Recombinant Treponema pallidum protein Tp0965 activates endothelial cells and increases the permeability of endothelial cell monolayer

Endothelial dysfunction of syphilis: Pathogenesis

Treponema pallidum is the causative factor of syphilis, a sexually transmitted disease (STD) characterized by perivascular infiltration of inflammatory cells, vascular leakage, swelling and proliferation of endothelial cells (ECs). The endothelium lining blood and lymphatic vessels is a key barrier separating body fluids from host tissues and is a major target of T. pallidum. In this review, we focus on how T. pallidum establish intimate interactions with ECs, triggering endothelial dysfunction such as endothelial inflammation, abnormal repairment and damage of ECs. In addition, we summarize that migration and invasion of T. pallidum across vascular ECs may occur through two pathways. These two mechanisms of transendothelial migration are paracellular and cholesterol-dependent, respectively. Herein, clarifying the relationship between T. pallidum and endothelial dysfunction is of great significance to provide novel strategies for diagnosis and prevention of syphilis, and has a great potential prospect of clinical application.

Clinical Insights: Antimicrobial Therapy for Infectious Uveitis

Infectious uveitis is a major global cause of vision impairment. Despite the eye's immune privilege, afforded by the blood-ocular barrier that restricts microbial entry, several pathogens such as bacteria, viruses, fungi, and parasites can still infiltrate and cause ocular infections and complications. Clinicians often encounter significant challenges in treating infectious uveitis due to limited or ineffective treatment options. Modern molecular techniques and imaging can aid in diagnosing and assessing intraocular infections. Various antimicrobial therapies exist, spanning topical and systemic treatments, but these are constrained by issues like drug concentration, penetration, effective duration, toxicity, and side effects. Treatment approaches also differ based on the infection's etiology. This review provides recent updates on antimicrobial therapies from a clinical perspective, covering topical, systemic, and regional treatments for infectious uveitis.

Neurosyphilis: insights into its pathogenesis, susceptibility, diagnosis, treatment, and prevention

Background and aim

Invasion of the central nervous system by Treponema pallidum can occur at any stage of syphilis. In the event that T. pallidum is not cleared promptly, certain individuals may experience progression to neurosyphilis, which manifests as cognitive and behavioral abnormalities, limb paralysis, and potentially fatal outcomes. Early identification or prevention of neurosyphilis is therefore crucial. The aim of this paper is to conduct a critical and narrative review of the latest information focusing exclusively to the pathogenesis and clinical management of neurosyphilis.

Methodology

To compile this review, we have conducted electronic literature searches from the PubMed database relating to neurosyphilis. Priority was given to studies published from the past 10 years (from 2013 to 2023) and other studies if they were of significant importance (from 1985 to 2012), including whole genome sequencing results, cell structure of T. pallidum, history of genotyping, and other related topics. These studies are classic or reflect a developmental process.

Results

Neurosyphilis has garnered global attention, yet susceptibility to and the pathogenesis of this condition remain under investigation. Cerebrospinal fluid examination plays an important role in the diagnosis of neurosyphilis, but lacks the gold standard. Intravenous aqueous crystalline penicillin G continues to be the recommended therapeutic approach for neurosyphilis. Considering its sustained prominence, it is imperative to develop novel public health tactics in order to manage the resurgence of neurosyphilis.

Conclusion

This review gives an updated narrative description of neurosyphilis with special emphasis on its pathogenesis, susceptibility, diagnosis, treatment, and prevention.

A Rare Case of Blindness Caused by Syphilis with Malignant Hypertensive Nephropathy

The number of patients with syphilis has been rapidly increasing. Without treatment, syphilis can damage various organs and become life-threatening. We herein report a 29-year-old woman diagnosed with neurosyphilis, acute hydrocephalus, syphilitic uveitis combined with hypertensive retinopathy, and malignant hypertensive nephropathy. To our knowledge, this is the first report of syphilis complicated with malignant hypertensive nephropathy proven by a renal biopsy. Neurosyphilis was successfully treated with intravenous penicillin G, and severe hypertension subsequently resolved. However, delayed medical examinations and complications of syphilitic uveitis and hypertensive retinopathy resulted in irreversible visual loss. To prevent irreversible organ damage, early treatment is essential.

