Exploring the Impact of Ketodeoxynonulosonic Acid in Host-Pathogen Interactions Using Uptake and Surface Display by Nontypeable Haemophilus influenzae.

Surface expression of the common vertebrate sialic acid (Sia) N-acetylneuraminic acid (Neu5Ac) by commensal and pathogenic microbes appears structurally to represent "molecular mimicry" of host sialoglycans, facilitating multiple mechanisms of host immune evasion. In contrast, ketodeoxynonulosonic acid (Kdn) is a more ancestral Sia also present in prokaryotic glycoconjugates that are structurally quite distinct from vertebrate sialoglycans. We detected human antibodies against Kdn-terminated glycans, and sialoglycan microarray studies found these anti-Kdn antibodies to be directed against Kdn-sialoglycans structurally similar to those on human cell surface Neu5Ac-sialoglycans. Anti-Kdn-glycan antibodies appear during infancy in a pattern similar to those generated following incorporation of the nonhuman Sia N-glycolylneuraminic acid (Neu5Gc) onto the surface of nontypeable Haemophilus influenzae (NTHi), a human commensal and opportunistic pathogen. NTHi grown in the presence of free Kdn took up and incorporated the Sia into its lipooligosaccharide (LOS). Surface display of the Kdn within NTHi LOS blunted several virulence attributes of the pathogen, including Neu5Ac-mediated resistance to complement and whole blood killing, complement C3 deposition, IgM binding, and engagement of Siglec-9. Upper airway administration of Kdn reduced NTHi infection in human-like Cmah null (Neu5Gc-deficient) mice that express a Neu5Ac-rich sialome. We propose a mechanism for the induction of anti-Kdn antibodies in humans, suggesting that Kdn could be a natural and/or therapeutic "Trojan horse" that impairs colonization and virulence phenotypes of free Neu5Ac-assimilating human pathogens.IMPORTANCE All cells in vertebrates are coated with a dense array of glycans often capped with sugars called sialic acids. Sialic acids have many functions, including serving as a signal for recognition of "self" cells by the immune system, thereby guiding an appropriate immune response against foreign "nonself" and/or damaged cells. Several pathogenic bacteria have evolved mechanisms to cloak themselves with sialic acids and evade immune responses. Here we explore a type of sialic acid called "Kdn" (ketodeoxynonulosonic acid) that has not received much attention in the past and compare and contrast how it interacts with the immune system. Our results show potential for the use of Kdn as a natural intervention against pathogenic bacteria that take up and coat themselves with external sialic acid from the environment.

Pseudaminic Acid on Exopolysaccharide of Acinetobacter baumannii Plays a Critical Role in Phage-Assisted Preparation of Glycoconjugate Vaccine with High Antigenicity.

Pseudaminic acid (Pse) has been known for participating in crucial bacterial virulence and thus is an attractive target in the development of glycoconjugate vaccine. Particularly, this therapeutic alternative was suggested to be a potential solution against antibiotic resistant Acinetobacter baumannii that poses a serious global health threat. Also, Pse was found to be involved in the exopolysaccharide (EPS) of mild antibiotic resistant A. baumannii strain 54149 ( Ab-54149) of which specific glycosyl linkage can be depolymerized by phage ΦAB6 tailspike protein (ΦAB6TSP). In this study, we found that the antibodies induced by Ab-54149 EPS was capable of recognizing a range of EPS of other clinical A. baumannii strains, and deemed as a great potential material for vaccination. To efficiently acquire homogeneous EPS-derived oligosaccharide with significant immunogenic activity for the production of glycoconjugate, we used the ΦAB6TSP for the fragmentation of Ab-54149 EPS instead of chemical methods. Moreover, insight into the ligand binding characterization of ΦAB6TSP suggested the branched Pse on the Ab-54149 EPS served as a recognition site of ΦAB6TSP. The serum boosted by ΦAB6TSP-digested product and carrier protein CRM197 conjugate complex displayed specific sensitivity toward Ab-54149 EPS with bacterial killing activity. Strikingly, Pse is an ideal epitope with strong antigenicity, profiting the application of the probe for pathogen detection and glyco-based vaccine.

