indirectly to allow the pathogen to evade the innate and adaptive immune responses of the host.

Lipooligosaccharide is required for the generation of infectious elementary bodies in Chlamydia trachomatis

Lipopolysaccharides (LPS) and lipooligosaccharides (LOS) are the main lipid components of bacterial outer membranes and are essential for cell viability in most Gram-negative bacteria. Here we show that small molecule inhibitors of LpxC [UDP-3-O-(R-3-hydroxymyristoyl)-GlcNAc deacetylase], the enzyme that catalyzes the first committed step in the biosynthesis of lipid A, block the synthesis of LOS in the obligate intracellular bacterial pathogen Chlamydia trachomatis. In the absence of LOS, Chlamydia remains viable and establishes a pathogenic vacuole ("inclusion") that supports robust bacterial replication. However, bacteria grown under these conditions were no longer infectious. In the presence of LpxC inhibitors, replicative reticulate bodies accumulated in enlarged inclusions but failed to express selected late-stage proteins and transition to elementary bodies, a Chlamydia developmental form that is required for invasion of mammalian cells. These findings suggest the presence of an outer membrane quality control system that regulates Chlamydia developmental transition to infectious elementary bodies and highlights the potential application of LpxC inhibitors as unique class of antichlamydial agents.

In vivo ultrastructural analysis of the intimate relationship between polymorphonuclear leukocytes and the chlamydial developmental cycle

We utilized a recently developed model of intracervical infection with Chlamydia muridarum in the mouse to elicit a relatively synchronous infection during the initial developmental cycle in order to examine at the ultrastructural level the development of both the chlamydial inclusion and the onset of the inflammatory response. At 18 h after infection, only a few elementary bodies attached to cells were visible, as were an occasional intracellular intermediate body and reticulate body. By 24 h, inclusions had 2 to 5 reticulate bodies and were beginning to fuse. A few polymorphonuclear leukocytes (PMNs) were already present in the epithelium in the vicinity of and directly adjacent to infected cells. By 30 h, the inclusions were larger and consisted solely of reticulate bodies, but by 36 to 42 h, they contained intermediate bodies and elementary bodies as well. Many PMNs were adjacent to or actually inside infected cells. Chlamydiae appeared to exit the cell either (i) through disintegration of the inclusion membrane and rupture of the cell, (ii) by dislodgement of the cell from the epithelium by PMNs, or (iii) by direct invasion of the infected cell by the PMNs. When PMNs were depleted, the number of released elementary bodies was significantly greater as determined both visually and by culture. Interestingly, depletion of PMNs revealed the presence of inclusions containing aberrant reticulate bodies, reminiscent of effects seen in vitro when chlamydiae are incubated with gamma interferon. In vivo evidence for the contact-dependent development hypothesis, a potential mechanism for triggering the conversion of reticulate bodies to elementary bodies, and for translocation of lipid droplets into the inclusion is also presented.

Is the role of Chlamydia trachomatis underestimated in patients with suspected reactive arthritis?

Reactive arthritis is usually caused by bacteria of either the enteric or genital tracts. In the genital tract, Chlamydia trachomatis is perhaps the only aetiological agent. In Iran, newer evidence suggests that as C. trachomatis is more commonly found in the general population than was previously believed, its role in reactive arthritis may well be currently overlooked. In this review, as well as emphasizing the potential role of C. trachomatis in reactive arthritis in patients from developing countries, we also make recommendations for further clinical studies to determine its prevalence. Moreover, we also stress the need for standardization of new testing methodologies for C. trachomatis, including the use of new commercial systems in an attempt to determine a truer picture of chlamydial infection in reactive arthritis.

The proinflammatory cytokine response to Chlamydia trachomatis elementary bodies in human macrophages is partly mediated by a lipoprotein, the macrophage infectivity potentiator, through TLR2/TLR1/TLR6 and CD14

Chlamydiae components and signaling pathway(s) responsible for the production of proinflammatory cytokines by human monocytes/macrophages are not clearly identified. To this aim, Chlamydia trachomatis-inactivated elementary bodies (EB) as well as the following seven individual Ags were tested for their ability to induce the production of proinflammatory cytokines by human monocytes/macrophages and THP-1 cells: purified LPS, recombinant heat shock protein (rhsp)70, rhsp60, rhsp10, recombinant polypeptide encoded by open reading frame 3 of the plasmid (rpgp3), recombinant macrophage infectivity potentiator (rMip), and recombinant outer membrane protein 2 (rOmp2). Aside from EB, rMip displayed the highest ability to induce release of IL-1beta, TNF-alpha, IL-6, and IL-8. rMip proinflammatory activity could not be attributed to Escherichia coli LPS contamination as determined by the Limulus Amoebocyte lysate assay, insensitivity to polymyxin B (50 microg/ml), and different serum requirement. We have recently demonstrated that Mip is a "classical" bacterial lipoprotein, exposed at the surface of EB. The proinflammatory activity of EB was significantly attenuated in the presence of polyclonal Ab to rMip. Native Mip was able to induce TNF-alpha and IL-8 secretion, whereas a nonlipidated C20A rMip variant was not. Proinflammatory activity of rMip was unaffected by heat or proteinase K treatments but was greatly reduced by treatment with lipases, supporting a role of lipid modification in this process. Stimulating pathways appeared to involve TLR2/TLR1/TLR6 with the help of CD14 but not TLR4. These data support a role of Mip lipoprotein in pathogenesis of C. trachomatis-induced inflammatory responses.

