Investigation on the agonistic and antagonistic biological activities of synthetic Chlamydia lipid A and its use in in vitro enzymatic assays

The synthetic 1,4′-bisphosphorylated penta-acyl and tetra-acyl lipid A structures representing the major molecular species of natural chlamydial lipid A were tested for their endotoxic activities as measured by interleukin-8 release from human embryonic kidney (HEK) 293 cells expressing Toll-like receptor (TLR) 2 or TLR4. Both compounds were unable to activate HEK293 cells transiently transfected with TLR2. The penta-acyl lipid A was a weak activator of HEK293 cells expressing TLR4/MD-2/CD14 whereas tetra-acyl lipid A was inactive even at high concentrations. The weak activity of the penta-acyl lipid A could be antagonized by the tetra-acyl derivative of Escherichia coli lipid A (compound 406) or the anti-CD14 monoclonal antibody MEM-18. Both, tetra- and pentaacyl lipid A were unable to antagonize the activity of synthetic E. coli-type lipid A (compound 506) or smooth lipopolysaccharide of Salmonella enterica serovar Friedenau. Tetra- and penta-acyl lipid A served as acceptors for Kdo transferases from E. coli, Chlamydia trachomatis and Chlamydophila psittaci as shown by in vitro assays and detection of the products by thin layer chromatography and immune staining with monoclonal antibody.

Invited review: Lipopolysaccharide biosynthesis: which steps do bacteria need to survive?

A detailed knowledge of LPS biosynthesis is of the utmost importance in understanding the function of the outer membrane of Gram-negative bacteria. The regulation of LPS biosynthesis affects many more compartments of the bacterial cell than the outer membrane and thus contributes to the understanding of the physiology of Gram-negative bacteria in general, on the basis of which only mechanisms of virulence and antibiotic resistance can be studied to find new targets for antibacterial treatment. The study of LPS biosynthesis is also an excellent example to demonstrate the limitations of `genomics' and `proteomics', since secondary gene products can be studied only by the combined tools of molecular genetics, enzymology and analytical structural biochemistry. Thus, the door to the field of `glycomics' is opened.

Monoclonal antibodies against 3-deoxy-α-D-manno-oct-2-ulosonic acid (Kdo) and D-glycero-α-D-talo-oct-2-ulosonic acid (Ko)

Monoclonal antibodies (mAbs) were obtained after immunization of mice with neoglycoconjugates containing as a ligand the disaccharide Kdo(2→ 4)Ko or Ko(2→4)Kdo, representing structural elements of the core region of lipopolysaccharides (LPSs) from Acinetobacter haemolyticus and Burkholderia cepacia, respectively. One antibody, S67-9, bound with high specificity to Ko(2→ 4)Kdo-BSA showing no cross reactivity with Kdo(2→ 4)Kdo-BSA and the other antigens tested. A second mAb, S68-12, bound preferentially to Kdo(2→ 4)Ko-BSA but cross reacted with Ko(2→ 4)Kdo-BSA and Kdo(2→ 4)Kdo-BSA. A third mAb, S67-27, was found to bind Kdo monosaccharide. Although mAbs S67-9 and S68-12 did not bind to LPS of Burkholderia or Acinetobacter as expected, the mAbs will be useful tools in studying the biosynthesis of LPS containing Ko.

Glycosyltransferases involved in the biosynthesis of the inner core region of different lipopolysaccharides

The inner core of lipopolysaccharide (LPS) structures in Gram-negative bacteria is considered a highly conserved region. The sugar connecting the membrane-associated lipid A moiety with the hydrophilic saccharide moiety, 3-deoxy-alpha-d-manno-oct-2-ulosonic acid (Kdo) is present in every LPS molecule investigated but it may be partially replaced by d-glycero-alpha-d-talo-oct-2-ulosonic acid (Ko). l-Glycero-alpha-d-manno-heptose (Hep) and phosphate residues are part of most but not all LPS structures and additionally, modifications with 4-amino-4-deoxy-beta-l-arabinose (Ara4N) residues occur in some. A number of different glycosyltransferases is involved in the biosynthesis of the inner core region of different lipopolysaccharides. Here, we report the characterization of Kdo transferases, heptosyltransferases and Ara4N transferases from a variety of bacteria.