Immune response profiling of primary monocytes and oral keratinocytes to different Tannerella forsythia strains and their cell surface mutants.

The oral pathogen Tannerella forsythia possesses a unique surface (S-) layer with a complex O-glycan containing a bacterial sialic acid mimic in the form of either pseudaminic acid or legionaminic acid at its terminal position. We hypothesize that different T. forsythia strains employ these stereoisomeric sugar acids for interacting with the immune system and resident host tissues in the periodontium. Here, we show how T. forsythia strains ATCC 43037 and UB4 displaying pseudaminic acid and legionaminic acid, respectively, and selected cell surface mutants of these strains modulate the immune response in monocytes and human oral keratinocytes (HOK) using a multiplex immunoassay. When challenged with T. forsythia, monocytes secrete proinflammatory cytokines, chemokines and vascular endothelial growth factor (VEGF) with the release of interleukin-1ß (IL-1ß) and IL-7 being differentially regulated by the two T. forsythia wild-type strains. Truncation of the bacteria's O-glycan leads to significant reduction of IL-1ß and regulates macrophage inflammatory protein-1. HOK infected with T. forsythia produce IL-1Ra, chemokines and VEGF. Although the two wild-type strains elicit preferential immune responses for IL-8, both truncation of the O-glycan and deletion of the S-layer result in significantly increased release of IL-8, granulocyte-macrophage colony-stimulating factor and monocyte chemoattractant protein-1. Through immunofluorescence and confocal laser scanning microscopy of infected HOK we additionally show that T. forsythia is highly invasive and tends to localize to the perinuclear region. This indicates, that the T. forsythia S-layer and attached sugars, particularly pseudaminic acid in ATCC 43037, contribute to dampening the response of epithelial tissues to initial infection and hence play a pivotal role in orchestrating the bacterium's virulence.

Exploring the cross-reactivity of S25-2: complex with a 5,6-dehydro-Kdo disaccharide.

The near-germline antibody S25-2 exhibits a remarkable cross-reactivity for oligosaccharides containing the bacterial lipopolysaccharide carbohydrate 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo). The recent synthesis of a variety of Kdo analogues permits a detailed structural analysis of the importance of specific interactions in antigen recognition by S25-2. The Kdo disaccharide analogue Kdo-(2→4)-5,6-dehydro-Kdo lacks a 5-OH group on the second Kdo residue and has been cocrystallized with S25-2. The structure reveals that the modification of the Kdo residue at position 5 results in a rearrangement of intramolecular hydrogen bonds in the antigen that allows it to assume a novel conformation in the antibody-combining site. The cross-reactive binding of S25-2 to this synthetic ligand highlights the adaptability of this antibody to non-natural synthetic analogues.

Photodegradation of lipopolysaccharides and the inhibition of macrophage activation by anthraquinone-boronic acid hybrids.

Target-selective photodegradation of 3-deoxy-D-manno-2-octulopyranosonic acid (KDO) was achieved without additives and under neutral conditions using a designed anthraquinone-boronic acid hybrid and long wavelength UV light irradiation. The hybrid can photodegrade lipopolysaccharides (LPS) and inhibit macrophage activation induced by LPS.

Synthesis and immunomodulatory activities of Helicobacter pylori lipophilic terminus of lipopolysaccharide including lipid A.

Helicobacter pylori, a Gram-negative bacterium, causes gastroduodenal inflammatory diseases such as chronic gastritis and peptic ulcers, and is also a risk factor for gastric carcinogenesis. In this article, we review recent developments and findings in the chemical synthesis and immunomodulatory activities of H. pylori lipid A and 3-deoxy-D-manno-2-octulosonic acid (Kdo)-lipid A, to clarify the structural basis for the inflammatory response to H. pylori LPS. The synthetic methods include a new divergent synthetic approach with a widely applicable key intermediate for other types of lipid A structures, as well as a selective α-glycosylation reaction between Kdo and lipid A. Cytokine induction assays of the chemically synthesized lipid A structures showed selective cytokine induction depending on the patterns of acyl groups and phosphate groups. The results of cytokine induction assay suggested that H. pylori LPS can modulate the immune response during infection, and also plays a role in chronic inflammatory responses.

