The genus-specific antigen of Chlamydia: resemblance to the lipopolysaccharide of enteric bacteria

Host cell death during infection with Chlamydia: a double-edged sword

The phylum Chlamydiae constitutes a group of obligate intracellular bacteria that infect a remarkably diverse range of host species. Some representatives are significant pathogens of clinical or veterinary importance. For instance, Chlamydia trachomatis is the leading infectious cause of blindness and the most common bacterial agent of sexually transmitted diseases. Chlamydiae are exceptionally dependent on their eukaryotic host cells as a consequence of their developmental biology. At the same time, host cell death is an integral part of the chlamydial infection cycle. It is therefore not surprising that the bacteria have evolved exquisite and versatile strategies to modulate host cell survival and death programs to their advantage. The recent introduction of tools for genetic modification of Chlamydia spp., in combination with our increasing awareness of the complexity of regulated cell death in eukaryotic cells, and in particular of its connections to cell-intrinsic immunity, has revived the interest in this virulence trait. However, recent advances also challenged long-standing assumptions and highlighted major knowledge gaps. This review summarizes current knowledge in the field and discusses possible directions for future research, which could lead us to a deeper understanding of Chlamydia's virulence strategies and may even inspire novel therapeutic approaches.

Chlamydia Lipooligosaccharide Has Varied Direct and Indirect Roles in Evading both Innate and Adaptive Host Immune Responses

Chlamydia bacteria are obligate intracellular pathogens which can cause a variety of disease in humans and other vertebrate animals. To successfully complete its life cycle, Chlamydia must evade both intracellular innate immune responses and adaptive cytotoxic T cell responses. Here, we report on the role of the chlamydial lipooligosaccharide (LOS) in evading the immune response. Chlamydia infection is known to block the induction of apoptosis. However, when LOS synthesis was inhibited during Chlamydia trachomatis infection, HeLa cells regained susceptibility to apoptosis induction following staurosporine treatment. Additionally, the delivery of purified LOS to the cytosol of cells increased the levels of the antiapoptotic protein survivin. An increase in survivin levels was also detected following C. trachomatis infection, which was reversed by blocking LOS synthesis. Interestingly, while intracellular delivery of lipopolysaccharide (LPS) derived from Escherichia coli was toxic to cells, LOS from C. trachomatis did not induce any appreciable cell death, suggesting that it does not activate pyroptosis. Chlamydial LOS was also a poor stimulator of maturation of bone marrow-derived dendritic cells compared to E. coli LPS. Previous work from our group indicated that LOS synthesis during infection was necessary to alter host cell antigen presentation. However, direct delivery of LOS to cells in the absence of infection did not alter antigenic peptide presentation. Taken together, these data suggest that chlamydial LOS, which is remarkably conserved across the genus Chlamydia, may act both directly and indirectly to allow the pathogen to evade the innate and adaptive immune responses of the host.

Epidemiology of Chlamydia trachomatis infection in women and the cost-effectiveness of screening

BACKGROUND

The majority of Chlamydia trachomatis infections in women are asymptomatic, but may give rise to pelvic inflammatory disease (PID) and tubal infertility. Screening programmes aim at reducing morbidity in individuals by early detection and treatment, and at decreasing the overall prevalence of infection in the population. A number of modelling studies have tried to calculate the threshold prevalence of chlamydia lower genital tract infection above which screening becomes cost-effective. There is considerable debate over the exact complication rates after chlamydia infections, and more precise estimates of PID and tubal infertility are needed, for instance to be inserted in economic models.

METHODS

With reference to key studies and systematic reviews, an overview is provided focusing on the epidemiology of chlamydia infection and the risk-estimates of its late complications.

RESULTS

In the literature, the generally assumed risk of developing PID after lower genital tract chlamydia infection varies considerably, and is up to 30%. For developing tubal infertility after PID the risks are 10-20%. This implies that the risk of test-positive women of developing tubal infertility would range between 0.1 and 6%. We included chlamydia IgG antibody testing in a model and estimated a risk of tubal infertility up to 4.6%.

CONCLUSION

The risk of developing late complications after chlamydia lower genital tract infection appears low. High quality RCTs dealing with the transition from cervicitis to infertility are needed to broaden the evidence. In screening programmes, chlamydia antibody testing, as an intermediate marker for potential adverse sequelae, might enable more precise estimates.

The proinflammatory cytokine response to Chlamydia trachomatis elementary bodies in human macrophages is partly mediated by a lipoprotein, the macrophage infectivity potentiator, through TLR2/TLR1/TLR6 and CD14

Chlamydiae components and signaling pathway(s) responsible for the production of proinflammatory cytokines by human monocytes/macrophages are not clearly identified. To this aim, Chlamydia trachomatis-inactivated elementary bodies (EB) as well as the following seven individual Ags were tested for their ability to induce the production of proinflammatory cytokines by human monocytes/macrophages and THP-1 cells: purified LPS, recombinant heat shock protein (rhsp)70, rhsp60, rhsp10, recombinant polypeptide encoded by open reading frame 3 of the plasmid (rpgp3), recombinant macrophage infectivity potentiator (rMip), and recombinant outer membrane protein 2 (rOmp2). Aside from EB, rMip displayed the highest ability to induce release of IL-1beta, TNF-alpha, IL-6, and IL-8. rMip proinflammatory activity could not be attributed to Escherichia coli LPS contamination as determined by the Limulus Amoebocyte lysate assay, insensitivity to polymyxin B (50 microg/ml), and different serum requirement. We have recently demonstrated that Mip is a "classical" bacterial lipoprotein, exposed at the surface of EB. The proinflammatory activity of EB was significantly attenuated in the presence of polyclonal Ab to rMip. Native Mip was able to induce TNF-alpha and IL-8 secretion, whereas a nonlipidated C20A rMip variant was not. Proinflammatory activity of rMip was unaffected by heat or proteinase K treatments but was greatly reduced by treatment with lipases, supporting a role of lipid modification in this process. Stimulating pathways appeared to involve TLR2/TLR1/TLR6 with the help of CD14 but not TLR4. These data support a role of Mip lipoprotein in pathogenesis of C. trachomatis-induced inflammatory responses.

Synthesis of spacer-containing chlamydial disaccharides as analogues of the alpha-Kdop-(2-->8)-alpha-Kdop-(2-->4)-alpha-Kdop trisaccharide epitope

On the basis of high-resolution crystal structures of the antigen binding fragment of the chlamydia-specific monoclonal antibody S25-2 in complex with the trisaccharide alpha-Kdop-(2-->8)-alpha-Kdop-(2-->4)-alpha-Kdop and part structures thereof, seven modified alpha-Kdop-(2-->8)-alpha-Kdop disaccharide derivatives were synthesized starting from the protected disaccharide allyl ketoside 1. Hydroboration and subsequent oxidation as well as ozonolysis, respectively, followed by Wittig-reaction for chain elongation were used to install a terminal carboxylic group on spacer entities of various chain lengths. Furthermore, addition of methyl 2-thioacetate to the allyl group furnished the corresponding thioether derivative. Standard deprotection gave the target disaccharides as simplified trisaccharide analogues, which will be used to probe the contribution of the proximal carboxylic group in the binding of chlamydia-specific di- and trisaccharide-reactive monoclonal antibodies.

