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Background/PurposeTo search for a transmissible agent involved in lupus pathogenesis, we investigated the faecal microbiota of patients with systemic lupus erythematosus (SLE) for candidate pathobiont(s) and evaluated them for special relationships with host immunity.MethodsIn a cross-sectional discovery cohort, matched blood and faecal samples from 61 female patients with SLE were obtained. Faecal 16 S rRNA analyses were performed, and sera profiled for antibacterial and autoantibody responses, with findings validated in two independent lupus cohorts.ResultsCompared with controls, the microbiome in patients with SLE showed decreased species richness diversity, with reductions in taxonomic complexity most pronounced in those with high SLE disease activity index (SLEDAI). Notably, patients with SLE had an overall 5-fold greater representation of Ruminococcus gnavus (RG) of the Lachnospiraceae family, and individual communities also displayed reciprocal contractions of a species with putative protective properties. Gut RG abundance correlated with serum antibodies to only 1/8 RG strains tested. Anti-RG antibodies correlated directly with SLEDAI score and antinative DNA levels, but inversely with C3 and C4. These antibodies were primarily against antigen(s) in an RG strain-restricted pool of cell wall lipoglycans. Novel structural features of these purified lipoglycans were characterised by mass spectrometry and NMR. Highest levels of serum anti-RG strain-restricted antibodies were detected in those with active nephritis (including Class III and IV) in the discovery cohort, with findings validated in two independent cohorts.ConclusionThese findings suggest a novel paradigm in which specific strains of a gut commensal may contribute to the immune pathogenesis of lupus nephritis.

Disrupting transmission of Borrelia burgdorferi sensu lato complex (B. burgdorferi) from infected ticks to humans is one strategy to prevent the significant morbidity from Lyme disease. We have previously shown that an anti-OspA human mAb, 2217, prevents transmission of B. burgdorferi from infected ticks in animal models. Maintenance of a protective plasma concentration of a human mAb for tick season presents a significant challenge for a preexposure prophylaxis strategy. Here, we describe the optimization of mAb 2217 by amino acid substitutions (2217LS: M428L and N434S) in the Fc domain. The LS mutation led to a 2-fold increase in half-life in cynomolgus monkeys. In a rhesus macaque model, 2217LS protected animals from tick transmission of spirochetes at a dose of 3 mg/kg. Crystallographic analysis of Fab in complex with OspA revealed that 2217 bound an epitope that was highly conserved among the B. burgdorferi, B. garinii, and B. afzelii species. Unlike most vaccines that may require boosters to achieve protection, our work supports the development of 2217LS as an effective preexposure prophylaxis in Lyme-endemic regions, with a single dose at the beginning of tick season offering immediate protection that remains for the duration of exposure risk.

Extracellular vesicle production is a ubiquitous process in Gram-negative bacteria, but little is known about such process in Gram-positive bacteria. We report the isolation of extracellular vesicles from the supernatants of Bacillus anthracis, a Gram-positive bacillus that is a powerful agent for biological warfare. B. anthracis vesicles formed at the outer layer of the bacterial cell had double-membrane spheres and ranged from 50 to 150 nm in diameter. Immunoelectron microscopy with mAbs to protective antigen, lethal factor, edema toxin, and anthrolysin revealed toxin components and anthrolysin in vesicles, with some vesicles containing more than one toxin component. Toxin-containing vesicles were also visualized inside B. anthracis-infected macrophages. ELISA and immunoblot analysis of vesicle preparations confirmed the presence of B. anthracis toxin components. A mAb to protective antigen protected macrophages against vesicles from an anthrolysin-deficient strain, but not against vesicles from Sterne 34F2 and Sterne δT strains, consistent with the notion that vesicles delivered both toxin and anthrolysin to host cells. Vesicles were immunogenic in BALB/c mice, which produced a robust IgM response to toxin components. Furthermore, vesicle-immunized mice lived significantly longer than controls after B. anthracis challenge. Our results indicate that toxin secretion in B. anthracis is, at least, partially vesicle-associated, thus allowing concentrated delivery of toxin components to target host cells, a mechanism that may increase toxin potency. Our observations may have important implications for the design of vaccines, for passive antibody strategies, and provide a previously unexplored system for studying secretory pathways in Gram-positive bacteria.