Sialoside-based pattern recognitions discriminating infections from tissue injuries.

Recognition of pathogens-associated molecular patterns (PAMPs) by Toll-like receptors (TLRs), NOD-like receptors (NLRs) and RIG-I-like receptors (RLR) plays a critical role in protecting host against pathogens. In addition, TLR and NLR also recognize danger-associated molecular patterns (DAMPs) to initiate limited innate immune responses. While innate immune response to DAMPs may be important for tissue repairs and wound healing, it is normally well controlled to avoid autoimmune destruction. Recent data support a role for sialoside-based pattern recognition by members of the Siglec family to attenuate innate immunity. In particular, since CD24-Siglec 10/G interaction selectively dampens host response to DAMPs but not PAMPs, this sialoside-based pattern recognition may serve as a foundation to discriminate PAMPs from DAMPs.

The role of CDR H3 in antibody recognition of a synthetic analog of a lipopolysaccharide antigen.

In order to explore the structural basis for adaptability in near germline monoclonal antibodies (mAb), we have examined the specificity of the promiscuous mAb S67-27 to both naturally derived carbohydrate antigens and a variety of synthetic nonnatural antigens based on the bacterial lipopolysaccharide component 3-deoxy-alpha-D-manno-oct-2-ulosonic acid (Kdo). One such analog, a 7-O-methyl (7-O-Me) Kdo disaccharide, was found to bind to the antibody with at least 30-fold higher affinity than any other antigen tested. The structure of S67-27 in complex with this analog and three other naturally occurring Kdo antigens revealed that the enhanced affinity of the mAb for the synthetic analog was accomplished by the strategic positioning of CDR H3 away from a conserved Kdo binding pocket that allowed the formation of new antibody-antigen contacts. Furthermore, the comparison of this structure with the structures of related mAbs revealed how the position and structure of CDR H3 influence the specificity or promiscuity of near-germline carbohydrate-recognizing antibodies by altering the architecture of the combining site.

Synthesis and antigenic properties of C-7-modified Kdo mono- and disaccharide ligands and Kdo disaccharide interresidue lactones.

In order to define binding interactions of Kdo-specific monoclonal antibodies directed against the chlamydial alpha-(2-->8)-linked Kdo disaccharide epitope on a molecular level, modifications at the 7-position of the proximal and distal Kdo unit were investigated. The synthesis of 7-O-methyl and 7-azido-7-deoxy-7-epi-Kdo monosaccharide derivatives was achieved via an 8-O-TBS protected derivative, whereas methylation of O-7 at the proximal Kdo unit of the alpha-(2-->8)-linked Kdo disaccharide was conveniently accomplished via a 4,5; 4',5'; 7',8'-tri-O-carbonyl-protected disaccharide intermediate. Attempted epimerization at C-5 of the inner unit of a alpha-(2-->4)-linked Kdo disaccharide, however, resulted in formation of the corresponding 5,6-dehydro derivative, which was fully deprotected. Treatment of unprotected alpha-(2-->8)- as well as alpha-(2-->4)-linked Kdo disaccharides in neat acetic acid furnished the corresponding interresidue lactone derivatives. The lactones displayed limited stability under neutral conditions and were hydrolyzed at pH 7 within 3 days. Access to the lactones, however, provides a means for selective derivatization of the carboxylic group located at the distal Kdo residue, which was demonstrated by methanolysis of the lactone to afford the monomethyl ester of the alpha-(2-->8)-linked Kdo disaccharide. ELISA inhibition experiments of the ligands with two Kdo-specific monoclonal antibodies showed slightly reduced reactivity for the binding of the alpha-(2-->8) Kdo-specific antibody S25-2, whereas the 7-O-methyl disaccharide antigen displayed high binding affinity toward the Kdo monosaccharide-specific antibody S67-27.

Two Kdo-heptose regions identified in Hafnia alvei 32 lipopolysaccharide: the complete core structure and serological screening of different Hafnia O serotypes.