Detection of Chlamydophila pneumoniae IgG in paired serum samples: comparison of serological techniques in pneumonia cases

Serological diagnosis of Chamydophila pneumoniae is usually undertaken by complement fixation test (CFT) or by microimmunofluorescence (MIF). A number of commercial methods for detecting C. pneumoniae-specific IgG have been developed. The aim of this study was to compare the performance characteristics of six methods for the diagnosis of pneumonia due to C. pneumoniae, including CFT (in house), MIF (Vircell, Spain), and four ELISAs (Medac, Germany; Savyon, Israel; Serion, Germany; and DRG, Germany). ELISA-Medac, ELISA-Savyon, ELISA-DRG and MIF use C. pneumoniae antigens while ELISA-Serion and CFT use Chlamydophila genus-specific antigen. Acute and convalescent samples from 85 pneumonia patients were studied. Using CFT, cases were initially classified as due to Chlamydophila (43 cases); to other agents (23 cases) (influenza A and B, Mycoplasma pneumoniae, respiratory syncytial virus, adenovirus and Legionella pneumophila); or as negative (19 cases). Cases were considered positive if they showed seroconversion, a significant rise in titer or high titer; and were finally classified as positive if they gave a positive result in at least three assays. Sensitivity values ranged from 87% to 97.8%; and specificity from 84.6% to 97.4%. In conclusion, the assays compared appear to be useful tools for the diagnosis of pneumonia due to Chlamydophila.

Chlamydiae modulate gamma interferon, interleukin-1 beta, and tumor necrosis factor alpha receptor expression in HeLa cells

Chlamydia psittaci was found to modulate receptor expression for the cytokine receptors that are involved in the synergistic induction of indoleamine dioxygenase in epithelial cells. Increases in receptor expression were seen even with inactivated Chlamydia, suggesting that chlamydial antigens and not products of infection are important for up-regulating cytokine receptor expression.

A monoclonal antibody against a carbohydrate epitope in lipopolysaccharide differentiates Chlamydophila psittaci from Chlamydophila pecorum, Chlamydophila pneumoniae, and Chlamydia trachomatis

Lipopolysaccharide (LPS) of Chlamydophila psittaci but not of Chlamydophila pneumoniae or Chlamydia trachomatis contains a tetrasaccharide of 3-deoxy-alpha-d-manno-oct-2-ulopyranosonic acid (Kdo) of the sequence Kdo(2-->8)[Kdo(2-->4)] Kdo(2-->4)Kdo. After immunization with the synthetic neoglycoconjugate antigen Kdo(2-->8)[Kdo(2-->4)]Kdo(2-->4) Kdo-BSA, we obtained the mouse monoclonal antibody (mAb) S69-4 which was able to differentiate C. psittaci from Chlamydophila pecorum, C. pneumoniae, and C. trachomatis in double labeling experiments of infected cell monolayers and by enzyme-linked immunosorbent assay (ELISA). The epitope specificity of mAb S69-4 was determined by binding and inhibition assays using bacteria, LPS, and natural or synthetic Kdo oligosaccharides as free ligands or conjugated to BSA. The mAb bound preferentially Kdo(2-->8)[Kdo(2-->4)]Kdo(2-->4)Kdo(2-->4) with a K(d) of 10 microM, as determined by surface plasmon resonance (SPR) for the monovalent interaction using mAb or single chain Fv. Cross-reactivity was observed with Kdo(2-->4)Kdo(2-->4) Kdo but not with Kdo(2-->8)Kdo(2-->4)Kdo, Kdo disaccharides in 2-->4- or 2-->8-linkage, or Kdo monosaccharide. MAb S69-4 was able to detect LPS on thin-layer chromatography (TLC) plates in amounts of <10 ng by immunostaining. Due to the high sensitivity achieved in this assay, the antibody also detected in vitro products of cloned Kdo transferases of Chlamydia. The antibody can therefore be used in medical and veterinarian diagnostics, general microbiology, analytical biochemistry, and studies of chlamydial LPS biosynthesis. Further contribution to the general understanding of carbohydrate-binding antibodies was obtained by a comparison of the primary structure of mAb S69-4 to that of mAb S45-18 of which the crystal structure in complex with its ligand has been elucidated recently (Nguyen et al., 2003, Nat. Struct. Biol., 10, 1019-1025).

Germline antibody recognition of distinct carbohydrate epitopes

High-resolution structures reveal how a germline antibody can recognize a range of clinically relevant carbohydrate epitopes. The germline response to a carbohydrate immunogen can be critical to survivability, with selection for antibody gene segments that both confer protection against common pathogens and retain the flexibility to adapt to new disease organisms. We show here that antibody S25-2 binds several distinct inner-core epitopes of bacterial lipopolysaccharides (LPSs) by linking an inherited monosaccharide residue binding site with a subset of complementarity-determining regions (CDRs) of limited flexibility positioned to recognize the remainder of an array of different epitopes. This strategy allows germline antibodies to adapt to different epitopes while minimizing entropic penalties associated with the immobilization of labile CDRs upon binding of antigen, and provides insight into the link between the genetic origin of individual CDRs and their respective roles in antigen recognition.

Cross-reactive monoclonal antibodies raised against the lipopolysaccharide antigen of Salmonella minnesota Re chemotype: diagnostic relevance

Three cross-reactive monoclonal antibodies (MAbs) of IgM and IgG2b isotype were generated in two separate fusions after immunization of BALB/c mice with heat killed Salmonella minnesota R595 of Re chemotype and acid-treated bacteria, coated with Re lipopolysaccharide (LPS) antigen. The specificity of the MAbs was demonstrated as the Re LPS antigen. The activity and cross-reactivity against purified elementary bodies of Chlamydia trachomatis and various S- and R-LPS antigens of other Gram-negative bacteria were characterized in enzyme-linked immunosorbent assay, passive hemolysis assay, immunoblot and immunofluorescence with the available chlamydial strains. The results demonstrated cross-reaction between the Re LPS antigen, the genus-specific chlamydial LPS and the LPS antigens of Escherichia coli O119 and Acinetobacter baumannii, suggesting the presence of identical or similar epitopes in the lipopolysaccharide antigens. The findings are implying the necessity of novel approaches, improving the specificity of serologic assays in the laboratory diagnosis of chlamydial infections.

Endotoxic activity and chemical structure of lipopolysaccharides from Chlamydia trachomatis serotypes E and L2 and Chlamydophila psittaci 6BC

The lipopolysaccharide (LPS) of Chlamydia trachomatis serotype E was isolated from tissue culture-grown elementary bodies and analyzed structurally by mass spectrometry and 1H, 13C and 31P nuclear magnetic resonance. The LPS is composed of the same pentasaccharide bisphosphate alphaKdo-(2-8)-alphaKdo-(2-4)-alphaKdo-(2-6)-betaGlcN-4P-(1-6)-alphaGlcN-1P (Kdo is 3-deoxy-alpha-d-manno-oct-2-ulosonic acid) as reported for C. trachomatis serotype L2[Rund, S., Lindner, B., Brade, H. and Holst, O. (1999) J. Biol. Chem. 274, 16819-16824]. The glucosamine disaccharide backbone is substituted with a complex mixture of fatty acids with ester or amide linkage whereby no ester-linked hydroxy fatty acids were found. The LPS was purified carefully (with contaminations by protein or nucleic acids below 0.3%) and tested for its ability to induce proinflammatory cytokines in several readout systems in comparison to LPS from C. trachomatis serotype L2 and Chlamydophila psittaci strain 6BC as well as enterobacterial smooth and rough LPS and synthetic hexaacyl lipid A. The chlamydial LPS were at least 10 times less active than typical endotoxins; specificity of the activities was confirmed by inhibition with the LPS antagonist, B1233, or with monoclonal antibodies against chlamydial LPS. Like other LPS, the chlamydial LPS used toll-like receptor TLR4 for signalling, but unlike other LPS activation was strictly CD14-dependent.

