Species-, serogroup-, and serovar-specific epitopes are juxtaposed in variable sequence region 4 of the major outer membrane proteins of some Chlamydia trachomatis serovars

Human antibody signatures towards the Chlamydia trachomatis major outer membrane protein after natural infection and vaccination

BACKGROUND

Chlamydia trachomatis (CT) Major Outer Membrane Protein (MOMP) holds a neutralising epitope in the Variable Domain 4 (VD4), and this region's immune dominance during infection is well known. This study aimed to assess the antibody response induced after infection and compare it for specificity and functionality to the response following vaccination with the vaccine CTH522, which contains VD4's from serovars D, E, F, and G.

METHODS

We assessed the antibody epitopes in MOMP by a high density peptide array. Furthermore, the role of the VD4 epitope in neutralisation was explored by competitive inhibition experiments with a fusion protein holding the neutralising VD4 linear epitope. This was done in two independent groups: 1) MOMP seropositive individuals infected with CT (n = 10, from case-control study) and 2) CTH522/CAF®01-vaccinated females (n = 14) from the CHLM-01 clinical trial.

FINDINGS

We identified the major antigenic regions in MOMP as VD4 and the conserved region just before VD3 in individuals infected with CT. The same regions, with the addition of VD1, were identified in vaccine recipients. Overall, the VD4 peptide responses were uniform in vaccinated individuals and led to inhibition of infection in vitro in all tested samples, whereas the VD4 responses were more heterogenous in individuals infected with CT, and only 2 out of 10 samples had VD4-mediated neutralising antibody responses.

INTERPRETATION

These data provide insights into the role of antibodies against MOMP VD4 induced after infection and vaccination, and show that their functionality differs. The induction of functional VD4-specific antibodies in vaccine recipients mimics previous results from animal models.

FUNDING

This work was supported by the European Commission through contract FP7-HEALTH-2011.1.4-4-280873 (ADITEC) and Fonden til Lægevidenskabens Fremme.

Obtaining an ELISA test based on a recombinant protein of Chlamydia trachomatis

Chlamydia trachomatis is considered as a public health problem due to its high prevalence and increased rates of gynecological disorders. The major outer membrane protein (MOMP) of this bacterium is the most abundant protein in its membrane and has been evaluated not only as a vaccine development candidate but also is used in many diagnostic tests. The MOMP weighs 69 kDa and contains four variable segments (VS 1-4) separated by constant regions. Several research groups have developed recombinant single-variable segments of MOMP expressed in Escherichia coli cytoplasm. But, all variable segments have been used minimally for the diagnosis of a chlamydial infection. In this experiment, the authors obtained the recombinant MOMP of C. trachomatis (rMOMP) in E. coli rMOMP and extracted, purified, and partially characterized it. This was later used to identify anti-Chlamydia trachomatis antibodies in sera of infertile patients by immunodetection assays, enzyme-linked immunosorbent assay (ELISA), and indirect immunofluorescence tests. The ELISA test showed high sensitivity and low specificity of 100 and 58.3%, respectively. The above results obtained were linked to the cross-reactivity of antibodies against C. pneumoniae or C. psittaci. Hence, an evaluation was performed to obtain an optimized test for the diagnosis of C. trachomatis infection.

Genetic diversity of Chlamydia among captive birds from central Argentina

To study the occurrence of Chlamydia spp. and their genetic diversity, we analysed 793 cloacal swabs from 12 avian orders, including 76 genera, obtained from 80 species of asymptomatic wild and captive birds that were examined with conventional nested polymerase chain reaction and quantitative polymerase chain reaction. Chlamydia spp. were not detected in wild birds; however, four species (Chlamydia psittaci, Chlamydia pecorum, Chlamydia pneumoniae and Chlamydia gallinacea) were identified among captive birds (Passeriformes, n = 20; Psittaciformes, n = 15; Rheiformes, n = 8; Falconiformes n = 2; Piciformes n = 2; Anseriformes n = 1; Galliformes n = 1; Strigiformes n = 1). Two pathogens (C. pneumoniae and C. pecorum) were identified simultaneously in samples obtained from captive birds. Based on nucleotide-sequence variations of the ompA gene, three C. psittaci-positive samples detected were grouped into a cluster with the genotype WC derived from mammalian hosts. A single positive sample was phylogenetically related to a new strain of C. gallinacea. This report contributes to our increasing understanding of the abundance of Chlamydia in the animal kingdom.