Hafnia alvei, a gram-negative bacterium, is an opportunistic pathogen associated with mixed hospital infections, bacteremia, septicemia, and respiratory diseases. Various 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo)-containing fragments different from known structures of core oligosaccharides were previously found among fractions obtained by mild acid hydrolysis of some H. alvei lipopolysaccharides (LPSs). However, the positions of these segments in the LPS structure were not known. Analysis of de-N,O-acylated LPS by nuclear magnetic resonance spectroscopy and mass spectrometry allowed the determination of the location of a Kdo-containing trisaccharide in the structure of H. alvei PCM 32 LPS. It was established that the trisaccharide {L-alpha-D-Hepp-(1-->4)-[alpha-D-Galp6OAc-(1-->7)]-alpha-Kdop-(2-->} is an integral part of the outer-core oligosaccharide of H. alvei 32 LPS. The very labile ketosidic linkage between -->4,7)-alpha-Kdop and -->2)-Glcp in the core oligosaccharide was identified. Screening for this Kdo-containing trisaccharide was performed on the group of 37 O serotypes of H. alvei LPSs using monospecific antibodies recognizing the structure. It was established that this trisaccharide is a characteristic component of the outer-core oligosaccharides of H. alvei 2, 32, 600, 1192, 1206, and 1211 LPSs. The weaker cross-reactions with LPSs of strains 974, 1188, 1198, 1204, and 1214 suggest the presence of similar structures in these LPSs, as well. Thus, we have identified new examples of endotoxins among those elucidated so far. This type of core oligosaccharide deviates from the classical scheme by the presence of the structural Kdo-containing motif in the outer-core region.

Exploration of specificity in germline monoclonal antibody recognition of a range of natural and synthetic epitopes.

To explore the molecular basis of antigen recognition by germline antibodies, we have determined to high resolution the structures of the near-germline monoclonal antibody S25-2 in complex with seven distinct carbohydrate antigens based on the bacterial sugar 3-deoxy-alpha-D-manno-oct-2-ulosonic acid (Kdo). In contrast to previous findings, the inherited germline Kdo monosaccharide binding site is not restricted to this bacterial sugar but is able to accommodate an array of substitutions and chemical modifications of Kdo, including naturally occurring antigens containing the related monosaccharide d-glycero-alpha-d-talo-oct-2-ulosonic acid as well as nonterminal Kdo residues. However, we show by surface plasmon resonance and ELISA how antibody S25-2 specificity is so dependent on the context in which the antigen is presented that a free disaccharide displays strong binding while the same lipid-A-bound disaccharide does not bind. These structures provide insight into how inherited germline genes code for immunoglobulins of limited flexibility that are capable of binding a range of epitopes from which affinity-matured antibodies are generated.

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.

Binding studies of a monoclonal antibody specific for 3-deoxy-D-manno-octulosonic acid with a panel of Klebsiella pneumoniae lipopolysaccharides representing all of the O serotypes.

A monoclonal antibody (MAb) raised against Salmonella minnesota R595 and specific for alpha-3-deoxy-D-manno-octulosonic acid (alpha-Kdo) of the inner core was tested for binding to lipopolysaccharides (LPS) of Klebsiella pneumoniae. The MAb was tested in several assay systems (enzyme-linked immunosorbent assay, passive hemolysis, and inhibition of passive hemolysis) with a large panel (n = 23) of K. pneumoniae LPS representing all nine currently known O serotypes. MAb 20 showed reactivity with almost all O serotypes of K. pneumoniae LPS, and this reactivity could be inhibited by synthetic Kdo. This suggests an epitope in the cores of these Klebsiella LPS much like that in the inner core of LPS of S. minnesota. Large differences in reactivity between LPS of different strains belonging to the same O serotype were observed. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis of LPS followed by immunoblotting, reactivity of MAb 20 was observed only with the fast-moving fraction possibly representing the nonsubstituted core. No binding was seen with the high-molecular-weight fraction that contained core material substituted with several units of O-antigen building blocks. The chemical basis for these differences in reactivity remains to be established. As far as we know, this is the first report containing comprehensive immunochemical data on the LPS core of K. pneumoniae.

A novel role of Periplaneta lectin as an opsonin to recognize 2-keto-3-deoxy octonate residues of bacterial lipopolysaccharides.