Follicular conjunctivitis caused by Chlamydia trachomatis in an infant Saharan population: molecular and clinical diagnosis

AIMS

To ascertain the prevalence of acute trachoma as a supposed endemic disease among infants in the Saharan refugee camps of Tindouf (Algeria) and to evaluate the efficacy of treatment with a single dose of azithromycin.

METHODS

527 children aged between 3 and 17 were evaluated in the camp schools in October 2001. All the children were clinically and microbiologically examined, including slit lamp checks of anterior segment and two conjunctival swabs, one for the detection of membrane lipopolysaccharide by quick immunoassay test Clearview Chlamydia MF and the other for the detection of specific DNA by chlamydia plasmid specific polymerase chain reaction (PCR) assay. After examination, a single dose of azithromycin was administered to each child. One month later samples from positive children and 12 random negative children by the first PCR were taken to perform a new PCR assay.

RESULTS

Chlamydia trachomatis was suspected in 2.47% of the children, papillary hypertrophy being the most frequently seen clinical sign. Scarring changes secondary to trachoma were detected in 11.7% of the children. Only four cases (0.8%) were positive to the immunoassay test and 12 cases (2.27%) were positive by PCR. After treatment a second PCR was performed on positive children and they were negative of chlamydia DNA amplification. However, one child who was negative and received the treatment was positive in the second PCR assay.

CONCLUSION

Acute trachoma prevalence is much lower than expected among infants in this Saharan population. The possible reasons could be the recent improvements in hygiene and health care. Cicatricial trachoma is more frequent. The Clearview immunoassay test has very low sensitivity in the detection of this disease. A single dose of azithromycin is sufficient to treat chlamydial conjunctivitis. However, a programme of improvement in hygiene and health care is necessary to prevent re-infection.

Bacterial lipopolysaccharides and innate immunity

Bacterial lipopolysaccharides (LPS) are the major outer surface membrane components present in almost all Gram-negative bacteria and act as extremely strong stimulators of innate or natural immunity in diverse eukaryotic species ranging from insects to humans. LPS consist of a poly- or oligosaccharide region that is anchored in the outer bacterial membrane by a specific carbohydrate lipid moiety termed lipid A. The lipid A component is the primary immunostimulatory centre of LPS. With respect to immunoactivation in mammalian systems, the classical group of strongly agonistic (highly endotoxic) forms of LPS has been shown to be comprised of a rather similar set of lipid A types. In addition, several natural or derivatised lipid A structures have been identified that display comparatively low or even no immunostimulation for a given mammalian species. Some members of the latter more heterogeneous group are capable of antagonizing the effects of strongly stimulatory LPS/lipid A forms. Agonistic forms of LPS or lipid A trigger numerous physiological immunostimulatory effects in mammalian organisms, but--in higher doses--can also lead to pathological reactions such as the induction of septic shock. Cells of the myeloid lineage have been shown to be the primary cellular sensors for LPS in the mammalian immune system. During the past decade, enormous progress has been obtained in the elucidation of the central LPS/lipid A recognition and signaling system in mammalian phagocytes. According to the current model, the specific cellular recognition of agonistic LPS/lipid A is initialized by the combined extracellular actions of LPS binding protein (LBP), the membrane-bound or soluble forms of CD14 and the newly identified Toll-like receptor 4 (TLR4)*MD-2 complex, leading to the rapid activation of an intracellular signaling network that is highly homologous to the signaling systems of IL-1 and IL-18. The elucidation of structure-activity correlations in LPS and lipid A has not only contributed to a molecular understanding of both immunostimulatory and toxic septic processes, but has also re-animated the development of new pharmacological and immunostimulatory strategies for the prevention and therapy of infectious and malignant diseases.

Cross-reaction between the genus-specific lipopolysaccharide antigen of Chlamydia spp. and the lipopolysaccharides of Porphyromonas gingivalis, Escherichia coli O119 and Salmonella newington: implications for diagnosis

Seven hybridoma clones, secreting monoclonal antibodies (MAbs) against the genus-specific chlamydial lipopolysaccharide (LPS) antigen were obtained after immunization of BALB/c mice with formalin killed Chlamydia psittaci. The antigen-binding properties of the MAbs were characterized in different immunologic reactions with purified chlamydial elementary bodies and LPS antigens from S- and R-forms of Gram-negative bacteria. Four MAbs reacted with the heterologous LPS antigens of Salmonella R-mutants, Escherichia coli Re chemotype and Acinetobacter calcoaceticus. Two MAbs demonstrated in addition a significant reactivity with Porphyromonas gingivalis, E. coli O119 and Salmonella newington LPS in ELISA, dot-ELISA and passive hemolysis assay (for clone 204G9). One MAb cross-reacted only with Salmonella minnesota Re LPS in ELISA. In indirect immunofluorescent assay six MAbs produced bright green fluorescence with all tested chlamydial strains and five of them reacted with the Re and Rb2 chemotypes of S. minnesota. The results demonstrate a wide cross-reactivity of the produced MAbs with LPS antigens of various Gram-negative bacteria, posing the question for careful consideration and interpretation of serology results for Chlamydia spp.

The significance of Chlamydia pneumoniae in symptomatic carotid stenosis

An association between symptomatic carotid stenosis and recent infection with Chlamydia pneumoniae is reported. Thirty-five patients (20 symptomatic and 15 asymptomatic) with carotid stenosis of 70% to 90% underwent carotid endarterectomy. Endarterectomy was performed without patch and shunt; the average occlusion time of the internal carotid artery was 14 +/- 3 min. The atheromatic plaque and a portion of the thyroid artery were examined with polymerase chain reaction and peripheral vein blood was obtained for serologic detection of systematic infection, and IgG and IgM antibodies to C. pneumoniae by enzyme-linked immunosorbent assay. Twenty of 35 patients (57.1%) had increased titers of IgG antibodies to C. pneumoniae. Eight patients revealed IgG plus IgM antibodies; two of the eight had IgG, IgM, and positive findings on polymerase chain reaction. No C. pneumoniae was detected on the thyroid arteries. Sixty-five percent (13/20) of the patients with increased IgG antibodies to C. pneumoniae, 87.5% (7/8) with IgG + IgM, and 100% with IgG + IgM + positive polymerase chain reaction were symptomatic. Plaque morphology in association with symptoms did not reveal a significant correlation between soft plaques and symptoms, whereas the majority of the symptomatic patients had plaques of type III-V. Patients having recent contamination and positive polymerase chain reaction had a significant relationship between C. pneumoniae infection and symptomatic carotid disease. This supports the hypothesis that C. pneumoniae infection can produce a kind of instability of the carotid plaque. The results of this study demonstrate that patients with advanced atherosclerotic carotid disease have an increased incidence of C. pneumoniae infection. Recent infection could be responsible for instability of the carotid plaque, causing cerebral ischemic episodes.