Advancements in the development of nucleic acid vaccines for syphilis prevention and control

Syphilis, a chronic systemic sexually transmitted disease, is caused by the bacterium Treponema pallidum (T. pallidum). Currently, syphilis remains a widespread infectious disease with significant disease burden in many countries. Despite the absence of identified penicillin-resistant strains, challenges in syphilis treatment persist due to penicillin allergies, supply issues, and the emergence of macrolide-resistant strains. Vaccines represent the most cost-effective strategy to prevent and control the syphilis epidemic. In light of the ongoing global coronavirus disease 2019 (COVID-19) pandemic, nucleic acid vaccines have gained prominence in the field of vaccine research and development, owing to their superior efficiency compared to traditional vaccines. This review summarizes the current state of the syphilis epidemic and the preliminary findings in T. pallidum nucleic acid vaccine research, discusses the challenges associated with the development of T. pallidum nucleic acid vaccines, and proposes strategies and measures for future T. pallidum vaccine development.

Syphilis vaccine: challenges, controversies and opportunities

Syphilis is a sexually or vertically (mother to fetus) transmitted disease caused by the infection of Treponema pallidum subspecie pallidum (TPA). The incidence of syphilis has increased over the past years despite the fact that this bacterium is an obligate human pathogen, the infection route is well known, and the disease can be successfully treated with penicillin. As complementary measures to preventive campaigns and early treatment of infected individuals, development of a syphilis vaccine may be crucial for controlling disease spread and/or severity, particularly in countries where the effectiveness of the aforementioned measures is limited. In the last century, several vaccine prototypes have been tested in preclinical studies, mainly in rabbits. While none of them provided protection against infection, some prototypes prevented bacteria from disseminating to distal organs, attenuated lesion development, and accelerated their healing. In spite of these promising results, there is still some controversy regarding the identification of vaccine candidates and the characteristics of a syphilis-protective immune response. In this review, we describe what is known about TPA immune response, and the main mechanisms used by this pathogen to evade it. Moreover, we emphasize the importance of integrating this knowledge, in conjunction with the characterization of outer membrane proteins (OMPs), to expedite the development of a syphilis vaccine that can protect against TPA infection.

CARE-NS, a research strategy for neurosyphilis

Neurosyphilis is a major clinical manifestation of syphilis. In recent years, an increase in neurosyphilis cases has been reported in many countries. The overall incidence of neurosyphilis remains unknown, and there is a lack of understanding of the disease pathogenesis, which hampers clinical management, development of prevention strategies, and control. This article proposes the CARE-NS research strategy to enhance the clinical management of neurosyphilis, which consists of six key features: comprehensive management including multidisciplinary treatment (C), alleviating neurological impairment and sequelae (A), risk factors and clinical epidemiology (R), etiology and pathogenesis (E), new diagnostic indicators and strategies (N), and social impact and cost-effectiveness analysis (S).

Treponema pallidum outer membrane proteins: current status and prospects

The outer membrane proteins (OMPs) of Treponema pallidum subsp. Pallidum (T. pallidum), the etiological agent of the sexually transmitted disease syphilis, has long been a hot research topic. Despite many hurdles to studying the pathogen, especially the inability to manipulate T. pallidum in vitro genetically1, considerable progress has been made in elucidating the structure, pathogenesis, and functions of T. pallidum OMPs. In this review, we integrate this information to garner fresh insights into the role of OMPs in the diagnosis, pathogenicity, and vaccine development of T. pallidum. Collectively, the essential scientific discussions herein should provide a framework for understanding the current status and prospects of T. pallidum OMPs.

