Chlamydia trachomatis paralyses neutrophils to evade the host innate immune response

Effectiveness of a serogroup B meningococcal vaccine against gonorrhea: A retrospective study

BACKGROUND

Outer membrane vesicle (OMV) meningococcal serogroup B (MenB) vaccines might be protective against gonorrhea. We evaluated the effectiveness of MenB-4C, an OMV MenB vaccine, against gonorrhea.

METHODS

We identified gonococcal mono-infections, chlamydial mono-infections, and gonococcal/chlamydial co-infections among persons aged 15-30 years in the electronic health records of Kaiser Permanente Northern California during 2016-2021. We determined MenB-4C vaccination status (vaccinated [≥1 MenB-4C vaccine dose] or unvaccinated [MenB-4C vaccine naïve]) at each infection. We used log-binomial regression with generalized estimating equations to calculate adjusted prevalence ratios (APR) and 95 % confidence intervals (CI) to determine if MenB-4C vaccination was protective against gonococcal mono-infections compared to chlamydial mono-infection. We also evaluated if MenB-4C vaccination was protective against gonococcal/chlamydial co-infections. Because of concerns with small sample size of vaccinated persons, we estimated effects using a limited model (adjusting for race/ethnicity only) and an expanded model (adjusting for additional potential confounders).

RESULTS

Of 68,454 persons, we identified 558 (0.8 %) MenB-4C vaccinated persons and 85,393 infections (13,000 gonococcal mono-infections, 68,008 chlamydial mono-infections, and 4385 gonococcal/chlamydial co-infections). After adjusting for race/ethnicity, MenB-4C vaccination was 23 % protective against gonococcal mono-infection compared to chlamydial mono-infection (APR = 0.77, 95 % CI = 0.64-0.99) in the limited model but not in the expanded model.

CONCLUSION

MenB-4C vaccination was protective against gonococcal mono-infection, independent of race/ethnicity. This protective effect was not observed when other potential confounders were included in the analysis. Protection against gonococcal/chlamydial co-infection was not observed. Efficacy data from clinical trials are needed.

Chlamydia-driven ISG15 expression dampens the immune response of epithelial cells independently of ISGylation

Excessive inflammation upon Chlamydia trachomatis infection can cause severe damages in the female genital tract. This obligate intracellular bacterium develops mainly in epithelial cells, whose innate response contributes to the overall inflammatory response to infection. The ubiquitin-like protein interferon-stimulated gene 15 (ISG15) stimulates interferon γ (IFNγ) production and is required for bacterial clearance in several infectious contexts. Here, we describe and investigate the consequences of the increase in ISG15 expression by epithelial cells infected with C. trachomatis. Infection of HeLa cells and primary ecto-cervical epithelial cells resulted in a transcriptional upregulation of ISG15 expression. This did not involve the canonical type I interferon (IFN-I) signaling pathway and depended instead on the activation of the STING/TBK1/IRF3 pathway. The absence or reduction of ISG15 synthesis led to increased production of several cytokines and chemokines, including interleukin (IL) 6 and IL8. This implicates that ISG15 normally dampens the immune response induced by C. trachomatis infection in epithelial cells. ISG15 exerted its control from an intracellular location, but without involving ISGylation. Finally, higher levels of inflammation and delayed bacterial clearance were observed in the genital tracts of ISG15-KO mice infected by C. trachomatis compared with wild-type animals; however, IFNγ production was unchanged. Altogether, our data show that ISG15 expression acts as a brake on the immune response to C. trachomatis infection in epithelial cells and limits bacterial burden and inflammation in mice.IMPORTANCEInfection of epithelial cells by Chlamydia trachomatis elicits an innate immune response by these cells. The signaling pathways involved, and their outcomes, are still very poorly understood. In this paper, we described how Chlamydia infection triggered the expression of ISG15, a small molecule normally associated to type I interferon (IFN-I) signaling and control of INF-γ production. ISG15 synthesis by epithelial cells attenuated their immune response to Chlamydia infection. In mice, we observed that ISG15 displayed a marginal role in modulating the production of IFN-γ, a key component of the host immune response to infection, but facilitated bacterial clearance. Overall, our study strengthens the importance of ISG15 not only in the resolution of viral but also of bacterial infection and document its role of "immune brake" in the context of Chlamydia infection.

Seminal plasma inhibits Chlamydia trachomatis infection in vitro, and may have consequences on mucosal immunity

Seminal plasma (SP) is the main vector of C. trachomatis (CT) during heterosexual transmission from male to female. It has immunomodulatory properties and impacts the susceptibility to HIV-1 infection, but its role has not been explored during CT infection. In the female reproductive tract (FRT), CT infection induces cytokine production and neutrophil recruitment. The role of neutrophils during CT infection is partially described, they could be at the origin of the pathology observed during CT infection. During this study, we developed an experimental in vitro model to characterize the impact of CT infection and SP on endocervical epithelial cell immune response in the FRT. We also studied the impact of the epithelial cell response on neutrophil phenotype and functions. We showed that the production by epithelial cells of pro-inflammatory cytokines increased during CT infection. Moreover, the pool of SP as well as individuals SP inhibited CT infection in a dose-dependent manner. The pool of SP inhibited cytokine production in a dose-dependent manner. The pool of SP altered gene expression profiles of infected cells. The culture supernatants of cells infected or not with CT, in presence or not of the pool of SP, had an impact on neutrophil phenotype and functions: they affected markers of neutrophil maturation, activation and adhesion capacity, as well as the survival, ROS production and phagocytosis ability. This study proposes a novel approach to study the impact of the environment on the phenotype and functions of neutrophils in the FRT. It highlights the impact of the factors of the FRT environment, in particular SP and CT infection, on the mucosal inflammation and the need to take into account the SP component while studying sexually transmitted infections during heterosexual transmission from male to female.

Isolation and characterization of Chlamydia felis and its pathogenesis in cats

Feline upper respiratory tract disease (URTD) is a common but complicated disease that occurs in domestic cats, worldwide. 396 cats in Guangxi Province, China were screened for URTD-associated pathogens from March 2022 to August 2023. Mycoplasma felis was found to be the most prevalent infectious agent with a positivity rate of 24.75 %, followed by feline calicivirus (FCV), Chlamydia felis, feline herpesvirus 1 (FHV-1) and feline influenza A virus (FeIAV) with rates of 15.91, 11.62, 5.56 and 1.52 %, respectively. In particular, C. felis and M. felis were found in 13 of 55 co-infected cats. Of the 46 C. felis-positive samples, one strain, named as GXNN36, was successfully isolated using chicken embryos and it was characterized both in vivo and in vitro. For the cat studies, both high- and low-dose challenged groups showed severe conjunctivitis, accompanied by transient fever and respiratory symptoms. C. felis replicated well in turbinate, trachea and lung tissues with high copy numbers and the infection subsequently spread to the livers, spleens, pancreas, kidneys, hearts and intestines. These findings will help our understanding of the role of C. felis in feline URTD and provide a valuable model to evaluate the efficacy of vaccines and therapeutic remedies in the future.

Immunity to Sexually Transmitted Bacterial Infections of the Female Genital Tract: Toward Effective Vaccines

Sexually transmitted infections (STIs) caused by bacterial pathogens Chlamydia trachomatis, Neisseria gonorrhoeae, and Treponema pallidum present significant public health challenges. These infections profoundly impact reproductive health, leading to pelvic inflammatory disease, infertility, and increased susceptibility to other infections. Prevention measures, including antibiotic treatments, are limited by the often-asymptomatic nature of these infections, the need for repetitive and continual screening of sexually active persons, antibiotic resistance for gonorrhea, and shortages of penicillin for syphilis. While vaccines exist for viral STIs like human papillomavirus (HPV) and hepatitis B virus (HBV), there are no vaccines available for bacterial STIs. This review examines the immune responses in the female genital tract to these bacterial pathogens and the implications for developing effective vaccines against bacterial STIs.

