Differences in growth characteristics and elementary body associated cytotoxicity between Chlamydia trachomatis oculogenital serovars D and H and Chlamydia muridarum

Recognition of Chlamydia trachomatis by Toll-like receptor 9 is altered during persistence

Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA (gDNA). Previous bioinformatic studies have demonstrated that the genome of the human pathogen Chlamydia trachomatis contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here, we present our evaluation of the stimulatory potential of C. trachomatis gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. Utilizing reporter cell lines, we demonstrate that purified gDNA from C. trachomatis can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while C. trachomatis is capable of signaling through hTLR9 and mTLR9 during live infections in HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion, exacerbated by the inhibition of lipooligosaccharide biosynthesis, and is significantly altered during the induction of aberrance/persistence. Our observations support the hypothesis that chlamydial gDNA is released during the conversion between the pathogen's replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly. Given that C. trachomatis inclusions do not co-localize with TLR9-containing vacuoles in the pro-monocytic cell line U937, our findings also hint that chlamydial gDNA is capable of egress from the inclusion, and traffics to TLR9-containing vacuoles via an as yet unknown pathway.

Recognition of Chlamydia trachomatis by Toll-Like Receptor 9 is altered during persistence

Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA. Previous bioinformatic studies have indicated that the genome of the human pathogen Chlamydia trachomatis contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here we present our evaluation of the stimulatory potential of C. trachomatis gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. We confirm that hTLR9 colocalizes with chlamydial inclusions in the pro-monocytic cell line, U937. Utilizing HEK293 reporter cell lines, we demonstrate that purified genomic DNA from C. trachomatis can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while C. trachomatis is capable of signaling through hTLR9 and mTLR9 during live infections in non-phagocytic HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion and exacerbated by the inhibition of lipooligosaccharide biosynthesis. The induction of aberrance / persistence also significantly alters Chlamydia-specific TLR9 signaling. Our observations support the hypothesis that chlamydial gDNA is released at appreciable levels by the bacterium during the conversion between its replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly.

Direct assessment of possible mutations in the 23S rRNA gene encoding macrolide resistance in Chlamydia trachomatis

Reports of potential treatment failure have raised particular concerns regarding the efficacy of the single dose azithromycin regimen in the treatment of urogenital and anorectal Chlamydia trachomatis (CT) infections. Several factors have been suggested, including heterotypic resistance. Antimicrobial susceptibility testing in CT requires cell culture with serial dilutions of antibiotics, which is laborious and for which there is no standardized testing methodology. One method to partly overcome these difficulties would be to use a genotypic resistance assay, however most current available assays do still require prior CT culture. In order to facilitate the assessment of genotypic resistance directly from clinical samples, without the need for prior culture, the aim of this study was to develop a CT specific PCR assay for the assessment of resistance associated mutations (RAMs) in the 23S rRNA gene, and to evaluate a sample of clinical cases in which CT PCR’s remained positive during follow-up despite azithromycin treatment. Neither the in silico analysis nor the analytical specificity testing demonstrated clinically relevant cross-reactivity with other bacterial species. These results in conjunction with the analytical sensitivity demonstrating consistent CT 23S rRNA gene detection in the range of 10e3 IFU/mL, exemplify the assay’s apt performance. Although no known macrolide RAMs were detected in the clinical cases, the described assay allows future culture independent macrolide RAM surveillance in CT, and increases accessibility for other laboratories to engage in screening.