Ultrastructural analysis of chlamydial antigen-containing vesicles everting from the Chlamydia trachomatis inclusion

Several chlamydial antigens have been detected in the infected epithelial cell cytosol and on the host cell surface prior to their presumed natural release at the end of the 72-96 h developmental cycle. These extra-inclusion antigens are proposed to influence vital host cell functions, antigen trafficking and presentation and, ultimately, contribute to a prolonged inflammatory response. To begin to dissect the mechanisms for escape of these antigens from the chlamydial inclusion, which are enhanced on exposure to antibiotics, polarized endometrial epithelial cells (HEC-1B) were infected with Chlamydia trachomatis serovar E for 36 h or 48 h. Infected cells were then exposed to chemotactic human polymorphonuclear neutrophils not loaded or pre-loaded in vitro with the antibiotic azithromycin. Viewed by electron microscopy, the azithromycin-mediated killing of chlamydiae involved an increase in chlamydial outer membrane blebbing followed by the appearance of the blebs in larger vesicles (i) everting from but still associated with the inclusion as well as (ii) external to the inclusion. Evidence that the vesicles originated from the chlamydial inclusion membrane was shown by immuno-localization of inclusion membrane proteins A, F, and G on the vesicular membranes. Chlamydial heat shock protein 60 (chsp60) copies 2 and 3, but not copy 1, were released from RB and incorporated into the everted inclusion membrane vesicles and delivered to the infected cell surface. These data represent direct evidence for one mechanism of early antigen delivery, albeit membrane-bound, beyond the confines of the chlamydial inclusion.

Chlamydia trachomatis enters a viable but non-cultivable (persistent) state within herpes simplex virus type 2 (HSV-2) co-infected host cells

Epidemiological and clinical studies have shown that double infection with herpes simplex virus type 2 (HSV-2) and Chlamydia trachomatis occurs in vivo. We hypothesized that co-infection would alter replication of these agents. To test this hypothesis, HeLa cells were infected with C. trachomatis serovar E, followed 24 h later by HSV-2 strain 333. Transmission electron microscopic (TEM) analyses indicated that, by 10 h after HSV addition, reticulate bodies (RBs) in co-infected cells were swollen, aberrantly shaped and electron-lucent. In infectious titre assays, HSV-2 co-infection abrogated production of infectious chlamydial progeny. Western blot analyses indicated that accumulation of chlamydial major outer membrane protein (MOMP) was decreased by HSV co-infection while accumulation of chlamydial heat-shock protein 60-1 (HSP60-1) was increased. Polymerase chain reaction (PCR) experiments indicated that chlamydial genome copy number was unaltered by HSV-2 superinfection. Semi-quantitative, reverse transcription PCR (RT-PCR) experiments demonstrated that levels of chlamydial groEL, ftsK, ftsW, dnaA and unprocessed 16S rRNA transcripts were not changed by HSV-2 super-infection. These data indicate that HSV-2 superinfection drives chlamydia into a viable but non-cultivable state, which is the hallmark of persistence. Because chlamydial HSP60-1 has been associated with immunopathology in vivo, these results also suggest that disease severity might be increased in co-infected individuals.

Ultrastructural studies on dengue virus type 2 infection of cultured human monocytes

Background

Early interaction of dengue virus and monocyte/macrophages could be an important feature for virus dissemination after its initial entry via the mosquito vector. Since ultrastructural analysis of this interaction has not been reported, dengue type 2 (DEN2) virus-infected human monocyte cultures were studied at 1, 2, 4 and 6 hours after infection.

Results

Typical dengue particles and fuzzy coated viral particles were 35 to 42 nm and 74 to 85 nm respectively. Viruses were engulfed by phagocytosis and macropicnocytosis leading to huge vacuoles and phagosomes inside the monocytes. Interaction of monocytes with DEN2 virus induced apoptosis, characterized by nuclear condensation and fragmentation, cellular shrinkage, blebbing and budding phenomena and phagocytosis of apoptotic cells by neighboring monocytes. This finding was confirmed by TUNEL. Ultrastructural features associated to DEN2 virus replication were not observed.

Conclusion

These data suggest that clearance of the virus by monocytes and cellular death are the main features during the initial interaction of DEN2 virus and monocytes and this could be important in the rapid elimination of the virus after infection by mosquito vector.