An inflammatory paradox: strategies inflammophilic oral pathobionts employ to exploit innate immunity via neutrophil manipulation

Inflammatory dysbiotic diseases present an intriguing biological paradox. Like most other infectious disease processes, the alarm bells of the host are potently activated by tissue-destructive pathobionts, triggering a cascade of physiological responses that ultimately mobilize immune cells like neutrophils to sites of active infection. Typically, these inflammatory host responses are critical to inhibit and/or eradicate infecting microbes. However, for many inflammatory dysbiotic diseases, inflammophilic pathobiont-enriched communities not only survive the inflammatory response, but they actually obtain a growth advantage when challenged with an inflammatory environment. This is especially true for those organisms that have evolved various strategies to resist and/or manipulate components of innate immunity. In contrast, members of the commensal microbiome typically experience a competitive growth disadvantage under inflammatory selective pressure, hindering their critical ability to restrict pathobiont proliferation. Here, we examine examples of bacteria-neutrophil interactions from both conventional pathogens and inflammophiles. We discuss some of the strategies utilized by them to illustrate how inflammophilic microbes can play a central role in the positive feedback cycle that exemplifies dysbiotic chronic inflammatory diseases.

A TriAdj-Adjuvanted Chlamydia trachomatis CPAF Protein Vaccine Is Highly Immunogenic in Pigs

Chlamydia trachomatis (Ct) infections are the most common sexually transmitted infection (STI). Despite effective antibiotics for Ct, undetected infections or delayed treatment can lead to infertility, ectopic pregnancies, and chronic pelvic pain. Besides humans, chlamydia poses similar health challenges in animals such as C. suis (Cs) in pigs. Based on the similarities between humans and pigs, as well as their chlamydia species, we use pigs as a large biomedical animal model for chlamydia research. In this study, we used the pig model to develop a vaccine candidate against Ct. The vaccine candidate consists of TriAdj-adjuvanted chlamydial-protease-like activity factor (CPAF) protein. We tested two weekly administration options-twice intranasal (IN) followed by twice intramuscular (IM) and twice IM followed by twice IN. We assessed the humoral immune response in both serum using CPAF-specific IgG (including antibody avidity determination) and also in cervical and rectal swabs using CPAF-specific IgG and IgA ELISAs. The systemic T-cell response was analyzed following in vitro CPAF restimulation via IFN-γ and IL-17 ELISpots, as well as intracellular cytokine staining flow cytometry. Our data demonstrate that while the IN/IM vaccination mainly led to non-significant systemic immune responses, the vaccine candidate is highly immunogenic if administered IM/IN. This vaccination strategy induced high serum anti-CPAF IgG levels with strong avidity, as well as high IgA and IgG levels in vaginal and rectal swabs and in uterine horn flushes. In addition, this vaccination strategy prompted a pronounced cellular immune response. Besides inducing IL-17 production, the vaccine candidate induced a strong IFN-γ response with CD4 T cells. In IM/IN-vaccinated pigs, these cells also significantly downregulated their CCR7 expression, a sign of differentiation into peripheral-tissue-homing effector/memory cells. Conclusively, this study demonstrates the strong immunogenicity of the IM/IN-administered TriAdj-adjuvanted Ct CPAF vaccine candidate. Future studies will test the vaccine efficacy of this promising Ct vaccine candidate. In addition, this project demonstrates the suitability of the Cs pre-exposed outbred pig model for Ct vaccine development. Thereby, we aim to open the bottleneck of large animal models to facilitate the progression of Ct vaccine candidates into clinical trials.

Neutrophil CD64 index as a potential blood biomarker for the diagnosis of neurosyphilis in secondary and tertiary syphilis: A retrospective study

Objective

To examine the correlation of neutrophil CD64 (nCD64) index with neurosyphilis (NS) across different stages of syphilis.

Methods

A total of 1243 syphilis patients at different stages (344 of primary, 385 of secondary, and 514 of tertiary) included in this study were divided into NS and non-NS (NNS). Correlations of nCD64 index with currently used syphilis biomarkers were explored using Spearman correlation test. Relationships between nCD64 index and NS at different stages were investigated by stratified analysis and restricted cubic spline model. The diagnostic performance of nCD64 index for NS was assessed by receiver operating characteristic (ROC) curve.

Results

Significant statistical correlations of nCD64 index with cerebrospinal fluid (CSF) NS indicators were found in secondary and tertiary syphilis. Increased nCD64 index was associated with increased risk of NS in secondary and tertiary syphilis. ROC analysis values further confirmed the diagnostic potential of nCD64 index for NS. Marked decrease of nCD64 index was observed in NS patients after effective antisyphilitic treatments.

Conclusions

The nCD64 index may help to the diagnosis of NS in secondary and tertiary syphilis.

Antibodies from chlamydia-infected individuals facilitate phagocytosis via Fc receptors

Non-neutralizing functions of antibodies, including phagocytosis, may play a role in Chlamydia trachomatis (CT) infection, but these functions have not been studied and assays are lacking. We utilized a flow-cytometry-based assay to determine whether serum samples from a well-characterized cohort of CT-infected and naïve control individuals enhanced phagocytosis via Fc-receptor-expressing THP-1 cells, and whether this activity correlated with antibody titers. Fc-receptor-mediated phagocytosis was detected only in CT+ donors. Phagocytosis generally did not correlate well with antibody titer. In addition, we found that complement from both CT+ and negative individuals enhanced phagocytosis of CT into primary neutrophils. These results suggest that anti-CT antibodies can have functions that are not reflected by titer. This method could be used to quantitively measure Fc-receptor-mediated function of anti-CT antibodies or complement activity and could reveal new immune correlates of protection.

Neutrophil Extracellular Traps in Tumors and Potential Use of Traditional Herbal Medicine Formulations for Its Regulation

Neutrophil extracellular traps (NETs) are extracellular fibers composed of deoxyribonucleic acid (DNA) and decorated proteins produced by neutrophils. Recently, NETs have been associated with the development of many diseases, including tumors. Herein, we reviewed the correlation between NETs and tumors. In addition, we detailed active compounds from traditional herbal medicine formulations that inhibit NETs, related nanodrug delivery systems, and antibodies that serve as "guiding moieties" to ensure targeted delivery to NETs. Furthermore, we discussed the strategies used by pathogenic microorganisms to evade NETs.

Understanding bacterial pathogenicity: a closer look at the journey of harmful microbes

Bacteria are the most prevalent form of microorganisms and are classified into two categories based on their mode of existence: intracellular and extracellular. While most bacteria are beneficial to human health, others are pathogenic and can cause mild to severe infections. These bacteria use various mechanisms to evade host immunity and cause diseases in humans. The susceptibility of a host to bacterial infection depends on the effectiveness of the immune system, overall health, and genetic factors. Malnutrition, chronic illnesses, and age-related vulnerabilities are the additional confounders to disease severity phenotypes. The impact of bacterial pathogens on public health includes the transmission of these pathogens from healthcare facilities, which contributes to increased morbidity and mortality. To identify the most significant threats to public health, it is crucial to understand the global burden of common bacterial pathogens and their pathogenicity. This knowledge is required to improve immunization rates, improve the effectiveness of vaccines, and consider the impact of antimicrobial resistance when assessing the situation. Many bacteria have developed antimicrobial resistance, which has significant implications for infectious diseases and favors the survival of resilient microorganisms. This review emphasizes the significance of understanding the bacterial pathogens that cause this health threat on a global scale.

Contributions of diverse models of the female reproductive tract to the study of Chlamydia trachomatis-host interactions

Chlamydia trachomatis is a common cause of sexually transmitted infections in humans with devastating sequelae. Understanding of disease on all scales, from molecular details to the immunology underlying pathology, is essential for identifying new ways of preventing and treating chlamydia. Infection models of various complexity are essential to understand all aspects of chlamydia pathogenesis. Cell culture systems allow for research into molecular details of infection, including characterization of the unique biphasic Chlamydia developmental cycle and the role of type-III-secreted effectors in modifying the host environment to allow for infection. Multicell type and organoid culture provide means to investigate how cells other than the infected cells contribute to the control of infection. Emerging comprehensive three-dimensional biomimetic systems may fill an important gap in current models to provide information on complex phenotypes that cannot be modeled in simpler in vitro models.