Host-Pathogen Interactions of Chlamydia trachomatis in Porcine Oviduct Epithelial Cells

Chlamydia trachomatis (Ct) causes the most prevalent bacterial sexually transmitted disease leading to ectopic pregnancy and infertility. Swine not only have many similarities to humans, but they are also susceptible to Ct. Despite these benefits and the ease of access to primary tissue from this food animal, in vitro research in swine has been underutilized. This study will provide basic understanding of the Ct host–pathogen interactions in porcine oviduct epithelial cells (pOECs)—the counterparts of human Fallopian tube epithelial cells. Using NanoString technology, flow cytometry, and confocal and transmission-electron microscopy, we studied the Ct developmental cycle in pOECs, the cellular immune response, and the expression and location of the tight junction protein claudin-4. We show that Ct productively completes its developmental cycle in pOECs and induces an immune response to Ct similar to human cells: Ct mainly induced the upregulation of interferon regulated genes and T-cell attracting chemokines. Furthermore, Ct infection induced an accumulation of claudin-4 in the Ct inclusion with a coinciding reduction of membrane-bound claudin-4. Downstream effects of the reduced membrane-bound claudin-4 expression could potentially include a reduction in tight-junction expression, impaired epithelial barrier function as well as increased susceptibility to co-infections. Thereby, this study justifies the investigation of the effect of Ct on tight junctions and the mucosal epithelial barrier function. Taken together, this study demonstrates that primary pOECs represent an excellent in vitro model for research into Ct pathogenesis, cell biology and immunity.

Dual RNA-seq analysis of in vitro infection multiplicity and RNA depletion methods in Chlamydia-infected epithelial cells

Dual RNA-seq experiments examining viral and bacterial pathogens are increasing, but vary considerably in their experimental designs, such as infection rates and RNA depletion methods. Here, we have applied dual RNA-seq to Chlamydia trachomatis infected epithelial cells to examine transcriptomic responses from both organisms. We compared two time points post infection (1 and 24 h), three multiplicity of infection (MOI) ratios (0.1, 1 and 10) and two RNA depletion methods (rRNA and polyA). Capture of bacterial-specific RNA were greatest when combining rRNA and polyA depletion, and when using a higher MOI. However, under these conditions, host RNA capture was negatively impacted. Although it is tempting to use high infection rates, the implications on host cell survival, the potential reduced length of infection cycles and real world applicability should be considered. This data highlights the delicate nature of balancing host-pathogen RNA capture and will assist future transcriptomic-based studies to achieve more specific and relevant infection-related biological insights.

Chlamydia muridarum Can Invade the Central Nervous System via the Olfactory and Trigeminal Nerves and Infect Peripheral Nerve Glial Cells

Chlamydia pneumoniae can infect the brain and has been linked to late-onset dementia. Chlamydia muridarum, which infects mice, is often used to model human chlamydial infections. While it has been suggested to be also important for modelling brain infection, nervous system infection by C. muridarum has not been reported in the literature. C. pneumoniae has been shown to infect the olfactory bulb in mice after intranasal inoculation, and has therefore been suggested to invade the brain via the olfactory nerve; however, nerve infection has not been shown to date. Another path by which certain bacteria can reach the brain is via the trigeminal nerve, but it remains unknown whether Chlamydia species can infect this nerve. Other bacteria that can invade the brain via the olfactory and/or trigeminal nerve can do so rapidly, however, whether Chlamydia spp. can reach the brain earlier than one-week post inoculation remains unknown. In the current study, we showed that C. muridarum can within 48 h invade the brain via the olfactory nerve, in addition to infecting the trigeminal nerve. We also cultured the glial cells of the olfactory and trigeminal nerves and showed that C. muridarum readily infected the cells, constituting a possible cellular mechanism explaining how the bacteria can invade the nerves without being eliminated by glial immune functions. Further, we demonstrated that olfactory and trigeminal glia differed in their responses to C. muridarum, with olfactory glia showing less infection and stronger immune response than trigeminal glia.

Chlamydia trachomatis and Chlamydia muridarum spectinomycin resistant vectors and a transcriptional fluorescent reporter to monitor conversion from replicative to infectious bacteria

