The species specificity of the microimmunofluorescence antibody test and comparisons with a time resolved fluoroscopic immunoassay for measuring IgG antibodies against Chlamydia pneumoniae

The serodiagnositic value of Chlamydia trachomatis antigens in antibody detection using luciferase immunosorbent assay

Introduction

Among the different antigens used in the detection of anti-Chlamydia trachomatis antibodies, significant differences in sensitivity and specificity have been observed. Further evaluation of C. trachomatis antigens in antibody detection is urgently needed for the development and application of C. trachomatis serologic assays.

Methods

Chlamydia trachomatis antigens Pgp3, TmeA, InaC, and HSP60 were selected and used in luciferase immunosorbent assay (LISA). The detection results obtained from well-defined C. trachomatis positive and negative samples were compared with the commercial C. trachomatis ELISA (Mikrogen) for performance evaluation.

Results

Pgp3, TmeA, InaC, and HSP60-based LISA showed sensitivity of 92.8, 88.8, 90.4, and 94.4%, and specificity of 99.2, 99.2, 99.2, and 92%, respectively. ROC analysis indicated that Pgp3-based LISA showed similar performance to Mikrogen ELISA (AUC 0.986 vs. 0.993, p = 0.207). Furthermore, four C. trachomatis antigens achieved strong diagnostic efficiency, i.e., positive likelihood ratios [+LR] ≥ 10 in C. trachomatis-infected women and negative likelihood ratios [-LR] ≤ 0.1 in C. trachomatis negative low exposure risk children, but only Pgp3 and TmeA showed strong diagnostic value in general adults. In addition, Pgp3, TmeA, and InaC, but not HSP60, achieved high performance, i.e., both positive predictive value (PPV) and negative predictive value (NPV) ≥ 90.9%, and showed no significant cross-reactivity with anti-Chlamydiapneumoniae.

Conclusion

Three C. trachomatis species-specific antigens Pgp3, TmeA, and InaC show superior performance in the detection of anti-C. trachomatis antibody, indicating the potential to be used in developing C. trachomatis serologic tests.

Peptide ELISA and FRET-qPCR Identified a Significantly Higher Prevalence of Chlamydia suis in Domestic Pigs Than in Feral Swine from the State of Alabama, USA

Chlamydia suis is an important, highly prevalent, and diverse obligate intracellular pathogen infecting pigs. In order to investigate the prevalence and diversity of C. suis in the U.S., 276 whole blood samples from feral swine were collected as well as 109 fecal swabs and 60 whole blood samples from domestic pigs. C. suis-specific peptide ELISA identified anti-C. suis antibodies in 13.0% of the blood of feral swine (26/276) and 80.0% of the domestic pigs (48/60). FRET-qPCR and DNA sequencing found C. suis DNA in 99.1% of the fecal swabs (108/109) and 21.7% of the whole blood (13/60) of the domestic pigs, but not in any of the assayed blood samples (0/267) in feral swine. Phylogenetic comparison of partial C. suis ompA gene sequences and C. suis-specific multilocus sequencing typing (MLST) revealed significant genetic diversity of the C. suis identified in this study. Highly genetically diverse C. suis strains are prevalent in domestic pigs in the USA. As crowding strongly enhances the frequency and intensity of highly prevalent Chlamydia infections in animals, less population density in feral swine than in domestic pigs may explain the significantly lower C. suis prevalence in feral swine. A future study is warranted to obtain C. suis DNA from feral swine to perform genetic diversity of C. suis between commercial and feral pigs.

Multi-peptide ELISAs overcome cross-reactivity and inadequate sensitivity of conventional Chlamydia pneumoniae serology

Cross-reactivity of classical chlamydial antigens compromises Chlamydia (C.) pneumoniae serology. By testing with 185 human antisera, we expanded 18 previously discovered C. pneumoniae-specific B-cell epitopes to 48 peptide antigens from 12 C. pneumoniae immunodominant proteins. For specific detection of antibodies against C. pneumoniae, we developed novel ELISAs with strongly reactive individual peptide antigens and mixtures of these peptides. By comparison to a composite reference standard (CRS) for anti-C. pneumoniae antibody status of human sera, the top-performing CpnMixF12 peptide assay showed 91% sensitivity at 95% specificity, significantly higher than 4 commercial anti-C. pneumoniae IgG ELISAs (36-12% sensitivity at 95% specificity). Human C. pneumoniae (Cpn) and C. trachomatis (Ctr) seroreactivity was 54% biased towards co-positivity in commercial Cpn and Ctr ELISAs, but unbiased in Cpn and Ctr peptide antibody assays, suggesting severe cross-reactivity of commercial ELISAs. Using hyperimmune mouse sera against each of 11 Chlamydia spp., we confirm that commercial Cpn and Ctr ELISA antigens are cross-reactive among all Chlamydia spp., but Cpn and Ctr peptide antigens react only with antisera against the cognate chlamydial species. With simultaneously high specificity and sensitivity, and convenient use for non-specialized laboratories, these ELISAs have the potential to improve serodiagnosis of C. pneumoniae infection.

Mixed Chlamydia trachomatis Peptide Antigens Provide a Specific and Sensitive Single-Well Colorimetric Enzyme-Linked Immunosorbent Assay for Detection of Human Anti-C. trachomatis Antibodies

For detection of anti-C. trachomatis antibodies by serological assays, use of classical chlamydial antigens results in high cross-reactivity and poor sensitivity. Previously, we discovered 48 strongly reactive peptide antigens of C. trachomatis-specific B-cell epitopes from 21 immunodominant proteins, and individual testing and combined scoring of 5 to 11 peptide antigens provided highly sensitive and specific detection of anti-C. trachomatis antibodies in chemiluminescent ELISAs. To simplify this method, this study established a single-well labor-saving colorimetric ELISA using a mixture of 12 strongly reactive C. trachomatis peptide antigens (Ctr Mix1) for detection of anti-C. trachomatis antibodies. This Ctr Mix1 ELISA (94% sensitivity and 98% specificity) outperformed 4 commercial ELISAs (49% to 79% sensitivity and 98% specificity). This ELISA can be easily implemented and commercialized, with convenient setup for use in nonspecialized laboratories. Thus, this mixed peptide assay with superior specificity and sensitivity will improve serodiagnosis of C. trachomatis infections.

Sensitive and specific detection of anti-Chlamydia trachomatis antibodies in standard enzyme-linked immunosorbent assays (ELISAs) is compromised by cross-reactivity and poor sensitivity of classical C. trachomatis antigens. Previously, we discovered 48 strongly reactive peptide antigens of C. trachomatis-specific B-cell epitopes from 21 immunodominant proteins. By comprehensive individual testing of 11 top-ranked peptide antigens, we found very high sensitivity and specificity for detection of anti-C. trachomatis antibodies in chemiluminescent ELISAs. The current study established a labor-saving colorimetric ELISA by using a mixture of 12 strongly reactive C. trachomatis peptide antigens (Ctr Mix1) in a single well/serum rather than assaying reactivity to each individual peptide. For performance evaluation, we used a simulated population of 212 anti-C. trachomatis antibody-positive and -negative sera from 125 women with NAAT-confirmed active C. trachomatis infection and from 87 healthy women at low risk for C. trachomatis infection. In comparison to a composite reference standard (CRS) for anti-C. trachomatis antibody status, the Ctr Mix1 IgG ELISA achieved 93.9% sensitivity, significantly superior to the 49% to 79% sensitivities of four commercial anti-C. trachomatis IgG ELISAs, and 98% specificity of all tested assays. Compared to the labor-intensive individual peptide testing, this mixed peptide ELISA retained high specificity with only marginal, ∼5% sensitivity loss. By ROC-AUC, likelihood ratio, and predictive value analyses, the Ctr Mix1 ELISA performed satisfactorily at 10% to 75% prevalence range of anti-C. trachomatis antibodies but significantly better than commercial ELISAs. Thus, the labor-saving mixed peptide colorimetric ELISA format provides simultaneously high specificity and sensitivity for detection of anti-C. trachomatis antibodies.