Insights into innate immune cell evasion by Chlamydia trachomatis

Chlamydia trachomatis, is a kind of obligate intracellular pathogen. The removal of C. trachomatis relies primarily on specific cellular immunity. It is currently considered that CD4+ Th1 cytokine responses are the major protective immunity against C. trachomatis infection and reinfection rather than CD8+ T cells. The non-specific immunity (innate immunity) also plays an important role in the infection process. To survive inside the cells, the first process that C. trachomatis faces is the innate immune response. As the "sentry" of the body, mast cells attempt to engulf and remove C. trachomatis. Dendritic cells present antigen of C. trachomatis to the "commanders" (T cells) through MHC-I and MHC-II. IFN-γ produced by activated T cells and natural killer cells (NK) further activates macrophages. They form the body's "combat troops" and produce immunity against C. trachomatis in the tissues and blood. In addition, the role of eosinophils, basophils, innate lymphoid cells (ILCs), natural killer T (NKT) cells, γδT cells and B-1 cells should not be underestimated in the infection of C. trachomatis. The protective role of innate immunity is insufficient, and sexually transmitted diseases (STDs) caused by C. trachomatis infections tend to be insidious and recalcitrant. As a consequence, C. trachomatis has developed a unique evasion mechanism that triggers inflammatory immunopathology and acts as a bridge to protective to pathological adaptive immunity. This review focuses on the recent advances in how C. trachomatis evades various innate immune cells, which contributes to vaccine development and our understanding of the pathophysiologic consequences of C. trachomatis infection.

Neisseria gonorrhoeae drives Chlamydia trachomatis into a persistence-like state during in vitro co-infection

Chlamydia trachomatis and Neisseria gonorrhoeae are the most prevalent bacterial sexually transmitted infections (STIs) globally. Despite frequent co-infections in patients, few studies have investigated how mono-infections may differ from co-infections. We hypothesized that a symbiotic relationship between the pathogens could account for the high rates of clinical co-infection. During in vitro co-infection, we observed an unexpected phenotype where the C. trachomatis developmental cycle was impaired by N. gonorrhoeae. C. trachomatis is an obligate intracellular pathogen with a unique biphasic developmental cycle progressing from infectious elementary bodies (EB) to replicative reticulate bodies (RB), and back. After 12 hours of co-infection, we observed fewer EBs than in a mono-infection. Chlamydial genome copy number remained equivalent between mono- and co-infections. This is a hallmark of Chlamydial persistence. Chlamydial persistence alters inclusion morphology but varies depending on the stimulus/stress. We observed larger, but fewer, Chlamydia during co-infection. Tryptophan depletion can induce Chlamydial persistence, but tryptophan supplementation did not reverse the co-infection phenotype. Only viable and actively growing N. gonorrhoeae produced the inhibition phenotype in C. trachomatis. Piliated N. gonorrhoeae had the strongest effect on C. trachomatis, but hyperpiliated or non-piliated N. gonorrhoeae still produced the phenotype. EB development was modestly impaired when N. gonorrhoeae were grown in transwells above the infected monolayer. C. trachomatis serovar L2 was not impaired during co-infection. Chlamydial impairment could be due to cytoskeletal or osmotic stress caused by an as-yet-undefined mechanism. We conclude that N. gonorrhoeae induces a persistence-like state in C. trachomatis that is serovar dependent.

Molecular pathogenesis of Chlamydia trachomatis

Chlamydia trachomatis is a strict intracellular human pathogen. It is the main bacterial cause of sexually transmitted infections and the etiologic agent of trachoma, which is the leading cause of preventable blindness. Despite over 100 years since C. trachomatis was first identified, there is still no vaccine. However in recent years, the advancement of genetic manipulation approaches for C. trachomatis has increased our understanding of the molecular pathogenesis of C. trachomatis and progress towards a vaccine. In this mini-review, we aimed to outline the factors related to the developmental cycle phase and specific pathogenesis activity of C. trachomatis in order to focus priorities for future genetic approaches. We highlight the factors known to be critical for developmental cycle stages, gene expression regulatory factors, type III secretion system and their effectors, and individual virulence factors with known impacts.

When Bacteria and Viruses Collide: A Tale of Chlamydia trachomatis and Sexually Transmitted Viruses

The global incidence of sexually transmitted infections (STIs) remains high, with the World Health Organization (WHO) estimating that over 1 million people acquire STIs daily. STIs can lead to infertility, pregnancy complications, and cancers. Co-infections with multiple pathogens are prevalent among individuals with an STI and can lead to heightened infectivity and more severe clinical manifestations. Chlamydia trachomatis (CT) is the most reported bacterial STI worldwide in both men and women, and several studies have demonstrated co-infection of CT with viral and other bacterial STIs. CT is a gram-negative bacterium with a unique biphasic developmental cycle including infectious extracellular elementary bodies (EBs) and metabolically active intracellular reticulate bodies (RBs). The intracellular form of this organism, RBs, has evolved mechanisms to persist for long periods within host epithelial cells in a viable but non-cultivable state. The co-infections of CT with the most frequently reported sexually transmitted viruses: human immunodeficiency virus (HIV), human papillomavirus (HPV), and herpes simplex virus (HSV) have been investigated through in vitro and in vivo studies. These research studies have made significant strides in unraveling the intricate interactions between CT, these viral STIs, and their eukaryotic host. In this review, we present an overview of the epidemiology of these co-infections, while specifically delineating the underlying mechanisms by which CT influences the transmission and infection dynamics of HIV and HSV. Furthermore, we explore the intricate relationship between CT and HPV infection, with a particular emphasis on the heightened risk of cervical cancer. By consolidating the current body of knowledge, we provide valuable insights into the complex dynamics and implications of co-infection involving CT and sexually transmitted viruses.

Neutrophil biology in injuries and diseases of the central and peripheral nervous systems

The role of inflammation in nervous system injury and disease is attracting increased attention. Much of that research has focused on microglia in the central nervous system (CNS) and macrophages in the peripheral nervous system (PNS). Much less attention has been paid to the roles played by neutrophils. Neutrophils are part of the granulocyte subtype of myeloid cells. These cells, like macrophages, originate and differentiate in the bone marrow from which they enter the circulation. After tissue damage or infection, neutrophils are the first immune cells to infiltrate into tissues and are directed there by specific chemokines, which act on chemokine receptors on neutrophils. We have reviewed here the basic biology of these cells, including their differentiation, the types of granules they contain, the chemokines that act on them, the subpopulations of neutrophils that exist, and their functions. We also discuss tools available for identification and further study of neutrophils. We then turn to a review of what is known about the role of neutrophils in CNS and PNS diseases and injury, including stroke, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, spinal cord and traumatic brain injuries, CNS and PNS axon regeneration, and neuropathic pain. While in the past studies have focused on neutrophils deleterious effects, we will highlight new findings about their benefits. Studies on their actions should lead to identification of ways to modify neutrophil effects to improve health.

Plasmid-mediated virulence in Chlamydia

Chlamydia trachomatis infection of ocular conjunctiva can lead to blindness, while infection of the female genital tract can lead to chronic pelvic pain, ectopic pregnancy, and/or infertility. Conjunctival and fallopian tube inflammation and the resulting disease sequelae are attributed to immune responses induced by chlamydial infection at these mucosal sites. The conserved chlamydial plasmid has been implicated in enhancing infection, via improved host cell entry and exit, and accelerating innate inflammatory responses that lead to tissue damage. The chlamydial plasmid encodes eight open reading frames, three of which have been associated with virulence: a secreted protein, Pgp3, and putative transcriptional regulators, Pgp4 and Pgp5. Although Pgp3 is an important plasmid-encoded virulence factor, recent studies suggest that chlamydial plasmid-mediated virulence extends beyond the expression of Pgp3. In this review, we discuss studies of genital, ocular, and gastrointestinal infection with C. trachomatis or C. muridarum that shed light on the role of the plasmid in disease development, and the potential for tissue and species-specific differences in plasmid-mediated pathogenesis. We also review evidence that plasmid-associated inflammation can be independent of bacterial burden. The functions of each of the plasmid-encoded proteins and potential molecular mechanisms for their role(s) in chlamydial virulence are discussed. Although the understanding of plasmid-associated virulence has expanded within the last decade, many questions related to how and to what extent the plasmid influences chlamydial infectivity and inflammation remain unknown, particularly with respect to human infections. Elucidating the answers to these questions could improve our understanding of how chlamydia augment infection and inflammation to cause disease.