Chlamydia trachomatis infections are the leading cause of sexually transmitted infections of bacterial origin. Lower genital tract infections are often asymptomatic, and therefore left untreated, leading to ascending infections that have long-term consequences on female reproductive health. Human pathology can be recapitulated in mice with the mouse adapted strain C. muridarum. Eight years into the post-genetic era, significant advances to expand the Chlamydia genetic toolbox have been made to facilitate the study of this important human pathogen. However, the need for additional tools remains, especially for C. muridarum. Here, we describe a new set of spectinomycin resistant E. coli-Chlamydia shuttle vectors, for C. trachomatis and C. muridarum. These versatile vectors allow for expression and localization studies of Chlamydia effectors, such as Inc proteins, and will be instrumental for mutant complementation studies. In addition, we have exploited the differential expression of specific Chlamydia genes during the developmental cycle to engineer an omcA::gfp fluorescent transcriptional reporter. This novel tool allows for monitoring RB to EB conversion at the bacterial level. Spatiotemporal tracking of GFP expression within individual inclusions revealed that RB to EB conversion initiates in bacteria located at the edge of the inclusion and correlates with the time post initiation of bacterial replication and inclusion size. Comparison between primary and secondary inclusions potentially suggests that the environment in which the inclusions develop influences the timing of conversion. Altogether, the Chlamydia genetic tools described here will benefit the field, as we continue to investigate the molecular mechanisms underlying Chlamydia-host interaction and pathogenesis.

Growth kinetics of Chlamydia trachomatis in primary human Sertoli cells

Chlamydia trachomatis (Ct) is the leading cause of bacterial sexually transmitted infections worldwide and has been associated with male infertility. Recently, it was hypothesized that Ct may infect the epithelium of the seminiferous tubule, formed by Sertoli cells, thus leading to impaired spermatogenesis. To date, there is a lack of data on Ct infection of the seminiferous epithelium; therefore, we aimed to characterize, for the first time, an in vitro infection model of primary human Sertoli cells. We compared Ct inclusion size, morphology and growth kinetics with those in McCoy cells and we studied F-actin fibres, Vimentin-based intermediate filaments and α-tubulin microtubules in Sertoli and McCoy cells. Our main finding highlighted the ability of Ct to infect Sertoli cells, although with a unique growth profile and the inability to exit host cells. Furthermore, we observed alterations in the cytoskeletal fibres of infected Sertoli cells. Our results suggest that Ct struggles to generate a productive infection in Sertoli cells, limiting its dissemination in the host. Nevertheless, the adverse effect on the cytoskeleton supports the notion that Ct may compromise the blood-testis barrier, impairing spermatogenesis.

Enumeration of Viable Chlamydia from Infected Animals Using Immunofluorescent Microscopy

An appropriate means of quantitating infectious Chlamydia from infected animals is essential for the evaluation of vaccines. However, unlike methods involving culture, nonculture methods, including detection of antigen or DNA, are not able to differentiate between viable and nonviable organisms. As an obligate intracellular bacterium, Chlamydia replicates inside host cells by forming unique organelles called inclusions. Here, we describe the enumeration of viable C. trachomatis from infected mice by culturing vaginal swabs on McCoy cells and counting inclusions via immunofluorescent microscopy.

Effect of cold water-induced stress on immune response, pathology and fertility in mice during Chlamydia muridarum genital infection

Genital infection by Chlamydia trachomatis is the most common bacterial sexually transmitted disease worldwide. It causes serious reproductive health complications, including pelvic inflammatory disease and infertility. Stress is implicated as a risk factor for various infections; however, its effect on chlamydia genital infection is unknown. We previously showed that repeated exposure of mice to cold water results in increased severity of chlamydia genital infection. In this study, cold water-induced stress resulted in (i) elevated levels of norepinephrine (NE) and epinephrine in the spleen and genital tract of stressed mice; (ii) elevated IL-1β, TNF-α, IL-6 and nitric oxide production in macrophage-rich peritoneal cells of mice; (iii) supplement of NE in vitro exerts an immunosuppressive effect on splenic T-cell production of cytokines; (iv) decreased C. muridarum shedding in the genital tract of β1Adr/β2Adr receptor KO mice; and (v) a higher rate of infertility in infected mice. These results suggest that cold water stress induces the production of catecholamines, which may play a critical role in the modulation of the immune system leading to increased intensity of C. muridarum genital infection.

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

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.

