HLA antigens in Omanis with blinding trachoma: markers for disease susceptibility and resistance

Chlamydia trachomatis and the HLA involvement in the development of infection and disease: a narrative review

Introduction

CT (Chlamydia trachomatis) is among the most common pathogens leading to sexually transmitted diseases. Considering the uncertain mechanism by which HLA polymorphisms influence the CT infection, reinfection, comorbidities or evolution and because there is no consensus regarding the alleles involved in the pathogenesis of the infection, we considered necessary to perform a review to summarize the current knowledge of HLA related to CT.

Methods

Pubmed was researched using key terms. Out of the 198 results found, we analyzed articles of all types which describe how the MHC, through HLA alleles, participates in the different stages of CT penetration in the body, including studies about cells or other molecules involved in the process.

Results

Almost 40% of the variation in the clinical course of CT infection depends on host genetic factors. There are haplotypes that influence the infection susceptibility/resistance, haplotypes that are involved in the recurrence of the infection, haplotypes that are related to tubal infertility, pelvic inflammatory disease development or trachoma. Antibody to Chsp60 (influenced by MHC genes) has been observed to correlate with late tissue-damaging sequelae. Toll-like receptors were found to increase the susceptibility to CT. The association of HLA-B27 creates susceptibility of reactive arthritis in the organisms infected by CT, but does not influence the carriage of CT.

Conclusion

We identified HLA haplotypes belonging both to MHC class l and ll, which influence different stages of CT infection. Genetic risk factors still need research, especially on Caucasians. Studies are moving towards designing a safe and effective vaccine.

The relative contribution of causal factors in the transition from infection to clinical chlamydial disease

Chlamydia is a major bacterial pathogen in humans and animals globally. Yet 80% of infections never progress to clinical disease. Decades of research have generated an interconnected network linking pathogen, host, and environmental factors to disease expression, but the relative importance of these and whether they account for disease progression remains unknown. To address this, we used structural equation modeling to evaluate putative factors likely to contribute to urogenital and ocular chlamydial disease in the koala (Phascolarctos cinereus). These factors include Chlamydia detection, load, and ompA genotype; urogenital and ocular microbiomes; host sex, age, weight, body condition; breading season, time of year; location; retrovirus co-infection; and major histocompatibility complex class II (MHCII) alleles. We show different microbiological processes underpin disease progression at urogenital and ocular sites. From each category of factors, urogenital disease was most strongly predicted by chlamydial PCR detection and load, koala body condition and environmental location. In contrast, ocular disease was most strongly predicted by phylum-level Chlamydiae microbiome proportions, sampling during breeding season and co-infection with koala retrovirus subtype B. Host MHCII alleles also contributed predictive power to both disease models. Our results also show considerable uncertainty remains, suggesting major causal mechanisms are yet to be discovered.

Podoconiosis, trachomatous trichiasis and cataract in northern Ethiopia: A comparative cross sectional study

BACKGROUND

Rural populations in low-income countries commonly suffer from the co-morbidity of neglected tropical diseases (NTDs). Podoconiosis, trachomatous trichiasis (both NTDs) and cataract are common causes of morbidity among subsistence farmers in the highlands of northern Ethiopia. We explored whether podoconiosis was associated with cataract or trachomatous trichiasis (TT) among this population.

METHODS

A comparative cross-sectional study was conducted in East Gojam region, Amhara, Ethiopia in May 2016. Data were collected from patients previously identified as having podoconiosis and from matched healthy neighbourhood controls. Information on socio-demographic factors, clinical factors and past medical history were collected by an interview-administered questionnaire. Clinical examination involved grading of podoconiosis by examination of both legs, measurement of visual acuity, direct ophthalmoscopy of dilated pupils to grade cataract, and eyelid and corneal examination to grade trachoma. Multiple logistic regression was conducted to estimate independent association and correlates of podoconiosis, TT and cataract.