IMPORTANCE For detection of anti-C. trachomatis antibodies by serological assays, use of classical chlamydial antigens results in high cross-reactivity and poor sensitivity. Previously, we discovered 48 strongly reactive peptide antigens of C. trachomatis-specific B-cell epitopes from 21 immunodominant proteins, and individual testing and combined scoring of 5 to 11 peptide antigens provided highly sensitive and specific detection of anti-C. trachomatis antibodies in chemiluminescent ELISAs. To simplify this method, this study established a single-well labor-saving colorimetric ELISA using a mixture of 12 strongly reactive C. trachomatis peptide antigens (Ctr Mix1) for detection of anti-C. trachomatis antibodies. This Ctr Mix1 ELISA (94% sensitivity and 98% specificity) outperformed 4 commercial ELISAs (49% to 79% sensitivity and 98% specificity). This ELISA can be easily implemented and commercialized, with convenient setup for use in nonspecialized laboratories. Thus, this mixed peptide assay with superior specificity and sensitivity will improve serodiagnosis of C. trachomatis infections.

Performance of Chlamydia trachomatis OmcB Enzyme-Linked Immunosorbent Assay in Serodiagnosis of Chlamydia trachomatis Infection in Women

Chlamydia trachomatis serological assays with improved sensitivity over commercially available assays are needed to evaluate the burden of C. trachomatis infection and the effectiveness of prevention efforts. We evaluated the performance of a C. trachomatis outer membrane complex protein B (OmcB) enzyme-linked immunosorbent assay (ELISA) in the detection of anti-C. trachomatis antibody responses in C. trachomatis-infected women. OmcB ELISA was less sensitive than our C. trachomatis elementary body (EB) ELISA, but it was highly specific. The magnitude of the antibody response was higher in African-Americans and those with prior C. trachomatis infection. Unlike EB ELISA, the IgG1 response to C. trachomatis OmcB was short-lived and was not maintained by repeat C. trachomatis infection.

Discovery of Human-Specific Immunodominant Chlamydia trachomatis B Cell Epitopes

Current serological assays for species-specific detection of anti-Chlamydia species antibodies suffer from well-known shortcomings in specificity and ease of use. Due to the high prevalences of both anti-C. trachomatis and anti-C. pneumoniae antibodies in human populations, species-specific serology is unreliable. Therefore, novel specific and simple assays for chlamydial serology are urgently needed. Conventional antigens are problematic due to extensive cross-reactivity within Chlamydia spp. Using accurate B cell epitope prediction and a robust peptide ELISA methodology developed in our laboratory, we identified immunodominant C. trachomatis B cell epitopes by screening performed with sera from C. trachomatis-infected women. We discovered 38 novel human host-dependent antigens from 20 immunodominant C. trachomatis proteins, in addition to confirming 10 host-independent mouse serum peptide antigens that had been identified previously. This extended set of highly specific C. trachomatis peptide antigens can be used in simple ELISA or multiplexed microarray formats and will provide high specificity and sensitivity to human C. trachomatis serodiagnosis.

Chlamydia species-specific serology is compromised by cross-reactivity of the gold standard microimmunofluorescence (MIF) or commercial enzyme-linked immunosorbent assays (ELISAs). This study was conducted to discover novel C. trachomatis-specific peptide antigens that were recognized only by the antibody response of the natural human host. We evaluated a library of 271 peptide antigens from immunodominant C. trachomatis proteins by reactivity with 125 C. trachomatis antibody-positive sera from women with PCR-confirmed C. trachomatis infection and 17 C. trachomatis antibody-negative sera from low-risk women never diagnosed with C. trachomatis infection. These C. trachomatis peptide antigens had been predicted in silico to contain B cell epitopes but had been nonreactive with mouse hyperimmune sera against C. trachomatis. We discovered 38 novel human host-dependent antigens from 20 immunodominant C. trachomatis proteins (PmpD, IncE, IncG, CT529, CT618, CT442, TarP, CT143, CT813, CT795, CT223, PmpC, CT875, CT579, LcrE, IncA, CT226, CT694, Hsp60, and pGP3). Using these human sera, we also confirmed 10 C. trachomatis B cell epitopes from 6 immunodominant C. trachomatis proteins (OmpA, PmpD, IncE, IncG, CT529, and CT618) as host species-independent epitopes that had been previously identified by their reactivity with mouse hyperimmune sera against C. trachomatis. ELISA reactivities against these peptides correlated strongly with the C. trachomatis microimmunofluorescence (MIF) text results (Pearson’s correlation coefficient [R] = 0.80; P < 10⁻⁶). These C. trachomatis peptide antigens do not cross-react with antibodies against other Chlamydia species and are therefore suitable for species-specific detection of antibodies against C. trachomatis. This study identified an extended set of peptide antigens for simple C. trachomatis-specific ELISA serology.

IMPORTANCE Current serological assays for species-specific detection of anti-Chlamydia species antibodies suffer from well-known shortcomings in specificity and ease of use. Due to the high prevalences of both anti-C. trachomatis and anti-C. pneumoniae antibodies in human populations, species-specific serology is unreliable. Therefore, novel specific and simple assays for chlamydial serology are urgently needed. Conventional antigens are problematic due to extensive cross-reactivity within Chlamydia spp. Using accurate B cell epitope prediction and a robust peptide ELISA methodology developed in our laboratory, we identified immunodominant C. trachomatis B cell epitopes by screening performed with sera from C. trachomatis-infected women. We discovered 38 novel human host-dependent antigens from 20 immunodominant C. trachomatis proteins, in addition to confirming 10 host-independent mouse serum peptide antigens that had been identified previously. This extended set of highly specific C. trachomatis peptide antigens can be used in simple ELISA or multiplexed microarray formats and will provide high specificity and sensitivity to human C. trachomatis serodiagnosis.

Comprehensive Molecular Serology of Human Chlamydia trachomatis Infections by Peptide Enzyme-Linked Immunosorbent Assays

For detection of anti-Chlamydia trachomatis antibodies by serological assays, use of classical whole-organism chlamydial antigens results in high cross-reactivity. These antigens bind mainly antibodies against the major outer membrane protein (OmpA) and bind antibodies against other immunodominant non-OmpA proteins to a lesser extent, resulting in poor assay sensitivity. The specificity of C. trachomatis serology is also compromised by the high prevalence of cross-reactive anti-C. pneumoniae antibodies in human populations. We previously identified 48 highly specific C. trachomatis B cell epitope peptide antigens of 21 immunodominant proteins. This study validated peptide antigen-based novel ELISAs that provide highly specific and sensitive detection of anti-C. trachomatis antibodies. Compared to four commercial ELISAs that achieved only poor sensitivities (51.5% to 64.8%), the combined signals of 5 to 11 peptides provided high sensitivity (86.5% to 91.8%) at the same 98% specificity. Thus, by using multiple peptide antigens of immunodominant proteins, we created simple ELISAs with specificity and sensitivity superior to standard C. trachomatis serodiagnosis.