Production of prostaglandin E2 in monocytes stimulated in vitro by Chlamydia trachomatis, Chlamydophila pneumoniae, and Mycoplasma fermentans

Chlamydia trachomatis (CT) as well as Chlamydophila pneumoniae (CP) cause chronic inflammatory diseases in humans. Persistently infected monocytes are involved in the pathogenesis by inducing mediators of inflammation. An in vitro system of chlamydial persistence in human peripheral blood monocytes (HPBM) was used to investigate prostaglandin E(2) (PGE(2)) production and the expression of the key enzyme for prostaglandin production, cyclooxygenase-2 (COX-2). PGE(2) production was determined by PGE(2)-ELISA of HPBM-culture supernatants. Cox-2 mRNA expression was measured by real-time RT-PCR of total RNA isolated from HPBM. Both, CT and CP, stimulated PGE(2) production of HPBM in vitro. Equivalent numbers of CT per host cell induced a higher PGE(2)-response compared to CP. The amount of synthesized PGE(2) depended on the chlamydial multiplicity of infection (MOI). Even at an MOI of 10 the amount of CT- and CP-induced prostaglandin, respectively, was lower than the amount of prostaglandin induced by E. coli lipopolysaccharide (LPS) at a concentration of 10microg/ml. In contrast to stimulation with LPS, Chlamydia-induced PGE(2) production as well as cox-2 mRNA decreased after day 1 post infection (p.i.). These data indicate that Chlamydia stimulate PGE(2) production in human monocytes. Since Chlamydia are often contaminated by mycoplasma, the influence of mycoplasma on the prostaglandin production was investigated additionally. Mycoplasma fermentans (MF) also stimulated PGE(2) production. The co-infection of mycoplasma and Chlamydia resulted in an additive effect in the production of PGE(2). Thus it is important to use host cells and Chlamydia free of mycoplasma contamination for the analysis of Chlamydia-induced prostaglandin production.

Chlamydia-induced arthritis

PURPOSE OF REVIEW

Chlamydia-induced arthritis is the most frequent form of reactive arthritis in Western countries. This article gives an overview of the recent findings with respect to diagnosis, pathogenesis, and therapy of the disease.

RECENT FINDINGS

Recent advances in the modification and standardization of polymerase chain reaction techniques give promise to identify Chlamydia more frequently from joint samples. Based on the sequenced chlamydial genome, considerable progress has been achieved in the understanding of the Chlamydia-host cell interaction, indicating that persistence is an alternate state of the bacteria used by Chlamydia to escape the immune system of the host rather than a general stress response. Furthermore, Chlamydia has the ability to reprogram the host cell by chlamydial effector proteins, which are transported from the inclusion into the host cell cytoplasm. The role of HLA-B27 is discussed in view of the pathogenesis of the disease. HLA-B27 should be considered a risk factor for chronic and/or axial disease rather than a true susceptibility factor for the development of Chlamydia-induced arthritis. No progress has been made in terms of causative therapy aiming at eradication of the bacteria. Tumor necrosis factor-alpha blocking agents may represent a new option in cases that are refractory to therapy.

SUMMARY

Molecular biology not only has improved the ability to detect Chlamydia in the joint for diagnostic purposes but also has extended the current understanding of the pathogenesis of the disease. In contrast to this progress, causative therapy of Chlamydia-induced arthritis is still an unfulfilled need.

How does Chlamydia cause arthritis?

Because the bacterial cause of CIA has been identified and proven to persist at the site of inflammation, the understanding of how Chlamydia cause arthritis has made much progress. The site of entry and the route of dissemination have been identified, the molecular state of persistence is increasingly described, some mechanisms of how Chlamydia can persist despite an actively reacting immune system have been identified, and data regarding how persistent Chlamydia induce inflammation have been obtained. What needs to be achieved in the future--in addition to better understanding the molecular basis of persistence--is to reveal how persisting bacteria can be eliminated. If this information is insufficient for a cure of the disease, it must be determined how the inflammation can be treated more specifically and effectively to cure CIA early and prevent the development of chronic forms that develop into spondyloarthritis.

Chlamydial antigens colocalize within IncA-laden fibers extending from the inclusion membrane into the host cytosol

Chlamydial IncA localizes to the inclusion membrane and to vesicular fibers extending away from the inclusion. Chlamydial outer membrane components, in the absence of developmental forms, are found within these fibers. This colocalization may explain how chlamydial developmental form antigens are localized outside of the inclusion within infected cells.