Genetic Diversity and Epizootiology ofChlamydophila psittaciPrevalent among the Captive and Feral Avian Species Based on VD2 Region ofompAGene

To study genetic diversity and occurrence of Chlamydophila psittaci, a total of 1,147 samples from 11 avian orders including 53 genera and 113 species of feral and captive birds were examined using ompA gene based nested PCR. Three types of chlamydiae: C. psittaci (94.12%), C. abortus (4.41%) and unknown Chlamydophila sp. (1.47%) were identified among 68 (5.93%) positive samples (Psittaciformes-59, Ciconiiformes-8 and Passeriformes-1). Based on nucleotide sequence variations in the VD2 region of ompA gene, all 64 detected C. psittaci strains were grouped into 4 genetic clusters. Clusters I, II, III and IV were detected from 57.35%, 19.12%, 10.29% and 7.35% samples respectively. A single strain of unknown Chlamydophila sp. was found phylogenetically intermediate between Chlamydophila species infecting avian and mammalian hosts. Among Psittaciformes, 28 out of 81 tested species including 10 species previously unreported were found to be chlamydiae positive. Chlamydiosis was detected among 8.97% sick and 48.39% dead birds as well 4.43% clinically normal birds. Therefore, it was observed that though various genetically diverse chlamydiae may cause avian chlamydiosis, only a few C. psittaci strains are highly prevalent and frequently associated with clinical/subclinical infections.

Adaptive evolution of the Chlamydia trachomatis dominant antigen reveals distinct evolutionary scenarios for B- and T-cell epitopes: worldwide survey

Background

Chlamydia trachomatis is one of the most disseminated human pathogens, for which no vaccine is available yet. Understanding the impact of the host pressure on pathogen antigens is crucial, but so far it was only assessed for highly-restricted geographic areas. We aimed to evaluate the evolutionary picture of the chlamydial key antigen (MOMP), which is one of the leading multi-subunit vaccine candidates, in a worldwide basis.

Methodology/Principal Findings

Using genetics, molecular evolution methods and mathematical modelling, we analyzed all MOMP sequences reported worldwide, composed by 5026 strains from 33 geographic regions of five continents. Overall, 35.9% of variants were detected. The evolutionary pattern of MOMP amino acid gains/losses was found to differ from the remaining chromosome, reflecting the demanding constraints of this porin, adhesin and dominant antigen. Amino acid changes were 4.3-fold more frequent in host-interacting domains (P<10⁻¹²), specifically within B-cell epitopes (P<10⁻⁵), where 25% of them are at fixation (P<10⁻⁵). According to the typical pathogen-host arms race, this rampant B-cell antigenic variation likely represents neutralization escape mutants, as some mutations were previously shown to abrogate neutralization of chlamydial infectivity in vitro. In contrast, T-cell clusters of diverse HLA specificities are under purifying selection, suggesting a strategy that may lead to immune subversion. Moreover, several silent mutations are at fixation, generating preferential codons that may influence expression, and may also reflect recombination-derived ‘hitchhiking-effect’ from favourable nonsilent changes. Interestingly, the most prevalent C. trachomatis genotypes, E and F, showed a mutation rate 22.3-fold lower than that of the remainder (P<10⁻²⁰), suggesting more fitted antigenic profiles.

Conclusions/Significance

Globally, the adaptive evolution of the C. trachomatis dominant antigen is likely driven by its complex pathogenesis-related function and reflects distinct evolutionary antigenic scenarios that may benefit the pathogen, and thus should be taking into account in the development of a MOMP-based vaccine.

Evolutionary dynamics of ompA, the gene encoding the Chlamydia trachomatis key antigen

Chlamydia trachomatis is the trachoma agent and causes most bacterial sexually transmitted infections worldwide. Its major outer membrane protein (MOMP) is a well-known porin and adhesin and is the dominant antigen. So far, investigation of MOMP variability has been focused mainly on molecular epidemiological surveys. In contrast, we aimed to evaluate the impact of the host pressure on this key antigen by analyzing its evolutionary dynamics in 795 isolates from urogenital infections, taking into account the MOMP secondary structure and the sizes/positions of antigenic regions. One-third of the specimens showed a mutational drift from the corresponding genotype, where approximately 42% of the mutations had never been described. Amino acid alterations were sixfold more frequent within B-cell epitopes than in the remaining protein (P = 0.027), and some mutations were also found within or close to T-cell antigenic clusters. Interestingly, the two most ecologically successful genotypes, E and F, showed a mutation rate 60.3-fold lower than that of the other genotypes (P < 10(-8)), suggesting that their efficacy may be the result of a better fitness in dealing with the host immune system rather than of specific virulence factors. Furthermore, the variability exhibited by some genetic variants involved residues that are known to play a critical role during the membrane mechanical movements, contributing to a more stable and flexible porin conformation, which suggests some plasticity to deal with environmental pressure. Globally, these MOMP mutational trends yielded no mosaic structures or important phylogenetic changes, but instead yielded point mutations on specific protein domains, which may enhance pathogen's infectivity, persistence, and transmission.

