Monoclonal antibodies against Haemophilus lipopolysaccharides: clone DP8 specific for Haemophilus ducreyi and clone DH24 binding to lacto-N-neotetraose

Emergence and significance of carbohydrate-specific antibodies

Carbohydrate-specific antibodies are widespread among all classes of immunoglobulins. Despite their broad occurrence, little is known about their formation and biological significance. Carbohydrate-specific antibodies are often classified as natural antibodies under the assumption that they arise without prior exposure to exogenous antigens. On the other hand, various carbohydrate-specific antibodies, including antibodies to ABO blood group antigens, emerge after the contact of immune cells with the intestinal microbiota, which expresses a vast diversity of carbohydrate antigens. Here we explore the development of carbohydrate-specific antibodies in humans, addressing the definition of natural antibodies and the production of carbohydrate-specific antibodies upon antigen stimulation. We focus on the significance of the intestinal microbiota in shaping carbohydrate-specific antibodies not just in the gut, but also in the blood circulation. The structural similarity between bacterial carbohydrate antigens and surface glycoconjugates of protists, fungi and animals leads to the production of carbohydrate-specific antibodies protective against a broad range of pathogens. Mimicry between bacterial and human glycoconjugates, however, can also lead to the generation of carbohydrate-specific antibodies that cross-react with human antigens, thereby contributing to the development of autoimmune disorders.

A model of Neisseria meningitidis vaccine based on LPS micelles detoxified by synthetic antiendotoxin peptides

We describe a model of vaccine based on detoxified endotoxin (LPS) conserving the supramolecular structure of micelles. Detoxification of LPS from Neisseria meningitidis group A, strain A1 (LPS A1), has been achieved by complex formation with a synthetic anti-endotoxin peptide (SAEP 2) binding to the lipid A moiety of LPS A1 with high affinity. Following subcutaneous injection in SW mice, LPS A1/SAEP 2 complex induced high titers of boostable IgG antibodies against the immunotype determinants of LPS A1, cross-reactive with group B LPS in either purified or cell-associated form. These antibodies were able to functionally fix and activate homologous and heterologous species of complement after binding to LPS A1-coated sheep erythrocytes. None of the IgG antibodies induced were specific for lipid A or SAEP 2 and none of the IgG antibodies cross-reacted with heterologous LPS. The purified IgG polyclonal antibodies significantly inhibited serum TNF production in CD1 mice intravenously challenged by homologous but not heterologous LPS. The immunogenic properties of LPS A1/SAEP 2 complex, investigated by the kinetic, magnitude and sub-isotype composition of the polyclonal antibodies induced, were comparable to those of a glycoconjugate obtained by covalent binding of LPS A1, detoxified by SAEP 2, to BSA working as a T-cell dependent carrier protein. The results obtained suggest that LPS behaves in vivo as a T-cell dependent antigen. The strategy of properly delivering to the immune system of mammalians, non-toxic LPS fully expressing its supramolecular antigenic structure, represents a novel approach for development of a new generation of R- and S-LPS/SAEP complex-based vaccines for prophylaxis of specific Gram-negative infections leading to sepsis and endotoxemia.

New rapid enzyme-linked immunosorbent assay to detect antibodies against bacterial surface antigens using filtration plates

An easy and rapid ELISA system, Filtration ELISA, to detect antibodies against bacterial cell surface antigens was developed using a 96-well filtration plate fitted with a 0.22microm membrane (MultiScreen-GV, Millipore). Bacterial whole cells were used as antigens without fixing the cells with formalin etc. The whole cell antigens were washed by vacuum filtration through a filter and resuspended in washing buffer. Assay reactions could be done in the wells without losing the solution. The technique was established using antisera of mice immunized with Escherichia coli, and then evaluated by assaying antibodies to Shiga-toxin producing E. coli O157:H7 (STEC), Staphylococcus aureus and Lactobacillus acidophilus in fecal extracts of 157 children who had eaten school lunches contaminated with STEC in comparison with 25 age-matched control children. The lunch group showed significantly higher IgA antibody titers against STEC than the control group (p<0.0005), but not against L. acidphilus. The results indicate that Filtration ELISA is a quantitative and specific technique for measuring antibodies against antigens on the surface of bacteria without extracting antigens from the bacteria. This technique is widely applicable to the assay of antibodies in various samples including serum and fecal extract against various kinds of bacteria.