A Chlamydia trachomatis UDP-N-acetylglucosamine acyltransferase selective for myristoyl-acyl carrier protein. Expression in Escherichia coli and formation of hybrid lipid A species

Chlamydia trachomatis lipid A is unusual in that it is acylated with myristoyl chains at the glucosamine 3 and 3' positions. We have cloned and expressed the gene encoding UDP-N-acetylglucosamine 3-O-acyltransferase of C. trachomatis (CtlpxA), the first enzyme of lipid A biosynthesis. C. trachomatis LpxA displays approximately 20-fold selectivity for myristoyl-ACP over R/S-3-hydroxymyristoyl-ACP under standard assay conditions, consistent with the proposed structure of C. trachomatis lipid A. CtLpxA is the first reported UDP-N-acetylglucosamine acyltransferase that prefers a non-hydroxylated acyl-ACP to a hydroxyacyl-ACP. When CtlpxA was expressed in RO138, a temperature-sensitive lpxA mutant of Escherichia coli, five new hybrid lipid A species were made in vivo after 2 h at 42 degrees C, in place of Escherichia coli lipid A. These compounds were purified and analyzed by matrix-assisted laser desorption ionization/time of flight mass spectrometry. In each case, a myristoyl chain replaced one or both of the ester linked 3-hydroxymyristoyl residues of E. coli lipid A. With prolonged growth at 42 degrees C, all the ester-linked 3-hydroxymyristoyl residues were replaced with myristate chains. Re-engineering the structure of E. coli lipid A should facilitate the microbiological production of novel agonists or antagonists of the innate immunity receptor TLR-4, with possible uses as adjuvants or anti-inflammatory agents.

Detection of chlamydial antibody by fetal serology--an aid to the diagnosis of ovine abortion

Two serological tests (indirect immunofluorescence and enzyme-linked immunosorbent assay) were developed for the detection of fetal antibody to Chlamydia psittaci. Fetal blood and thoracic fluid from 126 field cases of suspected ovine chlamydial abortion were examined using both tests. Placenta and fetal tissues (lung, liver, and kidney) from the same animals were also examined by the following conventional diagnostic methods: isolation in McCoy cells, detection of chlamydial lipopolysaccharide (LPS), modified Ziehl-Nielsen staining, and direct fluorescent antibody staining of chlamydia in frozen cryostat sections. Seventy cases were positive by fetal serology, and of these, 68 were also positive by isolation and/or LPS detection. The remaining 56 cases had negative fetal serology, and of these, 39 were positive by isolation and/or LPS detection. Results indicate that fetal serology, although less sensitive than either isolation in McCoy cells or detection of chlamydial LPS antigen, may be of particular use when placenta is not available.

Immunity to murine Chlamydia trachomatis genital tract reinfection involves B cells and CD4(+) T cells but not CD8(+) T cells

CD4(+) T-helper type 1 (Th1) responses are essential for the resolution of a primary Chlamydia trachomatis genital tract infection; however, elements of the immune response that function in resistance to reinfection are poorly understood. Defining the mechanisms of immune resistance to reinfection is important because the elements of protective adaptive immunity are distinguished by immunological memory and high-affinity antigen recognition, both of which are crucial to the development of efficacious vaccines. Using in vivo antibody depletion of CD4(+) and CD8(+) T cells prior to secondary intravaginal challenge, we identified lymphocyte populations that functioned in resistance to secondary chlamydial infection of the genital tract. Depletion of either CD4(+) or CD8(+) T cells in immune wild-type C57BL/6 mice had a limited effect on resistance to reinfection. However, depletion of CD4(+) T cells, but not CD8(+) T cells, in immune B-cell-deficient mice profoundly altered the course of secondary infection. CD4-depleted B-cell-deficient mice were unable to resolve a secondary infection, shed high levels of infectious chlamydiae, and did not resolve the infection until 3 to 4 weeks following the discontinuation of anti-CD4 treatment. These findings substantiated a predominant role for CD4(+) T cells in host resistance to chlamydial reinfection of the female genital tract and demonstrated that CD8(+) T cells are unnecessary for adaptive immune resistance. More importantly, however, this study establishes a previously unrecognized but very significant role for B cells in resistance to chlamydial reinfection and suggests that B cells and CD4(+) T cells may function synergistically in providing immunity in this model of chlamydial infection. Whether CD4(+) T cells and B cells function independently or dependently is unknown, but definition of those mechanisms is fundamental to understanding optimum protective immunity and to the development of highly efficacious immunotherapies against chlamydial urogenital infections.

Amino acid transport into cultured McCoy cells infected with Chlamydia trachomatis

Amino acid transport into McCoy cells infected with strains representative of the two major biovars of Chlamydia trachomatis has been studied to determine if uptake is increased during infection. Preliminary work suggested that the transport systems L, A/ASC (for neutral amino acid transport), N (for transport of Asn, Gln, and His) and y+ (for cationic amino acids) were present in McCoy cells. With lymphogranuloma venereum biovar strain 434, little difference in the influx of representative amino acids Trp, His, and Lys or the analogue 2-aminoisobutyric acid (AIB) was observed during infection. With trachoma biovar strain DK20, a small increase in the initial entry rate and equilibrium concentration of each amino acid was found. McCoy cells appear to have great capacity for concentrating amino acids, which might obviate the need for transport induction by chlamydiae under conditions favoring the growth of infectious organisms.

