Immunopathogenesis of conjunctival scarring in trachoma

High prevalence of active trachoma and associated factors among school-aged children in Southwest Ethiopia

BACKGROUND

Active trachoma is a highly contagious ongoing stage of trachoma that predominantly occurs during childhood in an endemic area. This study assessed the prevalence and factors associated with active trachoma among school-aged children.

METHODOLOGY/PRINCIPAL FINDINGS

A community-based analytical cross-sectional study was done from March 1st to June 30th, 2021, in Southwest Ethiopia's people's regional state. A total of 1292 school-aged children were surveyed. The quantitative data were collected using a pre-tested, structured interview-based questionnaire and observation check list. The World health organization (WHO) simplified trachoma grading system was used to assess stages of trachoma. In this study, the prevalence of active trachoma was 570(44.1%), 95% CI (41.4, 46.9). Also, age group 6-10; being female; flies at household (HH), flies on child's face, improved water source, improved sanitation, presence of ocular discharge, presence of nasal discharge, and unclean faces of the child were significantly associated with active trachoma.

CONCLUSIONS/SIGNIFICANCE

The very high prevalence of active trachoma in the study area is significantly associated with; age group 6-10, female gender, presence of flies in household and on child's face, presence of ocular and nasal discharge, unclean faces, improved water source, improved sanitation in the household. Thus, environmental sanitation and facial cleans trachoma elimination strategy should be intensified in the study area.

Longitudinal changes in tear cytokines and antimicrobial proteins in trachomatous disease

BACKGROUND

Trachoma is a neglected tropical disease caused by ocular infection with Chlamydia trachomatis, where repeated infections and chronic inflammation can ultimately result in scarring, trichiasis and blindness. While scarring is thought to be mediated by a dysregulated immune response, the kinetics of cytokines and antimicrobial proteins in the tear film have not yet been characterised.

METHODOLOGY

Pooled tears from a Gambian cohort and Tanzanian cohort were semi-quantitatively screened using a Proteome Profiler Array to identify cytokines differentially regulated in disease. Based on this screen and previous literature, ten cytokines (CXCL1, IP-10, IFN-γ, IL-1β, IL-8, IL-10, IL-12 p40, IL-1RA, IL-1α and PDGF), lysozyme and lactoferrin were assayed in the Tanzanian cohort by multiplex cytokine assay and ELISA. Finally, CXCL1, IP-10, IL-8, lysozyme and lactoferrin were longitudinally profiled in the Gambian cohort by multiplex cytokine assay and ELISA.

RESULTS

In the Tanzanian cohort, IL-8 was significantly increased in those with clinically inapparent infection (p = 0.0086). Lysozyme, IL-10 and chemokines CXCL1 and IL-8 were increased in scarring (p = 0.016, 0.046, 0.016, and 0.037). CXCL1, IP-10, IL-8, lysozyme and lactoferrin were longitudinally profiled over the course of infection in a Gambian cohort study, with evidence of an inflammatory response both before, during and after detectable infection. CXCL1, IL-8 and IP-10 were higher in the second infection episode relative to the first (p = 0.0012, 0.044, and 0.04).

CONCLUSIONS

These findings suggest that the ocular immune system responds prior to and continues to respond after detectable C. trachomatis infection, possibly due to a positive feedback loop inducing immune activation. Levels of CXC chemokines in successive infection episodes were increased, which may offer an explanation as to why repeated infections are a risk factor for scarring.

Losartan Inhibition of Myofibroblast Generation and Late Haze (Scarring Fibrosis) After PRK in Rabbits

PURPOSE

To study the effect of topical losartan compared to vehicle on the generation of myofibroblasts and development of late haze scarring fibrosis after photorefractive keratectomy (PRK) in rabbits.

METHODS

Twelve rabbits had -9.00 diopter (D) PRK in one eye followed by 50 µL of topical 0.2 mg/mL losartan or 50 µL of vehicle six times per day for 1 month. Standardized slit-lamp photographs were obtained prior to death. Duplex immunohistochemistry was performed on cryofixed corneas for myofibroblast marker alpha-smooth muscle actin (α-SMA) and keratocyte marker keratocan or collagen type IV and transforming growth factor (TGF)-β1. ImageJ software (National Institutes of Health) was used for quantitation.

RESULTS

Topical losartan compared to vehicle significantly decreased corneal opacity (P = .04) and anterior stromal myofibroblast generation (P = .01) at 1 month after PRK. Topical losartan compared to vehicle also decreased anterior stromal non-basement membrane collagen type IV at 1 month after PRK (P = .004).

CONCLUSIONS

Topical angiotensin converting enzyme II receptor inhibitor losartan, a known inhibitor of TGF-β signaling, decreased late haze scarring fibrosis and myofibroblast generation after -9.00 D PRK in rabbits compared to vehicle. It also decreases TGF-β-modulated, corneal fibroblast-produced, non-basement membrane stromal collagen type IV-likely also through inhibition of TGF-β signaling. [J Refract Surg. 2022;38(12):820-829.].

Magic Bullets: The Coming Age of Meaningful Pharmacological Control of the Corneal Responses to Injury and Disease

Corneal injuries from chemical burns, mechanical trauma, infections, immunological rejections, surgical complications, and some diseases are commonly associated with persistent epithelial defects (PED), neurotrophic epitheliopathy, scarring fibrosis, corneal neovascularization (CNV), and/or corneal endothelial damage that lead to vision loss. Several Food and Drug Administration (FDA) approved medications have recently become available, are currently in clinical trials, or are likely to enter clinical trials in the near future. For example, a 2-week course of topical human recombinant nerve growth factor is frequently an effective treatment for corneal neurotrophic epitheliopathy associated with PEDs. Topical losartan, an angiotensin converting enzyme II receptor antagonist that also inhibits TGF beta signaling, has been shown to effectively decrease myofibroblast generation and scarring fibrosis in alkali burn injury and Descemetorhexis rabbit models. Small molecule topical tyrosine kinase inhibitors, such as sunitinib and axitinib, FDA approved as chemotherapeutic agents to treat specific cancers, have also been found to be effective topical inhibitors of CNV in animal and human trials. Rho-kinase inhibitors, such as ripasudil and netarsudil, that are currently approved agents for the treatment of glaucoma in some countries, have been shown to stimulate corneal endothelial proliferation in animal studies and human trials, and may accelerate the regeneration of Descemet's membrane. These agents, as well as other drugs in development, will be used in targeted combinations to treat corneal pathophysiology associated with epithelial healing disorders, stromal scarring fibrosis, CNV, and corneal endothelial injury during the next decade.

More than Antibiotics: Latest Therapeutics in the Treatment and Prevention of Ocular Surface Infections

Ocular surface infections have been common issues for ophthalmologists for decades. Traditional strategies for infection include antibiotics, antiviral agents, and steroids. However, multiple drug-resistant bacteria have become more common with the prevalence of antibiotic use. Furthermore, an ideal treatment for an infectious disease should not only emphasize eliminating the microorganism but also maintaining clear and satisfying visual acuity. Immunogenetic inflammation, tissue fibrosis, and corneal scarring pose serious threats to vision, and they are not attenuated or prevented by traditional antimicrobial therapeutics. Herein, we collected information about current management techniques including stem-cell therapy, probiotics, and gene therapy as well as preventive strategies related to Toll-like receptors. Finally, we will introduce the latest research findings in ocular drug-delivery systems, which may enhance the bioavailability and efficiency of ocular therapeutics. The clinical application of improved delivery systems and novel therapeutics may support people suffering from ocular surface infections.