Sensitive species-specific detection of anti-Chlamydia trachomatis antibodies is compromised by cross-reactivity of the C. trachomatis antigens used in standard microimmunofluorescence (MIF) testing and enzyme-linked immunosorbent assays (ELISAs). Previously, we discovered 48 strongly reactive C. trachomatis-specific B cell epitope peptides from 21 immunodominant proteins. Here we comprehensively evaluated the 11 top-ranked C. trachomatis-specific peptide antigens from 8 proteins for use in C. trachomatis serology. Sera from 125 women with nucleic acid amplification test (NAAT)-confirmed active C. trachomatis infection and from 49 healthy women with a low risk of C. trachomatis infection were used as anti-C. trachomatis antibody-positive and -negative sera. Results obtained for detection of IgG1, IgG3, and IgA1 antibodies against the 11 C. trachomatis peptide antigens were compared to results from 4 commercial anti-C. trachomatis IgG ELISAs. Using composite reference standards (CRS) of all assays for anti-C. trachomatis antibody status, commercial ELISAs detected antibodies in antibody-positive women with sensitivities of 51.5% to 64.8%. In contrast, a combination of the results of all 11 peptides detected IgG (IgG1 and IgG3) antibodies with 91.8% sensitivity, and a labor-saving combination of the 5 optimal peptides still detected antibodies in antibody-positive women with 86.5% sensitivity (all at 98% specificity). The superior performance of the combined peptide ELISAs was confirmed by area under the receiver operating characteristic curve (ROC-AUC), likelihood ratio, and predictive value analyses. The higher sensitivity of the peptide assays results from using multiple B cell epitopes of several C. trachomatis immunodominant proteins, including OmpA, compared to exclusively using the OmpA antigens used in commercial ELISAs. Thus, ELISAs with combined use of synthetic peptide antigens for C. trachomatis antibody detection have the advantage of simultaneous high sensitivity and high specificity.

IMPORTANCE For detection of anti-Chlamydia trachomatis antibodies by serological assays, use of classical whole-organism chlamydial antigens results in high cross-reactivity. These antigens bind mainly antibodies against the major outer membrane protein (OmpA) and bind antibodies against other immunodominant non-OmpA proteins to a lesser extent, resulting in poor assay sensitivity. The specificity of C. trachomatis serology is also compromised by the high prevalence of cross-reactive anti-C. pneumoniae antibodies in human populations. We previously identified 48 highly specific C. trachomatis B cell epitope peptide antigens of 21 immunodominant proteins. This study validated peptide antigen-based novel ELISAs that provide highly specific and sensitive detection of anti-C. trachomatis antibodies. Compared to four commercial ELISAs that achieved only poor sensitivities (51.5% to 64.8%), the combined signals of 5 to 11 peptides provided high sensitivity (86.5% to 91.8%) at the same 98% specificity. Thus, by using multiple peptide antigens of immunodominant proteins, we created simple ELISAs with specificity and sensitivity superior to standard C. trachomatis serodiagnosis.

Seroprevalence of Chlamydophila Psittaci among Employees of Two German Duck Farms

Psittacosis is a zoonotic infectious disease that is caused by Chlamydophila psittaci. To determine the occupational risk of getting the infection, we investigated the seroprevalence of C. psittaci among employees of two German duck farms and two slaughterhouses according to their level of exposure to the pathogen during the years 2010, 2007, and 2004. In summary, we found low seroprevalence (≈ 8%) throughout the study population almost irrespective of the duty of a given worker. Surprisingly, in 2010, the anti-C. psittaci-specific antibody prevalence in the group of slaughterer (38.9%) was significantly increased in comparison to the non-exposed employees (p = 0.00578). This indicates that individuals in the surrounding of slaughterhouses exposed especially to aerosols containing C. psittaci elementary bodies bear a greater occupational risk of getting infected.

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.

Correlation of Chlamydia and Chlamydophila spp. IgG and IgM antibodies by microimmunofluorescence with antigen detection methods

Correlation of serologic titers for Chlamydia trachomatis with other tests has been based on direct fluorescence antibody (DFA) testing and culture, but not on nucleic acid-based tests that are used for screening. We retrospectively reviewed the specificity of antibodies against C. trachomatis, Chlamydia psittaci, and Chlamydophila pneumoniae by microimmunofluorescence (MIF) when compared with DFA, culture, nucleic acid probe, and transcription-mediated amplification. Over a 6-year period, 226 cases had both MIF and one of these other methods performed for comparison. Agreement between C. trachomatis antigen or nucleic acid detection and MIF results was 87% (197/226). C. trachomatis serology had a negative predictive value of 98%, and 10.6% of cases were positive by serology and negative by antigen testing. Of the 13 patients who had a positive C. trachomatis antigen or nucleic acid test result, 9 had IgG and/or IgM titers highest against C. trachomatis, 3 had IgG titers highest against C. pneumoniae, and 1 had undetectable titers for the three chlamydial species. Twenty-five patients had positive IgG and/or IgM titers to C. trachomatis but negative antigen test results. Serologic testing can increase the sensitivity of detecting C. trachomatis infections.

Impact of seroconversion and antichlamydial treatment on the rate of pre-eclampsia among Egyptian primigravidae

OBJECTIVE

To evaluate the effect of antichlamydial treatment and Chlamydia pneumoniae seroconversion on the incidence of pre-eclampsia among Egyptian primigravidae.

METHODS

The present prospective study included 600 healthy normotensive primigravidae who attended an outpatient clinic at 10-16weeks of pregnancy. A single venous blood sample was collected to test for C. pneumonia-specific immunoglobulin G (IgG) antibodies using an enzyme-linked immunosorbent assay. Seropositive women were randomly allocated to receive or not receive antichlamydial treatment before 20weeks of pregnancy. Seronegative participants had another test at delivery for the presence of C. pneumonia-specific IgG to determine seroconversion. All participants were followed up for up to 8weeks postpartum and observed for the development of pre-eclampsia.

RESULTS

The rate of pre-eclampsia among seropositive participants differed significantly depending on whether the women received treatment or not (6.5% and 19.1%, respectively; P=0.014). No statistically significant difference in the rate of pre-eclampsia was detected between seronegative participants who underwent seroconversion and those who did not.

CONCLUSION

The present results indirectly support the hypothesis that infectious agents (in particular C. pneumoniae) have a role in the development of pre-eclampsia. The findings also indicate that antichlamydial treatment might help to reduce the incidence of pre-eclampsia.

Serodiagnosis of Chlamydia pneumoniae infection using three inclusion membrane proteins

The Chlamydia pneumoniae genome-encoded open reading frames Cpn0146, Cpn0147, and Cpn0308 were expressed as recombinant proteins for detecting C. pneumoniae-specific antibodies in samples from three groups of individuals including 183 with C. pneumoniae-associated respiratory infection (group I), 60 healthy blood donors (group II), and 32 with no known respiratory infection (group III). The recombinant Cpn0146 was recognized by 71 (38.8% positive recognition rate), 15 (25%) and 1 (3.1%), Cpn0147 by 75 (40.9%), 14 (23.3%), and 2 (6.3%), and Cpn0308 by 82 (44.8%), 16 (26.7%), and 0 (0%) samples from groups I, II, and III, respectively. The positive recognition rates with any of the three antigens were significantly higher in group I than those in groups II and III, suggesting that more individuals from group I were likely infected with C. pneumoniae. This conclusion was confirmed with a commercially available whole organism-based ELISA kit (Savyon Diagnostics Ltd., Ashdod, Israel), which detected C. pneumoniae antibodies in 98 (64.1%), 26 (43.3%), and 4 (12.5%) samples from group I, II, and III, respectively. Comparing to the commercial kit, the recombinant antigen-based detection assays displayed >97% of detection specificity and >87% of sensitivity, suggesting that these recombinant antigens can be considered alternative tools for aiding in serodiagnosis of C. pneumoniae infection.