Recombinant polymorphic membrane protein D in combination with a novel, second-generation lipid adjuvant protects against intra-vaginal Chlamydia trachomatis infection in mice

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rPmpD in combination with SLA elicits significant protection against intra-vaginal Ct challenge.

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Antibodies induced by immunisation with rPmpD recognise Ct elementary bodies.

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SLA is a novel adjuvant class that may be widely used in future preclinical Ct vaccine development.

The development of a chlamydial vaccine that elicits protective mucosal immunity is of paramount importance in combatting the global spread of sexually transmitted Chlamydia trachomatis (Ct) infections. While the identification and prioritization of chlamydial antigens is a crucial prerequisite for efficacious vaccine design, it is likely that novel adjuvant development and selection will also play a pivotal role in the translational potential of preclinical Ct vaccines. Although the molecular nature of the immuno-modulatory component is of primary importance, adjuvant formulation and delivery systems may also govern vaccine efficacy and potency. Our study provides the first preclinical evaluation of recombinant Ct polymorphic membrane protein D (rPmpD) in combination with three different formulations of a novel second-generation lipid adjuvant (SLA). SLA was rationally designed in silico by modification of glucopyranosyl lipid adjuvant (GLA), a TLR4 agonistic precursor molecule currently in Phase II clinical development. We demonstrate robust protection against intra-vaginal Ct challenge in mice, evidenced by significantly enhanced resistance to infection and reduction in mean bacterial load. Strikingly, protection was found to correlate with the presence of robust anti-rPmpD serum and cervico-vaginal IgG titres, even in the absence of adjuvant-induced Th1-type cellular immune responses elicited by each SLA formulation, and we further show that anti-rPmpD antibodies recognize Ct EBs. These findings highlight the utility of SLA and rational molecular design of adjuvants in preclinical Ct vaccine development, but also suggest an important role for anti-rPmpD antibodies in protection against urogenital Ct infection.

Recombinant Human Peptidoglycan Recognition Proteins Reveal Antichlamydial Activity

Peptidoglycan recognition proteins (PGLYRPs) are innate immune components that recognize the peptidoglycan and lipopolysaccharides of bacteria and exhibit antibacterial activity. Recently, the obligate intracellular parasite Chlamydia trachomatis was shown to have peptidoglycan. However, the antichlamydial activity of PGLYRPs has not yet been demonstrated. The aim of our study was to test whether PGLYRPs exhibit antibacterial activity against C. trachomatis Thus, we cloned the regions containing the human Pglyrp1, Pglyrp2, Pglyrp3, and Pglyrp4 genes for subsequent expression in human cell lines. We obtained stable HeLa cell lines that secrete recombinant human PGLYRPs into culture medium. We also generated purified recombinant PGLYRP1, -2, and -4 and confirmed their activities against Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria. Furthermore, we examined the activities of recombinant PGLYRPs against C. trachomatis and determined their MICs. We also observed a decrease in the infectious ability of chlamydial elementary bodies in the next generation after a single exposure to PGLYRPs. Finally, we demonstrated that PGLYRPs attach to C. trachomatis elementary bodies and activate the expression of the chlamydial two-component stress response system. Thus, PGLYRPs inhibit the development of chlamydial infection.

Genital Chlamydia trachomatis: understanding the roles of innate and adaptive immunity in vaccine research

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted disease worldwide, and despite significant advances in chlamydial research, a prophylactic vaccine has yet to be developed. This Gram-negative obligate intracellular bacterium, which often causes asymptomatic infection, may cause pelvic inflammatory disease (PID), ectopic pregnancies, scarring of the fallopian tubes, miscarriage, and infertility when left untreated. In the genital tract, Chlamydia trachomatis infects primarily epithelial cells and requires Th1 immunity for optimal clearance. This review first focuses on the immune cells important in a chlamydial infection. Second, we summarize the research and challenges associated with developing a chlamydial vaccine that elicits a protective Th1-mediated immune response without inducing adverse immunopathologies.