Benzalkonium chloride-induced myofibroblastic transdifferentiation of Tenon's capsule fibroblasts is inhibited by coculture with corneal epithelial cells or by interleukin-10

Benzalkonium chloride (BAC) is used as a preservative in eyedrops but induces subconjunctival fibrosis that can result in failure of glaucoma surgery. Tenon's capsule fibroblasts in subconjunctival tissue interact with the corneal epithelium through tear fluid. With the use of a coculture system, we have now investigated the effect of human corneal epithelial (HCE) cells on myofibroblastic transdifferentiation of human Tenon fibroblasts (HTFs) induced by BAC (5 × 10^-6%). Immunofluorescence and immunoblot analyses revealed that the BAC-induced expression of α smooth muscle actin (αSMA) in HTFs was suppressed by coculture of these cells with HCE cells (p < 0.01). The concentration of interleukin-10 (IL-10) in culture supernatants of BAC-treated HTFs was increased by coculture with HCE cells (17.26-fold, vs. coculure, p < 0.001). Immunofluorescence and immunoblot analyses also showed that exogenous IL-10 (300 pg/ml) suppressed the BAC-induced expression of αSMA by 43.65% (p < 0.05) as well as the nuclear translocation of myocardin-related transcription factor-A (MRTF-A) by 39.32% (p < 0.01) in HTFs cultured alone. Our findings suggest that corneal epithelial cells may protect against subconjunctival fibrosis by maintaining IL-10 levels and preventing the MRTF-A-dependent transdifferentiation of HTFs into myofibroblasts.

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.

Elevated levels of prostaglandin E2 in the tears of patients with severe allergic conjunctivitis and primary cultured conjunctival cells are suppressed by ketotifen and dexamethasone

Objective

We examined the production of prostaglandin E₂ (PGE₂), which is the key prostaglandin involved in inflammatory disorders of the ocular surface. Tears and conjunctival fibroblasts were evaluated in order to assess allergic inflammation and the effect of specific drugs.

Methods and analysis

PGE₂ was measured in tears from both patients and normal volunteers. Primary cultures of human conjunctival fibroblasts were incubated with interleukin (IL)-4 and tumour necrosis factor (TNF)-α with or without ketotifen fumarate or dexamethasone. The culture supernatants were removed 24 hours after exposure and the concentrations of PGE₂ were quantified by ELISA.

Results

Significantly higher levels of PGE₂ were observed in the tears of patients with severe allergic conjunctivitis than in those with post-surgical inflammation (p=0.02), and this production was reduced by eye drops. Stimulation with IL-4 and TNF-α induced the generation of PGE₂ in supernatants of conjunctival fibroblasts, and this production was significantly downregulated by ketotifen fumarate or steroids.

Conclusion

PGE₂ may participate in the pathogenesis of severe ocular allergic disease, and both ketotifen fumarate and steroid reduce the production of PGE₂.

Stromal Fibroblasts Drive Host Inflammatory Responses That Are Dependent on Chlamydia trachomatis Strain Type and Likely Influence Disease Outcomes

Chlamydia trachomatis ocular strains cause a blinding disease known as trachoma. These strains rarely cause urogenital infections and are not found in the upper genital tract or rectum. Urogenital strains are responsible for a self-limited conjunctivitis and the sequelae of infertility, ectopic pregnancy, and hemorrhagic proctitis. However, the differential cellular responses that drive these clinically observed disease outcomes are not completely understood. Primary conjunctival, endocervical, and endometrial epithelial and stromal fibroblast cells, HeLa229 cells, and immortalized conjunctival epithelial (HCjE) cells were infected with the ocular A/Har-13 (A) and Ba/Apache-2 (Ba) strains and urogenital D/UW-3 (D) and E/Bour (E) strains. Infection rates, progeny production, and cytokine/chemokine secretion levels were evaluated in comparison with those in uninfected cells. All strain types infected all cell types with similar levels of efficacy and development. However, progeny production levels differed among primary cells: Ba produced significantly more progeny than E in endocervical and endometrial fibroblasts, while A progeny were less abundant than E progeny. C.trachomatis infection of primary epithelial cells elicited an increase in pro- and anti-inflammatory mediators compared to levels in uninfected cells, but there were no significant differences by strain type. In contrast, for primary fibroblasts, ocular strains elicited significant increases in the pro- and anti-inflammatory mediators macrophage inflammatory protein (MIP)-1β, thymus- and activation-regulated chemokine (TARC), interleukin (IL)-2, IL-12p70, and interferon gamma-induced protein 10 (IP-10) compared to levels in urogenital strains, while urogenital strains elicited a distinct and significant increase in the proinflammatory mediators IL-1α, IL-1β, IL-8, gamma interferon (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF). Our data indicate that primary fibroblasts, not epithelial cells, drive host inflammatory responses that are dependent on strain type and likely influence disease outcomes, establishing their importance as a novel model for studies of C. trachomatis disease pathogenesis.IMPORTANCEChlamydia trachomatis is a human pathogen and the leading cause of preventable blindness and sexually transmitted diseases in the world. Certain C. trachomatis strains cause ocular disease, while others cause upper genital tract pathology. However, little is known about the cellular or immunologic basis for these differences. Here, we compared the abilities of the strain types to infect, replicate, and initiate an immune response in primary human ocular and urogenital epithelial cells, as well as in fibroblasts from the underlying stroma. While there were no significant differences in infection rates or intracellular growth for any strain in any cell type, proinflammatory responses were driven not by the epithelial cells but by fibroblasts and were distinct between ocular and urogenital strains. Our findings suggest that primary fibroblasts are a novel and more appropriate model for studies of immune responses that will expand our understanding of the differential pathological disease outcomes caused by various C. trachomatis strain types.

Conjunctival transcriptome profiling of Solomon Islanders with active trachoma in the absence of Chlamydia trachomatis infection

BACKGROUND

Clinical signs of active (inflammatory) trachoma are found in many children in the Solomon Islands, but the majority of these individuals have no serological evidence of previous infection with Chlamydia trachomatis. In Temotu and Rennell and Bellona provinces, ocular infections with C. trachomatis were seldom detected among children with active trachoma; a similar lack of association was seen between active trachoma and other common bacterial and viral causes of follicular conjunctivitis. Here, we set out to characterise patterns of gene expression at the conjunctivae of children in these provinces with and without clinical signs of trachomatous inflammation-follicular (TF) and C. trachomatis infection.

METHODS

Purified RNA from children with and without active trachoma was run on Affymetrix GeneChip Human Transcriptome Array 2.0 microarrays. Profiles were compared between individuals with ocular C. trachomatis infection and TF (group DI; n = 6), individuals with TF but no C. trachomatis infection (group D; n = 7), and individuals without TF or C. trachomatis infection (group N; n = 7). Differential gene expression and gene set enrichment for pathway membership were assessed.