Arterial stiffness and Chlamydia pneumoniae infection in coronary artery disease. Is there a link?

BACKGROUND

We investigated the possible association between antichlamydial antibodies and pulse wave analysis (PWA) parameters in a cohort of patients with coronary artery disease (CAD).

METHODS

The augmentation index (AI), the reflection time index (RTI) and the time to the beginning of the reflected wave (CT-1) were estimated (Sphygmocor ATCOR Medical). IgA titers >or= 40 and IgG >or=80 were considered as positive (microimmunofluorescence test). Patients also underwent coronary angiography, ultrasound carotid measurements and 24 h ambulatory blood pressure (BP) measurements.

RESULTS

No differences existed in the traditional risk factors for CAD between the seronegative and seropositive IgA/ IgG groups. IgA seropositive subjects had higher values of AI (p < 0.01) comparing to seronegatives whilst the levels of CT-1 and RTI were lower (p < 0.011 and p < 0.02 respectively). No differences in AI, CT-1 and RTI values were found between IgG seropositive/ seronegatives patients.

CONCLUSIONS

An association was indicated between IgA antichlamydial titers and PWA parameters in patients with CAD, supporting that the connecting link between arterial stiffness and CAD might include this microorganism.

Evaluation of an in silico predicted specific and immunogenic antigen from the OmcB protein for the serodiagnosis of Chlamydia trachomatis infections

Background

The OmcB protein is one of the most immunogenic proteins in C. trachomatis and C. pneumoniae infections. This protein is highly conserved leading to serum cross reactivity between the various chlamydial species. Since previous studies based on recombinant proteins failed to identify a species specific immune response against the OmcB protein, this study evaluated an in silico predicted specific and immunogenic antigen from the OmcB protein for the serodiagnosis of C. trachomatis infections.

Results

Using the ClustalW and Antigenic programs, we have selected two predicted specific and immunogenic regions in the OmcB protein: the N-terminal (Nt) region containing three epitopes and the C-terminal (Ct) region containing two epitopes with high scores. These regions were cloned into the PinPoint Xa-1 and pGEX-6P-1 expression vectors, incorporating a biotin purification tag and a glutathione-S-transferase tag, respectively. These regions were then expressed in E. coli. Only the pGEX-6P-1 has been found suitable for serological studies as its tag showed less cross reactivity with human sera and was retained for the evaluation of the selected antigens. Only the Ct region of the protein has been found to be well expressed in E. coli and was evaluated for its ability to be recognized by human sera. 384 sera were tested for the presence of IgG antibodies to C. trachomatis by our in house microimmunofluorescence (MIF) and the developed ELISA test. Using the MIF as the reference method, the developed OmcB Ct ELISA has a high specificity (94.3%) but a low sensitivity (23.9). Our results indicate that the use of the sequence alignment tool might be useful for identifying specific regions in an immunodominant antigen. However, the two epitopes, located in the selected Ct region, of the 24 predicted in the full length OmcB protein account for approximately 25% of the serological response detected by MIF, which limits the use of the developed ELISA test when screening C. trachomatis infections.

Conclusion

The developed ELISA test might be used as a confirmatory test to assess the specificity of serological results found by MIF.

Evaluation and optimization of a commercial enzyme linked immunosorbent assay for detection of Chlamydophila pneumoniae IgA antibodies

BACKGROUND

Serologic diagnosis of Chlamydophila pneumoniae (Cpn) infection routinely involves assays for the presence of IgG and IgM antibodies to Cpn. Although IgA antibodies to Cpn have been found to be of interest in the diagnosis of chronic infections, their significance in serological diagnosis remains unclear. The microimmunofluorescence (MIF) test is the current method for the measurement of Cpn antibodies. While commercial enzyme linked immunosorbent assays (ELISA) have been developed, they have not been fully validated. We therefore evaluated and optimized a commercial ELISA kit, the SeroCP IgA test, for the detection of Cpn IgA antibodies.

METHODS

Serum samples from 94 patients with anti-Cpn IgG titers > or = 256 (study group) and from 100 healthy blood donors (control group) were tested for the presence of IgA antibodies to Cpn, using our in-house MIF test and the SeroCP IgA test. Two graph receiver operating characteristic (TG-ROC) curves were created to optimize the cut off given by the manufacturer.

RESULTS

The MIF and SeroCP IgA tests detected Cpn IgA antibodies in 72% and 89%, respectively, of sera from the study group, and in 9% and 35%, respectively, of sera from the control group. Using the MIF test as the reference method and the cut-off value of the ELISA test specified by the manufacturer for seropositivity and negativity, the two tests correlated in 76% of the samples, with an agreement of K = 0.54. When we applied the optimized cut-off value using TG-ROC analysis, 1.65, we observed better concordance (86%) and agreement (0.72) between the MIF and SeroCP IgA tests.

CONCLUSION

Use of TG-ROC analysis may help standardize and optimize ELISAs, which are simpler, more objective and less time consuming than the MIF test. Standardization and optimization of commercial ELISA kits may result in better performance.

Development of an internally controlled real-time PCR assay for detection of Chlamydophila psittaci in the LightCycler 2.0 system

A real-time PCR assay with a DNA purification and inhibition control (internal control; IC) was developed to detect Chlamydophila psittaci DNA in human clinical samples. Novel C. psittaci-specific primers targeting the ompA gene were developed. The IC DNA contained the same primer-binding sites and had the same length and nucleotide content as the C. psittaci DNA amplicon, but had a shuffled probe-binding region. The lower limit of detection was 80 target copies/PCR, corresponding to 6,250 copies/mL in a clinical sample. Specificity was tested using reference strains of 30 bacterial species. No amplification was observed from any of these samples. Respiratory samples from eight patients were positive with this PCR. Six of these patients were confirmed as positive for C. psittaci with serological testing. Two patients had increasing antibody titres, but did not fulfil criteria proposed previously for serologically proven Chlamydia spp. infection. The real-time PCR described in this paper is a sensitive, specific and rapid method to detect C. psittaci DNA in human clinical respiratory samples.

Chlamydia pneumoniae antibody levels before coronary events in the Helsinki Heart Study as measured by different methods

The lack of specific tests for the diagnosis of chronic Chlamydia pneumoniae infection has led to the use of enzyme immunoassay (EIA) instead of the gold standard, that is, microimmunofluorescence (MIF), in the measurement of C. pneumoniae antibodies. We assessed the predictive values of C. pneumoniae antibody levels and seroconversions measured by MIF and EIA for coronary events in the prospective Helsinki Heart Study. Sera from 239 cases with coronary events and 239 controls were available at the baseline and data from 210 cases and 211 controls before and after the event. The agreement between MIF and EIA antibody levels was best in high antibody titers. In conditional logistic regression analysis, only high IgA MIF titers (>/=40) at the baseline predicted future coronary events, and the participants with MIF seroconversion between consecutive sera had a higher (nonsignificant) risk for coronary events than the controls. The difference in the kinetics of EIA and MIF antibodies demonstrated that MIF should remain the gold standard.