In vitro infection of cells of the monocytic/macrophage lineage with bovine leukaemia virus

The oncogenic retrovirus bovine leukaemia virus (BLV) primarily infects B cells. Most infected animals remain asymptomatic for long periods of time before an increase in circulating B cells or localized tumours can be observed. This long clinical latency period may be explained by cells of the monocyte/macrophage lineage (M/M) becoming infected and acting as a reservoir for the virus, as shown for other retroviruses (human immunodeficiency virus-1, feline immunodeficiency virus). M/M cells in different stages of differentiation (HL-60, THP-1, U-937, J774, BGM, PM2, primary macrophages of sheep and cows) were cultured with BLV produced by permanently infected donor cells (FLKBLV and BLV-bat(2)). Donor cells were inhibited from multiplying by either irradiation or treatment with mitomycin C. In other experiments, supernatant from donor cells containing virus was used. In co-culture with the donor cells, the less differentiated monocytic cells showed severe cellular changes such as differentiation, vacuolization, cell lysis and membrane blebbing; apoptosis was a frequent phenomenon. Budding and extracellular viruses were also observed. The more differentiated macrophage cells, although they showed less signs of infection by microscopy, had a complete BLV protein profile, as seen by Western blotting; bands corresponding to p24CA (Gag) and its precursors were clearly seen. In addition, gp51SU was identified by syncytia formation assays. It is concluded that M/M cells may be infected by BLV, the consequences of the infection differing according to the type of cell.

Aetiological agents: their molecular biology and phagocyte-host interaction

Inflammatory joint disease can develop following an extra-articular infection. The term reactive arthritis was coined in order to differentiate this arthritis, which is often characterized by lack of culturable organisms in the joint, from septic arthritides. Bacteria known to trigger reactive arthritis include Campylobacter, Chlamydia, Salmonella, Shigella and Yersinia. Demonstration of bacteria or bacterial macromolecules in the joint has elicited the idea that reactive arthritis is a sterile process induced and maintained by antigenic material in the synovium. Continued synthesis of antigens to maintain synovial inflammation probably requires establishment of persistent bacterial infection in the joint, or at the primary site of infection. In the case of Chlamydia trachomatis, viable, metabolically-active organisms have been demonstrated to exist for extended periods in the joints of patients with reactive arthritis. In this chapter, we review the aetiological agents, and their molecular biology and phagocyte-host interactions, that are involved in reactive arthritis and spondylarthropathy.

The intracellular life of Chlamydia psittaci: how do the bacteria interact with the host cell?

Throughout the life of any organism interactions with the surrounding environment are always taking place, a process that leads to evolution. Chlamydia psittaci is an obligate intracellular parasite, but it must also be capable of extracellular survival in order to search for new host cells. Therefore, these peculiar prokaryotes have evolved two different particles and a unique developmental cycle that, together with a series of not yet fully understood interactions with their host cells, allow them to fulfil the requirements for their permanence in nature. These interactions are the subject of this paper. Particular attention is paid to the attachment and internalization of the bacteria, the chlamydial vacuole, and the avoidance of lysosomal degradation.

Localization of Chlamydia trachomatis heat shock proteins 60 and 70 during infection of a human endometrial epithelial cell line in vitro

Unlike chlamydial lipopolysaccharide, which is released from the developing inclusion to the surface of infected genital epithelial cells, both Chlamydia trachomatis heat shock protein (hsp) 60 and 70 antigens remained confined within the inclusion during the course of the chlamydial developmental cycle. Exposure of the infected cells to penicillin to induce a persistent infection or to a lipophilic microbicide did not potentiate secretion or exocytosis of the chlamydial hsp.

Internalization of Chlamydia by Dendritic Cells and Stimulation of Chlamydia-Specific T Cells

Chlamydia species are the causative agents of trachoma, various forms of pneumonia, and the most common sexually transmitted diseases. Although the infection cycle has been extensively characterized in epithelial cells, where the Chlamydia entry-vacuoles avoid fusion with host-cell lysosomes, the cellular immune response has received less attention. Moreover, despite the abundant presence of dendritic cells (DC) in the sites of infection, the interaction between Chlamydia and DC has never been studied. We observe that DC kill Chlamydia trachomatis and Chlamydia psittaci. The chlamydiae are internalized by the DC in a nonspecific manner through macropinocytosis, and the macropinosomes fuse subsequently with DC lysosomes expressing MHC class II molecules. The interaction induces maturation of the DC, since presentation of an exogenous Ag is severely inhibited after a 1-day incubation, although chlamydial Ags are still presented and recognized by Chlamydia-specific CD4+ T cells. Thus, DC most likely play a role in initiating the T cell response in vivo and could potentially be used in adoptive transfer therapies to vaccinate against Chlamydia.