Standardizing Chlamydia pneumoniae assays: recommendations from the Centers for Disease Control and Prevention (USA) and the Laboratory Centre for Disease Control (Canada)

Chlamydia pneumoniae has been associated with atherosclerosis and several other chronic diseases, but reports from different laboratories are highly variable and "gold standards" are lacking, which has led to calls for more standardized approaches to diagnostic testing. Using leading researchers in the field, we reviewed the available approaches to serological testing, culture, DNA amplification, and tissue diagnostics to make specific recommendations. With regard to serological testing, only use of microimmunofluorescence is recommended, standardized definitions for "acute infection" and "past exposure" are proposed, and the use of single immunoglobulin (Ig) G titers for determining acute infection and IgA for determining chronic infection are discouraged. Confirmation of a positive culture result requires propagation of the isolate or confirmation by use of polymerase chain reaction (PCR). Four of 18 PCR assays described in published reports met the proposed validation criteria. More consistent use of control antibodies and tissues and improvement in skill at identifying staining artifacts are necessary to avoid false-positive results of immunohistochemical staining. These standards should be applied in future investigations and periodically modified as indicated.

Microbial etiology of community-acquired pneumonia in the adult population of 4 municipalities in eastern Finland

To determine the etiology of community-acquired pneumonia in the adult population of a defined area, specific antibody responses in paired serum samples, levels of circulating pneumococcal immune complexes in serum samples, and pneumococcal antigen in urine were measured. Samples (304 paired serum samples and 300 acute urine samples) were obtained from 345 patients > or =15 years old with community-acquired, radiologically confirmed pneumonia, which comprised all cases in the population of 4 municipalities in eastern Finland during 1 year. Specific infecting organisms were identified in 183 patients (including 49 with mixed infection), as follows: Streptococcus pneumoniae, 125 patients; Haemophilus influenzae, 12; Moraxella catarrhalis, 8; chlamydiae, 37 (of which, Chlamydia pneumoniae, 30); Mycoplasma pneumoniae, 30; and virus species, 27. The proportion of patients with pneumococcal infections increased and of those with Mycoplasma infections decreased with age, but for each age group, the etiologic profile was similar among inpatients and among outpatients. S. pneumoniae was the most important etiologic agent. The annual incidence of pneumococcal pneumonia per 1000 inhabitants aged > or =60 years was 8.0.

Epidemiologic association of Chlamydia pneumoniae and atherosclerosis: the initial serologic observation and more

About 70% of persons with acute myocardial infarction (AMI) show a seroresponse to a chlamydial lipopolysaccharide (LPS) epitope. Elevated titers against Chlamydia pneumoniae in sera from such patients point to an exacerbation in a chronic infection as does a change in the nature of immune complexes containing chlamydial LPS. The presence of antibodies to C. pneumoniae proteins in immune complexes suggests an intimate association of the pathogen with the vascular system. In the first prospective study, elevated antibody titers or immune complexes containing chlamydial LPS were an independent significant risk factor (odds ratio, </=2.6) for AMI 3-6 months before the cardiac incident. The majority of later seroepidemiologic studies have verified the association. However, since serologic markers for C. pneumoniae infection also seem to be associated with uncomplicated atherosclerosis and other chronic conditions, their predictive value for cardiac events is small.

Vaccination against infections by Chlamydia pneumoniae

Chlamydia pneumoniae is an intracellularly growing bacterium that causes respiratory infections and is strongly associated with atherosclerosis. Antibodies against C. pneumoniae are frequently encountered in the adult population, indicating past exposure to the micro-organism. Immunity to reinfection is, however, only partial and does not prevent development of sequelae. Infections caused by and associated with C. pneumoniae are a major cause of morbidity and mortality world wide. Development of a vaccine capable of protecting against infections due to C. pneumoniae and their sequelae would prevent up to 10% of community-acquired pneumonias in adults and add a new dimension to the prevention of atherosclerosis and coronary heart disease.

Chlamydial lipopolysaccharide

Chlamydiae are obligatory intracellular parasites which are responsible for various acute and chronic diseases in animals and humans. The outer membrane of the chlamydial cell wall contains a truncated lipopolysaccharide (LPS) antigen, which harbors a group-specific epitope being composed of a trisaccharide of 3-deoxy-D-manno-oct-2-ulosonic (Kdo) residues of the sequence alpha-Kdo-(2-->8)-alpha-Kdo-(2-->4)-alpha-Kdo. The chemical structure was established using LPS of recombinant Escherichia coli and Salmonella enterica strains after transformation with a plasmid carrying the gene encoding the multifunctional chlamydial Kdo transferase. Oligosaccharides containing the Kdo region attached to the glucosamine backbone of the lipid A domain have been isolated or prepared by chemical synthesis, converted into neoglycoproteins and their antigenic properties with respect to the definition of cross-reactive and chlamydia-specific epitopes have been determined. The low endotoxic activity of chlamydial LPS is related to the unique structural features of the lipid A, which is highly hydrophobic due to the presence of unusual, long-chain fatty acids.

Structural analysis of the lipopolysaccharide from Chlamydia trachomatis serotype L2

The lipopolysaccharide (LPS) of Chlamydia trachomatis L2 was isolated from tissue culture-grown elementary bodies using a modified phenol/water procedure followed by extraction with phenol/chloroform/light petroleum. From a total of 5 x 10(4) cm2 of infected monolayers, 22.3 mg of LPS were obtained. Compositional analysis indicated the presence of 3-deoxy-D-manno-oct-2-ulopyranosonic acid (Kdo), GlcN, phosphorus, and fatty acids in a molar ratio of 2.8:2:2.1:4.5. Matrix-assisted laser-desorption ionization mass spectrometry performed on the de-O-acylated LPS gave a major molecular ion peak at m/z 1781.1 corresponding to a molecule of 3 Kdo, 2 GlcN, 2 phosphates, and two 3-hydroxyeicosanoic acid residues. The structure of deacylated LPS obtained after successive treatment with hydrazine and potassium hydroxide was determined by 600 MHz NMR spectroscopy as Kdoalpha2-->8Kdoalpha2-->4Kdoalpha2-->6D-GlcpNbeta1 -->6D-GlcpNalpha 1,4'-bisphosphate. These data, together with those published recently on the acylation pattern of chlamydial lipid A (Qureshi, N., Kaltashov, I., Walker, K., Doroshenko, V., Cotter, R. J., Takayama, K, Sievert, T. R., Rice, P. A., Lin, J.-S. L., and Golenbock, D. T. (1997) J. Biol. Chem. 272, 10594-10600) allow us to present for the first time the complete structure of a major molecular species of a chlamydial LPS.

Etiology of childhood pneumonia: serologic results of a prospective, population-based study

BACKGROUND

To investigate the etiology of pediatric community-acquired pneumonia, we conducted a prospective, population-based study covering the total population <15 years of age (n = 8851) in 4 municipalities in eastern Finland.