FINDINGS

A total of 700 participants were included in this study; 350 podoconiosis patients and 350 healthy neighbourhood controls. The prevalence of TT was higher among podoconiosis patients than controls (65 (18.6%) vs 43 (12.3%)) with an adjusted odds ratio OR 1.57 (95% CI 1.02-2.40), p = 0.04. There was no significant difference in prevalence of cataract between the two populations with an adjusted OR 0.83 (95% CI 0.55-1.25), p = 0.36. Mean best visual acuity was 0.59 (SD 0.06) in podoconiosis cases compared to 0.44 (SD 0.04) in controls, p<0.001. The proportion of patients classified as blind was higher in podoconiosis cases compared with healthy controls; 5.6% vs 2.0%; adjusted OR 2.63 (1.08-6.39), P = 0.03.

CONCLUSIONS

Individuals with podoconiosis have a higher burden of TT and worse visual acuity than their matched healthy neighbourhood controls. Further research into the environmental and biological reasons for this co-morbidity is required. A shared approach to managing these two NTDs within the same population could be beneficial.

Conjunctival fibrosis and the innate barriers to Chlamydia trachomatis intracellular infection: a genome wide association study

Chlamydia trachomatis causes both trachoma and sexually transmitted infections. These diseases have similar pathology and potentially similar genetic predisposing factors. We aimed to identify polymorphisms and pathways associated with pathological sequelae of ocular Chlamydia trachomatis infections in The Gambia. We report a discovery phase genome-wide association study (GWAS) of scarring trachoma (1090 cases, 1531 controls) that identified 27 SNPs with strong, but not genome-wide significant, association with disease (5 × 10⁻⁶ > P > 5 × 10⁻⁸). The most strongly associated SNP (rs111513399, P = 5.38 × 10⁻⁷) fell within a gene (PREX2) with homology to factors known to facilitate chlamydial entry to the host cell. Pathway analysis of GWAS data was significantly enriched for mitotic cell cycle processes (P = 0.001), the immune response (P = 0.00001) and for multiple cell surface receptor signalling pathways. New analyses of published transcriptome data sets from Gambia, Tanzania and Ethiopia also revealed that the same cell cycle and immune response pathways were enriched at the transcriptional level in various disease states. Although unconfirmed, the data suggest that genetic associations with chlamydial scarring disease may be focussed on processes relating to the immune response, the host cell cycle and cell surface receptor signalling.

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.

Genetic variation in Chlamydia trachomatis and their hosts: impact on disease severity and tissue tropism

Chlamydia trachomatis infections are a global health problem. This obligate intracellular bacterial pathogen comprises lymphogranuloma venereum (L1-L3), ocular (A-C) and genital (D-K) serovars. Although genetically similar, each serovar group differs in disease severity and tissue tropism through mechanisms that are not well understood. It is clear that host genetic differences also play a role in chlamydial disease outcome and key host polymorphisms are beginning to emerge from both human and experimental animal studies. In this review, we will highlight pathogen and host genes that link genetic diversity, disease severity and tissue tropism. We will also use this information to provide new insights that may be helpful in developing improved management strategies for these important pathogens.

Human leukocyte antigen (HLA)-B, DRB1, and DQB1 allotypes associated with disease and protection of trachoma endemic villagers

PURPOSE

Trachoma remains the leading preventable infectious cause of blindness in developing countries. Human leukocyte antigen (HLA) associations with ocular disease severity and persistent Chlamydia trachomatis infection of Tanzanians living in trachoma-endemic villages were examined to determine possible protective candidate allotypes for vaccine development.

METHODS

Buccal swab scrapes were taken from subjects in the Trichiasis Study Group (TSG), which studied females only, and the Family Trachoma Study (FTS), which compared persistently infected probands who had severe disease with disease-free siblings and parents. DNA was purified for polymerase chain reaction sequence-specific oligonucleotide identification of HLA-DRB1, DQB1, and B allotypes. Infection was detected from conjunctival scrapes using a C. trachomatis-specific PCR-enzyme immunoassay for the MOMP-1 gene.

RESULTS

In the TSG, DR*B11 (odds ratio [OR], 0.48; 95% confidence interval [CI], 0.26-0.90; P=0.02) was significantly associated with lack of trichiasis, whereas HLA-B*07 (OR, 3.26; 95% CI, 1.42-7.49; P=0.004) and HLA-B*08 (OR, 5.12; 95% CI, 1.74-15.05; P=0.001) were associated with trichiasis. In addition, HLA-B*14 was significantly associated with inflammatory trachoma + follicular trachoma (OR, 3.76; 95% CI, 1.70-8.33; P=0.04). There were no significant allele frequencies for the FTS.