1. Periplaneta lectin of the American cockroach was shown to have affinity to bacterial lipopolysaccharides (LPS) of chemotypes Rb-Re, but not to lipid A. 2. 2-Keto-3-deoxy octonate (KDO) was the most effective sugar so far tested for inhibition of the hemagglutinating activity of Periplaneta lectin. 3. Periplaneta lectin was suggested to participate in the clearance of bacteria injected into the abdominal cavity of the cockroach.

Development of an anti-idiotype monoclonal antibody mimicking the structure of lipopolysaccharide (LPS) inner-core determinants.

An anti-idiotype antibody has been developed which is specific for idiotypic determinants of a BALB/c mouse IgG3 monoclonal antibody (MAbY1-4A6) directed against the inner-core Kdo region of lipopolysaccharide (LPS). Armenian hamsters were immunized with MAbY1-4A6 and splenocytes from immunized animals fused with Sp2/0 myeloma cells. Eight clones secreting antibodies that bound to MAbY1-4A6, but not control IgG3, were identified and subcloned. Culture supernatants from one hybridoma, termed MAb4G2, contain monoclonal antibody that binds to the variable region of MAbY1-4A6 and dose-dependently inhibits binding of MAbY1-4A6 to Re chemotype rough mutant LPS (Re-LPS). This antibody also inhibits binding of three additional mouse monoclonal antibodies specific for the inner-core of Re-LPS. MAb4G2 also recognizes a significant proportion of antibodies present in polyclonal R-chemotype antisera generated in mice (Re-LPS) and rabbits (J5 Rc-LPS). Mice and hamsters immunized with MAb4G2 or Re-LPS generate antibodies which cross-react with both immunogens. Cumulatively, these data suggest that MAb4G2 can function as an internal image of the Kdo-specific monoclonal antibody, MAbY1-4A6, mimicking the antigenic structure and immunogenicity of a portion of the LPS inner-core Kdo region.

Differential effects of a monoclonal antibody recognizing 3-deoxy-D-manno-2-octulosonic acid on endotoxin-induced activation of pre-B cells and macrophages.

A monoclonal antibody (E1), which reacts with the 3-deoxy-D-manno-2-octulosonic acid region of lipopolysaccharides belonging to the rough Re chemotype (LPS-Re) was used to analyze in vivo and in vitro effects of endotoxin. E1 inhibited LPS-Re-induced activation of Z0Z/3 pre-B cells (expression of surface immunoglobulins) and mature splenic B cells (DNA synthesis) and blocked the binding of biotin-labeled LPS-Re to mouse peritoneal macrophages. However, other effects elicited by LPS-Re, such as the production of interleukin 6 and tumor necrosis factor alpha by macrophages, and the acute lethality in galactosamine-sensitized mice, were not inhibited by E1. The results suggest that the specificity of the LPS receptor which triggers the production of cytokines in macrophages is different from that of the LPS receptor which induces activation of pre-B and B lymphocytes, and is also different from that of the major LPS-binding sites of macrophages. This is consistent with the hypothesis that the large majority of LPS-binding sites of macrophages do not trigger cytokine production, and that the small number of "signaling LPS receptors" of macrophages have fine specificities which are different from those of B cells.

Preparation and binding specificity of a monoclonal antibody recognizing 3-deoxy-D-manno-2-octulosonic acid (Kdo) in lipopolysaccharides of Re chemotype.

A mouse monoclonal antibody (MAb E1) was raised against the lipopolysaccharide (LPS) of the Re mutant R595 of Salmonella minnesota. This IgG3 antibody (MAb E1), unstable at low pH and low ionic strength, was purified by chromatography on QAE Sepharose A50. The binding specificity of MAb E1 was characterized by direct and inhibition enzyme immunoassays, using natural LPSs from different strains and chemotypes, and synthetic analogs of LPS substructure of the 3-deoxy-D-manno-2-octulosonic acid (Kdo) and Lipid A regions. Among various LPSs, MAb E1 reacted exclusively with those of Re-chemotype. It recognized alpha-Kdo- monosaccharide and disaccharide structures present as non-reducing side chains in various Re-type LPSs and synthetic antigens. The antibody did not react with Lipid A or various lipids, and the presence of the lipid region was not necessary for the reaction. The recognition of the epitope was not reduced by the presence of a substituent at O-8 of one of the two Kdo units present in the Re LPS from Proteus mirabilis, but the reaction was inhibited by phosphorylation of O-4 of Kdo, by the proximity of core (heptose) or Lipid A (acylated glucosamine) residues, or by certain LPS-LPS interactions.