RESULTS

Conjunctival gene expression profiles were more similar within-group than between-group. Principal components analysis indicated that the first and second principal components combined explained almost 50% of the variance in the dataset. When comparing the DI group to the N group, genes involved in T-cell proliferation, B-cell signalling and CD8+ T cell signalling pathways were differentially regulated. When comparing the DI group to the D group, CD8+ T-cell regulation, interferon-gamma and IL17 production pathways were enriched. Genes involved in RNA transcription and translation pathways were upregulated when comparing the D group to the N group.

CONCLUSIONS

Gene expression profiles in children in the Solomon Islands indicate immune responses consistent with bacterial infection when TF and C. trachomatis infection are concurrent. The transcriptomes of children with TF but without identified infection were not consistent with allergic or viral conjunctivitis.

Dendrimer-conjugated peptide vaccine enhances clearance of Chlamydia trachomatis genital infection

Peptide-based vaccines have emerged in recent years as promising candidates in the prevention of infectious diseases. However, there are many challenges to maintaining in vivo peptide stability and enhancement of peptide immunogenicity to generate protective immunity which enhances clearance of infections. Here, a dendrimer-based carrier system is proposed for peptide-based vaccine delivery, and shows its anti-microbial feasibility in a mouse model of Chlamydia trachomatis. Chlamydiae are the most prevalent sexually transmitted bacteria worldwide, and also the causal agent of trachoma, the leading cause of preventable infectious blindness. In spite of the prevalence of this infectious agent and the many previous vaccine-related studies, there is no vaccine commercially available. The carrier system proposed consists of generation 4, hydroxyl-terminated, polyamidoamine (PAMAM) dendrimers (G4OH), to which a peptide mimic of a chlamydial glycolipid antigen-Peptide 4 (Pep4, AFPQFRSATLLL) was conjugated through an ester bond. The ester bond between G4OH and Pep4 is expected to break down mainly in the intracellular environment for antigen presentation. Pep4 conjugated to dendrimer induced Chlamydia-specific serum antibodies after subcutaneous immunizations. Further, this new vaccine formulation significantly protected immunized animals from vaginal challenge with infectious Chlamydia trachomatis, and it reduced infectious loads and tissue (genital tract) damage. Pep4 conjugated to G4OH or only mixed with peptide provided enhanced protection compared to Pep4 and adjuvant (i.e. alum), suggesting a potential adjuvant effect of the PAMAM dendrimer. Combined, these results demonstrate that hydroxyl-terminated PAMAM dendrimer is a promising polymeric nanocarrier platform for the delivery of peptide vaccines and this approach has potential to be expanded to other infectious intracellular bacteria and viruses of public health significance.

Fibroblasts profiling in scarring trachoma identifies IL-6 as a functional component of a fibroblast-macrophage pro-fibrotic and pro-inflammatory feedback loop

Trachoma is a conjunctiva scarring disease, which is the leading infectious cause of blindness worldwide. Yet, the molecular mechanisms underlying progressive fibrosis in trachoma are unknown. To investigate the contribution of local resident fibroblasts to disease progression, we isolated conjunctival fibroblasts from patients with scarring trachoma and matching control individuals, and compared their gene expression profiles and functional properties in vitro. We show that scarring trachoma fibroblasts substantially differ from control counterparts, displaying pro-fibrotic and pro-inflammatory features matched by an altered gene expression profile. This pro-inflammatory signature was exemplified by increased IL-6 expression and secretion, and a stronger response to macrophage-mediated stimulation of contraction. We further demonstrate that scarring trachoma fibroblasts can promote Akt phosphorylation in macrophages in an IL-6 –dependent manner. Overall this work has uncovered a distinctive molecular fingerprint for scarring trachoma fibroblasts, and identified IL-6- as a potential contributor to the chronic conjunctival fibrosis, mediating reciprocal pro-fibrotic/pro-inflammatory interactions between macrophages and fibroblasts.

Increased Epithelial Expression of CTGF and S100A7 with Elevated Subepithelial Expression of IL-1β in Trachomatous Trichiasis

Purpose

To characterize the histological appearance and expression of pro-inflammatory mediators, growth factors, matrix metalloproteinases and biomarkers of epithelial-mesenchymal transition (EMT) in healthy control and trachomatous trichiasis (TT) conjunctival tissue.

Methods

Conjunctival biopsies were taken from 20 individuals with TT and from 16 individuals with healthy conjunctiva, which served as controls. Study participants were of varying ethnicity and were living in a trachoma-endemic region of northern Tanzania. Formalin-fixed paraffin-embedded tissue sections were stained using hematoxylin and eosin or by immunohistochemistry using antibodies against: IL-1β, IL-6, IL-17A, IL-22, CXCL5, S100A7, cleaved caspase 1 (CC1), PDGF, CTGF, TGFβ2, MMP7, MMP9, E-cadherin, vimentin, and αSMA.

Results

Tissue from TT cases had a greater inflammatory cell infiltrate relative to controls and greater disruption of collagen structure. CTGF and S100A7 were more highly expressed in the epithelium and IL-1β was more highly expressed in the substantia propria of TT cases relative to controls. Latent TGFβ2 was slightly more abundant in the substantia propria of control tissue. No differences were detected between TT cases and controls in the degree of epithelial atrophy, the number of myofibroblasts or expression of EMT biomarkers.

Conclusions

These data indicate that the innate immune system is active in the immunopathology of trachoma, even in the absence of clinical inflammation. CTGF might provide a direct link between inflammation and fibrosis and could be a suitable target for therapeutic treatment to halt the progression of trachomatous scarring.

Progressive scarring of the conjunctiva in individuals with trachoma causes the eyelids to contract, drawing the eyelashes inwards (trichiasis) so that they scratch the cornea, causing pain and eventually blindness. Disease is initiated in childhood by repeated conjunctival infection with Chlamydia trachomatis (Ct), however, infection is not commonly found in adults, yet chronic inflammation and fibrosis progress throughout the lives of many individuals. A better understanding of the mechanisms driving inflammation and fibrosis are required in order to develop treatments to halt disease progression. The tissue expression and localization of a number of pro-inflammatory cytokines, growth and matrix factors were investigated in eyelid tissue from 20 individuals with trichiasis and from 16 control individuals. By staining tissue sections with dyes and specific antibodies, pro-inflammatory signaling molecules IL-1β and S100A7 and pro-fibrotic growth factor CTGF were found to be more highly expressed in individuals with trichiasis. CTGF and S100A7 were highly expressed in the epithelium; the outermost layer of the conjunctiva, whereas IL-1β was more highly expressed deeper in the tissue, where scarring occurs. Numerous inflammatory cells were found in the tissue of trichiasis patients even in the absence of clinically apparent inflammation. Future research should seek to describe a causative mechanism linking these factors.

Immunohistochemical Analysis of Scarring Trachoma Indicates Infiltration by Natural Killer and Undefined CD45 Negative Cells

INTRODUCTION

The phenotype and function of immune cells infiltrating the conjunctiva in scarring trachoma have yet to be fully characterized. We assessed tissue morphology and immunophenotype of cellular infiltrates found in trachomatous scarring compared to control participants.