CONCLUSIONS

The data suggest that HLA-DRB*11 may offer protection from trichiasis in trachoma hyperendemic villages. Complete allotype identification and designation of its respective protective CD4(+) T-cell antigens could provide a testable candidate vaccine for blindness prevention. Additionally, buccal swab DNA was sufficiently stable when acquired under harsh field conditions and stored long term in the freezer for low-resolution HLA typing.

Seroprevalence of Helicobacter pylori in Central-European uraemic patients and its possible association with presence of HLA-DR12 allele

OBJECTIVES

Renal disease at any stage is often accompanied by significant gastrointestinal symptoms, and Helicobacter pylori (H. pylori) is closely related to these disorders. A debate is still ongoing on the clinical significance of coexisting uraemia and H. pylori. HLA-class II genes have been repeatedly investigated for predisposition to H. pylori infection. The aim of our work was to evaluate the infection rate among uraemic patients, and study the relationship between HLA antigens and H. pylori serologic status in the same cohort.

MATERIALS AND METHODS

Data of 709 uraemic patients were collected and analyzed from 2001-2006. 58.7% of patients were male, 41.3% were female, mean age was 45.1 years (SD: +/-14.65). Microlymphocytotoxicity assay was used for typing of HLA class I, PCR-SSP for typing HLA class II alleles and enzyme immunofluorescency for specific H. pylori IgG.

RESULTS

Of 709 patients, 49.37% were seropositive for H. pylori. Age of H. pylori positive patients was 48.9 versus 41 years of negatives (P<0.0001). Prevalence of H. pylori decreased strongly with year of birth. Significant difference was observed in the occurrence of HLA-DR12 according to H. pylori serology. Of patients carrying DR12, 27 (73%) were H. pylori positive and 10 (27%) were negative [P=0.0037; risk ratios (RR): 2.76].

CONCLUSION

H. pylori infection rate and its decrease with year of birth was the same in the uraemic patients and in the normal population, according to specific prevalence figures. Frequency of HLA-DR12 was the same as in the general population; consequently, it might be a possible risk factor for H. pylori seropositivity, at least in a Central-European population.

Pathogenic diversity among Chlamydia trachomatis ocular strains in nonhuman primates is affected by subtle genomic variations

Chlamydia trachomatis is the etiological agent of trachoma, the leading cause of preventable blindness. Trachoma presents distinct clinical syndromes ranging from mild and self-limiting to severe inflammatory disease. The underlying host and pathogen factors responsible for these diverse clinical outcomes are unclear. To assess the role played by pathogen variation in disease outcome, we analyzed the genomes of 4 trachoma strains representative of the 3 major trachoma serotypes, using microarray-based comparative genome sequencing. Outside of ompA, trachoma strains differed primarily in a very small subset of genes (n = 22). These subtle genetic variations were manifested in profound differences in virulence as measured by in vitro growth rate, burst size, plaque morphology, and interferon-gamma sensitivity but most importantly in virulence as shown by ocular infection of nonhuman primates. Our findings are the first to identify genes that correlate with differences in pathogenicity among trachoma strains.

The role of major histocompatibility complex alleles in the susceptibility of Brazilian patients to develop the myogenic type of Graves' orbitopathy

OBJECTIVE

To assess the frequency of the genetic markers HLA-DRB1 and DQB1 in patients with Graves' orbitopathy (GO) with and without extraocular muscle involvement.

DESIGN

The frequencies of class II HLA-DRB1 and DQB1 allele groups were determined for 81 Brazilian patients with GO and 161 normal subjects. The patients were divided into myogenic and nonmyogenic groups based on the clinical characteristics of the orbitopathy and quantitative computed tomography analysis of the extraocular muscle (EOM) dimensions.

MAIN OUTCOME

Compared to the frequency obtained for samples of normal subjects of the Brazilian population, HLA-DRB1 16 ( pc=0.008) was overrepresented in myogenic and HLA-DRB1 03 ( pc=0.02) in nonmyogenic patients.

CONCLUSIONS

The association between the HLA-DRB1 16 and the myogenic subtype of GO suggests that EOM involvement in GO may be genetically predisposed.