Production and characterization of monoclonal antibodies to Chlamydia trachomatis

In order to develop an indigenous and reliable immunodiagnostic assay for Chlamydia trachomatis in India, monoclonal antibodies (MAbs) were developed. Serovar D of C. trachomatis (which was previously isolated from the genital tract of infected women) was propagated, purified, and used for production of monoclonal antibody. A total of 12 murine hybrid clones producing immunoglobulin G (IgG) class monoclonal antibodies to C. trachomatis (species-specific, B serogroup-specific, and serovar-specific) were developed. Enzyme-linked immunosorbent assay (ELISA) was used to screen developed murine MAbs with C. trachomatis antigen. Dot-ELISA was used to check the specificity of clones and was used for selecting hybridomas that produced anti-C. trachomatis MAb. There was no cross-reactivity of species-specific, B serogroup-specific, and D serovar-specific anti-major outer membrane protein (MOMP) monoclonal antibodies with other species of Chlamydiae i.e., C. pneumoniae and C. psitacci. Immunoblotting was done for further characterization of six of these clones, i.e., B2.2 and D5.1 (B serogroup-specific), D10.4 and G1.5 (species-specific), and H5.6 and E4.2 (D serovar-specific). Three of these clones D10.4 (species-specific), B2.2 (B serogroup-specific), and H5.6 (D serovar-specific) which reacted with 40 kd MOMP protein in Immunoblotting were used for further screening to detect C. trachomatis in endocervical specimens. The percent positivity with these clones for detection of C. trachomatis antigen by enzyme immunoassay (EIA) was 45% with D10.4, 43% with H5.6, and 35% with B2.2, while 46% of the specimens were found positive by cell culture method. This indicates a high prevalence of C. trachomatis infection in the female genital tract. The sensitivity and specificity of developed anti- MOMP monoclonal antibody in EIA for chlamydial antigen detection was 91.3% and 94.4% for D10.4 clone (species-specific), 91.30% and 98.1% for H5.6 (D serovar-specific) and 75.00% and 99.07% for B2.2 (B serogroup-specific) compared to cell culture method.

Close association of Chlamydia pneumoniae IgA seropositivity by ELISA with the presence of coronary artery stenosis in haemodialysis patients

BACKGROUND

Traditional risk factors of cardiovascular disease do not fully explain the accelerated atherosclerosis present in patients with end-stage renal disease (ESRD). The goal of this study was to identify the association of clinical and laboratory factors including seropositivity for Chlamydia pneumoniae determined by a specific enzyme-linked immunosorbent assay (ELISA) with the presence of coronary artery disease identified by coronary angiography in ESRD patients.

METHODS

We prospectively enrolled 161 consecutive ESRD patients undergoing haemodialysis for >6 months (106 men, 55 women; mean age 63.1+/-10.2 years; mean dialysis duration 91.3+/-90.1 months). All patients underwent coronary angiography within 1 week after blood sampling. The associations of coronary artery disease with clinical parameters including C. pneumoniae IgA and IgG seropositivity were analysed using multiple logistic regression models.

RESULTS

Coronary stenosis >50% was found in 102 of 161 haemodialysis patients (63.4%). Of the 102 patients, 75.5% were asymptomatic. Seropositivity for C. pneumoniae IgA was found in patients with coronary stenosis (77 out of 102, 75.5%) more frequently (P<0.001) than in patients without coronary stenosis (10 out of 59, 16.9%). Seropositivity for C. pneumoniae IgA but not IgG was strongly associated with the presence of coronary stenosis in multiple logistic regression analysis (odds ratio, 18.440; 95% confidence interval, 7.500-45.337), independently of the Framingham coronary risk factors, factors peculiar to ESRD or serum C-reactive protein levels.

CONCLUSIONS

C. pneumoniae IgA seropositivity determined by ELISA is an independent laboratory factor indicating the presence of coronary artery stenosis in ESRD patients undergoing maintenance haemodialysis.

Evaluation and optimization of ELISA for detection of anti-Chlamydophila pneumoniae IgG and IgA in patients with coronary heart diseases

We have evaluated and optimized a commercial enzyme-linked immunosorbent assay (ELISA; SeroCP Savyon, Israel), using the commercial microimmunofluorescence test (MIF; Labsystems; Helsinki, Finland) as reference method. This was done for the detection of anti-Chlamydophila pneumoniae IgG and IgA antibodies in patients with coronary heart disease (CHD). After optimization, a good agreement between the ELISA and MIF tests [IgG (P(0.05)=0.0008 and r=0.93) and IgA (P(0.05)=0.00072 and r=0.72)] was found. These ELISA tests proved to be a useful semiquantitative method for seroprevalence studies in CHD patients, with remarkable advantages over MIF test in terms of objective measurement, thus reproducibility, performance and interpretation.

Association of antibodies to chlamydial lipopolysaccharide with the endovascular presence of Chlamydophila pneumoniae in carotid artery disease

Atherosclerotic lesions often harbor Chlamydophila pneumoniae (C. pneumoniae). The objective of the present study was to examine whether serological tests are able to predict individual endovascular infection. Endarterectomy specimens from 70 patients with severe carotid artery stenosis were stained immunohistochemically for C. pneumoniae. Antibody titers to C. pneumoniae were measured in serum with a recombinant ELISA recognizing chlamydial lipopolysaccharide (cLPS) and with microimmunofluorescence (MIF). C. pneumoniae antigens were detected in 64 (91%) carotid artery specimens. Serum IgG antibodies to C. pneumoniae were detected in 43% of patients by cLPS-ELISA and in 77% by MIF test. Detection of C. pneumoniae positive cells within atherectomy specimens was strongly correlated to seroprevalence (P = 0.002) and to titers (P = 0.003) of cLPS-IgG antibodies, but not to results of the MIF-test. We conclude that cLPS-IgG antibodies hold promise as a surrogate marker to identify individuals with high endovascular antigen load.

Characterization of human humoral responses to the major outer membrane protein and OMP2 of Chlamydophila pneumoniae

Chlamydophila pneumoniae infection is associated with a range of diseases including pneumonia, asthma and heart disease. Although an obligate intracellular pathogen, high levels of antigen-specific antibody are induced and serology is frequently used to diagnose these infections. Proteins targeted by the humoral response include the major outer membrane protein (MOMP) and outer membrane protein 2 (OMP2). Using human anti-chlamydial sera we have defined the B cell epitopes recognized on MOMP and OMP2. Peptides from MOMP, unlike OMP2, were not strongly recognized. Two of these epitopes when linked to an inert carrier reacted strongly with high-titer anti-C. pneumoniae sera.