Ultrastructural and molecular analyses of the persistence of Chlamydia trachomatis (serovar K) in human monocytes

Previous studies have suggested that monocytes may play a role in the dissemination of Chlamydia trachomatis, and in establishment of persistent infection with this bacterium. Infection of cultured human peripheral blood monocytes with C. trachomatis serovar K produced persistent, nonproductive infection. Transmission electron microscopy of such infected cultures revealed single or multiple Chlamydia in monocyte inclusions over a culture period of 10 days. Those inclusions were aberrant, and normal reticulate bodies within the inclusions were not observed. Immunoelectron microscopy showed the chlamydial major outer membrane protein and lipopolysaccharide to be associated with the bacterial plasma membrane. Lipopolysaccharide was also identified in the monocyte cytoplasm. Molecular analyses of primary chlamydial rRNA transcripts demonstrated that the organism is viable and metabolically active within monocyte inclusions. However, attempts to overcome chlamydial growth arrest by incubation of Chlamydia-infected monocytes with tryptophan, and antibodies against alpha interferon, gamma interferon, or tumor necrosis factor, were all ineffective, suggesting that known mechanisms of growth inhibition do not hold in human monocytes. These observations indicate that infection of human peripheral blood monocytes with C. trachomatis may be involved in the genesis/maintenance of extra-urogenital inflammation, since non-culturable, metabolically active bacteria persist in those cells.

Current methods of laboratory diagnosis of Chlamydia trachomatis infections

Infections caused by Chlamydia trachomatis are probably the most common sexually transmitted diseases in the United States. Commonly unrecognized and often inadequately treated, chlamydial infections can ascend the reproductive tract and cause pelvic inflammatory disease, which often results in the devastating consequences of infertility, ectopic pregnancy, or chronic pelvic pain. C. trachomatis infections are also known to increase the risk for human immunodeficiency virus infection. The obligate intracellular life cycle of C. trachomatis has traditionally required laboratory diagnostic tests that are technically demanding, labor-intensive, expensive, and difficult to access. In spite of these historical challenges, however, laboratory diagnosis of C. trachomatis has been a rapidly advancing area in which there is presently a wide array of commercial diagnostic technologies, costs, manufacturers. This review describes and compares the diagnostic methods for C. trachomatis infection that are currently approved for use in the United States, including the newest DNA amplification technologies which are yet to be licensed for commercial use. Issues to consider in selecting a test for purposes of screening versus diagnosis based on prevalence, performance, legal, social, and cost issues are also discussed.

Ultrastructural changes in avian Chlamydia psittaci serovar A-, B-, and D-infected Buffalo Green Monkey cells

In order to find an explanation for the observed differences in levels of pathogenicity in turkeys of Chlamydia psittaci 84/55 (avian serovar A), 89/1326 (avian serovar B), 92/1293 (avian serovar D), and the Texas Turkey strain (avian serovar D) (P.B. Wyrick, J. Choong, S.T. Knight, D. Goyeau, E.S. Stuart, and A.B. MacDonald, Immunol. Infect. Dis. 4:131-141, 1994), the reproductive cycles of organisms of the four strains were studied in Buffalo Green Monkey cells by transmission electron microscopy, immunoelectron microscopy, and flow cytometry. Organisms of strains most pathogenic in turkeys, namely, the serovar A strain and the 92/1293 serovar D strain, (i) replicated faster, since at 50 h postinoculation significantly larger inclusions with more numerous infectious organisms were observed than with the less pathogenic strains; (ii) were often found devoid of inclusion membranes scattered throughout the cytoplasms; and (iii) induced severe degenerative changes in Buffalo Green Monkey cells. By immunoelectron microscopy and flow cytometry, chlamydial antigens could not be detected in the plasma membranes of infected host cells. However, the presence of chlamydial antigens in inclusion membranes was demonstrated by immunoelectron microscopy.

Tumor necrosis factor alpha activity in genital tract secretions of guinea pigs infected with chlamydiae

Previous studies using the guinea pig model of chlamydial genital infection demonstrated that primary infection is associated with a marked acute inflammatory response early on, while chronic inflammation appears later, at a time when the level of infection is reduced. Challenge infections result primarily in a chronic inflammatory response. The stimuli that initiate inflammation and lead to tissue damage have not been defined. We investigated the possibility that tumor necrosis factors (TNFs) play a role in the inflammatory response to chlamydial genital tract infection. Cytotoxicity assays for TNF were performed on genital tract secretions collected from female guinea pigs during infection with the Chlamydia psittaci agent of guinea pig inclusion conjunctivitis. During the early days of primary infection, high levels of TNF-alpha were detected in genital tract secretions from inbred S2 strain and outbred Hartley strain guinea pigs. Significantly lower levels of TNF-alpha were detected in secretions from both strains during challenge infection. In general, the intensity of the TNF-alpha response was proportional to the intensity of infection. High TNF-alpha levels were present during primary infection at a time of marked neutrophil influx. Thus, TNF-alpha may play an important role in the response to primary chlamydial genital tract infection.