Nitric Oxide-Producing Polymorphonuclear Neutrophils Confer Protection Against Chlamydia psittaci in Mouse Lung Infection

BACKGROUND

Whether polymorphonuclear neutrophils (PMN) exert a protective role upon chlamydial infection by expressing inducible nitric oxide (NO) synthase (iNOS) and producing NO remains unclear.

METHODS

This issue was addressed using BALB/c mice infected with Chlamydia psittaci 6BC strain. Methods included flow cytometry, immunofluorescence, qRT-PCR, and western blot.

RESULTS

The number of PMN was significantly increased during C. psittaci infection, which was accompanied by increased iNOS expression and NO production in the mouse lungs. PMN were the major source of NO during pulmonary C. psittaci infection and inhibited C. psittaci multiplication in an iNOS/NO-dependent manner. Depletion of PMN aggravated C. psittaci-induced disease and increased C. psittaci burden. Nuclear factor-κB (NF-κB) and STAT1 signaling pathways, but not MAPK signaling pathways, were required for the induction of iNOS expression and NO production in PMN by C. psittaci infection. Thus, our findings highlight the protective role of NO-producing PMN in C. psittaci infection.

CONCLUSIONS

NO-producing PMN confer a protective role during pulmonary C. psittaci infection in mice, and thus our study sheds new light on PMN function during Chlamydia infection.

The emerging complexity of Chlamydia trachomatis interactions with host cells as revealed by molecular genetic approaches

Chlamydia trachomatis (Ct) is an intracellular bacterial pathogen that relies on the activity of secreted proteins known as effectors to promote replication and avoidance of immune clearance. Understanding the contribution of Ct effectors to pathogenesis has proven to be challenging, given that these proteins often perform multiple functions during intracellular infection. Recent advances in molecular genetic analysis of Ct have provided valuable insights into the multifaceted nature of secreted effector proteins and their impact on the interaction between Ct and host cells and tissues. This review highlights significant findings from genetic analysis of Ct effector functions, shedding light on their diverse roles. We also discuss the challenges faced in this field of study and explore potential opportunities for further research.

Neisseria gonorrhoeae Coinfection during Chlamydia muridarum Genital Latency Does Not Modulate Murine Vaginal Bacterial Shedding

Chlamydia trachomatis and Neisseria gonorrhoeae are the most frequently reported agents of bacterial sexually transmitted disease worldwide. Nonetheless, C. trachomatis/N. gonorrhoeae coinfection remains understudied. C. trachomatis/N. gonorrhoeae coinfections are more common than expected by chance, suggesting C. trachomatis/N. gonorrhoeae interaction, and N. gonorrhoeae infection may reactivate genital chlamydial shedding in women with latent (quiescent) chlamydial infection. We hypothesized that N. gonorrhoeae would reactivate latent genital Chlamydia muridarum infection in mice. Two groups of C. muridarum-infected mice were allowed to transition into genital latency. One group was then vaginally inoculated with N. gonorrhoeae; a third group received N. gonorrhoeae alone. C. muridarum and N. gonorrhoeae vaginal shedding was measured over time in the coinfected and singly infected groups. Viable C. muridarum was absent from vaginal swabs but detected in rectal swabs, confirming C. muridarum genital latency and consistent with the intestinal tract as a C. muridarum reservoir. C. muridarum inclusions were observed in large intestinal, but not genital, tissues during latency. Oviduct dilation was associated with C. muridarum infection, as expected. Contradicting our hypothesis, N. gonorrhoeae coinfection did not reactivate latent C. muridarum vaginal shedding. In addition, latent C. muridarum infection did not modulate recovery of vaginal viable N. gonorrhoeae. Evidence for N. gonorrhoeae-dependent increased C. muridarum infectivity has thus not been demonstrated in murine coinfection, and the ability of C. muridarum coinfection to potentiate N. gonorrhoeae infectivity may depend on actively replicating vaginal C. muridarum. The proportion of mice with increased vaginal neutrophils (PMNs) was higher in N. gonorrhoeae-infected than in C. muridarum-infected mice, as expected, while that of C. muridarum/N. gonorrhoeae-coinfected mice was intermediate to the singly infected groups, suggesting latent C. muridarum murine infection may limit PMN response to subsequent N. gonorrhoeae infection. IMPORTANCE Our work builds upon the limited understanding of C. muridarum/N. gonorrhoeae coinfection. Previously, N. gonorrhoeae infection of mice with acute (actively replicating) vaginal C. muridarum infection was shown to increase recovery of viable vaginal N. gonorrhoeae and vaginal PMNs, with no effect on C. muridarum vaginal shedding (R. A. Vonck et al., Infect Immun 79:1566-1577, 2011). It has also been shown that chlamydial infection of human and murine PMNs prevents normal PMN responses, including the response to N. gonorrhoeae (K. Rajeeve et al., Nat Microbiol 3:824-835, 2018). Our findings show no effect of latent genital C. muridarum infection on the recovery of viable N. gonorrhoeae, in contrast to the previously reported effect of acute C. muridarum infection, and suggesting that acute versus latent C. muridarum infection may have distinct effects on PMN function in mice. Together, these studies to date provide evidence that Chlamydia/N. gonorrhoeae synergistic interactions may depend on the presence of replicating Chlamydia in the genital tract, while chlamydial effects on vaginal PMNs may extend beyond acute infection.

Beta lactamase-producing Neisseria gonorrhoeae alleviates Amoxicillin-induced chlamydial persistence in a novel in vitro co-infection model

Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) cause most bacterial sexually transmitted infections (STIs) worldwide. Epidemiological studies have shown high percentages of co-infections with CT/NG and indicate that NG co-infection can reactivate CT shedding during persistent chlamydial infection. These data also suggest that biological interaction between the two bacteria may increase susceptibility or transmissibility. CT is an obligate intracellular bacterium with a developmental cycle that alternates between two forms: infectious elementary bodies (EBs) which invade the epithelium and non-infectious reticulate bodies (RBs) which divide and replicate inside the inclusion. Adverse environmental conditions can interrupt chlamydial development, with a consequent temporary halt in RB division, reduction in infectious EB production and formation of enlarged chlamydiae (aberrant bodies, ABs) - characterizing chlamydial persistence. When the stressor is removed, the chlamydial developmental cycle is restored, together with production of infectious EBs. The beta-lactam amoxicillin (AMX) induces chlamydial persistence, both in vitro and in mice. We investigated the impact of penicillinase-producing NG strain (PPNG) on AMX-persistent chlamydial infection utilizing our recently developed, contact-independent in vitro model of co-infection. We hypothesized that co-infection with PPNG could prevent and/or reverse AMX-induced chlamydial persistence. Our results showed that PPNG can ameliorate AMX-persistence in two chlamydial species, CT and C. muridarum (CM), providing novel evidence for a range of Chlamydia/NG interactions.

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.

Mast cells selectively produce inflammatory mediators and impact the early response to Chlamydia reproductive tract infection

Introduction

Chlamydia trachomatis (C. trachomatis) is a Gram-negative obligate intracellular bacterium that causes reproductive tract complications in women, including ectopic pregnancies and tubal factor infertility. We hypothesized that mast cells, which are common at mucosal barriers, may contribute to responses to Chlamydia infection and aimed to define human mast cell responses to C. trachomatis.

Methods

Human cord blood-derived mast cells (CBMCs) were exposed to C. trachomatis to assess bacterial uptake, mast cell degranulation, gene expression, and production of inflammatory mediators. The role of formyl peptide receptors and Toll-like receptor 2 (TLR2) were investigated using pharmacological inhibitors and soluble TLR2. Mast cell-deficient mice and littermate controls were used to examine the in vivo role of mast cells in influencing the immune response to Chlamydia infection in the female reproductive tract.