Importance of methodology in determination of Chlamydia pneumoniae seropositivity in healthy subjects and in patients with coronary atherosclerosis

Enzyme immunoassays (EIAs) for the detection of Chlamydia pneumoniae antibodies were compared to the microimmunofluorescence (MIF) test, the reference method. Furthermore, we assessed the hypothesis that a possible relationship between Chlamydia pneumoniae immunoglobulin G (IgG) antibodies and coronary artery disease is dependent on the type of EIA. Sera from 112 healthy men (mean age, 50.1 years) were tested for antibodies against Chlamydia pneumoniae by five commercial test kits: Focus Chlamydia MIF IgG test, Labsystems Chlamydia pneumoniae IgG EIA (LS EIA), R-Biopharm Elegance Chlamydia pneumoniae IgG EIA (RB EIA), Medac Chlamydia pneumoniae IgG sandwich enzyme-linked immunosorbent assay ELISA (MCp sELISA) and Medac Chlamydia IgG recombinant enzyme-linked immunosorbent assay ELISA (MC rELISA). Sera from 106 consecutive male patients (mean age, 63.6 years) undergoing diagnostic coronary angiography were also examined using the Focus MIF, LS EIA, MCp sELISA, and MC rELISA techniques. The agreement between LS EIA (65 to 83% [controls-patients]) or MC rELISA (49 to 61%) and Focus MIF (78 to 83%) was average to fair (kappa = 0.597 and 0.234, respectively). MCp sELISA and RB EIA showed good agreement with MIF (kappa = 0.686 and 0.665, respectively), with 80 to 89 and 79% of individuals reacting positively. A significant difference in seroprevalence between patients and healthy subjects was observed with the LS EIA, while seropositivities in the two study groups appeared equal when the Focus MIF assay was applied. The MC rELISA and MCp sELISA gave statistically significant differences in antibody seroprevalence in patients with two-vessel disease or when the patient group combined individuals with a two- or a three-vessel disease, respectively. The concordance between MIF and other commonly used serological assays for C. pneumoniae IgG antibody detection is good to fair. The choice of serological assay has important implications for C. pneumoniae antibody seroprevalence, as well as for the relationship between C. pneumoniae seropositivity and coronary artery disease.

Measurement of IgG antibodies to Chlamydia trachomatis by commercial enzyme immunoassays and immunofluorescence in sera from pregnant women and patients with infertility, pelvic inflammatory disease, ectopic pregnancy, and laboratory diagnosed Chlamydia psittaci/Chlamydia pneumoniae infection

BACKGROUND

Screening for Chlamydia trachomatis specific antibodies is valuable in diagnosing asymptomatic pelvic inflammatory disease (PID) and tubal damage following repeated episodes of PID. The assays in current use are unsuitable for screening large numbers of samples so there is a need to develop more suitable assays.

AIMS

To compare the performance of several commercial C trachomatis enzyme immunoassays (EIAs) (SeroCT, C tracho(pep), Medac p-EIA, Vircell and Labsystems C trachomatis IgG EIAs) using major outer membrane protein (MOMP), an inactivated organism EIA (Genzyme Virotech EIA), and a genus specific EIA (Platelia Chlamydia IgG) with the whole cell inclusion immunofluorescence (WIF) assay. In addition, to adapt, using time resolved fluorescence technology, the assay showing the highest correlation with WIF.

METHODS

Ninety sera from patients presenting with ectopic pregnancies, 187 sera from those with a variety of types of infertility, 33 sera from cases of PID where a fourfold rise in WIF titre occurred, and 90 sera from antenatal clinic attenders were tested. A panel of 36 sera from laboratory diagnosed cases of Chlamydia psittaci/Chlamydia pneumoniae infection was also tested.

RESULTS

The Genzyme Virotech EIA showed the highest rank correlation coefficient (0.82) with WIF, particularly at high WIF titres. The MOMP specific assays varied in their correlation with WIF, with rank correlation coefficients ranging from 0.70 (Medac p-EIA) to 0.80 (Vircell EIA). The Genzyme Virotech assay showed poor specificity (5.6%; 95% confidence interval (CI), 0.68% to 18.7%)--it was reactive with 34 of the panel of 36 C psittaci/C pneumoniae positive sera. The MOMP based EIAs showed high specificity, particularly the Medac p-ELISA (97.2%; 95% CI, 85.5% to 99.9%)--only one serum was reactive. In view of the good correlation between WIF and the Genzyme Virotech EIA, a time resolved fluorescence immunoassay (TRFIA) was developed using the Genzyme Virotech antigen. Using an appropriate cut off the TRFIA assay showed excellent correlation with WIF.

CONCLUSIONS

The TRFIA assay may be useful as a screening assay, possibly in conjunction with one of the highly specific EIAs studied (for example, Medac p-EIA) to confirm the antibody specificity of sera selected by the screening assay.

Characterization of the humoral immune response to Chlamydia outer membrane protein 2 in chlamydial infection

Detection of antibodies to an outer membrane protein 2 (OMP2) by enzyme-linked immunosorbent assay (ELISA) by using either the Chlamydia trachomatis- or the Chlamydia pneumoniae-specific protein was investigated. OMP2 is an immunodominant antigen giving rise to antibody responses in humans infected with different C. trachomatis serovars (A to C and D to K) or with C. pneumoniae, which could be detected by OMP2 ELISA. OMP2 ELISA is not species specific, but antibody titers were usually higher on the homologous protein. The sensitivity of this assay was high but varied according to the "gold standard" applied. Levels of antibody to C. pneumoniae OMP2 as detected by ELISA seem to return to background or near-background values within a shorter period of time compared to antibodies to C. pneumoniae detected by microimmunofluorescence (MIF), making it more likely that positive results in ELISA reflect recent infection. Thus, OMP2 ELISA has distinct advantages over MIF and commercially available ELISAs and might be a useful tool for the serodiagnosis of chlamydial infection.

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 and atherosclerosis: critical assessment of diagnostic methods and relevance to treatment studies

A number of studies have found that inflammation of the vessel wall plays an essential role in both the initiation and progression of atherosclerosis and erosion and fissure and the eventual rupture of plaques. Chlamydia pneumoniae is one of the infectious agents that have been investigated as possible causes of this inflammation. Initial studies of the association of C. pneumoniae and cardiovascular disease (CVD) were seroepidemiologic, and these were followed by studies in which the organism was identified in vascular tissue from patients with CVD by electron microscopy, PCR and immunocytochemical staining (ICC). C. pneumoniae has also been isolated by culture from vascular tissue in a small number patients. However, no single serologic, PCR, or ICC assay has been used consistently across all studies. The assays used are also not standardized. Recent studies of serologic and PCR assays for diagnosis of C. pneumoniae infection have suggested that there may be substantial interlaboratory variation in the performance of these tests. It now appears that some of the inconsistency of results from study to study may be due, in part, to lack of standardized methods. Although initial seroepidemiologic studies demonstrated a significantly increased risk of adverse cardiac outcome in patients who were seropositive, subsequent prospective studies found either small or no increased risk. In addition to the lack of consistent serologic criteria, recent evaluations have demonstrated inherent problems with performance of the most widely used serologic methods. Most importantly, we do not have a reliable serologic marker for chronic or persistent C. pneumoniae infection.

PCR detection and molecular identification of Chlamydiaceae species

Recent taxonomic developments, based on 16s and 23s rRNA gene sequences, have divided the family Chlamydiaceae into two genera and nine species, of which five have been found to infect humans. Few simple methods are available to detect and identify all species sensitively and specifically. In this study the suitability of the omp2 gene as a target for molecular identification of Chlamydiaceae is demonstrated. Phylogenetic analysis of partial omp2 gene sequences from all nine species agrees with the recently published taxonomic changes based on the ribosomal genes. The use of a family-specific PCR primer pair, which is able to amplify the 5' end of the omp2 gene from all Chlamydiaceae except some Chlamydophila pecorum strains, is described. Identification of all nine species was achieved using restriction fragment length polymorphism analysis with a single enzyme, AluI, confirmed by DNA sequencing. A PCR enzyme-linked oligonucleotide assay was developed which can detect a single chlamydial genome and may be applied to DNA extracts from any specimen or culture for the detection of single or mixed human chlamydial infection.

