Antibodies to various bacterial cell wall peptidoglycans in human and rabbit sera

Borrelia burgdorferi peptidoglycan is a persistent antigen in patients with Lyme arthritis

Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most common vector-borne disease in North America. If early infection is untreated, it can result in late-stage manifestations, including arthritis. Although antibiotics are generally effective at all stages of the disease, arthritis may persist in some patients for months to several years despite oral and intravenous antibiotic treatment. Excessive, dysregulated host immune responses are thought to play an important role in this outcome, but the underlying mechanisms are not completely understood. This study identifies the B. burgdorferi peptidoglycan, a major component of the cell wall, as an immunogen likely to contribute to inflammation during infection and in cases of postinfectious Lyme arthritis.

Lyme disease is a multisystem disorder caused by the spirochete Borrelia burgdorferi. A common late-stage complication of this disease is oligoarticular arthritis, often involving the knee. In ∼10% of cases, arthritis persists after appropriate antibiotic treatment, leading to a proliferative synovitis typical of chronic inflammatory arthritides. Here, we provide evidence that peptidoglycan (PG), a major component of the B. burgdorferi cell envelope, may contribute to the development and persistence of Lyme arthritis (LA). We show that B. burgdorferi has a chemically atypical PG (PG^Bb) that is not recycled during cell-wall turnover. Instead, this pathogen sheds PG^Bb fragments into its environment during growth. Patients with LA mount a specific immunoglobulin G response against PG^Bb, which is significantly higher in the synovial fluid than in the serum of the same patient. We also detect PG^Bb in 94% of synovial fluid samples (32 of 34) from patients with LA, many of whom had undergone oral and intravenous antibiotic treatment. These same synovial fluid samples contain proinflammatory cytokines, similar to those produced by human peripheral blood mononuclear cells stimulated with PG^Bb. In addition, systemic administration of PG^Bb in BALB/c mice elicits acute arthritis. Altogether, our study identifies PG^Bb as a likely contributor to inflammatory responses in LA. Persistence of this antigen in the joint may contribute to synovitis after antibiotics eradicate the pathogen. Furthermore, our finding that B. burgdorferi sheds immunogenic PG^Bb fragments during growth suggests a potential role for PG^Bb in the immunopathogenesis of other Lyme disease manifestations.

Successful selection of an infection-protective anti-Staphylococcus aureus monoclonal antibody and its protective activity in murine infection models

Recent clinical trials to develop anti-methicillin-resistant Staphylococcus aureus (MRSA) therapeutic antibodies have met unsuccessful sequels. To develop more effective antibodies against MRSA infection, a panel of mAbs against S. aureus cell wall was generated and then screened for the most protective mAb in mouse infection models. Twenty-two anti-S. aureus IgG mAbs were obtained from mice that had been immunized with alkali-processed, deacetylated cell walls of S. aureus. One of these mAbs, ZBIA5H, exhibited life-saving effects in mouse models of sepsis caused by community-acquired MRSA strain MW2 and vancomycin-resistant S. aureus strain VRS1. It also had a curative effect in a MW2-caused pneumonia model. Curiously, the target of ZBIA5H was considered to be a conformational epitope of either the 1,4-β-linkage between N-acetylmuramic acid and N-acetyl-D-glucosamine or the peptidoglycan per se. Reactivity of ZBIA5H to S. aureus whole cells or purified peptidoglycan was weaker than that of most of the other mAbs generated in this study. However, the latter mAbs did not have the protective activities against S. aureus that ZBIA5H did. These data indicate that the epitopes that trigger production of high-yield and/or high-affinity antibodies may not be the most suitable epitopes for developing anti-infective antibodies. ZBIA5H or its humanized form may find a future clinical application, and its target epitope may be used for the production of vaccines against S. aureus infection.

