Analysis of the humoral immune response to Chlamydia pneumoniae by immunoblotting and immunoprecipitation

Analysis of humoral immune responses to recombinant Chlamydia pneumoniae antigens

OBJECTIVES

Chlamydia pneumoniae is a difficult to diagnose respiratory pathogen. This study was performed to systematically characterize humoral immune responses to selected C. pneumoniae antigens in order to provide novel serodiagnostic perspectives for clinical and epidemiological issues.

METHODS

Based on a literature search, gene library screening, and serological proteome analysis, 15 immunogenic surface-associated, virulence-associated, and hypothetical C. pneumoniae antigens were selected, recombinantly expressed, and lined on a nitrocellulose strip. Specific IgM and IgG reactivity was measured in a total of 172 PCR- and micro-immunofluorescence testing (MIF)-characterized serum samples from patients with respiratory infections. A theoretical model was conceived to approximate a putative course of C. pneumoniae antigen expression and assess the potential of early and late antigens.

RESULTS

While surface antigens performed poorly, the virulence-associated TARP was a reliable antigen for IgM detection, with a sensitivity of 80.0% and a diagnostic specificity of 90.2%. The hypothetical protein YwbM proved powerful for IgG detection with MIF-correlative sensitivities of up to 94.4% and a diagnostic specificity of 95.1%.

CONCLUSIONS

This study provides new insights into antibody profiles to immunogenic proteins in C. pneumoniae infection. The study findings offer antigen candidates for more reliable and standardized serological investigations of C. pneumoniae infections, including studies on seroprevalence and epidemiology.

Defining species-specific immunodominant B cell epitopes for molecular serology of Chlamydia species

Urgently needed species-specific enzyme-linked immunosorbent assays (ELISAs) for the detection of antibodies against Chlamydia spp. have been elusive due to high cross-reactivity of chlamydial antigens. To identify Chlamydia species-specific B cell epitopes for such assays, we ranked the potential epitopes of immunodominant chlamydial proteins that are polymorphic among all Chlamydia species. High-scoring peptides were synthesized with N-terminal biotin, followed by a serine-glycine-serine-glycine spacer, immobilized onto streptavidin-coated microtiter plates, and tested with mono-specific mouse hyperimmune sera against each Chlamydia species in chemiluminescent ELISAs. For each of nine Chlamydia species, three to nine dominant polymorphic B cell epitope regions were identified on OmpA, CT618, PmpD, IncA, CT529, CT442, IncG, Omp2, TarP, and IncE proteins. Peptides corresponding to 16- to 40-amino-acid species-specific sequences of these epitopes reacted highly and with absolute specificity with homologous, but not heterologous, Chlamydia monospecies-specific sera. Host-independent reactivity of such epitopes was confirmed by testing of six C. pecorum-specific peptides from five proteins with C. pecorum-reactive sera from cattle, the natural host of C. pecorum. The probability of cross-reactivity of peptide antigens from closely related chlamydial species or strains correlated with percent sequence identity and declined to zero at <50% sequence identity. Thus, phylograms of B cell epitope regions predict the specificity of peptide antigens for rational use in the genus-, species-, or serovar-specific molecular serology of Chlamydia spp. We anticipate that these peptide antigens will improve chlamydial serology by providing easily accessible assays to nonspecialist laboratories. Our approach also lends itself to the identification of relevant epitopes of other microbial pathogens.

Profiling antibody responses to infections by Chlamydia abortus enables identification of potential virulence factors and candidates for serodiagnosis

Enzootic abortion of ewes (EAE) due to infection with the obligate intracellular pathogen Chlamydia (C.) abortus is an important zoonosis leading to considerable economic loss to agriculture worldwide. The pathogen can be transmitted to humans and may lead to serious infection in pregnant women. Knowledge about epidemiology, clinical course and transmission to humans is hampered by the lack of reliable diagnostic tools. Immunoreactive proteins, which are expressed in infected animals and humans, may serve as novel candidates for diagnostic marker proteins and represent putative virulence factors. In order to broaden the spectrum of immunogenic C. abortus proteins we applied 2D immunoblot analysis and screening of an expression library using human and animal sera. We have identified 48 immunoreactive proteins representing potential diagnostic markers and also putative virulence factors, such as CAB080 (homologue of the “macrophage infectivity potentiator”, MIP), CAB167 (homologue of the “translocated actin recruitment protein”, TARP), CAB712 (homologue of the “chlamydial protease-like activity factor”, CPAF), CAB776 (homologue of the “Polymorphic membrane protein D”, PmpD), and the “hypothetical proteins” CAB063, CAB408 and CAB821, which are predicted to be type III secreted. We selected two putative virulence factors for further characterization, i.e. CAB080 (cMIP) and CAB063, and studied their expression profiles at transcript and protein levels. Analysis of the subcellular localization of both proteins throughout the developmental cycle revealed CAB063 being the first C. abortus protein shown to be translocated to the host cell nucleus.