Decades ago, researchers postulated that the poor surface antigenicity of T. pallidum is the basis for its ability to cause persistent infection. Still, they believed that the mysterious properties of T. pallidum should not be attributed to the presence of the outer membrane proteins (OMPs). Subsequent studies revealed that the OM, which lacks integral membrane proteins, prevents antibody binding2. Since the advent of recombinant DNA technology, the fragility of the OM, low protein content, and the lack of sequence relatedness between T. pallidum and Gram-negative OMPs have complicated efforts to characterize molecules residing at the host-pathogen interface. These hurdles have been overcome by using the genomic sequence with computational tools to identify proteins predicted to form beta barrels, the hallmark conformation of OMPs in many organisms. Diverse methodologies have also confirmed that some candidate OMPs from amphiphilic β-barrels are surface-exposed in T. pallidum. These studies have led to a structural homology model for BamA and established the bipartite topology of the T. pallidum repeat (Tpr) family of proteins. Recent bioinformatics has identified several structural orthologs for well-characterized Gram-negative OMPs, suggesting that the T. pallidum OMPs are more Gram-negative-like than previously supposed. Lipoprotein adhesins and proteases on the spirochete surface also may contribute to disease pathogenesis and protective immunity.

Possible effects of Treponema pallidum infection on human vascular endothelial cells

Pathogens can affect host cells in various ways, and the same effect can be found in the Treponema pallidum acting on the endothelium of host vessels, and the mechanism is often complex and multiple. Based on the existing T. pallidum of a cognitive framework, the first concerns involving T. pallidum or the bacteria protein directly acted on vascular endothelial cells of the host, the second concerns mainly involved in the process of T. pallidum infection in vivo blood lipid change, secretion of cytokines and the interactions between immune cells indirectly. Through both direct and indirect influence, this study explores the role of host by T. pallidum infect in the process of the vascular endothelium.

MiR-216a-5p-containing exosomes suppress rTp17-induced inflammatory response by targeting TLR4

Syphilis caused by Treponema pallidum (T. pallidum) infection is accompanied by inflammatory injury of tissue, and has a worldwide distribution and increasing incidence over the past decade. Tp17 has been reported to be a strong membrane immunogen, and was initially observed to play a role in inflammation during syphilis, reacting intensely with human syphilitic sera. We therefore used recombinant Tp17 (rTp17) as a stimulator in our study. Increasing evidence has demonstrated that microRNA (miRNA)-containing exosomes have emerged as a potential effective therapeutic target for many diseases. However, the biological functions and molecular mechanisms of miR-216a-5p in syphilis pathogenesis remain unknown. Our study first identified dramatically decreased miR-216a-5p in plasma of syphilis patients compared with the healthy control, which was negatively correlated with the expression of inflammatory cytokines, including IL-1β, IL-6, and TNF-α. Moreover, endothelial cells treated with miR-216a-5p-containing exosomes significantly attenuated the rTp17-induced inflammatory response. More importantly, we identified that miR-216a-5p could bind to the 3′-untranslated region (UTR) of Toll-like receptor (TLR) 4 (TLR4), and overexpression of TLR4 largely rescued the miR-216a-5p-mediated suppression of rTp17-induced inflammatory cytokine production and the TLR4-MYD88 signaling pathway. Thus, our results reveal a novel role of miR-216a-5p-containing exosomes in endothelial cells, implying a potential therapeutic target for inflammation in syphilis patients.