Frequencies of lipopolysaccharide-defined epitopes in Haemophilus influenzae type b and non-typable isolates determined with monoclonal antibodies

OBJECTIVE: To investigate the frequency of expression and stability of saccharide epitopes in 178 Haemophilus influenzae (39 type b and 138 non-typable) isolates from blood, cerebrospinal fluid, nasopharynx, pharynx, middle ear, conjunctiva, and pleural and bronchial fluid from symptomatic and asymptomatic children using five murine monoclonal antibodies (MAbs, MAHI 3, 4, 6, 8, 10) specific for the oligosaccharide moiety of the lipopolysaccharide (LPS) of H. influenzae, which recognize defined saccharide structures. METHODS: A whole bacteria enzyme immunoassay (EIA) and colony dot immunoblotting were used to determine the frequency of expression and stability of saccharide epitopes in the 178 H. influenzae isolates. RESULTS: Six main groups of strains were differentiated based on the EIA binding pattern with the MAbs: group A, reactive with all five MAbs (MAHI 3, 4, 6, 8 and 10); group B, reactive with four MAbs (MAHI 3, 6, 8 and 10); group C, reactive with three MAbs (MAHI 3, 6 and 8); group D, reactive with three MAbs (MAHI 3, 6 and 10); group E, reactive with two MAbs (MAHI 3 and 10); group F, reactive with MAb MAHI 3. Group B was the most common classification overall. None of the strains remained non-reactive. The frequencies of the binding patterns among the isolates obtained from different sources appeared to be statistically similar in most of the cases. Indications of phase variation of the LPS epitopes were observed with all the MAbs for strains obtained from all clinical sources as evaluated by colony dot immunoblotting. One of the epitopes displayed 22% phase variation, while four other epitopes were variably expressed, with about 50% on-off expression. CONCLUSIONS: This set of MAbs showed 100% reactivity among the isolates, in both EIA and colony dot immunoblotting, and allowed us to differentiate strains based on the LPS phenotype by whole bacteria EIA. Phase variation was indicated among all the isolates, independent of the source of isolation, and for all five MAbs. The LPS of isolates from different clinical sources often expressed some of the epitopes recognized by the MAbs, and most of the LPS phenotypes appeared at similar frequencies among isolates.

Antibodies specific to surface antigens are not effective in complement-mediated killing of Haemophilus ducreyi

The bactericidal activity of serum is an important primary host defence against gram-negative bacteria. Little is known regarding such antibodies that are specific to outer membrane (OM) antigens as pili and lipooligosaccharides (LOS) in the bactericidal killing of Haemophilus ducreyi. Presence of serum antibodies with specificity to a 430 kDa protein (polymer of the 24 kDa protein, named fine-tangled pili) and LOS in serum from chancroid patients and healthy individuals were investigated by ELISA. Using a bactericidal assay, we investigated the role of human and rabbit antibodies with the aforementioned specificity. Accessibility of LOS and of OM antigens, as well as the deposition of components of the complement (C) system on the surface of the bacteria, was further investigated by whole-cell ELISA and immunoelectron microscopy. Immunoglobulin G (IgG) antibodies specific to the 430 kDa polymer and to LOS were demonstrated in the majority of sera from chancroid patients and healthy individuals. However, sera from chancroid patients did not significantly enhance the C-mediated killing of H. ducreyi compared with normal human serum (NHS). Similar results were demonstrated using rabbit sera to whole bacteria, specific to the 430 kDa protein and LOS of H. ducreyi. However, using the same assay noncapsulatedH. influenzae was totally killed, as were H. influenzae type b in presence of specific antibodies. This suggests a limited effectiveness of antibodies specific to surface antigens in C-mediated killing of H. ducreyi. LOS was detectable on the surface of H. ducreyi with a specific monoclonal antibody in white-cell ELISA. However, a significant enhancement of LOS detection was demonstrated on washed bacteria. OM antigens of 26, 40, 45 kDa and the major outer membrane protein (MOMP) of 43 kDa were not detectable on the surface of nonwashed and washed bacteria by specific monoclonal antibodies, indicating a lack of accessibility of these antigens on the bacterial surface. However, the C6 to C9 components of C were detected on the bacterial surface, suggesting capacity of forming the membrane attack complex. Altogether, these findings imply that antibodies specific to surface antigens, such as the 430 kDa protein and LOS, are not capable of enhancing killing of bacteria. The demonstrated relative resistance is probably due not to a lack of deposition of the membrane attack complex components, but rather to a blocking of LOS accessibility and OM proteins as potential targets of bactericidal antibodies and C action.

Structurally defined epitopes of Haemophilus ducreyi lipooligosaccharides recognized by monoclonal antibodies