Comparison of two commercial microimmunofluorescence kits and an enzyme immunoassay kit for detection of serum immunoglobulin G antibodies to Chlamydia pneumoniae

We compared the MRL and the Labsystems Chlamydia pneumoniae microimmunofluorescence (MIF) immunoglobulin G (IgG) kits and the Labsystems enzyme immunoassay (EIA) kit in a blinded study of 83 serum samples in which we evaluated titers, cross-reactivity to other species, and reproducibility. There was no statistically significant difference between the MRL and the Labsystems MIF kits in the endpoint titers of IgG antibody to C. pneumoniae. The correlation between the results obtained with these two MIF kits was excellent (r = 0.95; P = 0.001). The cross-reactivity of the C. pneumoniae-positive sera with C. trachomatis- and C. psittaci-positive sera was assessed for each MIF kit. For C. pneumoniae-positive sera with titers of > or =32, the Labsystems MIF kit exhibited more cross-reactivity to C. psittaci than the MRL kit did. The values obtained with the Labsystems EIA kit represented single dilutions of serum specimens expressed as enzymeimmuno units on a continuous scale. The results obtained with the Labsystems EIA kit correlated moderately well with those obtained with each MIF kit when they were compared for their abilities to detect IgG antibodies to C. pneumoniae (for the MRL MIF kit, r = 0.79 [P = 0.001]; for the Labsystems MIF kit, r = 0.78 [P = 0.001]). The results obtained with the commercial MRL and Labsystems MIF kits and the Labsystems EIA kit tested were reproducible; and the kits were standardized, had quality control reagents, and are suitable for detection of C. pneumoniae antibodies in serum and for use in interlaboratory studies. Validation of the use of these kits for clinical diagnosis still needs further evaluation.

Chlamydial serology: comparative diagnostic value of immunoblotting, microimmunofluorescence test, and immunoassays using different recombinant proteins as antigens

To improve the reliability of the serodiagnosis of Chlamydia trachomatis infections, an immunoblot analysis, a microimmunofluorescence titration, and different immunoassays using synthetic peptides derived from species-specific epitopes in variable domain IV of the major outer membrane protein or recombinant antigens (heat shock protein 70 [hsp70], hsp60, hsp10, polypeptide encoded by open reading frame 3 of the plasmid [pgp3], macrophage infectivity potentiator, and a fragment of the total lipopolysaccharide) were evaluated. Because cross-reactions between chlamydial species have been reported, the microimmunofluorescence tests were also performed with Chlamydia pneumoniae and Chlamydia psittaci used as antigens, and C. pneumoniae-specific antibodies were also determined by immunoassays. Since the presence of antimicrobial antibodies must be interpreted in light of their prevalence in the general population, responses obtained with serum samples from patients with well-defined infection (i.e., with positive urethral or endocervical C. trachomatis DNA amplification) were compared to those obtained with samples from healthy blood donors. The best sensitivity (86%) with a specificity of 81% was obtained for immunoblotting results, when the number of individuals with > or =10 immunoglobulin G (IgG) and/or > or =2 IgM responses to the different C. trachomatis antigens was considered. A 13-kDa antigen was recognized by most of the samples (86% for IgG) from patients with acute urogenital infection but rarely (3%) by those from healthy blood donors (P < 0.0001). The sensitivity and specificity results obtained for serum antibodies to peptides or recombinant antigens were slightly lower than those results obtained for the number of responses to whole C. trachomatis antigens, which were 76 and 77%, respectively, when IgG responses to both recombinant hsp60 and pgp3 were considered.

A preliminary evaluation of a new enzyme immunoassay to detect Chlamydia pneumoniae-specific antibodies

New enzyme immunoassays (EIAs) for determination of specific IgG, IgA, and IgM antibody titers to Chlamydia pneumoniae were evaluated independently in three research laboratories. Specificity of the EIAs was enhanced by removing LPS from the chlamydial antigen. The performance of these EIAs was evaluated in comparison with the microimmunofluorescence (MIF) test using specimens from: (i) a group of adult patients with community-acquired pneumonia (CAP) previously diagnosed as having an acute chlamydial infection by the complement fixation test or the whole inclusion fluorescence test; (ii) from a group of adult patients with acute respiratory tract infections; and (iii) from a group of young children consecutively presenting with acute respiratory tract infections. The MIF test and the EIAs detected acute infections in paired serum specimens from 12 of 14 patients from the first group. Eleven of these 12 patients were positive in both tests. The MIF test detected seven acute infections in single convalescence serum specimens from eight patients. Two of these were also positive in the EIAs. Paired serum specimens from the second group of adult patients (n=12) were collected during an epidemic of C. pneumoniae. The EIAs detected six acute infections. The MIF test detected two additional patients with acute infections. From the group of young children (n=30), the EIAs detected two patients with acute infections. Our conclusion from this preliminary evaluation is that these EIAs could be useful for laboratory diagnosis of acute C. pneumoniae infections. Comprehensive prospective studies should provide suitable data to calculate the sensitivity, specificity, and predictive values.

The use of serologic tests for the diagnosis of chlamydial infections

Serology is commonly used for the diagnosis of acute Chlamydia pneumoniae infections and also for the diagnosis of complicated Chlamydia trachomatis infections. Furthermore, recent sero-epidemiological studies have linked C. pneumoniae infection with several diseases traditionally considered non-infectious. The objectives of this mini-review are to critically review and discuss some selected analytical and methodological aspects, controversies and current problems in chlamydial serodiagnosis. To illustrate our views we present some original data of the comparison of current technologies. The review of the literature revealed high variability in methodologies applied to different studies. This observation was supported by our own data, which explains occasional conflicting clinical interpretation. Although the microimmunofluorescence (MIF) technique is generally considered as the gold standard for serodiagnosis of chlamydial infections, assay conditions are highly variable and hence pose a major problem in the interpretation of the results. For instance, many recent studies linking C. pneumoniae and atherosclerosis have utilized MIF techniques with variable threshold criteria for the positivity, in combination with selection bias of cases and controls possibly leading to conflicting results. Variability of assay conditions is also a common problem with Western blots, and interpretation is problematic when both anti-C. pneumoniae and anti-C. trachomatis antibodies are present. Furthermore, there is a lot of disagreement in serological criteria applied to recently emerged enzyme immunoassay (EIA) techniques when these assays are used for acute and non-acute clinical conditions and their association with Chlamydiae. In conclusion, standardization of serological techniques and the development of uniform criteria for interpretation of serologic findings is necessary to increase our knowledge of the biology of Chlamydiae, pathogenesis of any chlamydial infection and chronic infections in particular.