A nuclear magnetic resonance spectroscopic investigation of Kdo-containing oligosaccharides related to the genus-specific epitope of Chlamydia lipopolysaccharides.

The 1H- and 13C-NMR parameters, chemical shifts and coupling constants, for the pentasaccharide of the genus-specific epitope of Chlamydia lipopolysaccharide and related di-, tri-, and tetra-saccharides have been measured and assigned completely using 1D and 2D techniques, and their structures have been confirmed. NOE experiments indicated the preferred conformation of the pentasaccharide and the component oligosaccharides. The 3JH,H demonstrate a change in conformation by rotation of the C-6-C-7 bond of the side chain of the (2----8)-linked Kdo (unit b) in alpha-Kdo-(2----8)-alpha-Kdo-(2----4)-alpha-Kdo-(2----6)-beta-GlcN-(1--- -6)- GlcNol, alpha-Kdo-(2----8)-alpha-Kdo-(2----4)-alpha-Kdo-(2----6)-beta-GlcNAc-(1- ---O)- allyl, and alpha-Kdo-(2----8)-alpha-Kdo-(2----4)-alpha-Kdo-(2----O)-allyl relative to that preferred in alpha-Kdo-(2----4)-alpha-Kdo-(2----6)-beta-GlcNAc-(1----O)-allyl, alpha-Kdo-(2----8)-alpha-Kdo-(2----O)-allyl, alpha-Kdo-(2----4)-alpha-Kdo-(2----O)-allyl, and alpha-Kdo-(2----6)-beta-GlcNAc-(1----O)-allyl, irrespective of the size of the aglycon, e.g., allyl or beta-D-GlcN residues. The conformational results have been substantiated by computer calculations using the HSEA approach.

A synthetic glycoconjugate representing the genus-specific epitope of chlamydial lipopolysaccharide exhibits the same specificity as its natural counterpart.

The tetrasaccharide 3-deoxy-alpha-D-manno-2-octulosonic acid (alpha-KDO) (2----8)-alpha-KDO(2----4)-alpha-KDO(2----6)-beta GlcNAc, a partial structure of chlamydial lipopolysaccharide (LPS) representing a genus-specific epitope, was synthesized and covalently linked to bovine serum albumin, resulting in an artificial glycoconjugate antigen. Mice were immunized with the glycoconjugate to prepare chlamydia-specific monoclonal antibodies. They were selected with chlamydia-specific LPS antigens and the structurally and antigenically related Re-type LPS of a Salmonella minnesota rough mutant. Characterization of the selected antibodies was by (i) hemagglutination of sheep erythrocytes coated with recombinant chlamydia-specific LPS, (ii) inhibition by synthetic polyacrylamide derivatives containing the genus-specific epitope or partial structures thereof, (iii) enzyme immunoassay with recombinant LPS and synthetic bovine serum albumin glycoconjugates as solid-phase antigens, (iv) immunofluorescence of L929 monolayers infected with Chlamydia psittaci or C. trachomatis, and (v) Western immunoblots with glycoconjugates and LPS as the antigen. Two groups of monoclonal antibodies were obtained; the monoclonal antibodies in one group cross-reacted with chlamydial and Re-type LPS, but those of the other group were chlamydia specific. Among the latter, KDO trisaccharide-specific antibodies that had the same epitope specificity as antibodies obtained after immunization with chlamydial elementary bodies were identified; however, they exhibited a more than 100-fold higher affinity. In addition, antibodies that bound preferentially to the 2.8-linked KDO disaccharide were detected, although with lower affinity. The data show that the artificial glycoconjugate antigen is similar to its natural counterpart.