The Staphylococcus aureus peptidoglycan protects mice against the pathogen and eradicates experimentally induced infection

Staphylococcus aureus, in spite of antibiotics, is still a major human pathogen causing a wide range of infections. The present study describes the new vaccine A170PG, a peptidoglycan-based vaccine. In a mouse model of infection, A170PG protects mice against a lethal dose of S. aureus. Protection lasts at least 40 weeks and correlates with increased survival and reduced colonization. Protection extends into drug-resistant (MRSA or VISA) and genetically diverse clinical strains. The vaccine is effective when administered - in a single dose and without adjuvant - by the intramuscular, intravenous or the aerosol routes and induces active as well as passive immunization. Of note, A170PG also displays therapeutic activity, eradicating staphylococci, even when infection is systemic. Sustained antibacterial activity and induction of a strong and rapid anti-inflammatory response are the mechanisms conferring therapeutic efficacy to A170PG.

The occurrence of natural antibodies to minimal component of bacterial cell wall (N-acetylglucosaminyl-N-acetylmuramyl dipeptide) in sera from healthy humans

ELISA assay showed that sera from each of 729 healthy donors contained antibodies to the minimal component of bacterial cell walls, N-acetylglucosaminyl-N-acetylmuramyl dipeptide (GMDP). Anti-GMDP antibody levels were determined for 686 sera which were classified into 3 groups: high (17.6%), medium (68.7%), and low responder (13.7%). Inhibition analysis performed on representative sera showed that a proportion contained specific anti-GMDP antibodies reacting only with GMDP (i.e., GMDP interaction with anti-GMDP antibodies was inhibited by GMDP only) whereas the remaining sera reacted both with GMDP and with the tetrasaccharide (GlcNAc-MurNAc)2 (i.e., GMDP interaction with anti-GMDP antibodies in the latter sera was inhibited by both GMDP and the tetrasaccharide). Inhibition analysis indicated, moreover, that the anti-GMDP antibodies contained in high-responder sera had higher affinity than those present in low-responder ones: GMDP inhibited the GMDP + anti-GMDP antibody interaction by 88.7% in the former sera vs. 53% in the latter. Sera contained both IgM and IgG antibodies to GDMP, but the mean level of anti-GMDP IgG antibodies in the high-responder sera was 30 times higher than in the low-responder ones.

Resistance to infection and activation of the monocyto-macrophage system caused by Bacillus firmus and its fractions

Crude lipids isolated from Bacillus firmus, but not from other bacilli, were previously found to induce significant resistance against Listeria monocytogenes infection in mice. In this study, formaldehyde- and heat-killed bacterins of eight Bacillus species and some cellular fractions of B. firmus were prepared and tested for further immunomodulatory activities. Crude lipids, their aqueous extract, LTA, Protodyne and Pex-residue preparations exhibited a strong anti-infection activity, whereas Pextract, P40 and all bacterins tested had no effect. Formaldehyde-killed bacterins, live bacteria and the P40 preparation of both B. firmus strains, as well as bacterins of both B. subtilis strains, induced pronounced splenomegaly in mice. Peptidoglycan and Pex-residue induced significant depression of cytochrome P-450 in mouse liver microsomes after application of 0.1 mg per mouse. Optimal conditions for obtaining a bacterial suspension exhibiting these immunomodulatory properties were elaborated.

Antibody response to oral streptococci in Behçet's disease

The serum antibody titers against oral streptococci were studied by enzyme-linked immunosorbent assay (ELISA) both in patients with Behçet's disease (BD) and control groups. The patients with BD showed significantly higher antibody titers to S. sanguis strains 113-20, 114-23, and 118-1 which were isolated from patients with BD, in comparison with control groups. Also, the reactions of high-titered sera to the crude cell wall and soluble (or membrane) fractions of the 113-20 strain were observed by western blot test. The sera of the patients with BD demonstrated strong bands of approximately 36 kDa, 82 kDa, and 87 kDa in the crude cell wall fractions, and many bands of 80 kDa to 150 kDa in the membrane fractions, indicating that these proteins are the ones leading the high antibody titers to this bacterium in the sera of patients with BD.