By use of enzyme-linked immunosorbent assay and immunoblotting techniques, the migration patterns and binding epitopes of lipooligosaccharides (LOS) from 10 Haemophilus ducreyi strains were investigated with two monoclonal antibodies (MAbs), MAHD6 and MAHD7, raised against LOS from H. ducreyi ITM 2665. Closely related LOS, with defined structures, from Haemophilus influenzae, Bordetella pertussis, Aeromonas spp., and synthetic glycoproteins were also included in the analyses. The MAbs bound to conserved epitopes of LOS exposed on the surface of H. ducreyi. The MAb MAHD6 reacted with 8 of the 10 LOS from H. ducreyi but with none of the other Haemophilus or Bordetella spp. with structurally defined LOS. It is suggested that MAb MAHD6 binds to a LOS epitope (-DD-Hepp-1-->6-beta-D-Glcp-). This LOS epitope is not present in the hexasaccharide structure of LOS from H. ducreyi ITM 4747 (E. K. H. Schweda, A. C. Sundström, L. M. Eriksson, J. A. Jonasson, and A. A. Lindberg, J. Biol. Chem. 269:12040-12048, 1994). Because MAb MAHD6 reacts with the epitope mentioned above, it also discriminates between the two LOS structures, the hexasaccharide group and the nonasaccharide group, of H. ducreyi strains. MAb MAHD7 recognizes the common conserved inner core region of the LOS because it reacts with all H. ducreyi strains and with LOS with minor components in the inner core epitope structure. Rabbit polyclonal sera raised against the LOS from strains CCUG 4438 and CCUG 7470 were tested with the 10 LOS from the H. ducreyi strains. The antiserum to CCUG 7470 reacted with all H. ducreyi strains as did MAb MAHD7, whereas the antiserum to CCUG 4438 reacted with only its homologous strain and strain ITM 4747. Also, the LOSs of our reference strains CCUG 4438 and CCUG 7470 were structurally analyzed by use of sugar analyses and electrospray ionization-mass spectrometry. The hexasaccharide and nonasaccharide structures obtained from LOS of strains CCUG 4438 and CCUG 7470 were identical to the described LOS structures from H. ducreyi ITM 4747 and ITM 2665, respectively. In conclusion, the MAb MAHD6 recognizes an epitope present in the nonasaccharide LOS group, whereas the MAb MAHD7 recognizes a conserved epitope on LOS of H. ducreyi, which is present in all strains of H. ducreyi tested. Two major groups of oligosaccharides were distinguished by their LOS structures and the reactivity of monoclonal as well as polyclonal antibodies. The majority of H. ducreyi strains possess a nonasaccharide structure of LOS.

Molecular mimicry of host structures by bacterial lipopolysaccharides and its contribution to disease

The core oligosaccharides of low-molecular-weight lipopolysaccharide (LPS), also termed lipooligosaccharide (LOS), of pathogenic Neisseria spp. mimic the carbohydrate moieties of glycosphingolipids present on human cells. Such mimicry may serve to camouflage the bacterial surface from the host. The LOS component is antigenically and/or chemically identical to lactoneoseries glycosphingolipids and can become sialylated in Neisseria gonorrhoeae when the bacterium is grown in the presence of cytidine 5'-monophospho-N-acetylneuraminic acid, the nucleotide sugar of sialic acid. Strains of Neisseria meningitidis and Haemophilus influenzae also express similarly sialylated LPS. Sialylation of the LOS influences susceptibility to bactericidal antibody, may decrease or prevent phagocytosis, cause down-regulation of complement activation, and decrease adherence to neutrophils and the subsequent oxidative burst response. The core oligosaccharides of LPS of Campylobacter jejuni serotypes which are associated with the development of the neurological disorder, Guillain-Barré syndrome (GBS), exhibit mimicry of gangliosides. Cross-reactive antibodies between C. jejuni LPS and gangliosides are considered to play an important role in GBS pathogenesis. In contrast, the O-chain of a number of Helicobacter pylori strains exhibit mimicry of Lewis(x) and Lewis(y) blood group antigens. The role of this mimicry remains to be investigated, but may play a role in bacterial camouflage, the induction of autoimmunity and immune suppression in H. pylori-associated disease.

The conserved 18,000-molecular-weight outer membrane protein of Haemophilus ducreyi has homology to PAL

Haemophilus ducreyi expresses an 18,000-molecular-weight outer membrane protein that contains a conserved surface-exposed epitope recognized by monoclonal antibody 3B9. Monoclonal antibody 3B9 cross-reacts with proteins of similar molecular weight found in many Haemophilus sp. strains, including P6, a candidate vaccine for Haemophilus influenzae. The gene encoding the 18,000-molecular-weight outer membrane protein was identified by screening a lambdagt11 genomic library with 3B9. The coding sequence of the gene was localized to a 471-bp open reading frame, designated pal (peptidoglycan-associated lipoprotein). Translation of pal predicted a mature polypeptide with a molecular weight of 15,000 that had extensive homology with P6 and Escherichia coli PAL. The predicted signal peptide had features characteristic of a prokaryotic lipoprotein, and processing of PAL was sensitive to globomycin in H. ducreyi. The sequences encoding mature H. ducreyi PAL were subcloned into the vector pRSET B and expressed as a polyhistidine-containing fusion protein that bound 3B9. In Western blot (immunoblot) analysis, serum samples obtained from healthy subjects and patients with chancroid or other genital ulcer diseases contained antibodies to purified PAL. Antibodies that bound to PAL were removed by absorption with a lysate of Haemophilus sp. antigens, suggesting that patients with chancroid do not develop an H. ducreyi-specific antibody response to PAL.