A Multi-Component Prime-Boost Vaccination Regimen with a Consensus MOMP Antigen Enhances Chlamydia trachomatis Clearance

BACKGROUND

A vaccine for Chlamydia trachomatis is of urgent medical need. We explored bioinformatic approaches to generate an immunogen against C. trachomatis that would induce cross-serovar T-cell responses as (i) CD4(+) T cells have been shown in animal models and human studies to be important in chlamydial protection and (ii) antibody responses may be restrictive and serovar specific.

METHODS

A consensus antigen based on over 1,500 major outer membrane protein (MOMP) sequences provided high epitope coverage against the most prevalent C. trachomatis strains in silico. Having designed the T-cell immunogen, we assessed it for immunogenicity in prime-boost regimens. This consensus MOMP transgene was delivered using plasmid DNA, Human Adenovirus 5 (HuAd5) or modified vaccinia Ankara (MVA) vectors with or without MF59(®) adjuvanted recombinant MOMP protein.

RESULTS

Different regimens induced distinct immune profiles. The DNA-HuAd5-MVA-Protein vaccine regimen induced a cellular response with a Th1-biased serum antibody response, alongside high serum and vaginal MOMP-specific antibodies. This regimen significantly enhanced clearance against intravaginal C. trachomatis serovar D infection in both BALB/c and B6C3F1 mouse strains. This enhanced clearance was shown to be CD4(+) T-cell dependent. Future studies will need to confirm the specificity and precise mechanisms of protection.

CONCLUSION

A C. trachomatis vaccine needs to induce a robust cellular response with broad cross-serovar coverage and a heterologous prime-boost regimen may be an approach to achieve this.

TLR2, TLR4 and TLR9 genotypes and haplotypes in the susceptibility to and clinical course of Chlamydia trachomatis infections in Dutch women

Chlamydia trachomatis infections demonstrate remarkable differences in clinical course that are approximately 40% based on host genetic variation. Here, we study the single nucleotide polymorphisms (SNPs) and their haplotypes in TLR2, TLR4 and TLR9 (TLR2 +2477G>A; TLR2 -16934T>A; TLR4+896A>G; TLR9 -1237T>C and TLR9 +2848G>A) in relation to the susceptibility to, and severity of C. trachomatis infections. We analysed the five SNPs in a cohort of 770 Dutch Caucasian women either attending a sexually transmitted diseases outpatient clinic (n = 731) or having complaints of subfertility (n = 39). Haplotype analyses showed a trend for TLR2 haplotype I (-16934T/+2477G) to protect against the development of symptoms and tubal pathology (Ptrend = 0.03) after Chlamydia infection. In the susceptibility cohort, TLR9 haplotype III (-1237C/+2848A) showed a significant decreasing trend in the development of symptoms after C. trachomatis infection (P = 0.02, OR: 0.55, 95%CI: 0.33-0.91). Logistic regression of the TLR2 haplotypes, TLR4+896A>G, and TLR9 haplotypes showed that the TLR2 haplotype combinations AG-TA and AG-TG confer risk (OR 3.4 (P = 0.01) and 1.6 (P = 0.03)), while the TLR9 haplotype combination TG-TA protects against C. trachomatis infections (OR: 0.4, P = 0.004). Our study shows that both TLR2 and TLR9 genes and SNP combinations do influence the clinical course of Chlamydia infections.

Serovar D and E of serogroup B induce highest serological responses in urogenital Chlamydia trachomatis infections

Background

Chlamydia trachomatis is the most prevalent bacterial sexually transmitted infection (STI) worldwide. A strong link between C. trachomatis serogroup/serovar and serological response has been suggested in a previous preliminary study. The aim of the current study was to confirm and strengthen those findings about serological IgG responses in relation to C. trachomatis serogroups and serovars.

Methods

The study population (n = 718) consisted of two patient groups with similar characteristics of Dutch STI clinic visitors. We performed genotyping of serovars and used titre based and quantitative commercially available ELISA kits (medac Diagnostika) to determine specific serum IgG levels. Optical density (OD) values generated by both tests were used to calculate the IgG titres (cut-off 1:50). Analyses were conducted stratified by gender.