METHODOLOGY

Clinical assessments and conjunctival biopsy samples were obtained from 34 individuals with trachomatous scarring undergoing trichiasis surgery and 33 control subjects undergoing cataract or retinal detachment surgery. Biopsy samples were fixed in buffered formalin and embedded in paraffin wax. Hematoxylin and eosin (H&E) staining was performed for assessment of the inflammatory cell infiltrate. Immunohistochemical staining of single markers on individual sections was performed to identify cells expressing CD3 (T-cells), CD4 (helper T-cells), CD8 (suppressor/cytotoxic T-cells and Natural Killer, NK, cells), NCR1 (NK cells), CD20 (B-cells), CD45 (nucleated hematopoietic cells), CD56 (NK and T-cells), CD68 (macrophages/monocytes) and CD83 (mature dendritic cells). The degree of scarring was assessed histologically using cross-polarized light to visualize collagen fibres.

PRINCIPLE FINDINGS

Scarring, regardless of clinical inflammation, was associated with increased inflammatory cell infiltrates on H&E and CD45 staining. Scarring was also associated with increased CD8+ and CD56+ cells, but not CD3+ cells, suggestive of a NK cell infiltrate. This was supported by the presence of NCR1+ cells. There was some increase in CD20+ cells, but no evidence for increased CD4+, CD68+ or CD83+ cells. Numerous CD45 negative cells were also seen in the population of infiltrating inflammatory cells in scarred conjunctiva. Disorganization of the normal collagen architecture was strongly associated with clinical scarring.

CONCLUSIONS/SIGNIFICANCE

These data point to the infiltration of immune cells with a phenotype suggestive of NK cells in conjunctival trachomatous scarring. A large proportion of CD45 negative inflammatory cells were also present. Future work should seek to understand the stimuli leading to the recruitment of these cells and their role in progressive scarring.

Tissue-Resident T Cells as the Central Paradigm of Chlamydia Immunity

For almost 2 decades, results from Chlamydia pathogenesis investigations have been conceptualized using a cytokine polarization narrative. Recent viral immunity studies identifying protective tissue-resident memory T cells (Trm) suggest an alternative paradigm based on localized immune networks. As Chlamydia vaccines enter the preclinical pipeline and, in the case of an attenuated trachoma vaccine, are given to human subjects, it may be useful to ask whether cytokine polarization is the appropriate framework for understanding and evaluating vaccine efficacy. In this review, we revisit C. trachomatis pathogenesis data from mice and humans using a Trm narrative and note a comfortable concordance with the Chlamydia pathogenesis literature.

Trachoma and Ocular Chlamydial Infection in the Era of Genomics

Trachoma is a blinding disease usually caused by infection with Chlamydia trachomatis (Ct) serovars A, B, and C in the upper tarsal conjunctiva. Individuals in endemic regions are repeatedly infected with Ct throughout childhood. A proportion of individuals experience prolonged or severe inflammatory episodes that are known to be significant risk factors for ocular scarring in later life. Continued scarring often leads to trichiasis and in-turning of the eyelashes, which causes pain and can eventually cause blindness. The mechanisms driving the chronic immunopathology in the conjunctiva, which largely progresses in the absence of detectable Ct infection in adults, are likely to be multifactorial. Socioeconomic status, education, and behavior have been identified as contributing to the risk of scarring and inflammation. We focus on the contribution of host and pathogen genetic variation, bacterial ecology of the conjunctiva, and host epigenetic imprinting including small RNA regulation by both host and pathogen in the development of ocular pathology. Each of these factors or processes contributes to pathogenic outcomes in other inflammatory diseases and we outline their potential role in trachoma.

Porcine retinal cell line VIDO R1 and Chlamydia suis to modelize ocular chlamydiosis

Human ocular Chlamydia trachomatis infections can lead to trachoma, the major cause of infectious blindness worldwide. Trachoma control strategies are very helpful but logistically challenging, and a trachoma vaccine is needed but not available. Pigs are a valuable large animal model for various immunological questions and could facilitate the study of human ocular chlamydial infections. In addition, a recent study identified the zoonotic potential of Chlamydia suis, the natural pathogen of pigs. In terms of the One Health Initiative, understanding the host-pathogen-interactions and finding a vaccine for porcine chlamydia infections would also benefit human health. Thus, we infected the porcine retinal cell line VIDO R1 with C. suis and analyzed the chlamydial life cycle and the innate immune response of the infected cells. Our results indicate that C. suis completes its life cycle in VIDO R1 cells within 48 h, comparable to C. trachomatis in humans. C. suis infection of VIDO R1 cells led to increased levels of various innate immune mediators like pathogen recognition receptors, cytokines and chemokines including IL6, TNFα, and MMP9, also most relevant in human C. trachomatis infections. These results illustrate the first steps in the host-pathogen-interactions of ocular C. suis infections in pigs and show their similarity to C. trachomatis infections in humans, justifying further testing of pigs as an animal model for human trachoma.

Trachoma

Trachoma is the most common infectious cause of blindness. Repeated episodes of infection with Chlamydia trachomatis in childhood lead to severe conjunctival inflammation, scarring, and potentially blinding inturned eyelashes (trichiasis or entropion) in later life. Trachoma occurs in resource-poor areas with inadequate hygiene, where children with unclean faces share infected ocular secretions. Much has been learnt about the epidemiology and pathophysiology of trachoma. Integrated control programmes are implementing the SAFE Strategy: surgery for trichiasis, mass distribution of antibiotics, promotion of facial cleanliness, and environmental improvement. This strategy has successfully eliminated trachoma in several countries and global efforts are underway to eliminate blinding trachoma worldwide by 2020.

Towards a safe and effective chlamydial vaccine: lessons from the eye

As well as being the most common bacterial sexually transmitted infection, Chlamydia trachomatis (Ct) is the leading infectious cause of blindness. The pathogenesis of ocular chlamydial infection (trachoma) is similar to that of genital infection. In the 1960s the efficacy of Ct vaccines against ocular infection was evaluated in major field trials in Saudi Arabia, Taiwan, The Gambia, India and Ethiopia. These trials showed that it was possible to induce short term immunity to ocular infection, and to reduce the incidence of inflammatory trachoma, by parenteral immunisation with killed or live whole organism vaccines. In one study, it was also shown that the incidence of scarring sequelae was reduced in vaccinated children. Detailed studies in non-human primates conducted at this time suggested that vaccination could lead to more severe inflammatory disease on subsequent challenge. Since that time there have been many studies on the immunological correlates of protective immunity and immunopathology in ocular Ct infection in humans and non-human primates, and on host genetic polymorphisms associated with protection from adverse sequelae. These have provided important information to guide the development and evaluation of a human Ct vaccine.

Trachoma: protective and pathogenic ocular immune responses to Chlamydia trachomatis

Trachoma, caused by Chlamydia trachomatis (Ct), is the leading infectious blinding disease worldwide. Chronic conjunctival inflammation develops in childhood and leads to eyelid scarring and blindness in adulthood. The immune response to Ct provides only partial protection against re-infection, which can be frequent. Moreover, the immune response is central to the development of scarring pathology, leading to loss of vision. Here we review the current literature on both protective and pathological immune responses in trachoma. The resolution of Ct infection in animal models is IFNγ-dependent, involving Th1 cells, but whether this is the case in human ocular infection still needs to be confirmed. An increasing number of studies indicate that innate immune responses arising from the epithelium and other innate immune cells, along with changes in matrix metalloproteinase activity, are important in the development of tissue damage and scarring. Current trachoma control measures, which are centred on repeated mass antibiotic treatment of populations, are logistically challenging and have the potential to drive antimicrobial resistance. A trachoma vaccine would offer significant advantages. However, limited understanding of the mechanisms of both protective immunity and immunopathology to Ct remain barriers to vaccine development.