MATERIALS AND METHODS

The number of patients was 201; chest radiographs were available for all cases and paired sera for serologic assays were available for >90% of cases. The methods included assays for antibody response to 3 pneumococcal antigens, specific pneumococcal immune complex assays and conventional antibody tests for mycoplasmal, chlamydial and viral infections.

RESULTS

Serologic evidence of specific microbial etiology was obtained in 133 (66%) of the pneumonia patients. Bacterial infection was diagnosed in 102 cases (51%) and viral infection in 51 cases (25%). Streptococcus pneumoniae was the most common agent (57 cases; 28%), followed by Mycoplasma pneumoniae (44; 22%), respiratory syncytial virus (43; 21%) and Chlamydia spp. (29; 14%). Haemophilus influenzae was identified in only 6% and Moraxella catarrhalis in only 3% of the children. More than one specific infection was found in 51 patients (25%). The proportion of pneumococcal cases varied from 24 to 36% by age. Mycoplasma infections were seen mostly in patients > or =5 years and Chlamydia infections in patients > or =10 years of age.

CONCLUSIONS

The results of our prospective, strictly population-based study confirm the importance of S. pneumoniae in the etiology of community-acquired pneumonia in children of all ages. M. pneumoniae and Chlamydia pneumoniae are important from the age of 5 years onwards.

Infectious causes of chronic inflammatory diseases and cancer

Powerful diagnostic technology, plus the realization that organisms of otherwise unimpressive virulence can produce slowly progressive chronic disease with a wide spectrum of clinical manifestations and disease outcomes, has resulted in the discovery of new infectious agents and new concepts of infectious diseases. The demonstration that final outcome of infection is as much determined by the genetic background of the patient as by the genetic makeup of the infecting agent is indicating that a number of chronic diseases of unknown etiology are caused by one or more infectious agents. One well-known example is the discovery that stomach ulcers are due to Helicobacter pylori. Mycoplasmas may cause chronic lung disease in newborns and chronic asthma in adults, and Chlamydia pneumoniae, a recently identified common cause of acute respiratory infection, has been associated with atherosclerosis. A number of infectious agents that cause or contribute to neoplastic diseases in humans have been documented in the past 6 years. The association and causal role of infectious agents in chronic inflammatory diseases and cancer have major implications for public health, treatment, and prevention.

Serological diagnosis of chlamydial abortion in sheep and goats: comparison of the complement fixation test and an enzyme-linked immunosorbent assay employing solubilised proteins as antigen

A new ELISA for antibodies against chlamydial abortion of ewes which uses detergent solubilised proteins (dsp) of Chlamydia psittaci as antigen (Anderson, I.E., Herring, A.J., Jones, G.E., Low, J.C., Greig, A., 1995. Development and evaluation of an indirect ELISA to detect antibodies to abortion strains of Chlamydia psittaci in sheep sera. Vet. Microbiol., 43, pp. 1-12] was compared with the complement fixation test (CFT) in screening 1000 ovine and caprine sera obtained from selected flocks/herds ('flocks') and submitted to a veterinary diagnostic laboratory. Fifteen of the 17 'flocks' had a history of abortion while the remaining two did not and were classified as 'negative flocks'. Infection with Chlamydia was confirmed during the study period in five 'flocks' using direct immunofluorescence and the modified Ziehl Neelsen stain on pathological material. The dspELISA and CFT identified 37 and 45 positive sera on 158 samples tested from these 'flocks'. Chlamydia antibodies were not detected in one of the two negative flocks, in two other flocks where the cause of abortion was undetermined and in three flocks in which the causes of abortion were diagnosed as Listeriosis and/or Salmonellosis. One of the 'negative flocks' yielded two positive reactors by CFT and five by dspELISA, suggesting infection with a cross-reactive subtype of C. pecorum. Of the five 'flocks' in which a definitive diagnosis from pathological material was not possible, four were positive by both serological tests, suggesting that the abortions were due to Chlamydia. The fifth flock, though negative by dspELISA and marginally positive in two samples by CFT, had experienced confirmed chlamydial abortions in previous lambing seasons, but culling and tetracycline treatment have prevented further abortions in the study period. Overall, the proportions of samples positive by CFT and dspELISA were similar (9.1% and 8.8%). These studies confirmed the value of the dspELISA as a screening test for chlamydial abortion. Furthermore, the dspELISA compared to the CFT is easier to perform, does not require reagent titration at each testing and uses automated assessment of results.

Characterization of serum antibody response to chlamydiae in patients with sexually acquired reactive arthritis

Sera from patients with sexually acquired reactive arthritis (SARA) with antibodies reacting with C. trachomatis and C. pneumoniae (group 1; n = 20) and also with C. psittaci (group 2; n = 19) were analyzed for antibody specificity. Sera from group 2 reacted significantly more often with C. trachomatis serotype E, H and K and had higher antibody titers to serotype E, as tested by microimmunofluorescence tests. Cross-reactivities occurring in microimmunofluorescence tests were related to the presence of antichlamydial lipopolysaccharide antibodies, adsorption of which by recombinant lipopolysaccharide removed microimmunofluorescence reactivity with C. psittaci antigen. In group 2, significantly more sera had antibodies to C. pneumoniae, remaining after lipopolysaccharide adsorption, as proved by adsorption with viable C. trachomatis and C. pneumoniae organisms. None of the sera had antibodies to Yersinia enterocolitica, Shigella flexneri, Sh. sonnei and Salmonella spp. It was observed that the frequency and titer of cross-reacting antibodies to chlamydial serotypes and species were related to the time period between the diagnosis of genital chlamydial infection and of SARA. Cross-reactivities were also related to the presence of lipopolysaccharide, but not heat shock protein 60- or neutralizing antibodies to chlamydiae. Antibody reactivity induced by antichlamydial lipopolysaccharide antibodies can be removed by lipopolysaccharide adsorption.

Chlamydia pneumoniae infection induces inflammatory changes in the aortas of rabbits

Chlamydia pneumoniae, a common human respiratory pathogen, has been associated with atherosclerosis in several seroepidemiological studies. Moreover, its presence in lesions of vessel walls has been demonstrated by culture, immunohistochemistry, PCR, and electron microscopy. In this study, we infected intranasally with C. pneumoniae New Zealand White rabbits which had been fed a normal diet. Reinfection was given 3 weeks later. Six of the nine reinfected animals showed inflammatory changes consisting of intimal thickening or fibroid plaques resembling atherosclerosis in 2 to 4 weeks after reinfection. One rabbit had calcified lesions. Immunohistochemistry for C. pneumoniae was strongly positive in the three older affected animals. No lesions were seen in the controls. The results suggest that C. pneumoniae infection is capable of inducing inflammatory atherosclerosis-like changes in the aortas of infected rabbits.

Association of chlamydial infection with cerebrovascular disease

BACKGROUND AND PURPOSE

Recent studies suggest an association of coronary heart disease and carotid atherosclerosis with Chlamydia pneumoniae infection. We investigated the frequency of chlamydial seropositivity and specific circulating immune complexes in patients with recent cerebrovascular disease.

METHODS

Specific antibodies to C pneumoniae in serum were measured by the microimmunofluorescence test in 58 consecutive patients (aged 18 to 50 years) with ischemic infarction (n = 39) or transient ischemic attacks (n = 19) and in 52 hospital control subjects without vascular disease, matched for sex, age, time, and locality.