Chlamydia pneumoniae DNA in non-coronary atherosclerotic plaques and circulating leukocytes

Earlier studies have associated atherosclerosis with Chlamydia pneumoniae infection. C. pneumoniae may circulate via monocytes and migrate into plaques by leukocyte infiltration; however, detection is difficult. We developed a novel polymerase chain reaction (PCR) method to test the hypothesis that C. pneumoniae DNA in circulating leukocytes is correlated with C. pneumoniae DNA in plaque material and that C. pneumoniae copy number is associated with disease severity. We obtained plaques from 130 patients who underwent surgery for carotid stenosis, aneurysm, or peripheral vascular disease. From 60 patients and 51 normal control subjects we also obtained circulating leukocytes. The C. pneumoniae 16 S rRNA gene was amplified with a highly specific quantitative PCR protocol relying on the TaqMan technology. Immunohistochemistry was performed with antibody against the C. pneumoniae outer membrane protein. C. pneumoniae DNA was present in 25% of atherosclerotic plaques and 20% of circulating leukocytes from patients. The copy number was not correlated with disease severity. C. pneumoniae DNA was more common in younger patients and smokers. C. pneumoniae antibody titers, C-reactive protein, fibrinogen, leukocyte count, cholesterol, and diabetes were not associated with C. pneumoniae DNA. Although immunostaining of plaque and PCR results were highly correlated, we found no relationship between C. pneumoniae DNA in plaques and that in circulating leukocytes. Finally, 13% of normal control subjects had positive leukocytes; however, their copy number was significantly lower than that of the patients. C. pneumoniae DNA is frequent in atherosclerotic plaques and is correlated with positive immunohistochemistry. C. pneumoniae DNA may also be found in circulating leukocytes; however, infected leukocytes and plaques do not coincide. Serology is unreliable in predicting C. pneumoniae DNA. Smoking increases the risk of harboring C. pneumoniae DNA. Our results do not suggest that either test for antibodies or C. pneumoniae DNA from leukocytes in blood is of value in predicting infected plaques.

Low grade inflammation and coronary heart disease: prospective study and updated meta-analyses

OBJECTIVE

To assess associations between baseline values of four different circulating markers of inflammation and future risk of coronary heart disease, potential triggers of systemic inflammation (such as persistent infection), and other markers of inflammation.

DESIGN

Nested case-control comparisons in a prospective, population based cohort.

SETTING

General practices in 18 towns in Britain.

PARTICIPANTS

506 men who died from coronary heart disease or had a non-fatal myocardial infarction and 1025 men who remained free of such disease until 1996 selected from 5661 men aged 40-59 years who provided blood samples in 1978-1980.

MAIN OUTCOME MEASURES

Plasma concentrations of C reactive protein, serum amyloid A protein, and serum albumin and leucocyte count. Information on fatal and non-fatal coronary heart disease was obtained from medical records and death certificates.

RESULTS

Compared with men in the bottom third of baseline measurements of C reactive protein, men in the top third had an odds ratio for coronary heart disease of 2.13 (95% confidence interval 1.38 to 3.28) after age, town, smoking, vascular risk factors, and indicators of socioeconomic status were adjusted for. Similar adjusted odds ratios were 1.65 (1.07 to 2.55) for serum amyloid A protein; 1.12 (0.71 to 1.77) for leucocyte count; and 0.67 (0.43 to 1.04) for albumin. No strong associations were observed of these factors with Helicobacter pylori seropositivity, Chlamydia pneumoniae IgG titres, or plasma total homocysteine concentrations. Baseline values of the acute phase reactants were significantly associated with one another (P<0.0001), although the association between low serum albumin concentration and leucocyte count was weaker (P=0.08).

CONCLUSION

In the context of results from other relevant studies these findings suggest that some inflammatory processes, unrelated to the chronic infections studied here, are likely to be involved in coronary heart disease.

Chlamydia pneumoniae IgG titres and coronary heart disease: prospective study and meta-analysis

OBJECTIVE

To examine the association between coronary heart disease and serum markers of chronic Chlamydia pneumoniae infection.

DESIGN

"Nested" case-control analysis in a prospective cohort study and an updated meta-analysis of previous relevant studies.

SETTING

General practices in 18 towns in Britain.

PARTICIPANTS

Of the 5661 men aged 40-59 who provided blood samples during 1978-80, 496 men who died from coronary heart disease or had non-fatal myocardial infarction and 989 men who had not developed coronary heart disease by 1996 were included.

MAIN OUTCOME MEASURES

IgG serum antibodies to C pneumoniae in baseline samples; details of fatal and non-fatal coronary heart disease from medical records and death certificates.

RESULTS

200 (40%) of the 496 men with coronary heart disease were in the top third of C pneumoniae titres compared with 329 (33%) of the 989 controls. The corresponding odds ratio for coronary heart disease was 1.66 (95% confidence interval 1.25 to 2.21), which fell to 1.22 (0.82 to 1.82) after adjustment for smoking and indicators of socioeconomic status. No strong associations were observed between C pneumoniae IgG titres and blood lipid concentrations, blood pressure, or plasma homocysteine concentration. In aggregate, the present study and 14 other prospective studies of C pneumoniae IgG titres included 3169 cases, yielding a combined odds ratio of 1. 15 (0.97 to 1.36), with no significant heterogeneity among the separate studies (chi(2)=10.5, df=14; P>0.1).

CONCLUSION

This study, together with a meta-analysis of previous prospective studies, reliably excludes the existence of any strong association between C pneumoniae IgG titres and incident coronary heart disease. Further studies are required, however, to confirm or refute any modest association that may exist, particularly at younger ages.

Chlamydia pneumoniae infection and mortality from ischaemic heart disease: large prospective study

OBJECTIVE

To determine whether there is an independent association between infection with Chlamydia pneumoniae and ischaemic heart disease.

DESIGN

Prospective study using a nested case-control design.

SETTING

Medical centre in London run by BUPA, a private medical organisation.

PARTICIPANTS

21 520 professional men aged 35-64 who attended for a medical examination in London between 1975 and 1982.

MAIN OUTCOME MEASURE

Death from ischaemic heart disease.

RESULTS

The distributions of concentrations of IgG and IgA antibodies to C pneumoniae were similar in the 647 men who subsequently died of ischaemic heart disease and in 1294 age matched controls who did not. There was no material association with heart disease irrespective of the cut-off point chosen to define seropositivity. At a cut-off point that defines 15% of controls as positive, for example, the odds ratios were 1.26 (95% confidence interval 0.95 to 1.68) for IgG and 1.09 (0.82 to 1.43) for IgA.

CONCLUSIONS

No material association was found between infection with C pneumoniae and ischaemic heart disease. The size and prospective design of the study and the socioeconomic homogeneity of the cohort minimise both random and systematic error.

Circulating Chlamydia pneumoniae DNA as a predictor of coronary artery disease

OBJECTIVE

To determine whether current vascular Chlamydia pneumoniae (CPn) infection as diagnosed by circulating CPn DNA is more common in subjects with coronary artery disease (CAD).

BACKGROUND

Serological, pathological and animal studies have associated CPn with CAD and preliminary trials suggest antibiotics may prevent adverse coronary events. C. pneumoniae is thought to disseminate systemically within macrophages. We therefore detected CPn DNA in blood to determine whether its presence was a predictor of CAD.

METHODS

One thousand, two hundred and five subjects attending for diagnostic and interventional coronary arteriography were recruited. The mononuclear cell layer and platelets were separated from collected blood and the polymerase chain reaction (PCR) was used to detect CPn DNA.

RESULTS

Circulating CPn DNA was found in 8.8% of 669 men with CAD compared with 2.9% of 135 men with normal coronary arteries (odds ratio [OR] 3.2, 95% confidence interval [CI] 1.1-8.9). In men with CAD, those with CPn DNA had higher mean platelet counts than those without CPn DNA. Monocyte counts and indirect fibrinogen levels were also raised but not significantly so. By contrast, no association of circulating CPn DNA and CAD was seen in women.

CONCLUSIONS

Circulating CPn DNA is a predictor of CAD in men. Unlike serology, it is a specific indicator of current infection and is a means of identifying subjects who may potentially benefit from antichlamydial therapy.