Results

We observed very significant differences when comparing the median IgG titres of three serogroups, B, C and I: in women for B vs. C: p < 0.0001 (median titres B 200 vs. C <50); B vs. I: p < 0.0001 (200 vs. 50), and in men for B vs. C: p = 0.0006 (150 vs. <50); B vs. I: p = 0.0001 (150 vs. <50); C vs. I was not significant for both sexes. Serovars D and E of serogroup B had the highest median IgG titres compared to the other serovars in both men and women: 200 and 200 vs. ≤ 100 for women and 100 and 200 vs. ≤ 75 for men, respectively.

Conclusions

This study shows that B group serovars induce higher serological responses compared to the C and I group serovars in vivo in both men and women.

Animal models for studying female genital tract infection with Chlamydia trachomatis

Chlamydia trachomatis is a Gram-negative obligate intracellular bacterial pathogen. It is the leading cause of bacterial sexually transmitted disease in the world, with more than 100 million new cases of genital tract infections with C. trachomatis occurring each year. Animal models are indispensable for the study of C. trachomatis infections and the development and evaluation of candidate vaccines. In this paper, the most commonly used animal models to study female genital tract infections with C. trachomatis will be reviewed, namely, the mouse, guinea pig, and nonhuman primate models. Additionally, we will focus on the more recently developed pig model.

Genomic features beyond Chlamydia trachomatis phenotypes: what do we think we know?

The obligate intracellular pathogen Chlamydia trachomatis is the causative agent of the blinding trachoma and the world's leading cause of bacterial sexually transmitted infections. Despite aggressive antibacterial control measures, C. trachomatis infections have been increasing, constituting a serious public health concern due to its morbidity and socioeconomic burden. Still, very little is known about the molecular basis underlying the phenotypic disparities observed among C. trachomatis serovars in terms of tissue tropism (ocular conjunctiva, epithelial-genitalia and lymph nodes), virulence (disease outcomes) and ecological success. This is in part due to the inexistence of straightforward tools to genetically manipulate Chlamydiae and host cell-free growth systems, hampering the elucidation of the biological role of loci. The recent release of tenths of full-genome C. trachomatis sequences depict a strains clustering scenario reflecting the organ/cell-type that they preferentially infect. However, the high degree of genomic conservation implies that few genetic features are involved in phenotypic dissimilarities. The purpose of this review is to gather the most relevant data dispersed throughout the literature concerning the genotypic evidences that support niche-specific phenotypes. This review focus on chromosomal dynamics phenomena like recombination and point-mutations, essentially involving outer and inclusion membrane proteins, type III secretion effectors, and hypothetical proteins with unknown function. The scrutiny of C. trachomatis loci involved in tissue tropism, pathogenesis and ecological success is crucial for the development of disease-specific prophylaxis.

Chlamydia trachomatis vaccine research through the years

Chlamydia trachomatis is a Gram-negative obligate intracellular bacterium. It is the leading cause of bacterial sexual transmitted infections (STIs). World Health Organization figures estimated that over 90 million new cases of genital C. trachomatis infections occur worldwide each year. A vaccination program is considered to be the best approach to reduce the prevalence of C. trachomatis infections, as it would be much cheaper and have a greater impact on controlling C. trachomatis infections worldwide rather than a screening program or treating infections with antibiotics. Currently, there are no vaccines available which effectively protect against a C. trachomatis genital infection despite the many efforts that have been made throughout the years. In this paper, the many attempts to develop a protective vaccine against a genital C. trachomatis infection will be reviewed.

Discovering and differentiating new and emerging clonal populations of Chlamydia trachomatis with a novel shotgun cell culture harvest assay

This assay, coupled with ompA and 16S rRNA sequencing, characterized clonal populations of C. trachomatis.