Experimental Chlamydia pneumoniae infection in mice: effect of reinfection and passive immunization

NIH/S mice were infected intranasally with Chlamydia pneumoniae isolate Kajaani 6 and rechallenged after either 28 or 70 days. A partial resistance to reinfection, indicated by a reduced recovery of live organisms, was noted at both time points of rechallenge: positive isolations from lung homogenates and/or bronchoalveolar lavage fluids were observed in fewer mice and the yields of isolated chlamydiae remained smaller, as compared to primary infection. However, a previous infection did not confer any protection against inflammatory changes. A strong peribronchial and perivascular inflammation with infiltrating lymphocytes and plasma cells was noted in the lungs of primary infected, as well as reinfected, mice. The effect of passive immunization was also studied. When mice were given convalescent or hyperimmune sera intraperitoneally before inoculation, lower C. pneumoniae isolation yields were detected. As in the rechallenge experiment, marked inflammation could still be seen in the lungs, now with polymorphonuclear leukocyte infiltration. The results suggest that immunological reactions play a role in the pathogenesis of C. pneumoniae infection. Antibodies may be important in reducing the amount of infective elementary bodies, but complete clearing of C. pneumoniae could not be achieved in these experiments, even less a protection against inflammatory lung changes.

Chlamydial envelope components and pathogen-host cell interactions

Few bacterial pathogens are as widespread in nature or as capable of eliciting such a diversity of disease syndromes as are the chlamydiae. As obligate intracellular organisms, they pose a special research challenge in defining the molecular components and mechanisms for productive growth within host cells and the overall progress of infection throughout host tissue. Although a comprehensive view of chlamydial envelope composition and respective functions in pathogenesis is far from complete, ongoing investigations continue to expose new and intriguing avenues for exploration.

The LPS localization might explain the lack of protection of LPS-specific antibodies in abortion-causing Chlamydia psittaci infections

Four monoclonal antibodies against chlamydial lipopolysaccharide (LPS) were used to study their localization and distribution in the Chlamydia psittaci AB7 abortion-causing strain by immunoelectron microscopy. A non-embedding technique on whole chlamydiae, together with a post-embedding technique on McCoy cells infected with the strain, were performed. Immunogold labelling was observed on the surface of reticular bodies (RB), but not on elementary bodies (EB). Immunolabelling was observed in ultrathin sections on both sides of the external chlamydial membrane, mainly on the inner side of EB and on the outer side of RB. Immunogold density was higher in EB than in RB; however, the absolute number of gold particles was higher in RB than EB, suggesting a loss of immunolabelling during the transformation of RB into EB. Specific labelling of LPS was also found in electrodense and adielectronic vacuoles near the surface of the cytoplasmic membrane of infected McCoy cells. These results suggest that the lack of protection against some chlamydial strains, despite the presence of anti-LPS specific antibodies, is due to the localization of LPS on the inner side of the external membrane of EB.

Staining of surface antigens of Chlamydia trachomatis L2 in tissue culture

Surface labeling of chlamydial elementary and reticulate bodies in L929 cells infected with Chlamydia trachomatis serotype L2 was monitored by using monoclonal antibodies (MAb) against the major outer membrane protein and lipopolysaccharide (LPS). Different staining and fixation procedures were used to detect these surface antigens during the developmental cycle. Anti-major outer membrane protein MAb yielded a clear staining pattern of exclusively chlamydial inclusions independent of the fixation or staining technique used. Anti-LPS MAb gave a faint staining pattern of reticulate bodies when methanol fixation was used and showed that LPS was released from chlamydiae into the host cell cytoplasm and into the surroundings of the infected host cell. However, when paraformaldehyde-glutardialdehyde fixation was used, extracellular LPS staining was not observed. The data show that chlamydial LPS is loosely bound in the bacterial outer membrane but suggest that shedding of LPS is a fixation artifact.

Presence of parasite antigen on the surface of P388D1 cells infected with Ehrlichia risticii

Indirect immunofluorescence staining of macrophages infected with Ehrlichia risticii by anti-E. risticii serum revealed a punctate staining pattern on the surface of the host cell. This pattern was distinguishable by fluorescence microscopy from E. risticii bound to the surface of the macrophage and from intracellular E. risticii. The surface localization of ehrlichial antigen on infected macrophages was confirmed by electron microscopy with immunoferritin labeling. As the intracellular ehrlichial burden increased, the amount of ehrlichial antigen on the host cell surface increased. Prokaryotic protein synthesis was necessary for the maintenance of ehrlichial antigen on the host cell surface, as demonstrated by disappearance of the surface antigen following treatment with oxytetracycline. However, host cell protein synthesis was not required, as demonstrated by the continued presence of ehrlichial antigen on the surface of host cells after cycloheximide treatment. Pronase treatment abolished the ehrlichial antigen present on the cell surface, indicating that this antigen is a protein. Anti-E. risticii serum or immunoglobulin G-mediated antibody-dependent cellular cytotoxicity of infected cells was demonstrated in a chromium release assay. These results imply that the parasite antigen on the host cell surface has a role in the pathogenesis of ehrlichiosis.