RESULTS

Twenty-seven patients (46.6%) and 12 control subjects (23.1%) had raised IgA titers > or = 1:16 (P = .018). IgG titers > or = 1:32 were measured in 74.1% of the patients and 77% of control subjects (P = .623). Specific IgG antibodies in circulating immune complexes, which were isolated by polyethylene glycol precipitation, were elevated > or = 1:8 in 24.1% of the patients and 7.7% of control subjects (P = .047). With the use of a conditional logistic regression model, the odds ratios were 1.70 (95% confidence interval [CI], 1.13 to 2.58) for elevated IgA titers, 1.91 (95% CI, 1.06 to 3.47) for the presence of immune complexes, and 1.96 (95% CI, 1.00 to 3.82) for the presence of both factors. After adjustment for the vascular risk factors hypertension, age, sex, and migraine, the odds ratios were 1.71 (95% CI, 1.08 to 2.70), 2.00 (95% CI, 1.07 to 3.76), and 2.20 (95% CI, 1.09 to 4.41), respectively.

CONCLUSIONS

We conclude that chronic infection with C pneumoniae is associated with an increased risk of stroke and transient ischemic events.

Relative bradycardia in infectious diseases

Relative bradycardia in infectious diseases is a poorly defined term. No exact and useful definition exists and the underlying mechanisms are unknown. Despite this, the term is often used in the literature and in clinical practice both as a clinical sign for an individual patient and as a characteristic feature of certain specific diseases. In this study a definition of relative bradycardia as a clinical sign in an individual patient and a definition of relative bradycardia as a characteristic feature of a specific disease were established based on a reference population comprising 673 patients with various infectious diseases. Relative bradycardia as a clinical sign in an individual patient held no predictive value regarding the likely type of infection. Relative bradycardia as a characteristic feature of specific disease was found for typhoid fever (P = 0.003), Legionnaire's disease (P = 0.005), and pneumonia caused by Chlamydia sp. (P = 0.0005), but not for mycoplasma pneumonia. It was not found for other pulmonary infections, infections caused by other Salmonella sp., other extracellular Gram-negative infections, or viral infections. Thus, relative bradycardia as a clinical sign has no predictive value for obtaining a tentative diagnosis, but relative bradycardia as a feature of specific disease is seen in typhoid fever, Legionnaire's disease, and pneumonia caused by Chlamydia sp. It seems that relative bradycardia as a feature of specific disease only occurs in diseases caused by organisms that are both Gram-negative and intracellular.

Serological response to Chlamydia pneumoniae in patients with sarcoidosis

The antigen-specific serological response to Chlamydia pneumoniae was studied in 24 patients with sarcoidosis and compared to that seen in acute C. pneumoniae respiratory infection. By the micro-immunofluorescence test, five sarcoidosis patients had acute antibody, 15 had chronic antibody and four had no antibody against C. pneumoniae. By enzyme immunoassay, 20 sarcoidosis patients had antibody against ReLPS but that cross-reacts with chlamydial LPS. Immunoblot analysis of sera using purified C. pneumoniae elementary bodies showed that recognition of the 40 kDa C. pneumoniae major outer membrane protein was rare (20%). Reactivities with proteins with Mw of 42 K (70%), 60 K (65%), 98 K (55%) and 52 K (50%) were often noted. To study reactivity of chlamydial HSP 60 in sarcoidosis sera, sarkosyl-soluble (contains the 60 kDa HSP) and sarkosyl-insoluble (contains the 60 kDa structural protein) fractions of C. pneumoniae elementary bodies were prepared. The 60 kDa structural protein was recognized with equal frequency by sera from patients with sarcoidosis and acute respiratory infection, while the HSP 60 was more frequently recognized by sera with acute respiratory infection than sarcoidosis. Recombinant fusion proteins expressed from pGEX-2T containing overlapping DNA fragments of the C. pneumoniae 60 kDa HSP gene were purified. Different recognition patterns were identified for sera from sarcoidosis patients and from patients with acute C. pneumoniae respiratory infection.

Chlamydia psittaci infections: a review with emphasis on avian chlamydiosis

In the first part of this article the general characteristics of Chlamydia psittaci namely the history, taxonomy, morphology, reproductive cycle, metabolism and genetics are reviewed. For the taxonomy in particular, a considerable amount of new information has become available in recent years, following the application of monoclonal antibodies and restriction enzymes. Using these techniques isolates of Chlamydia psittaci from birds have been subdivided in different serovars, a number of isolates have been classified in a new species (Chlamydia pecorum) and isolates from animals have been classified as Chlamydia trachomatis. In the second part of the article, the current knowledge on avian chlamydiosis is summarized. Emphasis is put on clinical signs, lesions, pathogenesis, epizootiology, immunity, diagnosis, prevention and treatment. Also the public health considerations are reviewed. It is concluded that the diagnosis of avian chlamydiosis is laborious and that there is still a need for more accurate, simple and rapid diagnostic tools, both for antigen and antibody detection in various species of birds.

Reiter's syndrome and reactive arthritis: a current view

This paper reviews advances in the understanding of the pathogenesis of reactive arthritis that have occurred over the last decade. Inflammatory aseptic joint disease has been linked with prior infection initiated by many different species of microorganisms. The presence of intra-articular bacterial antigens has now been firmly established with the demonstration of bacteria, bacterial fragments, DNA, RNA, and bacterial lipopolysaccharide in joints of patients with reactive arthritis. Chlamydia trachomatis, Salmonella enteritidis, and Shigella flexneri have all been detected in the joint by immunological techniques, although there is still some doubt as to the form in which they reach the joint and whether or not they persist. A number of phlogistic bacterial components could be acting as arthritogens. Negative joint culture results from patients with reactive arthritis make it unlikely that bacteria in the joint are viable, although chlamydial DNA has been shown in the joints of patients with sexually acquired reactive arthritis using the polymerase chain reaction. The use of antimicrobial therapy in the treatment of reactive arthritis is under review; data suggests that long-term antibiotic treatment warrants further study. The role of HLA-B27 in disease pathogenesis is discussed as are possible mechanisms of interplay between germ and gene. HLA-B27 might confer disease susceptibility by affecting immune mechanisms other than classical antigen presentation. The immunopathogenesis of joint inflammation in reactive arthritis is explored with reference to studies of humoral and cellular immune responses. Serological evidence to support the concept of molecular mimicry is far from conclusive; the results of relevant studies are summarized. Lymphocyte proliferation experiments suggest that antigen presenting cells play an important role. Finally, our views on reactive arthritis in the 1990s, and areas of new and potentially fruitful future research are presented.

The LPS localization might explain the lack of protection of LPS-specific antibodies in abortion-causing Chlamydia psittaci infections

Four monoclonal antibodies against chlamydial lipopolysaccharide (LPS) were used to study their localization and distribution in the Chlamydia psittaci AB7 abortion-causing strain by immunoelectron microscopy. A non-embedding technique on whole chlamydiae, together with a post-embedding technique on McCoy cells infected with the strain, were performed. Immunogold labelling was observed on the surface of reticular bodies (RB), but not on elementary bodies (EB). Immunolabelling was observed in ultrathin sections on both sides of the external chlamydial membrane, mainly on the inner side of EB and on the outer side of RB. Immunogold density was higher in EB than in RB; however, the absolute number of gold particles was higher in RB than EB, suggesting a loss of immunolabelling during the transformation of RB into EB. Specific labelling of LPS was also found in electrodense and adielectronic vacuoles near the surface of the cytoplasmic membrane of infected McCoy cells. These results suggest that the lack of protection against some chlamydial strains, despite the presence of anti-LPS specific antibodies, is due to the localization of LPS on the inner side of the external membrane of EB.