Kdo-(2 → 8)-Kdo-(2 → 4)-Kdo but not Kdo-(2 → 4)-Kdo-(2 → 4)-Kdo is an acceptor for transfer of L-glycero-α-D-manno-heptose by Escherichia coli heptosyltransferase I (WaaC)

Early steps in the biosynthesis of lipopolysaccharide (LPS) involve the transfer of 3-deoxy-α-D-manno-oct-2-ulopyranosonic acid (Kdo) to lipid A. Whereas Kdo transferases (WaaA) of Escherichia coli generate a (2 → 4)-linked Kdo disaccharide, Chlamydiae contain tri- or tetra-functional WaaA generating oligosaccharides with (2 → 8)- and (2 → 4)-linkages between Kdo. It has been suggested that the transfer of L-glycero-α-D-manno-heptose (Hep) to Kdo by an E. coli WaaC may not be possible in the presence of (2 → 8)-linked Kdo. E. coli double-mutants deficient in heptosyltransferases I (waaC) and II (waaF) and expressing waaA of Chlamydiae instead of their own, make Chlamydia-type Kdo oligosaccharides which are attached to an E. coli lipid A. Using such strains expressing waaA of Chlamydophila pneumoniae, Chlamydophila psittaci, or Chlamydia trachomatis, we have studied the effect of E. coli waaC gene expression on LPS structure. Structural analyses revealed the formation of two novel oligosaccharides Hep-(1 → 5)[Kdo-(2 → 4)]-Kdo and Hep-(1 → 5)[Kdo-(2 → 8)-Kdo-(2 → 4)]-Kdo showing that Hep is transferred in the presence of (2 → 8)-linked Kdo. Surprisingly, the transfer of Hep onto Kdo-(2 → 4)-Kdo-(2 → 4)-Kdo did not occur, despite the fact that Hep-(1 → 5)[Kdo-(2 → 4)-Kdo-(2 → 4)]-Kdo is found in nature as a partial structure of E. coli LPS. The premature end of the biosynthesis and incorporation of Hep into the LPS indicated that WaaC had access to the substrate before Kdo transfer was completed. We have observed differences between WaaA of C. trachomatis, C. pneumoniae and C. psittaci which indicate mechanistic differences between these Kdo transferases.

Field evaluation of a rapid point-of-care assay for targeting antibiotic treatment for trachoma control: a comparative study

BACKGROUND

Trachoma results from repeated episodes of conjunctival infection with Chlamydia trachomatis and is the leading infectious cause of blindness. To eliminate trachoma, control programmes use the SAFE strategy (Surgery, Antibiotics, Face cleanliness, and Environmental improvement). The A component is designed to treat C trachomatis infection, and is initiated on the basis of the prevalence of the clinical sign trachomatous inflammation-follicular (TF). Unfortunately, TF correlates poorly with C trachomatis infection. We sought to assess a newly developed point-of-care (POC) assay compared with presence of TF for guiding the use of antibiotics for trachoma control.

METHODS

We compared performance outcomes of the POC assay and presence of TF using commercial PCR as a comparator in 664 children aged 1-9 years in remote, trachoma-endemic villages in Tanzania. Signs of trachoma were graded according to the WHO simplified trachoma grading system.

FINDINGS

Of 664 participants, 128 (19%) were positive for ocular C trachomatis infection by PCR. Presence of TF had a sensitivity of 64.1% (95% CI 55.8-72.4), specificity of 80.2% (76.8-83.6), and positive predictive value of 43.6% (36.5-50.7). By contrast, the POC assay had a sensitivity of 83.6% (77.2-90.0), specificity of 99.4% (98.8-100.0), and positive predictive value of 97.3% (94.2-100.3). Interagreements and intra-agreements between four novice operators were 0.988 (0.973-1.000) and 0.950 (0.894-1.000), respectively.

INTERPRETATION

The POC assay is substantially more accurate than TF prevalence in identifying the presence or absence of infection. Additional studies should assess the use of the assay in the planning and monitoring of trachoma control activities.