Outcome of Chlamydia pneumoniae associated acute ischemic stroke in elderly patients: a case-control study

BACKGROUND

Limited data exists about the role of Chlamydia pneumoniae elderly patients with acute ischemic stroke.

OBJECTIVE

To study the role of C. pneumoniae in elderly patients (age more than 65 years) with acute ischemic stroke and its impact on stroke out come.

METHODS

We recruited 100 elderly patients with acute ischemic stroke and 100 age and sex matched controls over a period of 2 years. IgG and IgA anti C. pneumoniae antibodies were measured by microimmunofluorescence technique in patients and controls. Good outcome was defined as a Modified Rankin score (mRS) of ≤2.

RESULTS

We found C. pneumoniae antibodies in 35% stroke patients and in 18% control subjects (p=0.01). Good out come at 90 days follow up was found in 20/35(57.1%) seropositive stroke patients compared to 37/65(56.9%) seronegative stroke patients (p=0.9).

CONCLUSIONS

C. pneumoniae antibody positivity was independently associated with ischemic stroke in elderly patients and its presence does not alter the stroke outcome.

Seroprevalence of Chlamydia pneumoniae antibodies in stroke in young

BACKGROUND

Younger patients, aged below 45 years, usually lack the conventional risk factors of stroke whereas infections, especially in developing countries, may play a role. There have been many reports in the last decade about the association of Chlamydia pneumoniae (C. pneumoniae) and atherosclerosis involving cerebral vessels.

OBJECTIVE

To investigate the seroprevalence of C. pneumoniae IgG and IgA antibodies in patients aged below 45 years with acute ischemic stroke.

METHODS

This study was done at a tertiary care hospital in South India between January 2004 and December 2006 where we recruited consecutive patients aged less than 45 years with acute ischemic stroke. Age and sex matched controls were recruited from the outpatient department with non stroke diagnosis. All stroke patients underwent CT (Computerized Tomography), MRI (Magnetic Resonance Image), MRA (Magnetic Resonance Angiography), Transthoracic Echocardiography and Carotid Doppler for stroke sub group diagnosis. We measured C. pneumoniae antibodies IgG and IgA by microimmunofluorescence technique in all patients and controls.

RESULTS

A total of 120 patients and 120 controls were studied over a period of two years. We found C. pneumoniae antibodies in 29.1% (35/120) stroke patients and in 12.5% (15/120) control subjects (p=0.002). C. pneumoniae IgG antibodies were found in 27.5 % (33/120) of stroke patients and 12.5% (15/120) of controls (p=0.006). IgA antibodies were observed in 5% (6/120) of strokes and none in control group (p=0.03). After adjustment of all risk factors C. pneumoniae IgG seropositivity showed odds ratio of 2.6; 95% Confidence Interval 1.2-5.6.

CONCLUSIONS

C. pneumoniae IgG antibodies were found to be associated with ischemic stroke in young.

Identification and evaluation of a combination of chlamydial antigens to support the diagnosis of severe and invasive Chlamydia trachomatis infections

Chlamydia trachomatis is the most common sexually transmitted organism in industrialized countries. Nucleic acid amplification testing, using non-invasively collected specimens, is considered to be the method of choice for diagnosis of chlamydial infections of the urethra and the lower genital tract. Serological testing has the potential to circumvent the problem of specimen sampling in invasive C. trachomatis infections of the upper genital tract. However, only a few defined chlamydial antigens have been used in a standardized diagnostic assay format. In this study, we used serological two-dimensional proteomic analysis to broaden the spectrum of diagnostically relevant C. trachomatis proteins. The genes encoding an assortment of already known chlamydial antigens, as well as immunogenic proteins that have not been described before, were cloned, and the recombinant proteins were purified in order to compare their diagnostic usefulness in parallel with a newly developed line immunoassay. With 189 sera collected from patients with and without C. trachomatis infection, recombinant major outer membrane protein (MOMP), chlamydial protease-like activity factor (CPAF), outer membrane protein 2 (OMP2), translocated actin-recruiting protein, and polymorphic membrane protein D (PmpD) showed the highest level of diagnostic sensitivity and specificity. In patients suffering from ascending and invasive C. trachomatis infections, such as pelvic inflammatory disease and lymphogranuloma venereum, the sensitivity reached with these proteins ranged between 71% (PmpD) and 94% (OMP2), and the specificity ranged between 82% (PmpD) and 100% (MOMP and OMP2). Recombinant thio-specific antioxidant peroxidase, ribosomal protein S1 (RpsA) and hypothetical protein 17 showed lower sensitivity but comparably high specificity, ranging from 94% to 100%. The novel line immunoassay based on defined recombinant antigens has promise for improved serodiagnosis in severe and invasive C. trachomatis infections.