Treponema pallidum Induces the Secretion of HDVSMC Inflammatory Cytokines to Promote the Migration and Adhesion of THP-1 Cells

The pathological features of syphilis, a disease caused by Treponema pallidum (T. pallidum), are characterized by vascular involvement with endarteritis and periarteritis. Little is known about the interactions of infiltrating immunocytes with human dermal vascular smooth muscle cells (HDVSMCs) in arterioles during the immunopathogenesis of syphilis. In the present study, we demonstrated that stimulation of HDVSMCs with T. pallidum resulted in the upregulated gene transcription and protein expression of interleukin (IL)-6, monocyte chemoattractant protein-1 (MCP-1), and intercellular adhesion molecule-1 (ICAM-1) in a dose- and time-dependent manner. Moreover, the migration and adhesion of THP-1 cells to HDVSMCs were significantly suppressed by anti-MCP-1 and anti-ICAM-1 neutralizing antibodies, respectively. Further studies revealed that T. pallidum activated the NF-κB signaling pathway in HDVSMCs. Inhibition of NF-κB suppressed T. pallidum-induced IL-6, MCP-1, and ICAM-1 expression. In addition, the migration and adhesion of THP-1 cells to T. pallidum-treated HDVSMCs were significantly decreased by pretreatment with an NF-κB inhibitor. These findings demonstrate that T. pallidum induces the production of IL-6, MCP-1, and ICAM-1 in HDVSMCs and promotes the adherence and migration of THP-1 cells to HDVSMCs through the NF-κB signaling pathway, which may provide new insight into the pathogenesis of T. pallidum infection.

Treponema pallidum induces the activation of endothelial cells via macrophage-derived exosomes

Recent studies have shown that exosomes play a role in pathogenesis and in the treatment of inflammatory diseases and tumours. We explored the effects of Treponema pallidum-induced macrophage-derived exosomes on vascular endothelial cells to determine whether they are involved in the pathogenesis of syphilis. A syphilis infection model was established using rabbits to harvest T. pallidum at the peak of proliferation. Exosomes derived from macrophages were extracted using commercial kits and characterized by transmission electron microscopy, western blot assays, and nanoparticle tracking analysis. Secreted cytokine levels and the adhesion and permeability of human umbilical vein endothelial cells were evaluated in a co-culture model using the extracted exosomes. The results of this study revealed that exosomes derived from T. pallidum-infected macrophages enhanced cell adhesion and permeability. The levels of the secreted cytokines, including ICAM-1, VCAM-1, VEGF, and IL-8 were higher in the experimental group than in the control group. Our findings suggest that exosomes derived from T. pallidum-infected macrophages affect the cell adhesion and permeability of vascular endothelial cells. These changes may play important roles in syphilis pathogenesis. This study is the first to reveal the effects of exosomes derived from T. pallidum-infected macrophages on the adhesion, permeability, and secreted cytokines of human umbilical vein endothelial cells.

Immunogenicity and immunoreactivity of Tp0821 recombinant protein from Treponema pallidum

Treponema pallidum (Tp) is responsible for invading reproductive organs and the skin in early stages, and involves almost all organs/systems at advanced stages. In the present study, screening of the dominant epitope fragment of the Tp outer membrane protein, Tp0821, was performed and the prokaryotic expression vector pQE32/Tp0821 was constructed. The denaturation and dialysis of rTp0821 were achieved through ultrasound, inclusion body washing and dissolution. Experiments in purified rTp0821‑immune New Zealand rabbits indicated that the recombinant proteins were of high immunogenicity, and the irritation led a marked humoral immune response in the New Zealand rabbits. Western blot analysis showed that the purified recombinant proteins reacted with the Tp‑positive infected serum, confirming the high level of immunoreactivity. The delayed type hypersensitivity of rTp0821 recombinant proteins was positive, indicating that rTp0821 induced a specific cell immune response and was selected as a Tp vaccine candidate protein. The findings of the present study provided novel evidence, which provided information for further investigations on the pathogenic mechanism of Tp and the development of diagnostic reagents.