MHC class I and class II genes in mexican patients with Chagas disease

Chagas' disease contributes significantly to cardiovascular morbidity and mortality in several Latin-American countries. Previous studies have reported the effect of the human leukocyte antigen (HLA) molecules in the immune response regulation of Trypanosoma cruzi infection, and the association of HLA antigens with heart damage. We studied the major histocompatibility complex (MHC) class I (HLA-A and HLA-B), and class II (HLA-DR) genes in a sample of 66 serologically positive individuals with and without cardiomyopathy, and in 127 healthy controls. The total group of seropositive individuals revealed increased frequencies of HLA-B39 (pc=4.3x10(-5), odds ratio [OR]=3.35) and DR4 (pc=1.8x10(-5), OR=2.91) when compared to healthy controls. Increased frequencies of HLA-A68 and HLA-B39 were found in asymptomatic individuals when compared to patients with cardiomyopathy (pc=0.014, OR=4.99 and pc=0.001, OR=4.46, respectively). Also, patients with cardiomyopathy exhibited increased frequency of HLA-B35 when compared to healthy controls (pc=0.048, OR=2.56). The HLA-DR16 frequency was increased in patients with cardiomyopathy compared with asymptomatic individuals (pc=0.05, OR=No determined) and healthy controls (pc=0.02, OR=5.0). The results suggest that MHC alleles might be associated with the development of chronic infection and with heart damage in Chagas' disease. HLA-DR4 and HLA-B39 could be associated directly with the infection by T. cruzi, whereas, HLA-DR16 could be marker of susceptibility to heart damage and HLA-A68 might confer protection to develop cardiomyopathy.

Genetic factors underlying gluten-sensitive enteropathy

Genetic epidemiology clearly has shown that there is a genetic predisposition to gluten-sensitive enteropathy (GSE), or celiac disease. The strong genetic component, as determined by the lambda sib (lambda s), has been calculated to lie in the range of 7.5 to 30, based on a 5% to 10% recurrence risk for siblings. Ninety-five percent of northern European patients with GSE carry a particular HLA-DQ alpha beta heterodimer. Studies support the concept that the HLA-DQ gene acts as a dominant gene, and they also found that, in addition to HLA-DQ, a second locus within the major histocompatibility complex (MHC) is involved in the predisposition to GSE in the Dutch population. Genome scans conducted so far suggest that MHC and non-MHC loci collectively contribute to disease susceptibility. Since one, and probably even two, gene(s) from the MHC region itself determine at least 40% to 50% of the genetic predisposition to GSE, it is expected that the other loci each contribute only a little to the total genetic variation. The exact role of these additional genes (i.e., whether they are involved in the initiation or the progression of the disease) remains to be determined.

An infectious basis for multiple sclerosis: perspectives on the role of Chlamydia pneumoniae and other agents

The aetiology of multiple sclerosis (MS) remains unknown. Epidemiological, clinical and pathological data support the theory that MS is a complex disease/syndrome with many factors affecting its development and progression. It may be appropriate to regard MS as a syndrome with differing clinical and pathological features occurring along a spectrum. Patients with MS are more likely to have an affected relative than are individuals without MS, which suggests that there is a genetic component to this illness. Despite this genetic susceptibility, 85% of MS patients do not have an affected relative and only 1 in 3 monozygotic (identical) twins develops MS if the other twin already has it. These data strongly suggest that environmental factors influence the development of MS. Many putative infectious agents have been proposed to be involved in the aetiology of MS. Although research into identifying MS-causative agents dates back for more than 5 decades, no agent has yet emerged with any consensus as the cause of MS. This controversy is due to a number of factors, including lack of specificity of an agent to MS, lack of reproducibility in other laboratories, inappropriate controls, laboratory contamination and lack of a standard and easily reproducible assay system. Chlamydia pneumoniae is a recently described pathogen that may have a role in the pathogenesis of MS. C. pneumoniae is an intracellular bacterial organism that is infectious to humans. It has recently been detected in the cerebrospinal fluid (CSF) of MS patients but not in that of patients with other neurological diseases. There is also a case report of a patient with CNS C. pneumoniae infection and rapidly progressive MS responding to antimicrobial therapy directed against this pathogen. An association between C. pneumoniae in the CSF and MS is now apparent, but its role in the development of MS remains unknown. Further work exploring the role of C. pneumoniae in inflammatory demyelination is required. This may be accomplished either by developing an animal model or in a therapeutic trial in patients with MS.