Immunoelectron microscopy of Chlamydia psittaci with monoclonal antibodies

An immunoelectron microscopic study was performed to determine the distribution of antigenic components on particles of Chlamydia psittaci and infected cells using a number of monoclonal antibodies (MAbs). Of three anti-lipopolysaccharide (LPS) antibodies (4D5, A2 and 4G5), two antibodies (4D5 and A2) reacted with the surface of reticulate bodies (RBs) but not with that of elementary bodies (EBs). The other antibody (4G5) reacted with both EBs and RBs. Examination of infected cells in thin sections revealed that 4D5 and A2 combined with the membranes of both EBs and RBs. These results indicate that each LPS epitope localized at a different position in the chlamydial membrane. Most MAbs directed to protein antigens reacted on the surface of both EBs and RBs though 3E9 specific for the 90 kDa and 50 kDa protein components combined with RBs only.

Examination of chlamydial glycolipid with monoclonal antibodies: cellular distribution and epitope binding

A chlamydial glycolipid antigen (GLXA) is shed into the medium of C. trachomatis-infected cell cultures. This study screened monoclonal antibodies (mAb), prepared in different laboratories by immunization with embryonated egg propagated elementary bodies (EB), for their ability to bind with infected cells and to react with purified GLXA isolated from supernatants of infected McCoy cells. The fluorescent antibody (FA) staining pattern exhibited by a number of mAb indicated that they bound antigen present within the inclusion and at the inner membrane surface of infected cells; the observed pattern differs significantly from the distribution seen when anti-lipopolysaccharide (LPS) (mAb) were used. The staining pattern observed by immunofluorescence was confirmed and extended by ultrastructure studies of immunogold-labelled, infected human endometrial gland epithelial cells (HEGEC) and a human endometrial carcinoma-derived cell line (RL95-2). Additionally, the immunoelectron microscope studies revealed binding within the inclusion and on reticulate bodies, within the cell cytoplasm and at the surface of infected cells. The specificity of the reactive mAb, examined by molecular shift chromatography and isolated, affinity-purified GLXA, indicated that two mAb of the IgG isotype recognized an antigen which had been purified from tissue culture supernatants by affinity chromatography using an IgM mAb. The results suggest that GLXA is an important determinant whose role and function during in vitro and in vivo infections deserves further analyses.

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.

Chlamydia and sudden infant death syndrome. A study of 166 SIDS and 30 control cases

Chlamydia inclusions could be demonstrated by an immunofluorescence assay in formalin-fixed lung sections in 32 of 166 cases (19.4%) of Sudden Infant Death Syndrome (SIDS) and in the lungs of only 1 of 30 infants with a known cause of death (3.3%). The difference is statistically significant (P = 0.04). Chlamydia trachomatis is an agent of pneumonia in 1-4 month-old infants who have acquired the disease from an infected cervix during birth, but other chlamydia species are also capable of causing pneumonia. The lung sections of the 32 chlamydia positive SIDS cases did not show typical histological signs of pneumonia. Even though chlamydia inclusions were detected in the lungs of 32 SIDS cases a causal relation between chlamydia infection and SIDS could not be demonstrated.

Expression of a repeating phosphorylated disaccharide lipophosphoglycan epitope on the surface of macrophages infected with Leishmania donovani

Murine peritoneal macrophages were infected with living, virulent Leishmania donovani promastigotes. At intervals after infection, the macrophage surfaces were probed for the expression of lipophosphoglycan (LPG) epitopes by immunofluorescence with anti-LPG monoclonal antibodies. A repeating phosphorylated disaccharide epitope of LPG was detected as early as 5 to 10 min postinfection and was initially localized to the immediate area of internalization of the promastigote into the macrophage. The epitopes were evenly distributed over the entire macrophage surface by 25 min postinfection. Treatments which inhibited macrophage phagolysosomal degradation processes had no effect on epitope expression, whereas reagents that affected macrophage membrane flow and, thus, phagocytosis drastically reduced or abolished expression. Purified LPG or phosphoglycan, the delipidated form of the LPG molecule, was also shown to bind to a variety of different cell types in a temperature-independent manner. Since LPG has been implicated as having an immunoprotective role in leishmaniasis, these results suggest a further mechanism(s) by which Leishmania LPG might be involved in parasite pathogenicity and virulence.