Immunoproteomic identification and serological responses to novel Chlamydia pneumoniae antigens that are associated with persistent C. pneumoniae infections

The controversial discussion about the role of Chlamydia pneumoniae in atherosclerosis cannot be solved without a reliable diagnosis that allows discrimination between past and persistent infections. Using a proteomic approach and immunoblotting with human sera, we identified 31 major C. pneumoniae Ags originating from 27 different C. pneumoniae proteins. More than half of the proteins represent Chlamydia Ags not described previously. Using a comparative analysis of spot reactivity Pmp6, OMP2, GroEL, DnaK, RpoA, EF-Tu, as well as CpB0704 and CpB0837, were found to be immunodominant. The comparison of Ab-response patterns of sera from subjects with and without evidence for persisting C. pneumoniae, determined by multiple PCR analysis of PBMC and vasculatory samples, resulted in differential reactivity for 12 proteins, which is not reflected by reactivity of the sera in the microimmunofluorescence test, the current gold standard for serodiagnosis. Although reactivity of sera from PCR-positive donors was increased toward RpoA, MOMP, YscC, Pmp10, PorB, Pmp21, GroEL, and Cpaf, the reactivity toward YscL, Rho, LCrE, and CpB0837 was decreased, reflecting the altered protein expression of persisting C. pneumoniae in vitro. Our data provide the first evidence of a unique Ab-response pattern associated with persistent C. pneumoniae infections, which is a prerequisite for the serological determination of persistently infected patients.

Chlamydia pneumoniae antibodies in various subtypes of ischemic stroke in Indian patients

BACKGROUND

As infections occur more frequently in developing countries, we carried out this prospective case-control study, to establish the association, if any, between C. pneumoniae antibodies and ischemic stroke particularly in relation to its subtypes.

DESIGN

Antibodies (IgG and IgA) to C. pneumoniae in serum were measured by microimmunofluorescence test in 200 consecutive ischemic stroke patients and 200 age and sex matched controls.

RESULTS

Seventy two out of 200 ischemic stroke patients (36%) had positive C. pneumoniae antibodies (IgG or IgA), compared to 35 out of 200 controls (17.5%) (p<0.0001). IgG antibody was positive in 64/200 (32%) ischemic stroke patients, compared to 34/200(17%) controls (p<0.0001) and IgA was positive in 20/200(10%) ischemic stroke patients compared to 1/200(0.5%) controls (p<0.0001). Logistic regression analysis showed statistically significant association between C. pneumoniae antibody positivity and ischemic stroke, thereby establishing it as an independent risk factor. Prevalence of C. pneumoniae antibodies was significantly higher in all stroke subtypes (except the stroke of undetermined etiology) compared to controls.

CONCLUSION

Significant and independent association was found between C. pneumoniae antibodies and ischemic stroke in this sample of south Indian population. The association was found in all ischemic stroke subtypes, except stroke of undetermined etiology.

Chlamydia pneumoniae-specific serum immune complexes in patients with multiple sclerosis

The significance of Chlamydia pneumoniae infection in patients with multiple sclerosis (MS) is unclear. We determined the frequency of serum C. pneumoniae-specific immune complexes in patients with MS, neurological (OND) and healthy controls in a blinded, cross-sectional study. C. pneumoniae immune complexes were detected in 24% (38/156) of MS patients, 16% (11/69) of OND and 15% (77/499) of healthy controls. The odds ratio for all MS patients was 3.95 (95% CI: 2.15 to 7.24; P < 0.0001) accounting for the covariates: sex, age, socio-economic status and area of residence. The odds ratio for recently diagnosed MS patients was 4.33 (95% CI: 1.76 to 10.64; P = 0.001). Systemic C. pneumoniae infection is more frequent in MS patients than the healthy population and occurs early in the course of the disease. Multiple Sclerosis 2007; 14: 292—299. http://msj.sagepub.com

Descripción de inmunógenos de Chlamydia pneumoniae reconocidos por el suero de sujetos con enfermedad arterial periférica

BACKGROUND AND OBJECTIVE

The relationship between antibodies to C. pneumoniae and presence of the bacteria was studied in individuals with peripheral arterial disease.