Genotyping of Chlamydia trachomatis from endocervical specimens in Brazil

BACKGROUND

There is no data concerning genotyping of Chlamydia trachomatis from Brazilian samples.

GOAL

To characterize the genotype of C. trachomatis detected in women assisted at a STD public clinic and establish the prevalence of this infection in that population.

STUDY DESIGN

Endocervical samples of a group of 100 women were tested for chlamydial infection with PCR directed to C. trachomatis cryptic plasmid. Genotyping of positive samples were done after omp1 amplification and sequencing.

RESULTS

The overall prevalence of C. trachomatis infection was 19%, with the highest prevalence in women between 15 and 25 years old (68.4%). Four genotypes were found associated with endocervical infections: D, E, F, and K. Sequence analysis revealed a coinfection of genotypes D and E in 1 woman.

CONCLUSIONS

To our knowledge this is the first study to characterize Brazilian C. trachomatis endocervical samples and Brazilian C. trachomatis genotype coinfection. Our results also emphasize the importance of routine diagnosis of C. trachomatis for the control of this STD.

Detection of Chlamydia pneumoniae-specific antibodies binding to the VD2 and VD3 regions of the major outer membrane protein

Although Chlamydia pneumoniae is an important human pathogen, the antigens eliciting a specific humoral immune response remain elusive. We scrutinized several recombinant chlamydial surface proteins for species-specific recognition by a panel of human sera previously tested for the presence of anti-C. pneumoniae and anti-C. trachomatis antibodies by microimmunofluorescence and enzyme-linked immunosorbent assay. The 15-kDa cysteine-rich protein (CrpA), porin-b (PorB), 9-kDa outer membrane protein (OMP3), 60-kDa outer membrane protein (OMP2), and four fragments of the major outer membrane protein (MOMP) representing each variable domain (VD) were overexpressed in Escherichia coli, affinity purified, and employed for Western blot analysis. None of the sera tested contained antibodies recognizing PorB and OMP3 of C. pneumoniae. Sera from C. pneumoniae-immune patients cross-reacted with OMP2 of C. trachomatis, and sera from C. trachomatis-immune patients cross-reacted with CrpA of C. pneumoniae, indicating that some of chlamydial surface molecules share antigenic epitopes. In contrast, the VD2, as well as the VD3, regions of the MOMP of C. pneumoniae were only recognized by C. pneumoniae-positive sera, suggesting the existence of species-specific epitopes. The identification of such epitopes of cell surface molecules provides new insights into C. pneumoniae-specific immune responses and may be of value for the improvement of C. pneumoniae-specific diagnostic assay systems based on defined recombinant antigens.

Determinants of trachoma endemicity using Chlamydia trachomatis ompA DNA sequencing

A six-year prospective study of Chlamydia trachomatis infection and ocular disease in Tanzanian village children was conducted to identify the determinants of trachoma endemicity using sequencing of ompA. Overall, 749 conjunctival samples were obtained, with 176 children sampled in both 1989 and 1995. 31.1% (233/749) were positive by PCR-enzyme immunoassay, and 76% (176/233) of the positives were sequenced in variable domains (VD) 1 to 4 (22 children in both 1989 and 1995). Twenty-six ompA genotypes of serovar A, and 19 of B/Ba were identified, and only 20% of genotypes identified in 1995 matched those found in 1989. In particular, B/Ba genotypes exhibited a 15-base region in VD 2 with increased nucleotide substitution, and these types were associated with age and water availability. Homotypic infection and infection with multiple genotypes and high chlamydial load did predict subsequent severe trachoma (odds ratio (OR) = 10.14, 95% confidence interval (CI): 1.71, 60.23; OR = 6.40, 95% CI: 0.75, 54.41; OR = 6.74, 95% CI: 0.82, 55.38, respectively). And, multitypic infection was clustered with residence of village and associated with familial cattle ownership. In conclusion, high ompA polymorphism and the inability of some hosts to clear infection with the same ompA genotype suggest two distinct but converging mechanisms of endemic severe trachoma.