Innate immune responses and modified extracellular matrix regulation characterize bacterial infection and cellular/connective tissue changes in scarring trachoma

Trachoma is the most common infectious cause of blindness and a major public health problem in many developing countries. It is caused by recurrent ocular infection with Chlamydia trachomatis in childhood, with conjunctival scarring seen later in life. The pathogenesis of trachomatous scarring, however, is poorly understood, and this study was carried out to investigate the immunofibrogenic correlates of trachomatous conjunctival scarring. A case-control study of 363 cases with conjunctival scarring and 363 control participants was conducted. Investigations included in vivo confocal microscopy (IVCM) assessment, quantitative real-time PCR gene expression, C. trachomatis detection, and nonchlamydial bacterial culture. Trachomatous scarring was found to be strongly associated with a proinflammatory, innate immune response with increased expression of psoriasin, interleukin-1β, tumor necrosis factor alpha, defensin-β4A, chemokine ligand 5, and serum amyloid A1. There was also differential expression of various modifiers of the extracellular matrix, including metalloproteinases 7, 9, 10, and 12, tissue inhibitor of matrix metalloproteinase 1, and secreted protein acidic cystein-rich-like 1. The expression of many of these genes was also significantly associated with the presence of nonchlamydial bacterial infection. These infections had a marked effect on conjunctival immune processes, including an increased inflammatory infiltrate and edema seen with IVCM. This study supports the possibility that the immunofibrogenic response in scarring trachoma is partly stimulated by nonchlamydial bacterial infection, which is characterized by the expression of innate factors.

In vivo confocal microscopy of trachoma in relation to normal tarsal conjunctiva

OBJECTIVE

To describe the in vivo confocal microscopy (IVCM) appearances of the tarsal conjunctiva in trachoma compared with the appearance of healthy conjunctiva and to develop grading systems for IVCM examination of the tarsal conjunctiva for use in future studies on trachoma and other conjunctival diseases.

DESIGN

Prospective observational study.

PARTICIPANTS

In vivo confocal microscopy examination was performed on 302 clinically normal adults, 16 clinically normal children, 750 adults with trachomatous conjunctival scarring, and 25 children with active trachoma.

METHODS

Clinical evaluation was performed with ×2.5 loupes, and IVCM examination of the upper tarsal conjunctiva was carried out with a Heidelberg Retina Tomograph 3 with the Rostock Cornea Module (Heidelberg Engineering GmbH, Dossenheim, Germany).

MAIN OUTCOME MEASURES

In vivo confocal microscopy images were analyzed for cellular and tissue changes associated with trachomatous inflammation and scarring compared with healthy subjects.

RESULTS

Trachomatous subjects with follicular and papillary inflammation had an increased inflammatory cellular infiltrate, including dendritiform cells, discrete follicular and papillary structures, and cystic lacunae suggestive of tissue edema. Trachomatous conjunctival scarring was seen with IVCM as organization of the subepithelial connective tissue into bands/sheets. Grading systems for inflammatory changes and scarring were developed, with the system for scarring showing good interobserver agreement with an intraclass coefficient of 0.88.

CONCLUSIONS

In vivo confocal microscopy provides a powerful tool for examining the ocular surface. Numerous cellular and tissue changes were observed in subjects with trachoma, the first time IVCM has been applied to this disease. These changes both complement and add to previous histologic analyses. In vivo confocal microscopy promises to provide new insights into the pathogenesis of trachoma and other conjunctival diseases.

Conjunctival transcriptome in scarring trachoma

Trachoma is a poorly understood immunofibrogenic disease process, initiated by Chlamydia trachomatis. Differences in conjunctival gene expression profiles between Ethiopians with trachomatous trichiasis (with [TTI] or without [TT] inflammation) and controls (C) were investigated to identify relevant host responses. Tarsal conjunctival swab samples were collected for RNA isolation and C. trachomatis PCR. Transcriptome-wide microarray experiments were conducted on 42 samples (TTI, n = 13; TT, n = 15; C, n =14). Specific results were confirmed by using multiplex quantitative reverse transcription-PCR for 16 mRNA targets in an independent collection of case-control samples: 386 case-control pairs (TTI, n = 244; TT, n = 142; C, n = 386). The gene expression profiles of cases were consistent with squamous metaplasia (keratins, SPRR), proinflammatory cytokine production (IL1β, CXCL5, and S100A7), and tissue remodeling (MMP7, MMP9, MMP12, and HAS3). There was no difference in the level of IFNγ between cases and controls. However, cases had increased INDO, NOS2A, and IL13RA2 and reduced IL13. C. trachomatis was detected in 1/772. Cases show evidence of ongoing inflammation and tissue remodeling, which were more marked where clinical inflammation was also present. Significantly, these processes appear to be active in the absence of current C. trachomatis infection. There was limited evidence of a T(H)1 response (INDO and NOS2A) and no association between a T(H)2 response and cases. The epithelium appears to be actively involved in late cicatricial stages of trachoma through the production of proinflammatory factors (IL1β, CXCL5, and S100A7). Longitudinal studies are needed to investigate which etiological factors and pathways are associated with progressive scarring and whether simply controlling chlamydial infection will halt progression in people with established cicatricial disease.

Conjunctival expression of matrix metalloproteinase and proinflammatory cytokine genes after trichiasis surgery

PURPOSE. Trachoma, the leading infectious cause of blindness, is a chronic inflammatory scarring condition. Blindness follows the development of trichiasis, which is treated surgically. Unfortunately, it frequently recurs, compromising the treatment. In this study, gene expression analysis was used to examine factors that may be involved in the inflammation and tissue remodeling after surgery. METHODS. Subjects were examined before and at 1 and 4 years after surgery. Conjunctival swab samples were collected for bacterial culture, Chlamydia trachomatis PCR, and RNA isolation at 1 year. Quantitative real-time PCR was performed to measure the expression of tumor necrosis factor-alpha (TNF), interleukin-1beta (IL1B), matrix metalloproteinase-1 (MMP1), MMP-2, MMP-9, tissue inhibitor of matrix metalloproteinase 1 (TIMP-1), TIMP-2, and hypoxanthine phosphoribosyl transferase-1 (HPRT1). RESULTS. Two hundred forty individuals with trachomatous trichiasis were recruited. One year after surgery, recurrent trichiasis was associated with a reduced MMP-1/TIMP-1 ratio (P = 0.029). IL1B expression was elevated in the presence of either conjunctival bacterial infection (P = 0.011) or inflammation (P = 0.002). TNF expression was greater in the Mandinka ethnic group (P < 0.0001), and it was increased when clinical inflammation was associated with nonchlamydial bacterial infection (P = 0.012). MMP-9 expression increased when conjunctival inflammation was associated with bacterial infection (P = 0.007). CONCLUSIONS. Recurrent trichiasis was associated with a reduced MMP-1 to TIMP-1 ratio, which may favor the accumulation of fibrotic tissue. Nonchlamydial bacterial infection may induce factors that contribute to conjunctival tissue remodeling and recurrent trichiasis in trachoma. Prospective studies are needed to assess the potential importance of these and other factors in progressive disease.