Production and characterization of a monoclonal antibody to the O-acetylated peptidoglycan of Proteus mirabilis

A monoclonal antibody (PmPG5-3) specific for the O-acetylated peptidoglycan of Proteus mirabilis 19 was produced by an NS-1 myeloma cell line and purified from ascites fluid by a combination of ammonium sulfate precipitation and affinity chromatography. The monoclonal antibody (an immunoglobulin M) was characterized by a competition enzyme-linked immunosorbent assay to be equally specific for both insoluble and soluble O-acetylated peptidoglycan but weakly recognized chemically de-O-acetylated P. mirabilis peptidoglycan, the non-O-acetylated peptidoglycans from Escherichia coli and Bacillus subtilis, and the peptidoglycan monosaccharide precursors N-acetylglucosamine and N-acetylmuramic acid dipeptide. The monoclonal antibody did not react with D-alanine or lipopolysaccharide isolated from P. mirabilis. Based on this evidence, the binding epitope on the P. mirabilis peptidoglycan is predicted to be linear and to comprise the glycan backbone, including both the N- and O-acetyl moieties. Monoclonal antibody PmPG5-3 was used to localize the O acetylation of the P. mirabilis peptidoglycan by immunoelectron microscopy. Murein sacculi of P. mirabilis were heavily and randomly labelled with the immunogold, whereas very little labelling and no labelling were observed on the sacculi isolated from de-O-acetylated P. mirabilis and E. coli, respectively. Based on the apparent pattern of immunogold labelling, a physiological role for peptidoglycan O acetylation in P. mirabilis is proposed.

Antibodies to staphylococcal peptidoglycan and its peptide epitopes, teichoic acid, and lipoteichoic acid in sera from blood donors and patients with staphylococcal infections

Antibodies to the staphylococcal antigens peptidoglycan, beta-ribitol teichoic acid, and lipoteichoic acid, as well as to the peptidoglycan epitopes L-Lys-D-Ala-D-Ala, L-Lys-D-Ala, and pentaglycine, were found over a wide range of concentrations in sera from both blood donors and patients with verified or suspected staphylococcal infections. The patient group was heterogeneous with regard to both age and type of staphylococcal infections, being representative for sera sent to our laboratory. In single-antigen assays antibodies to pentaglycine had the highest predictive positive value (67%), although only 32% of the patients had elevated levels of such antibodies. Combinations of test antigens could yield positive predictive values as high as 100%, but then the fraction of positive sera was low. Indeed, the fraction of patient sera which was positive in multiple-antigen tests never exceeded 61%. The clinical usefulness of these seroassays for identifying Staphylococcus aureus as a causative agent was limited, owing to the considerable overlap in the range of antibody concentrations between patient and blood donor sera.

Immunoblots, antimicrobial resistance, and bacteriophage typing of oxacillin-resistant Staphylococcus aureus

An immunoblotting system was developed for typing of oxacillin-resistant Staphylococcus aureus. Clinical isolates recovered during a 40-month period at a single institution were evaluated with this typing scheme. Results were compared with susceptibility patterns and with bacteriophage typing results for 100 clinical isolates and with plasmid fingerprints for 14 isolates. Immunoblotting was found to be a useful method with good reproducibility that distinguished seven major groups of patient isolates that were clinically and epidemiologically related. Susceptibility patterns showed specific correlations with other typing results but were inferior to immunoblotting and phage typing for differentiating major groups of organisms. Plasmid profiles failed to distinguish two major groups that were readily identified by immunoblots and phage typing. There was evidence of increasing antimicrobial resistance of endemic hospital strains. Immunoblotting correlated well with phage typing, offered an alternative method for typing isolates that could not be typed by phage typing, and was superior to susceptibility testing and plasmid profiles for distinguishing different groups of oxacillin-resistant S. aureus at our institution.

Monoclonal antibodies evoked by the free oligopeptide (Gly)5 reacting specifically with peptidoglycan from staphylococci

Murine monoclonal antibodies reactive with the Staphylococcus aureus peptidoglycan (PG) epitope (Gly)5 were obtained using the synthetic oligopeptide (Gly)5 in its free form as immunogen. The selected monoclonal antibodies were of the IgM kappa isotype and reacted specifically with PG from S. aureus and Staphylococcus epidermidis, but gave no reaction with PG from Streptococcus pyogenes, Bacillus subtilis and Micrococcus lysodeikticus. Affinity chromatography showed that the antibodies were reactive with the N-terminus of the (Gly)5 peptide. These monoclonal antibodies can be used for the detection of staphylococcal PG in solution.