PATIENTS AND METHOD

An observational analytical, case-control study was performed in 118 patients (68 cases, 50 controls) to investigate immunoglobulin (Ig) G and A against C. pneumoniae in serum, using Western-blot (commercial and no commercial methods), ELISA and MIF; DNA of the bacteria in vascular tissue biopsy specimens was studied by polymerase chain reaction.

RESULTS

Using commercial Western-blot, significant presence of IgG anti-39 kDa and anti-54 kDa was found in cases and was related to MIF results and C. pneumoniae DNA findings; IgA anti-LPS, anti-92 kDa and anti-Hsp60 kDa were also found and related to DNA presence. Using no commercial Western-blot, significant presence of 128.8 and 9.2 kDa bands for IgG was detected in cases and associated with DNA presence; 70.8, 58.9, 47.9, 47.5, 18.4, 12.1, 10.6, 8.1, and 7.6 kDa bands for IgG were found in cases; and DNA was present when 54.6 and 1.1 kDa bands for IgG and 79.4, 50.1, and 18.4 kDa bands for IgA were also detected.

CONCLUSIONS

Using Western-blot, a greater serologic response was found against certain proteins of the bacteria in individuals with peripheral arterial disease. This may reflect an initial stage with presence of DNA and specific IgG. Subsequently, even in absence of the bacteria, an immunomediated disease may develop with presence of IgA and IgG.

Production of Chlamydia pneumoniae proteins in Bacillus subtilis and their use in characterizing immune responses in the experimental infection model

Due to intracellular growth requirements, large-scale cultures of chlamydiae and purification of its proteins are difficult and laborious. To overcome these problems we produced chlamydial proteins in a heterologous host, Bacillus subtilis, a gram-positive nonpathogenic bacterium. The genes of Chlamydia pneumoniae major outer membrane protein (MOMP), the cysteine-rich outer membrane protein (Omp2), and the heat shock protein (Hsp60) were amplified by PCR, and the PCR products were cloned into expression vectors containing a promoter, a ribosome binding site, and a truncated signal sequence of the alpha-amylase gene from Bacillus amyloliquefaciens. C. pneumoniae genes were readily expressed in B. subtilis under the control of the alpha-amylase promoter. The recombinant proteins MOMP and Hsp60 were purified from the bacterial lysate with the aid of the carboxy-terminal histidine hexamer tag by affinity chromatography. The Omp2 was separated as an insoluble fraction after 8 M urea treatment. The purified proteins were successfully used as immunogens and as antigens in serological assays and in a lymphoproliferation test. The Omp2 and Hsp60 antigens were readily recognized by the antibodies appearing after pulmonary infection following intranasal inoculation of C. pneumoniae in mice. Also, splenocytes collected from mice immunized with MOMP or Hsp60 proteins proliferated in response to in vitro stimulation with the corresponding proteins.

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.

Rapid and standardized detection of Chlamydia pneumoniae using LightCycler real-time fluorescence PCR

In order to meet the need of many microbiological laboratories for a standardized system for detecting Chlamydia pneumoniae in respiratory specimens, a hybridization probe-based LightCycler (Roche Diagnostics, Germany) PCR assay was developed. The assay's analytical sensitivity and specificity were evaluated according to the recommendations of the Centers for Disease Control and Prevention (USA) and Laboratory Centre for Disease Control (Canada). Seventy-four bacterial species other than Chlamydia pneumoniae, including strains of Chlamydia trachomatis, Chlamydia psittaci, and Chlamydia pecorum, tested negative. Six of six representative Chlamydia pneumoniae strains tested positive. An analytical sensitivity of 1 inclusion forming unit per ml of bronchoalveolar lavage fluid, corresponding to 0.02 inclusion forming units per PCR reaction, was observed. The assay showed 100% specificity and sensitivity for Chlamydia pneumoniae when testing DNA preparations from 12 specimens of patients with known pulmonary Chlamydia pneumoniae infection and from 78 specimens of patients with respiratory tract disease of other origin. The newly developed LightCycler assay may contribute to the urgently needed standardization of laboratory diagnosis of Chlamydia pneumoniae.