OmpA genotypic evidence for persistent ocular Chlamydia trachomatis infection in Tanzanian village women

BACKGROUND

Trachoma is still a significant problem in the developing world. Adult women are at higher risk of developing scarring and trichiasis, the potentially blinding sequelae, compared to men. In part, the higher risk may be due to more frequent infections in women because of their frequent contact with children, the main reservoir of C. trachomatis infection. However, other factors associated with infection, particularly constant infection, in adult women need to be identified.

METHODS

A group of 118 women who were infected with C. trachomatis and 118 women who were not infected, but of similar age and trachoma status, were identified in 1996 from a population-based sample of women age 16 and older from eleven villages in Kongwa, Tanzania. This group of 236 was re-contacted three years later to ascertain trachoma status and determine infection status using polymerase chain reaction-enzyme immunoassay (PCR-EIA). Positive samples at both time points were examined for serovar and genotype shift, using ompA sequencing information.

RESULTS

Of the original 236 women, 165 (70%) completed exams in 1999. Fifty-eight (35%) of the 165 women were excluded from this analysis because they received antibiotic treatment for trachoma in the six months prior to the second exam. Infection at baseline was the most important predictor of infection three years later (Age-adjusted odds ratio (95% confidence interval) 6.6 (1.8-24.4)). A total of 17 women (16%) were infected at the two examinations, and of the 15 for whom genotyping could be done, 11 (73%) were infected with the same ompA genotype at both time points. Chronically infected women were more likely to have trichiasis, scarring, and active trachoma at baseline than those never infected or infected only once. Only 41% of the chronically infected women were living in houses with infected pre-school children, but 24% were in houses with no children. Four of ten women with trichiasis developed incident corneal opacity over the three years.

CONCLUSIONS

The data provide evidence for persistence of infection in a sub-group of women. The strongest predictor of infection at follow-up was baseline infection, and most were infected with the same genotype at both time points. For women with persistent infection, at least half were either not living with children or not living with infected children, suggesting that continual re-exposure from a close family member was less likely. Chronic infection is likely related to both exposure and immunological factors, and these need to be further identified. Inclusion of women in community-based treatment programs, regardless of whether a child is present in the house, is likely to be important in preventing the progression of inflammatory trachoma and scarring to trichiasis.

Histocompatibility antigens in Omanis: Comparison with other Gulf populations and implications for disease association

BACKGROUND

This is the first comprehensive report of HLA antigens in Omanis, and the first application of HLA sequence-specific primer (SSP) DNA typing in a Gulf population. The objective was to compare the findings with other Gulf populations and assess their implications for disease association.

PATIENTS AND METHODS

HLA typing was carried out on 321 healthy Omanis. One hundred and twenty-six of these were typed for Class II antigens by low-resolution SSP DNA typing. The results were compared with other HLA antigen frequencies recorded from Kuwait and Saudi Arabia.

RESULTS

The Omani population was characterized by a very high incidence of HLA-DR2 (66%), with associated HLA-DQ1 (76%) and a reduced incidence of DR4, DR7 and DR53. The incidence of DR2 is the highest recorded worldwide. HLA-A11, A32, B17, B35 and B40 were significantly higher than in Kuwait and Saudi Arabia, and A9, B21(B50) significantly lower (Pc<0.05). HLA-B27 is very low in the Omani population (0.3%). The high incidence of HLA-DR2 in Oman and disparities in the frequency of other antigens would indicate that there has not been any significant migration from northern Arabia. Class II DNA typing revealed that DR16 was the predominant split of DR2 (63%), with DR15 being 18% and both DR15 and 16 being found in 6%, giving a total of 87% for A centAADR2A centAA-associated antigens (serology of the same individuals gave a DR2 incidence of 74%). The major disparity between serology and DNA typing was in the definition of DR4 (serology 8%, DNA 14%) and DR51 (53% vs. 70%).

CONCLUSION

The frequency of many HLA antigens in Omanis differs significantly from frequencies found in the populations of Kuwait and Saudi Arabia, possibly reflecting different migration patterns. The high incidence of HLA-DR2 in Oman may have important implications for disease association.