Efficacy of topical cyclosporine A in the treatment of severe trachomatous dry eye

PURPOSE

The purpose of this study was to evaluate the efficacy of topical cyclosporine A (CsA) treatment in patients with severe trachomatous dry eye.

METHODS

Sixty-four severe trachomatous dry eye patients who had undergone Schirmer testing with topical anaesthetic measured 5 mm or less and a tear film break-up time (TFBUT) of 5 s or less were included in the study. Thirty-two patients were treated with CsA 0.05% ophthalmic emulsion twice daily and concomitant five times daily non-preserved artificial tear, and the other 32 patients who were designated as the control group received vehicle emulsion twice daily and non-preserved artificial tear five times daily. Pretreatment and post-treatment evaluations included subjective assessment of the patients (total symptoms scores and ocular surface disease index [OSDI] scores), Schirmer testing with topical anaesthesia, TFBUT, rose Bengal and fluorescein staining scores, conjunctival impression cytological scoring and goblet cell counting.

RESULTS

Following 6 months of CsA treatment, the differences between the pretreatment and post-treatment test results including total symptoms scores and OSDI scores, the rose Bengal and fluorescein staining scores, TFBUT values, and the Schirmer testing measurements were found to be statistically significant. Impression cytology also showed improvement of squamous metaplasia in 26 patients (81.25%) and increase in goblet cell density in 23 patients (71.88%).

CONCLUSIONS

Topical CsA was effective in the treatment of severe trachomatous dry eye, yielding improvements in both objective and subjective measurements with a safety profile.

Role of activins and inducible nitric oxide in the pathogenesis of ectopic pregnancy in patients with or without Chlamydia trachomatis infection

Chlamydia trachomatis infection can lead to pelvic inflammatory disease, ectopic pregnancy (EP), infertility, and chronic pelvic pain in women. Activins and inducible nitric oxide synthase (iNOS) are produced by the human fallopian tube, and we speculate that tubal activins and iNOS may be involved in the immune response to C. trachomatis in humans and their pathological alteration may result in tubal pathology and the development of EP. Blood and fallopian tubes were collected from 14 women with EP. Sera were analyzed by enzyme-linked immunosorbent assay to detect antibodies against chlamydial heat shock protein 60 (chsp60) and the major outer membrane protein of C. trachomatis. Confirmation of C. trachomatis serology was made using the microimmunofluorescence test. The patients were classified into three groups according to their serological results, and immunohistochemistry and quantitative reverse transcription-PCR were performed to investigate the expression of candidate molecules by tubal epithelial cells among the three groups. This is the first study to show an increase in the expression of activin betaA subunit, type II receptors, follistatin, and iNOS within the human fallopian tube of EP patients who were serologically positive for C. trachomatis. A similar expression profile was observed in the fallopian tubes with detectable antibodies only against chsp60. These results were shown at the mRNA and protein levels. We suggest that tubal activin A, its type II receptors, follistatin, and NO could be involved in the microbial-mediated immune response within the fallopian tube, and their pathological expression may lead to tubal damage and the development of EP.

The development of an age-structured model for trachoma transmission dynamics, pathogenesis and control

BACKGROUND

Trachoma, the worldwide leading infectious cause of blindness, is due to repeated conjunctival infection with Chlamydia trachomatis. The effects of control interventions on population levels of infection and active disease can be promptly measured, but the effects on severe ocular sequelae require long-term monitoring. We present an age-structured mathematical model of trachoma transmission and disease to predict the impact of interventions on the prevalence of blinding trachoma.

METHODOLOGY/PRINCIPAL FINDINGS

The model is based on the concept of multiple reinfections leading to progressive conjunctival scarring, trichiasis, corneal opacity and blindness. It also includes aspects of trachoma natural history, such as an increasing rate of recovery from infection and a decreasing chlamydial load with subsequent infections that depend upon a (presumed) acquired immunity that clears infection with age more rapidly. Parameters were estimated using maximum likelihood by fitting the model to pre-control infection prevalence data from hypo-, meso- and hyperendemic communities from The Gambia and Tanzania. The model reproduces key features of trachoma epidemiology: 1) the age-profile of infection prevalence, which increases to a peak at very young ages and declines at older ages; 2) a shift in this prevalence peak, toward younger ages in higher force of infection environments; 3) a raised overall profile of infection prevalence with higher force of infection; and 4) a rising profile, with age, of the prevalence of the ensuing severe sequelae (trachomatous scarring, trichiasis), as well as estimates of the number of infections that need to occur before these sequelae appear.

CONCLUSIONS/SIGNIFICANCE

We present a framework that is sufficiently comprehensive to examine the outcomes of the A (antibiotic) component of the SAFE strategy on disease. The suitability of the model for representing population-level patterns of infection and disease sequelae is discussed in view of the individual processes leading to these patterns.

The effect of topical cyclosporine A treatment on corneal thickness in patients with trachomatous dry eye

PURPOSE

The purpose of the present study was to evaluate the effect of topical cyclosporine A (CsA) treatment on corneal thickness (CT) in patients with trachomatous dry eye.

METHODS

Sixty-four patients with trachomatous dry eye with a Schirmer test showing 5 mm or less and a tear film break-up time (TFBUT) of five seconds or less were included. Thirty-two patients were treated with twice daily application of CsA (0.05% ophthalmic emulsion) plus non-preserved artificial tears, while the remaining 32 patients serving as controls received only non-preserved artificial tears. CT was measured using ultrasonic pachymetry at five locations of the central (CCT) and mid-peripheral cornea, at baseline and after one, three and six months of treatment.

RESULTS

At the sixth month of treatment, CT measurements were significantly changed in both groups, compared to baseline. In the CsA treatment group, the mean CCT before and after six months of treatment were 517.4 +/- 36.2 and 546.5 +/- 32.4 microm, respectively (p < 0.001); yielding an average CCT increase of 29.1 +/- 8.0 microm (5.62 per cent) from baseline. In the control group, corresponding figures were 520.2 +/- 34.2 and 526.0 +/- 35.4 microm, respectively (p < 0.01), with an average increase of 5.8 +/- 3.1 microm (1.11 per cent).

CONCLUSIONS

In the present study, the CsA treatment group exhibited significantly greater increases in CT compared to controls. Such an increase may indicate an improvement in the integrity of the ocular surface and resolution of the underlying inflammation as a consequence of topical CsA treatment.

Identification of novel single nucleotide polymorphisms in inflammatory genes as risk factors associated with trachomatous trichiasis

Background

Trachoma is the leading preventable cause of global blindness. A balanced Th1/Th2/Th3 immune response is critical for resolving Chlamydia trachomatis infection, the primary cause of trachoma. Despite control programs that include mass antibiotic treatment, reinfection and recurrence of trachoma are common after treatment cessation. Furthermore, a subset of infected individuals develop inflammation and are at greater risk for developing the severe sequela of trachoma known as trachomatous trichiasis (TT). While there are a number of environmental and behavioral risk factors for trachoma, genetic factors that influence inflammation and TT risk remain ill defined.