Results

C. trachomatis bacteria were taken up by human mast cells but did not replicate efficiently inside CBMCs. C. trachomatis-activated mast cells did not degranulate but maintained viability and exhibited cellular activation with homotypic aggregation and upregulation of ICAM-1. However, they significantly enhanced the gene expression of IL1B, CCL3, NFKB1, CXCL8, and IL6. Inflammatory mediators were produced, including TNF, IL-1β, IL-1RA, IL-6, GM-CSF, IL-23, CCL3, CCL5, and CXCL8. Endocytic blockade resulted in reduced gene expression of IL6, IL1B, and CCL3, suggesting C. trachomatis induced mast cell activation in both extracellular and intracellular locations. The IL-6 response to C. trachomatis was reduced when CBMCs were treated with C. trachomatis coated with soluble TLR2. Mast cells derived from TLR2-deficient mice also demonstrated a reduced IL-6 response to C. muridarum. Five days following C. muridarum infection, mast cell-deficient mice showed attenuated CXCL2 production and significantly reduced numbers of neutrophils, eosinophils, and B cells in the reproductive tract when compared with mast cell-containing littermates.

Discussion

Taken together, these data demonstrate that mast cells are reactive to Chlamydia spp. through multiple mechanisms that include TLR2-dependent pathways. Mast cells also play an important role in shaping in vivo immune responses in Chlamydia reproductive tract infection through both effector cell recruitment and modification of the chemokine microenvironment.

Methods for the Assessment of NET Formation: From Neutrophil Biology to Translational Research

Several studies have indicated that a neutrophil extracellular trap (NET) formation, apart from its role in host defense, can contribute to or drive pathogenesis in a wide range of inflammatory and thrombotic disorders. Therefore, NETs may serve as a therapeutic target or/and a diagnostic tool. Here, we compare the most commonly used techniques for the assessment of NET formation. Furthermore, we review recent data from the literature on the application of basic laboratory tools for detecting NET release and discuss the challenges and the advantages of these strategies in NET evaluation. Taken together, we provide some important insights into the qualitative and quantitative molecular analysis of NETs in translational medicine today.

Role of the human vaginal microbiota in the regulation of inflammation and sexually transmitted infection acquisition: Contribution of the non-human primate model to a better understanding?

The human vaginal microbiota has a central role in the regulation of the female reproductive tract (FRT) inflammation. Indeed, on one hand an optimal environment leading to a protection against sexually transmitted infections (STI) is associated with a high proportion of Lactobacillus spp. (eubiosis). On the other hand, a more diverse microbiota with a high amount of non-Lactobacillus spp. (dysbiosis) is linked to a higher local inflammation and an increased STI susceptibility. The composition of the vaginal microbiota is influenced by numerous factors that may lead to a dysbiotic environment. In this review, we first discuss how the vaginal microbiota composition affects the local inflammation with a focus on the cytokine profiles, the immune cell recruitment/phenotype and a large part devoted on the interactions between the vaginal microbiota and the neutrophils. Secondly, we analyze the interplay between STI and the vaginal microbiota and describe several mechanisms of action of the vaginal microbiota. Finally, the input of the NHP model in research focusing on the FRT health including vaginal microbiota or STI acquisition/control and treatment is discussed.

The Multiple Faces of Nitric Oxide in Chronic Granulomatous Disease: A Comprehensive Update

Nitric oxide (NO), a signaling molecule, regulates multiple biological functions, including a variety of physiological and pathological processes. In this regard, NO participates in cutaneous inflammations, modulation of mitochondrial functions, vascular diseases, COVID-19, neurologic diseases, and obesity. It also mediates changes in the skeletal muscle function. Chronic granulomatous disease (CGD) is a primary immunodeficiency disorder characterized by the malfunction of phagocytes caused by mutations in some of the genes encoding subunits of the superoxide-generating phagocyte NADPH (NOX). The literature consulted shows that there is a relationship between the production of NO and the NADPH oxidase system, which regulates the persistence of NO in the medium. Nevertheless, the underlying mechanisms of the effects of NO on CGD remain unknown. In this paper, we briefly review the regulatory role of NO in CGD and its potential underlying mechanisms.

Moraxella catarrhalis evades neutrophil oxidative stress responses providing a safer niche for nontypeable Haemophilus influenzae

Moraxella catarrhalis and nontypeable Haemophilus influenzae (NTHi) are pathogenic bacteria frequently associated with exacerbation of chronic obstructive pulmonary disease (COPD), whose hallmark is inflammatory oxidative stress. Neutrophils produce reactive oxygen species (ROS) which can boost antimicrobial response by promoting neutrophil extracellular traps (NET) and autophagy. Here, we showed that M. catarrhalis induces less ROS and NET production in differentiated HL-60 cells compared to NTHi. It is also able to actively interfere with these responses in chemically activated cells in a phagocytosis and opsonin-independent and contact-dependent manner, possibly by engaging host immunosuppressive receptors. M. catarrhalis subverts the autophagic pathway of the phagocytic cells and survives intracellularly. It also promotes the survival of NTHi which is otherwise susceptible to the host antimicrobial arsenal. In-depth understanding of the immune evasion strategies exploited by these two human pathogens could suggest medical interventions to tackle COPD and potentially other diseases in which they co-exist.

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Mcat induces ROS and NET production to a lesser extent than NTHi in dHL-60 cells

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Mcat interferes with ROS-related responses in chemically-activated cells

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Mcat subverts the autophagic pathway surviving intracellularly while NTHi does not

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Intracellular survival of NTHi is enhanced by the co-infecting bacterium Mcat

Intracellular Staphylococcus aureus Infection Decreases Milk Protein Synthesis by Preventing Amino Acid Uptake in Bovine Mammary Epithelial Cells

Staphylococcus aureus (S. aureus) is one of the main pathogens in cow mastitis, colonizing mammary tissues and being internalized into mammary epithelial cells, causing intracellular infection in the udder. Milk that is produced by cows that suffer from mastitis due to S. aureus is associated with decreased production and changes in protein composition. However, there is limited information on how mastitis-inducing bacteria affect raw milk, particularly with regard to protein content and protein composition. The main purpose of this work was to examine how S. aureus infection affects milk protein synthesis in bovine mammary epithelial cells (BMECs). BMECs were infected with S. aureus, and milk protein and amino acid levels were determined by ELISA after S. aureus invasion. The activity of mTORC1 signaling and the transcription factors NF-κB and STAT5 and the expression of the amino acid transporters SLC1A3 and SLC7A5 were measured by western blot or immunofluorescence and RT-qPCR. S. aureus was internalized by BMECs in vitro, and the internalized bacteria underwent intracellular proliferation. Eight hours after S. aureus invasion, milk proteins were downregulated, and the level of BMECs that absorbed Glu, Asp, and Leu from the culture medium and the exogenous amino acids induced β-casein synthesis declined. Further, the activity of mTORC1 signaling, NF-κB, and STAT5 was impaired, and SLC1A3 and SLC7A5 were downregulated. Eight hours of treatment with 100 nM rapamycin inhibited NF-κB and STAT5 activity, SLC1A3 and SLC7A5 expression, and milk protein synthesis in BMECs. Thus mTORC1 regulates the expression of SLC1A3 and SLC7A5 through NF-κB and STAT5. These findings constitute a model by which S. aureus infection suppresses milk protein synthesis by decreasing amino acids uptake in BMECs.

Bacteria-Cancer Interface: Awaiting the Perfect Storm

Epidemiological evidence reveal a very close association of malignancies with chronic inflammation as a result of persistent bacterial infection. Recently, more studies have provided experimental evidence for an etiological role of bacterial factors disposing infected tissue towards carcinoma. When healthy cells accumulate genomic insults resulting in DNA damage, they may sustain proliferative signalling, resist apoptotic signals, evade growth suppressors, enable replicative immortality, and induce angiogenesis, thus boosting active invasion and metastasis. Moreover, these cells must be able to deregulate cellular energetics and have the ability to evade immune destruction. How bacterial infection leads to mutations and enriches a tumour-promoting inflammatory response or micro-environment is still not clear. In this review we showcase well-studied bacteria and their virulence factors that are tightly associated with carcinoma and the various mechanisms and pathways that could have carcinogenic properties.