Lipopolysaccharide smooth-rough phase variation in bacteria of the genus Chlamydia

In two strains of Chlamydia psittaci and in Chlamydia trachomatis serotype L1, we have detected a so-far-unknown antigen which (i) is resistant to heat and proteolytic digestion, (ii) can be extracted with phenol-water into the water phase, (iii) gives a ladder-like banding pattern in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, (iv) is immunogenic in rabbits and mice, and (v) contains immunoreactivity of lipid A, a common and characteristic component of gram-negative lipopolysaccharides (LPS). Thus, chlamydiae contain, in addition to the known rough-type LPS, another LPS type which is phenotypically smooth (S-LPS). S-LPS was observed preferentially in chlamydiae grown in the yolk sac of embryonated eggs; it was, however, also detected by immunofluorescence in tissue culture-grown chlamydiae with a monoclonal antibody against S-LPS.

Preparation and structural analysis of oligosaccharide monophosphates obtained from the lipopolysaccharide of recombinant strains of Salmonella minnesota and Escherichia coli expressing the genus-specific epitope of Chlamydia lipopolysaccharide

The lipopolysaccharide of the recombinant strain Salmonella minnesota r595-207 expressing the genus-specific epitope of Chlamydia lipopolysaccharide [Holst, O., Brade, L., Kosma, P. and Brade, H. (1991) J. Bacteriol, 173, 1862-1866] was sequentially de-O- and de-N-acylated by mild hydrazinolysis and treatment with 4 M KOH, respectively. The resulting mixture of compounds was separated by high-performance anion-exchange chromatography and gel-permeation chromatography, yielding four oligosaccharide phosphates two of which were readily identified by their 1H-NMR- and 13C-NMR spectra as alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcpN-(1-6)-alpha-D-Glcp N 1,4'-bisphosphate (tetrasaccharide bisphosphate; Kdo = 3-deoxy-D-manno-octulopyranosonic acid) and alpha-Kdo-(2-8)-alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcpN-(1-6) -alpha-D- GlcpN 1,4'-bisphosphate (pentasaccharide bisphosphate) [Holst, O., Broer, W., Thomas-Oates, J.E., Mamat, U. and Brade, H. (1993) Eur. J. Biochem. 214, 703-710]. The structures of the other two compounds were established by chemical analysis, NMR spectroscopy, and fast-atom-bombardment mass spectrometry as alpha-Kdo- (2-4)-alpha-Kdo-(2-6)-beta-D-GlcpN-(1-6)-alpha-D-GlcpN 1-phosphate (tetrasaccharide 1-phosphate) and alpha-Kdo-(2-8)-alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcpN-(1-6) -alpha-D- GlcpN 1-phosphate (pentasaccharide 1-phosphate). alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcpN-(1-6)-alpha/beta- D-GlcpN 4'-phosphate (tetrasaccharide 4'-phosphate) and alpha-Kdo-(2-8)-alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcpN-(1-6) -alpha/beta-D-GlcpN 4'-phosphate (pentasaccharide 4'-phosphate) were prepared from the 1,4'-bisphosphates isolated from the recombinant strain Escherichia coli F515-207 by treatment with alkaline phosphatase and purification by high-performance anion-exchange chromatography and gel-permeation chromatography. Their structures were characterised by chemical analysis, NMR spectroscopy, and fast-bombardment mass spectrometry.

Occurrence of antibodies against chlamydial lipopolysaccharide in human sera as measured by ELISA using an artificial glycoconjugate antigen

An artificial glycoconjugate containing, as a ligand, the deacylated carbohydrate backbone of a recombinant Chlamydia-specific lipopolysaccharide was used as a solid-phase antigen in ELISA to measure antibodies against chlamydial LPS. The specificity and reproducibility of the assay was shown by using a panel of prototype monoclonal antibodies representing the spectrum of antibodies also occurring in patient sera. These mAbs recognized Chlamydia-specific epitopes [alpha 2-->8-linked disaccharide of 3-deoxy-D-manno-octulosonic acid (Kdo) or the trisaccharide alpha Kdo-(2-->8)-alpha Kdo-(2-->4)-alpha Kdo] or those shared between chlamydial and Re-type LPS (alpha Kdo, alpha 2-->4-linked Kdo disaccharide). The assay was used to measure IgG, IgA and IgM antibodies against chlamydial LPS in patients with genital or respiratory tract infections. In comparison to the results obtained with sera from blood donors, it became evident that both types of infection result in significant changes in the profile of LPS antibodies.

Comparison of serological tests for the detection of antibodies against Chlamydia trachomatis and Chlamydia pneumoniae in rheumatological patients

In cases of reactive arthritis, a suspected Chlamydia trachomatis infection is often detected by serological methods. However, mostly tests with genus-specific antigens are used, neglecting the fact that antibodies against Chlamydia pneumoniae are highly prevalent in the adult population. Therefore we tested sera of 129 patients with various rheumatological disorders and of 18 healthy persons in parallel with a genus-specific test (IPAZYME) and with the species-specific microimmunofluorescence test for C. trachomatis and C. pneumoniae antibodies. The data showed that 55% of the 64 IPA-positive results were caused by antibodies (IgG) against Chlamydia pneumoniae, only 6% by anti-Chlamydia trachomatis IgG and 20% by both specificities. For IgA antibodies, the percentages were 44%, 12.5% and 12.5% respectively. In 12 IPA-positive cases, the MIF showed no reaction. 58% of all 147 sera tested with MIF had IgG antibodies against C. pneumoniae, 5% had anti-C. trachomatis IgG and 8% IgG against both species. The percentages for IgA were 29%, 2% and 2%, respectively. IgM positivity in MIF disappeared after absorption with rheumatoid factor absorbent. No significant differences were found between the various groups of patients. The data suggest that due to the high prevalence of anti-C. pneumoniae antibody, genus-species tests cannot be used as screening tests for the serological diagnosis of C. trachomatis infections.

Evaluation of serological methods in the diagnosis of Chlamydia pneumoniae pneumonia during an epidemic in Finland

A complement fixation (CF) test, a micro-immunofluorescence (micro-IF) test and an enzyme immunoassay (EIA) using Re-lipopolysaccharide as antigen were compared in the diagnosis of chlamydial infection in 136 mainly elderly patients hospitalized with community-acquired pneumonia during a Chlamydia pneumoniae epidemic in Finland in 1986-1987. Chlamydial pneumonia was diagnosed in 58 (42.6%) of the 136 pneumonia patients; 44 (75.9%) of them could be shown by micro-IF to be caused by Chlamydia pneumoniae, three by Chlamydia psittaci and four by Chlamydia spp. Only 5 (11.4%) of 44 patients with Chlamydia pneumoniae pneumonia were IgM-positive, indicating that the majority of cases were reinfections. In this population of mainly elderly patients the CF test was insensitive, being positive in only 6 (10.3%) of 58 cases of chlamydial pneumonia. The EIA detected 72.4% of cases and micro-IF 87.9% of cases (including infections with Chlamydia pneumoniae, Chlamydia psittaci and Chlamydia spp.). In the EIA 77% of positive cases were positive in serum samples taken a week apart, whereas the corresponding figure for micro-IF was 50%. In micro-IF the measurement of IgA antibody levels is recommended and IgM-positive sera should be retested after removal of IgG antibody to avoid false-positive findings due to presence of rheumatoid factor. The collection of a third serum sample, for instance one month after onset, is also recommended, since half of the patients showed a diagnostic response in the micro-IF only in the sera taken one month apart.