Methodology/Findings

We identified single nucleotide polymorphisms (SNP) in 36 candidate inflammatory genes and interactions among these SNPs that likely play a role in the overall risk for TT. We conducted a case control study of 538 individuals of Tharu ethnicity residing in an endemic region of Nepal. Trachoma was graded according to World Health Organization guidelines. A linear array was used to genotype 51 biallelic SNPs in the 36 genes. Analyses were performed using logic regression modeling, which controls for multiple comparisons. We present, to our knowledge, the first significant association of TNFA (-308GA), LTA (252A), VCAM1 (-1594TC), and IL9 (T113M) polymorphisms, synergistic SNPs and risk of TT. TT risk decreased 5 times [odds ratio = 0.2 (95% confidence interval 0.11.–0.33), p = 0.001] with the combination of TNFA (-308A), LTA (252A), VCAM1 (-1594C), SCYA 11 (23T) minor allele, and the combination of TNFA (-308A), IL9 (113M), IL1B (5′UTR-T), and VCAM1 (-1594C). However, TT risk increased 13.5 times [odds ratio = 13.5 (95% confidence interval 3.3–22), p = 0.001] with the combination of TNFA (-308G), VDR (intron G), IL4R (50V), and ICAM1 (56M) minor allele.

Conclusions

Evaluating genetic risk factors for trachoma will advance our understanding of disease pathogenesis, and should be considered in the context of designing global control programs.

Trachoma

Trachoma is a keratoconjunctivitis caused by ocular infection with Chlamydia trachomatis. Repeated or persistent episodes lead to increasingly severe inflammation that can progress to scarring of the upper tarsal conjunctiva. Trichiasis develops when scarring distorts the upper eyelid sufficiently to cause one or more lashes to abrade the cornea, scarring it in turn and causing blindness. Active trachoma affects an estimated 84 million people; another 7.6 million have end-stage disease, of which about 1.3 million are blind. Trachoma should stand on the brink of extinction thanks to a 1998 initiative launched by WHO--the Global Elimination of Trachoma by 2020. This programme advocates control of trachoma at the community level with four inter-related population-health initiatives that form the SAFE strategy: surgery for trichiasis, antibiotics for active trachoma, facial cleanliness, and environmental improvement. Evidence supports the effectiveness of this approach, and if current world efforts continue, blinding trachoma will indeed be eliminated by 2020.

Unilateral eyelid lag and retraction as sequelae of trachoma

A 42-year-old woman had a large right palpebral fissure 13 mm high with 0.5 mm of scleral show both superiorly and inferiorly due to upper and lower eyelid retraction. The upper eyelid showed eyelid lag behind the globe only during the initial ocular movement. Superior tarsal height measured 7.5 mm with palpebral conjunctival cicatrization and Arlt's line. Severe cases of trachoma may lead to contracture of the conjunctiva and deeper tissues including Müller muscle and the tarsal plate, which supports the insertion of the levator aponeurosis. Shortening of the posterior lamella and fornix contracture would explain eyelid retraction and failure of the upper eyelid to smoothly follow the globe on downgaze.

Expression of growth factors in the conjunctiva from patients with active trachoma

PURPOSE

The blinding complications of trachoma are associated with progressive conjunctival fibrosis due to excessive accumulation of extracellular matrix (ECM) components. We studied the processes involved in the regulation of fibrosis in trachoma by investigating the expression of the fibrogenic and angiogenic connective tissue growth factor (CTGF) and basic fibroblast growth factor (bFGF), the angiogenic vascular endothelial growth factor (VEGF), the angiogenesis-associated endothelial cell marker CD105 (endoglin), and the ECM protein tenascin in the conjunctiva.

METHODS

Conjunctival biopsy specimens from six patients with active trachoma, and six control subjects were studied by immunohistochemical techniques using monoclonal and polyclonal antibodies directed against CTGF, bFGF, VEGF, CD105, and tenascin.

RESULTS

In the normal conjunctiva, weak immunoreactivity for VEGF was observed in epithelial cells. There was no immunoreactivity for the other antibodies. In all trachoma specimens, immunoreactivity for CTGF and bFGF was localized in monocytes/macrophages, positive for the CD68 marker. Strong immunoreactivity for VEGF was observed in epithelial cells and on vascular endothelial cells. CD105 immunoreactivity was observed on vascular endothelial cells. Immunoreactivity for tenascin was noted in the upper substantia propria.

CONCLUSIONS

These findings suggest that macrophages play an active role in conjunctival scarring, upregulated local production of CTGF, bFGF, and VEGF contributes to both fibrous tissue growth and angiogenesis, vascular endothelial cells are activated and are undergoing active angiogenesis, and deposition of tenascin reflect remodelling of the conjunctiva in trachomatous conjunctivitis.

Temporal cytokine gene expression patterns in subjects with trachoma identify distinct conjunctival responses associated with infection

Ocular chlamydial disease is clinically diagnosed by the appearance of characteristic inflammatory changes and development of lymphoid follicles in the conjunctiva. Nucleic acid amplification tests and relatively non-invasive methods of sampling the conjunctival surface can be used to quantify the expression of chlamydial and host genes. Using quantitative real-time polymerase chain reaction to detect the presence of Chlamydia trachomatis (CT) 16S rRNA and human interleukin (IL)-1beta, IL-10, IL-12p40, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha transcripts we examined the immune response at the conjunctival surface in a cohort of children living in a trachoma-endemic village in The Gambia. Elevated cytokine transcript levels were associated with the presence of CT 16S rRNA. Subclinical infection (CT infection without clinical signs of disease) elicited an immune response that is proinflammatory in nature, with elevations in the transcription of IL-1beta, IFN-gamma and IL-12p40. Clinically apparent infections were associated with the elevation of mRNA for the multi-functional cytokine TNF-alpha (fibrotic, type 1 inflammatory and regulatory) and the counter regulatory cytokine, IL-10, in addition to the other proinflammatory cytokines. A positive correlation between IFN-gamma transcript levels and the amount of CT 16S rRNA expressed in conjunctiva was found.

Clinical examination and laboratory tests for estimation of trachoma prevalence in a remote setting: what are they really telling us?

Worldwide, an estimated 84 million people have active trachoma and 7.6 million people have trachomatous trichiasis. WHO's SAFE strategy is an effective tool in the worldwide effort to eliminate blinding trachoma, but its institution and monitoring requires a simple, reliable, and cost-effective method to detect disease. To date, clinical examination has provided the main method of diagnosis. Detection of Chlamydia trachomatis with nucleic acid amplification tests does not always correlate well with clinical findings, which has prompted the suggestion that these methods should replace clinical examination. However, a review of the research carried out in animals and human beings suggests the relation between laboratory tests and clinical examination is due to the kinetics of trachoma and not to an inherent problem in either detection system. Given the increased difficulties of using laboratory tests in parts of the world where trachoma is endemic, we should not abandon clinical grading as a tool to assess the need for, and the effectiveness of, trachoma intervention programmes.

Cytokine and fibrogenic gene expression in the conjunctivas of subjects from a Gambian community where trachoma is endemic

The role of immunity in blinding trachoma is unclear. Conjunctival gene expression was measured in a population where trachoma is endemic. Proinflammatory (tumor necrosis factor alpha and interleukin-1beta [IL-1beta]), anti-inflammatory (IL-10), and fibrogenic (matrix metalloprotease 9) gene expression was increased in active trachoma. Markers indicative of T-cell response (gamma interferon, IL-4, IL-12p40, and perforin) were increased when chlamydial infection was present.