Newly characterized species-specific immunogenic Chlamydophila pneumoniae peptide reactive with murine monoclonal and human serum antibodies

A monoclonal antibody (MAb) directed against an unknown Chlamydophila pneumoniae epitope has been characterized, and the respective peptide mimotope has been identified. A murine MAb specific for C. pneumoniae was used to select peptides from phage display libraries. The peptides identified from the phage display library clones reacted specifically with the respective target murine MAb and with human sera previously identified as having antibody titers to C. pneumoniae. The selected peptide mimotope sequences tended to be composed of charged residues surrounding a core of hydrophobic residues. The peptide with the best binding could inhibit >95% of binding to the MAb, suggesting that the selected peptide binds the paratope of the respective MAb. The peptide reacted with human sera previously determined by microimmunofluorescence to have anti-C. pneumoniae antibodies. The peptide was competitively competed with the MAb against Renografin-purified, sonicated C. pneumoniae in an enzyme-linked immunosorbent assay and with whole-cell C. pneumoniae in an indirect fluorescence assay format, demonstrating its potential utility in the development of diagnostics. The use of this novel peptide may allow investigators to establish standardized assays free from cross-reactive Chlamydia trachomatis and Chlamydophila psittaci epitopes and immunoreactivity.

Chlamydia pneumoniae major outer membrane protein is a surface-exposed antigen that elicits antibodies primarily directed against conformation-dependent determinants

The major outer membrane protein (MOMP) of Chlamydia trachomatis serovariants is known to be an immunodominant surface antigen. Moreover, it is known that the C. trachomatis MOMP elicits antibodies that recognize both linear and conformational antigenic determinants. In contrast, it has been reported that the MOMP of Chlamydia pneumoniae is not surface exposed and is immunorecessive. We hypothesized that the discrepancies between C. trachomatis and C. pneumoniae MOMP exposure on intact chlamydiae and immunogenic properties might be because the focus of the host's immune response is directed to conformational epitopes of the C. pneumoniae MOMP. We therefore conducted studies aimed at defining the surface exposure of MOMP and the conformational dominance of MOMP antibodies. We present here a description of C. pneumoniae species-specific monoclonal antibody (MAb), GZD1E8, which recognizes a conformational epitope on the surface of C. pneumoniae. This MAb is potent in the neutralization of C. pneumoniae infectivity in vitro. Another previously described C. pneumoniae species-specific monoclonal antibody, RR-402, displayed very similar characteristics. However, the antigenic determinant recognized by RR-402 has yet to be identified. We show by immunoprecipitation of C. pneumoniae with GZD1E8 and RR-402 MAbs and by mass spectrometry analysis of immunoprecipitated proteins that both antibodies GZD1E8 and RR-402 recognize the MOMP of C. pneumoniae and that this protein is localized on the surface of the organism. We also show that human sera from C. pneumoniae-positive donors consistently recognize the MOMP by immunoprecipitation, indicating that the MOMP of C. pneumoniae is an immunogenic protein. These findings have potential implications for both C. pneumoniae vaccine and diagnostic assay development.

A multi-antigen print immunoassay for the development of serological diagnosis of infectious diseases

Serological diagnosis of infectious diseases that generate a highly heterogeneous antibody repertoire, such as tuberculosis, requires tests based on cocktails of antigens. We describe a new method called multi-antigen print immunoassay (MAPIA) for cocktail-based serological diagnosis. The assay entails the application of antigen to nitrocellulose membranes by micro-aerosolization (printing), followed by antibody detection using standard chromogenic immunodevelopment. Cocktails of protein antigens of Mycobacterium tuberculosis tested by MAPIA were found to maintain the serological activity of each of their components. In contrast, the same cocktails tested by enzyme-linked immunosorbent assay (ELISA) had a serological activity that was lower than the sum of the activities of their components. Consequently, cocktail-based MAPIA attained the diagnostic sensitivity expected on the basis of single antigen results, while a significant loss of diagnostic sensitivity was observed with cocktail-based ELISA. Thus, the MAPIA format is superior to conventional ELISA for the serological diagnosis of infectious diseases characterized by heterogeneous antibody responses.