Host cell death during infection with Chlamydia: a double-edged sword

The phylum Chlamydiae constitutes a group of obligate intracellular bacteria that infect a remarkably diverse range of host species. Some representatives are significant pathogens of clinical or veterinary importance. For instance, Chlamydia trachomatis is the leading infectious cause of blindness and the most common bacterial agent of sexually transmitted diseases. Chlamydiae are exceptionally dependent on their eukaryotic host cells as a consequence of their developmental biology. At the same time, host cell death is an integral part of the chlamydial infection cycle. It is therefore not surprising that the bacteria have evolved exquisite and versatile strategies to modulate host cell survival and death programs to their advantage. The recent introduction of tools for genetic modification of Chlamydia spp., in combination with our increasing awareness of the complexity of regulated cell death in eukaryotic cells, and in particular of its connections to cell-intrinsic immunity, has revived the interest in this virulence trait. However, recent advances also challenged long-standing assumptions and highlighted major knowledge gaps. This review summarizes current knowledge in the field and discusses possible directions for future research, which could lead us to a deeper understanding of Chlamydia's virulence strategies and may even inspire novel therapeutic approaches.

Investigation of Possible Role of Chlamydia in Pseudoexfoliation Syndrome

Background: Pseudoexfoliation syndrome (PES) is a systemic disease characterized by the aggregation of fibrillar extracellular material in intraocular and extraocular tissues with unknown etiology. Clarifying the etiopathogenesis of PES would be important for public health. Objectives: We aimed to investigate the possible role of Chlamydia in the etiology of PES. Methods: This cross-sectional study was carried out in the ophthalmology clinic of a tertiary hospital. The study included two groups, including the patient group (PES patients with nuclear cataracts) and the control group (patients with nuclear cataracts). Patients with other ophthalmic problems and systemic diseases were excluded. Blood samples and conjunctival swabs taken from 49 patients and 42 controls were used in the study. Anti-Chlamydia trachomatis IgG and IgM, anti-C. pneumoniae IgG and IgM, Interleukin (IL)-6, and IL-20 were studied in the serum samples. The PCR study was performed with conjunctival swab samples and sequence analysis of PCR-positive samples was performed. Results: According to the results of the study, there was no statistically significant difference between the groups in terms of anti-C. trachmatis IgG, anti-C. trachmatis IgM, anti-C. pneumoniae IgM, IL-6, and PCR results. There was a statistically significant difference between patient and control groups in terms of anti-C. pneumoniae IgG and IL-20 levels. The DNA sequencing of all PCR products was found to be compatible with C. pneumoniae. Conclusions: It seems that C. pneumoniae might have an important role in the etiology and development of PES. However, further studies in larger groups are needed to clarify these results.

Pelvic Inflammatory Disease Due to Neisseria gonorrhoeae and Chlamydia trachomatis: Immune Evasion Mechanisms and Pathogenic Disease Pathways

Pelvic inflammatory disease (PID) results from ascension of sexually transmitted pathogens from the lower genital tract to the uterus and/or fallopian tubes in women, with potential spread to neighboring pelvic organs. Patients may present acutely with lower abdominal or pelvic pain and pelvic organ tenderness. Many have subtle symptoms or are asymptomatic and present later with tubal factor infertility, ectopic pregnancy, or chronic pelvic pain. Neisseria gonorrhoeae and Chlamydia trachomatis are the 2 most commonly recognized PID pathogens. Their ability to survive within host epithelial cells and neutrophils highlights a need for T-cell-mediated production of interferon γ in protection. Data indicate that for both pathogens, antibody can accelerate clearance by enhancing opsonophagocytosis and bacterial killing when interferon γ is present. A study of women with N. gonorrhoeae- and/or C. trachomatis-induced PID with histologic endometritis revealed activation of myeloid cell, cell death, and innate inflammatory pathways in conjunction with dampening of T-cell activation pathways. These findings are supported by multiple studies in mouse models of monoinfection with N. gonorrhoeae or Chlamydia spp. Both pathogens exert multiple mechanisms of immune evasion that benefit themselves and each other at the expense of the host. However, similarities in host immune mechanisms that defend against these 2 bacterial pathogens instill optimism for the prospects of a combined vaccine for prevention of PID and infections in both women and men.

The role of an enzymatically inactive CPAF mutant vaccination in Chlamydia muridarum genital tract infection

Chlamydia trachomatis urogenital tract infection causes pelvic inflammatory disease and infertility, increases the risk of co-infection with HPV and HIV. Chlamydial vaccination is considered the most promising approach to prevent and control its infection. Among various chlamydial vaccine candidates, chlamydial protease-like activity factor (CPAF) have been reported to provide robust protective immunity against genital chlamydial infection in mice with reduced vaginal shedding and oviduct pathology. However, CPAF is a serine protease which has enzymatical activity to degrade a large number of substrates. In order to increase the safety of CPAF vaccine, in this study, we used a mutant CPAF that is deficient in enzymatical activity to determine whether proteolytic activity of CPAF affect its vaccine efficacy. The wild type or mutant CPAF immunization causes a significant lower chlamydial shedding from the vaginal and resolve the infection as early as day 20, compared to day 28 in adjuvant control mice. More important, reduced upper reproductive tract pathology were also observed in these two groups. The mutant or wild type CPAF immunization induced not only robust splenic IFN-γ and serum IgG2a but also sIgA secretion in the vaginal fluids. Furthermore, neutralization of chlamydia with immune sera did not provide protection against oviduct pathology. However, adoptive transfer of CD4⁺ splenocytes isolated from the mutant or wild type CPAF immunized mice resulted in a significant and comparable reduced oviduct pathology. Our results indicate mutant CPAF vaccination is as same efficacy as wild type, and the protection relies on CD4⁺ T cells, which will further promote the development of CPAF as clinical chlamydial vaccine.

To Trap a Pathogen: Neutrophil Extracellular Traps and Their Role in Mucosal Epithelial and Skin Diseases

Neutrophils are the most abundant circulating innate immune cells and comprise the first immune defense line, as they are the most rapidly recruited cells at sites of infection or inflammation. Their main microbicidal mechanisms are degranulation, phagocytosis, cytokine secretion and the formation of extracellular traps. Neutrophil extracellular traps (NETs) are a microbicidal mechanism that involves neutrophil death. Since their discovery, in vitro and in vivo neutrophils have been challenged with a range of stimuli capable of inducing or inhibiting NET formation, with the objective to understand its function and regulation in health and disease. These networks composed of DNA and granular components are capable of immobilizing and killing pathogens. They comprise enzymes such as myeloperoxidase, elastase, cathepsin G, acid hydrolases and cationic peptides, all with antimicrobial and antifungal activity. Therefore, the excessive formation of NETs can also lead to tissue damage and promote local and systemic inflammation. Based on this concept, in this review, we focus on the role of NETs in different infectious and inflammatory diseases of the mucosal epithelia and skin.

Mediation of Interleukin-23 and Tumor Necrosis Factor-Driven Reactive Arthritis by Chlamydia-Infected Macrophages in SKG Mice

OBJECTIVE

ZAP-70^W163C BALB/c (SKG) mice develop reactive arthritis (ReA) following infection with Chlamydia muridarum. Since intracellular pathogens enhance their replicative fitness in stressed host cells, we examined how myeloid cells infected with C muridarum drive arthritis.

METHODS

SKG, Il17a-deficient SKG, and BALB/c female mice were infected with C muridarum or C muridarum luciferase in the genitals. C muridarum dissemination was assessed by in vivo imaging or genomic DNA amplification. Macrophages were depleted using clodronate liposomes. Anti-tumor necrosis factor (anti-TNF) and anti-interleukin-23p19 (anti-IL-23p19) were administered after infection or arthritis onset. Gene expression of Hspa5, Tgtp1, Il23a, Il17a, Il12b, and Tnf was compared in SKG mice and BALB/c mice.

RESULTS

One week following infection with C muridarum, macrophages and neutrophils were observed to have infiltrated the uteri of mice and were also shown to have carried C muridarum DNA to the spleen. C muridarum load was higher in SKG mice than in BALB/c mice. Macrophage depletion was shown to reduce C muridarum load and prevent development of arthritis. Compared with BALB/c mice, expression of Il23a and Il17a was increased in the uterine and splenic neutrophils of SKG mice. The presence of anti-IL-23p19 during infection or Il17a deficiency suppressed arthritis. Tnf was overexpressed in the joints of SKG mice within 1 week postinfection, and persisted beyond the first week. TNF inhibition during infection or at arthritis onset suppressed the development of arthritis. Levels of endoplasmic reticulum stress were constitutively increased in the joints of SKG mice but were induced, in conjunction with immunity-related GTPase, by C muridarum infection in the uterus.