Typing Chlamydia psittaci--a review of methods and recent findings

When the present chlamydial classification was established it was recognized that a wide variety of types were contained within the arbitrary designation Chlamydia psittaci. Early workers relied mostly on observations of growth characteristics to differentiate the types of C. psittaci isolated from a wide range of different hosts. The differences between isolates were confirmed serologically using a variety of tests of which the most sensitive was the micro-immunofluorescence (MIF) test which was able to recognize nine immunotypes among the mammalian isolates alone. This approach has recently been improved by the use of monoclonal antibodies in the MIF test which has confirmed most of the mammalian immunotypes and divided the avian strains into four groups. Studies on the nucleic acid of C. psittaci isolates show clear differences in the size distribution of DNA fragments produced by restriction endonuclease digestion of the genomes of the various types. Most importantly, studies of DNA/DNA homologies showed that at least four of the types identified by biological, serological and restriction endonuclease tests were sufficiently different to be considered separate species. Most recently, attention has been focused on DNA sequence comparisons of C. psittaci genes amplified by the polymerase chain reaction (PCR). The usual target has been the major outer membrane protein gene for which much sequence information is now available. The combination of PCR and MIF with monoclonals has provided a set of practical techniques with which all chlamydial isolates can be detected and typed with relative ease. It is likely that these developments will lead to the reclassification of the genus and, hopefully, a rapid increase of our understanding of the diseases caused by C. psittaci.

Structural analysis of two oligosaccharide bisphosphates isolated from the lipopolysaccharide of a recombinant strain of Escherichia coli F515 (Re chemotype) expressing the genus-specific epitope of Chlamydia lipopolysaccharide

The lipopolysaccharide of the recombinant strain Escherichia coli F515-207, expressing the genus-specific epitope of Chlamydia lipopolysaccharide, was sequentially de-O- and de-N-acylated by mild hydrazinolysis and treatment with 4 M KOH, respectively, yielding two oligosaccharide bisphosphates which were isolated by high-performance anion-exchange chromatography and gel-permeation chromatography. Their structures were determined by chemical analysis, NMR spectroscopy, and mass spectrometry as alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcN-(1-6)-alpha-D-GlcN 1,4'-P2 (tetrasaccharide bisphosphate) and alpha-Kdo-(2-8)-alpha-Kdo-(2-4)-alpha-Kdo-(2-6)-beta-D-GlcN-(1-6)-alpha- D-GlcN 1,4'-P2 (pentasaccharide bisphosphate).

Purification of Chlamydia psittaci antigen by affinity chromatography on polymyxin B agarose for use in the enzyme-linked immunosorbent assay (ELISA)

The purification of cell wall antigens of Chlamydia psittaci by affinity chromatography on polymyxin B agarose is described. Chlamydial cell wall antigens were prepared using different methods: heat treatment, ultrasonication and sodium deoxycholate treatment. The antigens were subsequently purified by gel chromatography. The highest amount of cell wall antigens was obtained by heat treatment of the chlamydiae at 90 degrees C and pH 8.5. The purified antigens showed molecular weights of 450 kDa to 700 kDa. Treatment of heat-extracted antigens with trypsin, pronase E or proteinase K did not destroy antigenic activity or alter the molecular weight. On the other hand, potassium metaperiodate treatment led to a significant decrease of both. Chlamydial cell wall antigens extracted by heat treatment and purified by affinity chromatography were used as ELISA-antigen. Using this ELISA and the complement fixation test (CFT), a total of 576 bovine sera was tested. 92 of these sera reacted positively in the ELISA and only 13 in the CFT. In addition, the prepared ELISA was compared with a commercial ELISA. 12 out of 15 sera tested were positive when using the ELISA described and 10 were positive when using the commercial ELISA.

Establishment of a particle-counting method for purified elementary bodies of chlamydiae and evaluation of sensitivities of the IDEIA Chlamydia kit and DNA probe by using the purified elementary bodies

To evaluate the sensitivity of commercially available test kits for detection of chlamydiae, we established a method of purifying Chlamydia trachomatis and Chlamydia pneumoniae elementary bodies (EBs). We then subjected the purified EBs, together with the purified EBs of Chlamydia psittaci, to the IDEIA Chlamydia (IDEIA) and DNA probe test kits to determine the EB numbers at the detection limits. The sensitivities of the test kits were thus compared. The results can be summarized as follows. (i) Intact EBs in the purified preparations were present at 100, 96.3, and 97% for the C. psittaci Cal 10, C. trachomatis L2/434/Bu (L2), and C. pneumoniae TW-183 strains, respectively. The preparations of the L2 and TW-183 EBs contained a few EB envelopes, which reacted with antilipopolysaccharide monoclonal antibodies, as did the intact EBs, indicating that elimination of EB envelopes is not required for testing of the IDEIA kit's sensitivity. (ii) We established a method of counting intact EBs and EB envelopes under a scanning electron microscope after sedimentation of EBs on a coverslip by centrifugation. (iii) The EB numbers per assay at the cutoff level, which is set up in the IDEIA kit, were 9.6 x 10(2), 6.5 x 10(3), and 2.5 x 10(4) for the L2, TW-183, and Cal 10 strains, respectively. When the same EB preparations were applied to the DNA probe kit, the EB number at the cutoff level was 7.5 x 10(3) per assay for the L2 strain, but no reaction occurred for the Cal 10 and TW-183 strains at any EB number, indicating that the DNA probe kit is highly specific for C. trachomatis. Although the IDEIA kit designed for detection of C. trachomatis showed a sensitivity superior to that of the DNA probe, the chlamydial species was not determined by the IDEIA kit.

Staining of surface antigens of Chlamydia trachomatis L2 in tissue culture

Surface labeling of chlamydial elementary and reticulate bodies in L929 cells infected with Chlamydia trachomatis serotype L2 was monitored by using monoclonal antibodies (MAb) against the major outer membrane protein and lipopolysaccharide (LPS). Different staining and fixation procedures were used to detect these surface antigens during the developmental cycle. Anti-major outer membrane protein MAb yielded a clear staining pattern of exclusively chlamydial inclusions independent of the fixation or staining technique used. Anti-LPS MAb gave a faint staining pattern of reticulate bodies when methanol fixation was used and showed that LPS was released from chlamydiae into the host cell cytoplasm and into the surroundings of the infected host cell. However, when paraformaldehyde-glutardialdehyde fixation was used, extracellular LPS staining was not observed. The data show that chlamydial LPS is loosely bound in the bacterial outer membrane but suggest that shedding of LPS is a fixation artifact.