Chlamydia trachomatis is the leading cause of preventable blindness and bacterial sexually transmitted diseases worldwide. Plaque assays have been used to clonally segregate laboratory-adapted C. trachomatis strains from mixed infections, but no assays have been reported to segregate clones from recent clinical samples. We developed a novel shotgun cell culture harvest assay for this purpose because we found that recent clinical samples do not form plaques. Clones were strain-typed by using outer membrane protein A and 16S rRNA sequences. Surprisingly, ocular trachoma reference strain A/SA-1 contained clones of Chlamydophila abortus. C. abortus primarily infects ruminants and pigs and has never been identified in populations where trachoma is endemic. Three clonal variants of reference strain Ba/Apache-2 were also identified. Our findings reflect the importance of clonal isolation in identifying constituents of mixed infections containing new or emerging strains and of viable clones for research to more fully understand the dynamics of in vivo strain-mixing, evolution, and disease pathogenesis.

Interaction of Chlamydia trachomatis serovar E with male genital tract epithelium results in secretion of proinflammatory cytokines

Although much has been reported on the in vitro interaction of Chlamydia trachomatis with cells derived from the female genital tract, little is known of its interaction with male genital tract epithelium. The aim of this work was to investigate the effect of C. trachomatis serovar E on immortalized normal human urethral epithelial cells and on immortalized normal adult human prostate epithelial cells with regard to chlamydial growth and secretion of cytokines. After infection, these epithelial cells were assessed for their support of chlamydial growth in comparison with HeLa cells, and cytokine levels in cell culture supernatants were determined by ELISA. Although the male-derived epithelial cells supported growth of chlamydiae, the best growth was seen in HeLa cells. In contrast to prostate epithelial cells, the urethral epithelial cells released much larger quantities of interleukin 1alpha (IL-1alpha) following infection, whereas both IL-6 and IL-8 were produced in larger quantities by infected prostate cells. At 7 days post-infection, HeLa cells consistently produced large quantities of all three cytokines. In conclusion, the male-derived cell lines were shown to support the invasion of C. trachomatis and initiate a proinflammatory response to infection. From in vitro studies the suggestion that high levels of IL-6 could be a possible marker for chlamydial prostatitis is confirmed. Although not as marked a change, it is also suggested that higher IL-8 levels could be associated more with infection of the prostate than the urethra. Differential cytokine production by different male-derived epithelial cells could help determine the site of chlamydial infection and help in the study of pathogenesis.

Chlamydial interferon gamma immune evasion influences infection tropism

Chlamydia trachomatis is a human pathogen and Chlamydia muridarum is a mouse pathogen but paradoxically, they share near genomic synteny. The majority of strain-variable genes are located primarily in a hyper-variable region termed the plasticity zone. Tryptophan synthase and cytotoxin are plasticity zone genes unique to the human and murine strains, respectively. Tryptophan synthase is a virulence factor that differentiates C. trachomatis strains into genital and ocular disease pathotypes, whereas cytotoxin(s) is a virulence factor linked to murine infection tropism. Divergence in these loci is strongly correlated with host-specific interferon gamma effector activities, suggesting that these virulence genes have co-evolved with their respective hosts as a primary mechanism to evade innate immunity. These findings have important implications for chlamydial animal modeling studies.

Efficacy of an immune modulator in experimental Chlamydia trachomatis infection of the female genital tract

Objective. The aim of this study was to determine if vaginal application of the immune response modifier imiquimod (Aldara cream, 3M Pharmaceuticals, St Paul, Minn) would alter the course and/or outcome of female genital tract infection with a human isolate of Chlamydia trachomatis in a murine model. Methods. Groups of CF-1 mice were treated with Aldara on three different schedules: (1) ongoing beginning 5 days prior to and continuing through day 5 of infection; (2) a single prophylactic dose 2 hours prior to infection; and (3) therapeutic from day 4 to day 14 of infection. Mice were infected vaginally with a serovar D strain of C trachomatis, and monitored by culture to determine the level of shedding and duration of infection. Results. We observed a significant reduction in both duration of infection and the level of shedding during the acute phase in mice treated on an ongoing basis commencing 5 days prior to infection. There was no effect with respect to the other regimens. Conclusion. These results demonstrate that ongoing Aldara treatment has efficacy and may enhance local innate immunity which reduces the duration of subsequent infection with human isolates of C trachomatis in a murine model of female genital tract infection.