Tongxinluo Regulates Expression of Tight Junction Proteins and Alleviates Endothelial Cell Monolayer Hyperpermeability via ERK-1/2 Signaling Pathway in Oxidized Low-Density Lipoprotein-Induced Human Umbilical Vein Endothelial Cells

Vascular hyperpermeability resulting from distortion of endothelial junctions is associated with a number of cardiovascular diseases. Endothelial tight junction regulates the paracellular permeability of macromolecules, a function of Human Umbilical Vein Endothelial Cells (HUVEC) monolayers that can be regulated by oxidized Low-density Lipoprotein (ox-LDL). However, the understanding of drug regulation of vascular hyperpermeability is so far limited. This study thus aimed to investigate the role of Tongxinluo (TXL) in the maintenance of the vascular endothelial paracellular permeability. Here, changes in permeability were determined by measuring the paracellular flux of FITC-dextran 40000 (FD40), while protein expression and intercellular distribution were examined by western blot and immunofluorescence assay, respectively. We found that TXL alleviated the ox-LDL-induced increase in flux of FD40 and then reduced the hyperpermeability. Moreover, ox-LDL-induced disruptions of ZO-1, occludin, and claudin1 were also restored. This is via the activation of ERK1/2 in the vascular endothelial cells. Our results provide insights into the molecular mechanism by which TXL alleviates ox-LDL-induced hyperpermeability and provide the basis for further investigations of TXL as regulators of vascular barrier function.

Clinicopathologic features, microvessel density, and immunohistochemical expression of ICAM-1 and VEGF in 15 cases of secondary syphilis with oral manifestations

BACKGROUND

Several studies have reported the clinical aspects of oral syphilis, but few papers have considered the involved immunoinflammatory mechanisms.

OBJECTIVE

To analyze the clinicopathologic features and expression of immunoinflammatory and vascular proteins in oral secondary syphilis.

STUDY DESIGN

Fifteen patients with oral secondary syphilis were included; histologic features were analyzed using hematoxylin-eosin-stained histologic slides and immunohistochemical reactions were performed against intercellular adhesion molecule 1 (ICAM-1), vascular endothelial growth factor (VEGF), and CD34.

RESULTS

Lesions presented as multiple plaques and ulcers mostly located on the tongue, lips, and palate. They were covered by a stratified epithelium of irregular thickness showing exocytosis associated with a subjacent plasma cell infiltrate arranged in perivascular and perineural patterns. ICAM-1 and VEGF were expressed on endothelial cells and leukocytes, and microvessel density was similar on the superficial and deep regions of the connective tissue.

CONCLUSIONS

Expression of immunoinflammatory and vascular proteins was intense, suggesting their participation on the pathogenesis of oral secondary syphilis.

Genital Cytomegalovirus Replication Predicts Syphilis Acquisition among HIV-1 Infected Men Who Have Sex with Men

Objective

Sexually transmitted infections (STI) are common among HIV-infected men who have sex with men (MSM). While behavioral factors are important in STI acquisition, other biological factors such as immune modulation due to chronic viral infection may further predispose to STI acquisition.

Design

Post Hoc analysis including data collected over 12 months of follow-up from 131 HIV-infected MSM receiving antiretroviral therapy and screened for incident bacterial STI every 3 months.

Methods

Genital secretions collected at baseline were used to measure herpesvirus replication and inflammatory cytokines. Baseline predictors of STI were determined using survival analysis of time to incident STI.

Results

All participants were seropositive for cytomegalovirus (CMV), and 52% had detectable genital CMV at baseline. Thirty-five individuals acquired STI during follow-up, sometimes with multiple pathogen (17 syphilis, 21 gonorrhea, 14 chlamydia). Syphilis acquisition was associated with genital CMV replication at baseline (19.1% CMV-shedders versus 4.8% non-shedders, p=0.03) and younger age (p=0.02). Lower seminal MCP-1 was associated with higher seminal CMV levels and with syphilis acquisition (p<0.01). For syphilis acquisition, in multivariable Cox-Proportional Hazard model adjusted hazard rates were 3.56 (95%CI:1.00–12.73) for baseline CMV replication and 2.50 (0.92–6.77) for younger age.

Conclusions

This post hoc analysis suggest that CMV-associated decrease in seminal MCP-1 levels might predispose HIV-infected MSM to syphilis acquisition, but not other STI. Future studies should determine underlying mechanisms and if a causal association exists.