CONCLUSION

C muridarum load is higher in SKG mice than in BALB/c mice. Whereas proinflammatory IL-23 produced by neutrophils contributes to the initiation of C muridarum-mediated ReA, macrophage depletion reduces C muridarum dissemination to other tissues, tissue burden, and the development of arthritis. TNF inhibition was also shown to suppress arthritis development. Our data suggest that enhanced bacterial dissemination in macrophages of SKG mice drives the TNF production needed for persistent arthritis.

Insights Into Host Cell Cytokines in Chlamydia Infection

Chlamydial infection causes a number of clinically relevant diseases and induces significant morbidity in humans. Immune and inflammatory responses contribute to both the clearance of Chlamydia infection and pathology in host tissues. Chlamydia infection stimulates host cells to produce a large number of cytokines that trigger and regulate host immune responses against Chlamydia. However, inappropriate responses can occur with excessive production of cytokines, resulting in overreactive inflammatory responses and alterations in host or Chlamydia metabolism. As a result, Chlamydia persists and causes wound healing delays, leading to more severe tissue damage and triggering long-lasting fibrotic sequelae. Here, we summarize the roles of cytokines in Chlamydia infection and pathogenesis, thus advancing our understanding chlamydial infection biology and the pathogenic mechanisms involved.

Identification of differentially expressed genes and signaling pathways in human conjunctiva and reproductive tract infected with Chlamydia trachomatis

Background

Currently, Chlamydia trachomatis–specific host defense mechanisms in humans remain poorly defined. To study the characteristics of host cells infected early with Chlamydia trachomatis, we used bioinformatics methods to analyze the RNA transcription profiles of the conjunctiva, fallopian tubes, and endometrium in humans infected with Chlamydia trachomatis.

Method

The gene expression profiles of GSE20430, GSE20436, GSE26692, and GSE41075 were downloaded from the Gene Expression Synthesis (GEO) database. Then, we obtained the differentially expressed genes (DEGs) through the R 4.0.1 software. STRING was used to construct protein–protein interaction (PPI) networks; then, the Cytoscape 3.7.2 software was used to visualize the PPI and screen hub genes. GraphPad Prism 8.0 software was used to verify the expression of the hub gene. In addition, the gene–miRNA interaction was constructed on the NetworkAnalyst 3.0 platform using the miRTarBase v8.0 database.

Results

A total of 600 and 135 DEGs were screened out in the conjunctival infection group and the reproductive tract infection group, respectively. After constructing a PPI network and verifying the hub genes, CSF2, CD40, and CSF3 in the reproductive tract infection group proved to have considerable statistical significance.

Conclusion

In our research, the key genes in the biological process of reproductive tract infection with Chlamydia trachomatis were clarified through bioinformatics analysis. These hub genes may be further used in clinical treatment and clinical diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-021-00313-8.

An endometrial organoid model of interactions between Chlamydia and epithelial and immune cells

Our understanding of how the obligate intracellular bacterial pathogen Chlamydia trachomatis reprograms the function of infected cells in the upper genital tract is largely based on observations made in cell culture with transformed epithelial cell lines. Here, we describe a primary organoid system derived from endometrial tissue to recapitulate epithelial cell diversity, polarity and ensuing responses to Chlamydia infection. Using high-resolution and time-lapse microscopy, we catalog the infection process in organoids from invasion to egress, including the reorganization of the cytoskeleton and positioning of intracellular organelles. We show this model is amenable to screening C. trachomatis mutants for defects in the fusion of pathogenic vacuoles, the recruitment of intracellular organelles and inhibition of cell death. Moreover, we reconstructed a primary immune cell response by co-culturing infected organoids with neutrophils, and determined that effectors like CPAF (also known as CT858) and TepP (also known as CT875) limit the recruitment of neutrophils to infected organoids. Collectively, our model can be applied to study the cell biology of Chlamydia infections in three-dimensional structures that better reflect the diversity of cell types and polarity encountered by Chlamydia in their animal hosts.

Pharmacokinetic considerations regarding the treatment of bacterial sexually transmitted infections with azithromycin: a review

Rates of bacterial sexually transmitted infections (STIs) continue to rise, demanding treatments to be highly effective. However, curing infections faces significant challenges due to antimicrobial resistance in Neisseria gonorrhoeae and Mycoplasma genitalium and especially treating STIs at extragenital sites, particularly rectal chlamydia and oropharyngeal gonorrhoea. As no new antimicrobials are entering the market, clinicians must optimize the currently available treatments, but robust data are lacking on how the properties or pharmacokinetics of antimicrobials can be used to inform STI treatment regimens to improve treatment outcomes. This paper provides a detailed overview of the published pharmacokinetics of antimicrobials used to treat STIs and how factors related to the drug (tissue distribution, protein binding and t½), human (pH, inflammation, site of infection, drug side effects and sexual practices) and organism (organism load and antimicrobial resistance) can affect treatment outcomes. As azithromycin is commonly used to treat chlamydia, gonorrhoea and M. genitalium infections, and its pharmacokinetics are well studied, it is the main focus of this review. Suggestions are also provided on possible dosing regimens when using extended and/or higher doses of azithromycin, which appropriately balance efficacy and side effects. The paper also emphasizes the limitations of currently published pharmacokinetic studies including oropharyngeal gonococcal infections, where very limited data exist around ceftriaxone pharmacokinetics and its use in combination with azithromycin. In future, the different anatomical sites of infections may require alternative therapeutic approaches.

The Role of Neutrophils in Brucellosis

Brucellosis is a bacterial disease of domestic animals and humans. The pathogenic ability of Brucella organisms relies on their stealthy strategy and their capacity to replicate within host cells and to induce long-lasting infections. Brucella organisms barely induce neutrophil activation and survive within these leukocytes by resisting microbicidal mechanisms. Very few Brucella-infected neutrophils are found in the target organs, except for the bone marrow, early in infection. Still, Brucella induces a mild reactive oxygen species formation and, through its lipopolysaccharide, promotes the premature death of neutrophils, which release chemokines and express "eat me" signals. This effect drives the phagocytosis of infected neutrophils by mononuclear cells that become thoroughly susceptible to Brucella replication and vehicles for bacterial dispersion. The premature death of the infected neutrophils proceeds without NETosis, necrosis/oncosis, or classical apoptosis morphology. In the absence of neutrophils, the Th1 response exacerbates and promotes bacterial removal, indicating that Brucella-infected neutrophils dampen adaptive immunity. This modulatory effect opens a window for bacterial dispersion in host tissues before adaptive immunity becomes fully activated. However, the hyperactivation of immunity is not without a price, since neutropenic Brucella-infected animals develop cachexia in the early phases of the disease. The delay in the immunological response seems a sine qua non requirement for the development of long-lasting brucellosis. This property may be shared with other pathogenic alphaproteobacteria closely related to Brucella We propose a model in which Brucella-infected polymorphonuclear neutrophils (PMNs) function as "Trojan horse" vehicles for bacterial dispersal and as modulators of the Th1 adaptive immunity in infection.

Increase of leucocyte-derived extracellular traps (ETs) in semen samples from human acute epididymitis patients-a pilot study

PURPOSE

To study the effector mechanism against pathogens of polymorphonuclear neutrophils (PMN) and macrophages, called ETosis, involving the release of extracellular traps (ETs) in patients with acute epididymitis. To assess the different ET phenotypes present in semen samples and to identify correlations between ETosis and clinical parameters.

MATERIALS AND METHODS

Samples from patients diagnosed with acute epididymitis were examined and compared with samples from uninfected controls. Biochemical analyses of seminal fluid included determination of peroxidase, α-glucosidase, fructose, and elastase levels. ETosis in semen was determined through presence of citrullinated histones, global histones, and extracellular DNA. Different ETosis phenotypes such as spread ETs, aggregated ETs, and diffuse ETs were identified by co-localisation of extruded DNA with myeloperoxidase and global histones. Anti-CD15⁺ and anti-CD68⁺ antibodies were used to identify different cell lines.