The CD14 functional gene polymorphism -260 C>T is not involved in either the susceptibility to Chlamydia trachomatis infection or the development of tubal pathology

BACKGROUND

The functional polymorphism -260 C>T in the LPS sensing TLR4 co-receptor CD14 gene enhances the transcriptional activity and results in a higher CD14 receptor density. Individuals carrying the T/T genotype also have significantly higher serum levels of soluble CD14. The T allele of this polymorphism has recently been linked to Chlamydia pneumoniae infection. We investigated the role of the CD14 -260 C>T polymorphism in the susceptibility to and severity (defined as subfertility and/or tubal pathology) of C. trachomatis infection in Dutch Caucasian women.

METHODS

The different CD14 -260 C>T genotypes were assessed by PCR-based RFLP analysis in three cohorts: 1) A cohort (n = 576) of women attending a STD clinic, 2) a cohort (n = 253) of women with subfertility, and 3) an ethnically matched control cohort (n = 170). The following variables were used in the analysis: In cohort 1 the CT-DNA status, CT IgG serology status, self-reported symptoms and in cohort 2, the CT IgG serology status and the tubal status at laparoscopy.

RESULTS

In the control cohort the CC, CT and TT genotype distribution was: 28.2%, 48.2%, and 23.5% respectively. No differences were found in the overall prevalence of CD14 -260 genotypes (28.1%, 50.7%, and 21.2%) in cohort 1 when compared to the control cohort. Also no differences were observed in women with or without CT-DNA, with or without serological CT responses, with or without symptoms, or in combinations of these three variables. In subfertile women with tubal pathology (cohort 2, n = 50) the genotype distribution was 28.0%, 48.0%, and 24.0% and in subfertile women without tubal pathology (n = 203), 27.6%, 49.3% and 23.2%. The genotype distribution was unchanged when CT IgG status was introduced in the analyses.

CONCLUSION

The CD14 -260 C>T genotype distributions were identical in all three cohorts, showing that this polymorphism is not involved in the susceptibility to or severity of sequelae of C. trachomatis infection.

Acquired homotypic and heterotypic immunity against oculogenital Chlamydia trachomatis serovars following female genital tract infection in mice

Background

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen causing female genital tract infection throughout the world. Reinfection with the same serovar, as well as multiple infections with different serovars, occurs in humans. Using a murine model of female C. trachomatis genital tract infection, we determined if homotypic and/or heterotypic protection against reinfection was induced following infection with human oculogenital strains of C. trachomatis belonging to two serovars (D and H) that have been shown to vary significantly in the course of infection in the murine model.

Methods

Groups of outbred CF-1 mice were reinfected intravaginally with a strain of either serovar D or H, two months after initial infection with these strains. Cellular immune and serologic status, both quantitative and qualitative, was assessed following initial infection, and the course of infection was monitored by culturing vaginal samples collected every 2–7 days following reinfection.

Results

Serovar D was both more virulent (longer duration of infection) and immunogenic (higher level of circulating and vaginal IgG and higher incidence of IgA in vaginal secretions) in the mouse genital tract. Although both serovars induced cross-reacting antibodies during the course of primary infection, prior infection with serovar H resulted in only a slight reduction in the median duration of infection against homotypic reinfection (p ~ 0.10), while prior infection with serovar D resulted in significant reduction in the median duration of infection against both homotypic (p < 0.01) and heterotypic reinfection (p < 0.01) when compared to primary infection in age and conditions matched controls.

Conclusion

Serovar D infection resulted in significant homotypic and heterotypic protection against reinfection, while primary infection with serovar H resulted in only slight homotypic protection. In addition to being the first demonstration of acquired heterotypic immunity between human oculogenital serovars, the differences in the level and extent of this immunity could in part explain the stable difference in serovar prevalence among human isolates.