Differential regulation of inflammatory cytokine secretion by human dendritic cells upon Chlamydia trachomatis infection

Chlamydia trachomatis is an obligate intracellular gram-negative bacterium responsible for a wide spectrum of diseases in humans. Both genital and ocular C. trachomatis infections are associated with tissue inflammation and pathology. Dendritic cells (DC) play an important role in both innate and adaptive immune responses to microbial pathogens and are a source of inflammatory cytokines. To determine the potential contribution of DC to the inflammatory process, human DC were infected with C. trachomatis serovar E or L2. Both C. trachomatis serovars were found to infect and replicate in DC. Upon infection, DC up-regulated the expression of costimulatory (B7-1) and cell adhesion (ICAM-1) molecules. Furthermore, chlamydial infection induced the secretion of interleukin-1beta (IL-1beta), IL-6, IL-8, IL-12p70, IL-18, and tumor necrosis factor alpha (TNF-alpha). The mechanisms involved in Chlamydia-induced IL-1beta and IL-18 secretion differed from those of the other cytokines. Chlamydia-induced IL-1beta and IL-18 secretion required infection with viable bacteria and was associated with the Chlamydia-induced activation of caspase-1 in infected host cells. In contrast, TNF-alpha and IL-6 secretion did not require that the Chlamydia be viable, suggesting that there are at least two mechanisms involved in the Chlamydia-induced cytokine secretion in DC. Interestingly, an antibody to Toll-like receptor 4 inhibited Chlamydia-induced IL-1beta, IL-6, and TNF-alpha secretion. The data herein demonstrate that DC can be infected by human C. trachomatis serovars and that chlamydial components regulate the secretion of various cytokines in DC. Collectively, these data suggest that DC play a role in the inflammatory processes caused by chlamydial infections.

CD4+ T cells in the pathogenesis of murine ocular toxoplasmosis

The role of CD4(+) T cells in the pathogenesis of ocular toxoplasmosis was investigated in murine models utilizing inbred C57BL/6 mice deficient either in CD4(+), CD8(+), or B cells (microMT). Severe necrosis and inflammation with replicating parasites were observed in the eyes of control mice after primary ocular infection, and near-normal histology with few tachyzoites was observed in the eyes of mice immunized intraperitoneally with the avirulent ts-4 strain followed by intraocular challenge with the RH strain of Toxoplasma gondii. In contrast, mild inflammation without evidence of necrosis associated with increased parasite burdens were observed in the eyes of CD4 knockout (KO) mice after both primary ocular infection and challenge with RH tachyzoites. CD8 KO mice, as well as microMT mice, demonstrated increased ocular necrosis in response to either primary ocular infection or challenge. The parasite burden was increased in the eyes of both CD8 KO and microMT mice in which the parasite load was even higher. As expected, there were no increases in the levels of immunoglobulin G in serum or aqueous humor in microMT mice, and there was no increase in the levels of gamma interferon and tumor necrosis factor alpha in the sera of CD4 KO mice after both infection and challenge. These results suggest that the ocular inflammatory response to the parasite is mediated primarily by the CD4(+)-T-cell response. CD8(+) T cells and B cells may play an important role in limiting tachyzoite proliferation in the eyes. Mice deficient in CD8(+) CD4(+) T cells or B cells exhibit diminished vaccine-induced resistance and increased ocular parasite burden after challenge.

Expression of gelatinase B in trachomatous conjunctivitis

BACKGROUND/AIMS

Gelatinase B is a matrix metalloproteinase involved in extracellular matrix (ECM) breakdown often associated with scarring and other pathological disorders. It was investigated whether gelatinase B is involved in the pathogenesis of ECM degradation associated with trachomatous conjunctivitis.

METHODS

Conjunctival biopsy specimens obtained from six patients with active trachoma, six patients with active vernal keratoconjunctivitis (VKC), and seven control subjects were studied. Immunohistochemical techniques and a specific monoclonal antibody against human gelatinase B were used, and a monoclonal antibody against macrophage CD68 to identify mononuclear cells with gelatinase B immunoreactivity. In addition, quantitative zymography was used to compare the activity of gelatinase B in conjunctival biopsy specimens from seven patients with active trachoma and seven control subjects.

RESULTS

Gelatinase B was detected by immunohistochemistry only in polymorphonuclear cells located in the vascular lumens in three normal conjunctival biopsy specimens. In all trachoma specimens and in five VKC specimens, gelatinase B was localised in monocyte/macrophage cells, positive for the CD68 marker, and in polymorphonuclear cells. The majority of the latter cell type was located in intravascular spaces. Compared with VKC specimens, trachoma specimens showed significantly more immunoreactive gelatinase B monocyte/macrophage cells (52.3 (21.9) v 8.2 (6.4); p <0.001) and polymorphonuclear cells (23.2 (14.2) v 6.3 (5.4); p = 0. 013). Activated macrophages with giant cell morphology clearly stained with the gelatinase B specific monoclonal antibody were observed in trachoma specimens. Zymography revealed that gelatinase B levels in trachoma specimens were significantly higher than the levels found in normal conjunctiva (1739.6 (1078.3) v 609.3 (395.9) scanning units; p = 0.0127).

CONCLUSIONS

The increased activity of gelatinase B and numbers of inflammatory cells containing gelatinase B in trachoma specimens suggest that this enzyme plays a part in the pathogenesis of conjunctival scarring in trachoma.

IFN-gamma knockout mice show Th2-associated delayed-type hypersensitivity and the inflammatory cells fail to localize and control chlamydial infection

Delayed-type hypersensitivity (DTH) has been demonstrated to be a Th1 type immune response which is important in the host defense against infection with intracellular bacteria, including Chlamydia. In the present study, we surprisingly observed that C. trachomatis mouse pneumonitis MoPn-infected IFN-gamma gene knockout (KO) mice mounted strong DTH responses following foopad challenge with inactivated organisms. The DTH responses in IFN-gamma KO mice were associated with Th2 cytokine production and partially blocked by anti-IL-4 monoclonal antibodies. In addition, the inflammatory cells in IFN-gamma KO mice failed to target the cellular sites of chlamydial inclusions in infected tissues and failed to clear the infection. The data, in conjunction with previous studies, suggest that different types (Th1 and Th2 associated) of DTH responses may function differently in host defense against chlamydial infection and that the functional differences in DTH responses may account for the dual role that DTH is speculated to play in chlamydial protective immunity and immunopathology. Moreover, the data suggest that the IFN-gamma KO mouse is a useful model system for studying chlamydial pathogenesis.

Chlamydia trachomatis: the role of cellular and humoral immune mechanisms in the development of blindness

Ocular infection with Chlamydia trachomatis leading to trachoma is the commonest cause of treatable blindness worldwide. Although effectively controlled by improved sanitation, a chlamydial vaccine may prove a more cost-effective method of protection against this disease in the medium term. The development of vaccines against Chlamydia trachomatis has been hampered by a lack of understanding of the immune responses leading to protection or pathology, particularly in humans. Although a strong cell-mediated immune response (T helper lymphocyte type 1) is almost certainly necessary to resolve intracellular chlamydial infection, a humoral (T helper lymphocyte type 2) response may protect against colonization and limit immunopathological events. Recent studies addressing this potential conflict are reviewed.