RESULTS

Revealed a high number of ETs compared with the control group. The mean number of CD15⁺PMN and CD68⁺ macrophages was higher in the acute epididymitis group. ETosis increase in ejaculates correlated with clinical parameters such as enhancement of elastase concentrations and diminution of fructose in the semen.

CONCLUSIONS

This work shows for the first time the presence of ETs and their components in semen from patients with acute epididymitis. The presence of infections is an important factor for induction of ETs in semen. Furthermore, the presence of ETosis in ejaculates is suggestive of developing infectious processes and might possibly have a diagnostic value.

What Is the Evolutionary Fingerprint in Neutrophil Granulocytes?

Over the years of evolution, thousands of different animal species have evolved. All these species require an immune system to defend themselves against invading pathogens. Nevertheless, the immune systems of different species are obviously counteracting against the same pathogen with different efficiency. Therefore, the question arises if the process that was leading to the clades of vertebrates in the animal kingdom-namely mammals, birds, amphibians, reptiles, and fish-was also leading to different functions of immune cells. One cell type of the innate immune system that is transmigrating as first line of defense in infected tissue and counteracts against pathogens is the neutrophil granulocyte. During the host-pathogen interaction they can undergo phagocytosis, apoptosis, degranulation, and form neutrophil extracellular traps (NETs). In this review, we summarize a wide spectrum of information about neutrophils in humans and animals, with a focus on vertebrates. Special attention is kept on the development, morphology, composition, and functions of these cells, but also on dysfunctions and options for cell culture or storage.

Opsonophagocytosis of Chlamydia pneumoniae by Human Monocytes and Neutrophils

The human respiratory tract pathogen Chlamydia pneumoniae, which causes mild to severe infections, has been associated with the development of chronic inflammatory diseases. To understand the biology of C. pneumoniae infections, several studies have investigated the interaction between C. pneumoniae and professional phagocytes. However, these studies have been conducted under nonopsonizing conditions, making the role of opsonization in C. pneumoniae infections elusive. Thus, we analyzed complement and antibody opsonization of C. pneumoniae and evaluated how opsonization affects chlamydial infectivity and phagocytosis in human monocytes and neutrophils. We demonstrated that IgG antibodies and activation products of complement C3 and C4 are deposited on the surface of C. pneumoniae elementary bodies when incubated in human serum. Complement activation limits C. pneumoniae infectivity in vitro and has the potential to induce bacterial lysis by the formation of the membrane attack complex. Coculture of C. pneumoniae and freshly isolated human leukocytes showed that complement opsonization is superior to IgG opsonization for efficient opsonophagocytosis of C. pneumoniae in monocytes and neutrophils. Neutrophil-mediated phagocytosis of C. pneumoniae was crucially dependent on opsonization, while monocytes retained minor phagocytic potential under nonopsonizing conditions. Complement opsonization significantly enhanced the intracellular neutralization of C. pneumoniae in peripheral blood mononuclear cells and neutrophils and almost abrogated the infectious potential of C. pneumoniae In conclusion, we demonstrated that complements limit C. pneumoniae infection in vitro by interfering with C. pneumoniae entry into permissive cells by direct complement-induced lysis and by tagging bacteria for efficient phagocytosis in both monocytes and neutrophils.

Identification of differentially expressed circular RNAs in HeLa cells infected with Chlamydia trachomatis

Non-coding circular RNAs (circRNAs) have been shown to have important roles in many diseases; however, no study has indicated circRNAs are involved in Chlamydia trachomatis infection. In this study, we used circRNA microarray to measure the global circRNA expression profiles in HeLa cells with or without C. trachomatis serovar E (Ct.E) infection. CircRNA/miRNA/mRNA interactions were predicted and bioinformatics analyses were performed. The differentially expressed circRNAs were selected according to our criterion for validation by reverse-transcription and quantitative polymerase chain reaction (RT-qPCR). The mRNA microarray was used to detect the mRNA expression profiles after Ct.E infection. Among 853 differentially expressed circRNAs, 453 were upregulated and 400 were downregulated after Ct.E infection. Target miRNAs and miRNA-targeted mRNAs of these circRNAs were predicted. RT-qPCR analysis indicated hsa_circRNA_001226, hsa_circRNA_007046 and hsa_circRNA_400027 were elevated similar to those determined in the circRNA microarray analysis. The mRNA microarray results showed 915 genes were upregulated and 619 genes were downregulated after Ct.E infection. Thirty-four differentially expressed genes overlapped in the bioinformatics and mRNA microarray results. KEGG pathway analysis revealed several signaling pathways, including endocytosis, MAPK and PI3P-Akt signaling pathways, that were targeted by circRNAs may play important roles in Chlamydia infection. This study provides evidence that circRNAs in host cells are involved in the process of Chlamydia infection.

Neutrophil chemoattractant receptors in health and disease: double-edged swords

Neutrophils are frontline cells of the innate immune system. These effector leukocytes are equipped with intriguing antimicrobial machinery and consequently display high cytotoxic potential. Accurate neutrophil recruitment is essential to combat microbes and to restore homeostasis, for inflammation modulation and resolution, wound healing and tissue repair. After fulfilling the appropriate effector functions, however, dampening neutrophil activation and infiltration is crucial to prevent damage to the host. In humans, chemoattractant molecules can be categorized into four biochemical families, i.e., chemotactic lipids, formyl peptides, complement anaphylatoxins and chemokines. They are critically involved in the tight regulation of neutrophil bone marrow storage and egress and in spatial and temporal neutrophil trafficking between organs. Chemoattractants function by activating dedicated heptahelical G protein-coupled receptors (GPCRs). In addition, emerging evidence suggests an important role for atypical chemoattractant receptors (ACKRs) that do not couple to G proteins in fine-tuning neutrophil migratory and functional responses. The expression levels of chemoattractant receptors are dependent on the level of neutrophil maturation and state of activation, with a pivotal modulatory role for the (inflammatory) environment. Here, we provide an overview of chemoattractant receptors expressed by neutrophils in health and disease. Depending on the (patho)physiological context, specific chemoattractant receptors may be up- or downregulated on distinct neutrophil subsets with beneficial or detrimental consequences, thus opening new windows for the identification of disease biomarkers and potential drug targets.

Transcervical Mouse Infections with Chlamydia trachomatis and Determination of Bacterial Burden

Chlamydia trachomatis is an obligate human pathogen. It infects the genital tract of humans ascending into the fallopian tube, exacerbated by chronic pelvic pain, pelvic inflammatory disease, and fallopian tube scaring resulting in infertility and other malignancies. The major hurdle in controlling chlamydial spread is that the infection remains asymptomatic, thus leading to chronic, recurrent and persistent infections, with no vaccines developed so far. Being a human pathogen, we do not have an in vivo model of C. trachomatis infection. C. trachomatis do not cause ascending infections and fallopian tube pathology in the mouse urogenital tract when infected vaginally. To overcome this hurdle trans cervical method of infection must be adapted. In this protocol the method of establishing trans-cervical Chlamydial infection with the procedure to determine the bacterial load is detailed. This method will facilitate to deliver the bacteria past the cervix establishing an ascending infection into the uterine horns reciprocating human fallopian tube infections.

Chlamydial Infection From Outside to Inside

Chlamydia are obligate intracellular bacteria, characterized by a unique biphasic developmental cycle. Specific interactions with the host cell are crucial for the bacteria’s survival and amplification because of the reduced chlamydial genome. At the start of infection, pathogen-host interactions are set in place in order for Chlamydia to enter the host cell and reach the nutrient-rich peri-Golgi region. Once intracellular localization is established, interactions with organelles and pathways of the host cell enable the necessary hijacking of host-derived nutrients. Detailed information on the aforementioned processes will increase our understanding on the intracellular pathogenesis of chlamydiae and hence might lead to new strategies to battle chlamydial infection. This review summarizes how chlamydiae generate their intracellular niche in the host cell, acquire host-derived nutrients in order to enable their growth and finally exit the host cell in order to infect new cells. Moreover, the evolution in the development of molecular genetic tools, necessary for studying the chlamydial infection biology in more depth, is discussed in great detail.