Chlamydophila pneumoniae induces p44/p42 mitogen-activated protein kinase activation in human fibroblasts through Toll-like receptor 4

Chlamydophila pneumoniae, an obligately intracellular Gram-negative bacterium and a common causative agent of respiratory tract infections, has been implicated in the induction and progression of atherosclerosis and coronary artery disease. In this study, the signalling mechanism of C. pneumoniae in human fibroblasts, a prominent cell population in chronic inflammation and persistent infection, contributing to plaque formation, was investigated. C. pneumoniae elementary bodies were demonstrated to up-regulate the phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK) in human fibroblasts. The effect was independent of the chlamydial lipopolysaccharide and was likely to be mediated by a heat-labile chlamydial protein. Furthermore, an anti-Toll-like receptor 4 (TLR4) antibody was shown to abolish C. pneumoniae-induced cell activation, whereas an anti-TLR2 antibody had no effect, indicating the role of TLR4 in p44/p42 MAPK activation. Ca2+/calmodulin-dependent protein kinase inhibitor KN-62 and phosphodiesterase 4 (PDE 4) inhibitor Rolipram enhanced C. pneumoniae-induced MAPK phosphorylation and attenuated C. pneumoniae infectivity in vitro. Together the results indicate that C. pneumoniae triggers rapid TLR4-mediated p44/p42 MAPK activation in human fibroblasts and chemical enhancement of MAPK phosphorylation modulates in vitro infection at the molecular level.

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.

Chlamydia trachomatis-induced death of human spermatozoa is caused primarily by lipopolysaccharide

Elementary bodies (EBs) of Chlamydia trachomatis serovar E are more toxic to sperm than those from serovar LGV. In this study, lipopolysaccharide (LPS) was prepared from the EBs of both serovars and incubated with human spermatozoa at concentrations that matched the LPS concentration of EBs. The effects of EBs and LPS on sperm motility, viability and acrosomal status were then determined. Sperm motility was measured by computer-assisted sperm analysis and the hypo-osmotic swelling test was used to determine the proportion of dead cells. Acrosomal status was examined using a standard mAb assay. Over a 6 h incubation, LPS from both serovars resulted in a marked reduction in sperm motility (and a concomitant increase in the proportion of dead spermatozoa) in a manner similar to that seen in response to EBs of serovar E. In addition, when sperm were incubated with a range of doses of EBs and LPS, probit analysis revealed that the greater spermicidal effects of EBs from serovar E (when compared with serovar LGV) were not observed when sperm were incubated with LPS from the two serovars. This suggests that the more potent effect of EBs of serovar E cannot be explained entirely by differences in the composition of LPS. Interestingly, Escherichia coli LPS was required in doses 500 times more concentrated than chlamydial LPS in order to kill a similar proportion of sperm, suggesting that bacterial LPSs may differ in their spermicidal properties. However, that chlamydial LPS was spermicidal was demonstrated by the use of polymyxin B (a polycationic antibiotic known to neutralize LPS effects), confirming that the effects observed were primarily a result of LPS activity.

KN-62 enhances Chlamydia pneumoniae-induced p44/p42 mitogen-activated protein kinase activation in murine fibroblasts and attenuates in vitro infection

Chlamydia pneumoniae elementary bodies were demonstrated to increase the proliferation of murine fibroblast cell line L-929 and rapidly activate p44/p42 mitogen-activated protein kinase (MAPK) in a protein kinase C (PKC) and protein kinase A (PKA)-independent way. Ca(2+)/calmodulin-dependent protein kinase (CaM kinase) inhibitor KN-62 significantly enhanced C. pneumoniae-induced MAPK phosphorylation, suggesting negative control of CaM kinase pathway on the MAPK cascade. In in vitro infection assay, the upstream MAPK kinase 1/2 inhibitor U0126 increased 2.5-fold C. pneumoniae infectivity in L-929 cells, while KN-62 reduced the infection by 36%. Our findings provide insight into the molecular mechanisms of bacterium-host cell interactions and demonstrate the protective role of MAPK in murine fibroblasts, suggesting novel therapeutic approaches to the treatment and prevention of chlamydial infections.

Monoclonal antibody of IgG isotype against a cross-reactive lipopolysaccharide epitope of Chlamydia and Salmonella Re chemotype enhances infectivity in L-929 fibroblast cells

A murine monoclonal antibody (MAb) 202D7 of IgG3 isotype recognizes a lipopolysaccharide (LPS) epitope of Chlamydia spp. and cross-reacts with the Re chemotype LPS of Salmonella and Escherichia coli. The antibody exhibits strong complement activating properties and stimulates phagocytosis of Salmonella enterica serovar Minnesota Re mutant by murine macrophages. Salmonella Re mutants are non-invasive for cell monolayers but still can enter and replicate in L-929 murine fibroblast cells. The entry of bacteria within the cells increases five-fold in the presence of MAb 202D7. The antibody mediates attachment and enhances five-fold the infectivity of Chlamydia pneumoniae into L-929 cells, which suggests a possible IgG-mediated mechanism of entry and survival of the pathogen in fibroblast cells.

Comparison of eleven commercial tests for Chlamydia pneumoniae-specific immunoglobulin G in asymptomatic healthy individuals

The seroprevalence of anti-Chlamydia pneumoniae-specific immunoglobulin G (IgG) antibodies is high in the adult population. Experience is required to perform a microimmunofluorescence test (MIF), the current "gold standard" for serological diagnosis, and the assay still lacks standardization. Partially automated enzyme-linked immunosorbent assays (ELISAs) and enzyme immunoassays (EIAs), which are more standardized and for which the reading of results is less subjective, have been developed. The different commercially available serological tests differ in their sensitivities and specificities, depending primarily on the antigen used. Therefore, we evaluated 11 different tests (10 were species specific, 1 was genus specific) for IgG antibodies using serum samples of 80 apparently healthy volunteers. The interpretation of the results was based on the results of the gold standard, MIF: a sample was judged positive if it was positive by at least three of the four different MIFs. Based on this internal standard, we found that 71% of the samples were positive, while 8% were false positive by some tests. The correlations between the results of the different MIFs ranged from 83 to 99%, and the correlations between the results of the MIFs and the different ELISAs and EIAs ranged from 78 to 98%. Comparison of the IgG titers measured by MIF showed good agreement (r = 0.76 to 0.91). This analysis revealed that some ELISAs and EIAs fail to detect low IgG titers. The specificities of the species-specific tests varied from 95 to 100%, and the sensitivities varied from 58 to 100%. These results indicate that serological assays for the detection of anti-C. pneumoniae-specific IgG vary greatly in their sensitivities and specificities. MIF must still be considered the best method for the detection of IgG in apparently healthy subjects, but the sensitivities and specificities of new ELISAs approximate those of MIFs.

Chemical structure and immunoreactivity of the lipopolysaccharide of the deep rough mutant I-69 Rd-/b+ of Haemophilus influenzae

From the lipopolysaccharide of the deep rough mutant I-69 Rd--/b+ of Haemophilus influenzae two oligosaccharides were obtained after de-O-acylation and separation by high-performance anion exchange chromatography. Their chemical structures were determined by one- and two-dimensional 1H-, 13C- and 31P-NMR spectroscopy as alphaKdo-4P-(2-->6)-betaGlcN-4P-(1-->6)-alphaGlcN-1P and alphaKdo-5P-(2-->6)-betaGlcN-4P-(1-->6)-alphaGlcN-1P. The specificity of mAbs S42-21 and S42-16 specific for Kdo-4P or Kdo-5P, respectively [Rozalski, A., Brade L., Kosma P., Moxon R., Kusumoto S., & Brade H. (1997). Mol. Microbiol. 23, 569--577] was confirmed with neoglycoconjugates obtained by conjugation of the isolated oligosaccharides to BSA. In addition, a mAb S42-10-8 with unknown epitope specificity could be assigned using the neoglycoconjugates described herein. This mAb binds to an epitope composed of the bisphosphorylated glucosamine backbone of lipid A and Kdo-4P, whereby the latter determines the specificity strictly by the position of the phosphate group.

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.

Chlamydia pneumoniae in atherosclerosis

Chlamydia pneumoniae is currently the infectious agent most often associated with the inflammation found in atherosclerosis. The seroepidemiological association and the actual presence of pathogen in lesions has been confirmed in numerous studies, in which technical difficulties seem to be the only limitation. Besides animal experiments and intervention trials, we need information of possible pathogenic mechanisms. Recently, several studies have suggested mechanisms by which C. pneumoniae infection could participate in the development of atherosclerosis.

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.

A Chlamydia pneumoniae component that induces macrophage foam cell formation is chlamydial lipopolysaccharide

Chlamydia pneumoniae infection is associated with atherosclerotic heart and vessel disease, but a causal relationship between this pathogen and the disease process has not been established. Recently, it was reported that C. pneumoniae induces human macrophage foam cell formation, a key event in early atheroma development, suggesting a role for the organism in atherogenesis. This study further examines C. pneumoniae-induced foam cell formation in the murine macrophage cell line RAW-264.7. Infected RAW cells accumulated cholesteryl esters when cultured in the presence of low-density lipoprotein in a manner similar to that described for human macrophages. Exposure of C. pneumoniae elementary bodies to periodate, but not elevated temperatures, inhibited cholesteryl ester accumulation, suggesting a role for chlamydial lipopolysaccharide (cLPS) in macrophage foam cell formation. Purified cLPS was found to be sufficient to induce cholesteryl ester accumulation and foam cell formation. Furthermore, the LPS antagonist lipid X inhibited C. pneumoniae and cLPS-induced lipid uptake. These data indicate that cLPS is a C. pneumoniae component that induces macrophage foam cell formation and suggest that infected macrophages chronically exposed to cLPS may accumulate excess cholesterol to contribute to atheroma development.

Characterization of a neutralizing monoclonal antibody directed at the lipopolysaccharide of Chlamydia pneumoniae

Identification of protective epitopes is one of the first steps in the development of a subunit vaccine. One approach to accomplishing this is to identify structures or epitopes by using monoclonal antibodies (MAb) that can attenuate infectivity in vitro and in vivo. To date attempts to use this approach with Chlamydia pneumoniae have failed. This report is the first description of a MAb directed to the lipopolysaccharide (LPS) of Chlamydia that neutralizes both in vitro and in vivo the infectivity of C. pneumoniae. MAb CP-33, an immunoglobulin G2b (IgG2b), was identified from a fusion using splenocytes from mice immunized with C. pneumoniae TW-183. By Western blot analysis, MAb CP-33 exhibited genus-specific reactivity in that it recognized the LPSs of C. pneumoniae, Chlamydia trachomatis, and Chlamydia psittaci. MAb CP-33 did not react with 15 genera of gram-negative and gram-positive bacteria and Candida albicans. By using isolated LPS of Re mutants of Escherichia coli, Salmonella enterica serovar Minnesota, and recombinants expressing the 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) transferase gene kdtA of C. trachomatis, MAb CP-33 was shown to require for binding the presence of the genus-specific trisaccharide epitope alphaKdo(2-->8)alphaKdo(2-->4)alphaKdo. By employing synthetic oligosaccharides and neoglycoconjugates in an enzyme immunoassay (EIA) and EIA inhibition, it was further shown that MAb CP-33 differed from the extensively investigated prototype chlamydial LPS MAb S25-23. Most likely, MAb CP-33 recognizes a conformational epitope in which the alphaKdo(2-->8)alphaKdo(2-->4)alphaKdo trisaccharide is an essential structural component. When tested in an in vitro neutralization assay, MAb CP-33 gave a 50% neutralization titer of 8 ng/ml against C. pneumoniae TW-183. However, this MAb did not neutralize other C. pneumoniae strains, C. trachomatis, or C. psittaci. C. pneumoniae TW-183 was treated with either MAb CP-33 or a control IgG and then used to inoculate mice by the respiratory route. Five days after inoculation, there was a difference between the mice inoculated with the control IgG-treated inoculum and those inoculated with the MAb CP-33-treated organisms as to the number of mice infected as well as the number of inclusion-forming units recovered from lung cultures (P < 0.05). In summary, a Chlamydia-specific LPS MAb was able to neutralize in vitro the infectivity of C. pneumoniae TW-183.