Background. A dramatic increase in morbidity and mortality from Clostridium difficile infection (CDI) due to the recent emergence of virulent, antibiotic-resistant strains has led to a search for alternatives to antibiotics, including vaccines and immune-based therapy that target the 2 key toxins—TcdA and TcdB. Methods. We investigated the efficacy of specific human monoclonal antibodies (HuMab) and alpaca polyclonal antibodies against each toxin separately and in combination in the gnotobiotic piglet model of CDI. Additionally, the HuMab and polyclonal antibodies were exploited to investigate the precise contribution of each toxin to systemic and/or gastrointestinal (GI) tract disease. Results. Our results indicate that TcdB is an important virulence factor associated with GI and systemic pathology. Administration of anti-TcdB antibody alone or with anti-TcdA protected 100% of piglets from development of systemic CDI and minimized GI lesions. Conversely, 100% of piglets administered only anti-TcdA developed severe GI and systemic disease, with 67%–83% fatality, faring worse than placebo-treated control animals. Conclusions. These results highlight the importance of TcdB in the pathogenesis of CDI and the effectiveness of TcdB-specific antibody in treating CDI. However, the results raise new questions regarding the nature of TcdA interaction with therapeutic antibodies.

Lipopolysaccharide (LPS) O-antigen (O-Ag) is known to limit antibody binding to surface antigens, although the relationship between antibody, O-Ag and other outer-membrane antigens is poorly understood. Here we report, immunization with the trimeric porin OmpD from Salmonella Typhimurium (STmOmpD) protects against infection. Atomistic molecular dynamics simulations indicate this is because OmpD trimers generate footprints within the O-Ag layer sufficiently sized for a single IgG Fab to access. While STmOmpD differs from its orthologue in S . Enteritidis (SEn) by a single amino-acid residue, immunization with STmOmpD confers minimal protection to SEn. This is due to the OmpD-O-Ag interplay restricting IgG binding, with the pairing of OmpD with its native O-Ag being essential for optimal protection after immunization. Thus, both the chemical and physical structure of O-Ag are key for the presentation of specific epitopes within proteinaceous surface-antigens. This enhances combinatorial antigenic diversity in Gram-negative bacteria, while reducing associated fitness costs. The O-antigen of LPS is known to limit the binding of antibody to bacterial surface antigens. Here the AUs show that the chemical and physical structure of the O-antigen are central factors in limiting the exposure of surface antigens to antibodies during Salmonella infection, thus defining their protective qualities.

The VD4 region from the Chlamydia trachomatis major outer membrane protein contains important neutralizing B-cell epitopes of relevance for antibody-mediated protection against genital tract infection. We developed a multivalent vaccine construct based on VD4s and their surrounding constant segments from serovars D, E, and F. Adjuvanted with cationic liposomes, this construct promoted strong immune responses to serovar-specific epitopes, the conserved LNPTIAG epitope and neutralized serovars D, E, and F. Vaccinated mice were protected against challenge, with protection defined as reduced bacterial numbers in vagina and prevention of pathological changes in the upper genital tract. Adoptive transfer of serum and T-cell depletion experiments demonstrated a dominant role for antibodies and CD4⁺ T cells in the protective immune response. Integrating a multivalent VD4 construct into the sequence of the major outer membrane protein resulted in a protective and broadly neutralizing vaccine. Our findings emphasize the important role of antibodies in protection against Chlamydia trachomatis.

This protocol for bacterial flow cytometry incubates bacterial cells with an antibody-containing bodily fluid, visualizes bound antibody with secondary reagents and quantifies bacteria using flow cytometry, with numerous advantages over standard ELISA and western blotting techniques. Antibacterial antibody responses that target surfaces of live bacteria or secreted toxins are likely to be relevant in controlling bacterial pathogenesis. The ability to specifically quantify bacterial-surface-binding antibodies is therefore highly attractive as a quantitative correlate of immune protection. Here, binding of antibodies from various body fluids to pure-cultured live bacteria is made visible with fluorophore-conjugated secondary antibodies and measured by flow cytometry. We indicate the necessary controls for excluding nonspecific binding and also demonstrate a cross-adsorption technique for determining the extent of cross-reactivity. This technique has numerous advantages over standard ELISA and western blotting techniques because of its independence from scaffold binding, exclusion of cross-reactive elements from lysed bacteria and ability to visualize bacterial subpopulations. In addition, less than 10 5 bacteria and less than 10 μg of antibody are required per sample. The technique requires 3–4 h of hands-on experimentation and analysis. Moreover, it can be combined with automation and mutliplexing for high-throughput applications.

Commensal bacteria in the lower intestine of mammals are 10 times as numerous as the body's cells. We investigated the relative importance of different immune mechanisms in limiting the spread of the intestinal microbiota. Here, we reveal a flexible continuum between innate and adaptive immune function in containing commensal microbes. Mice deficient in critical innate immune functions such as Toll-like receptor signaling or oxidative burst production spontaneously produce high-titer serum antibodies against their commensal microbiota. These antibody responses are functionally essential to maintain host-commensal mutualism in vivo in the face of innate immune deficiency. Spontaneous hyper-activation of adaptive immunity against the intestinal microbiota, secondary to innate immune deficiency, may clarify the underlying mechanisms of inflammatory diseases where immune dysfunction is implicated.

The most promising means of controlling anthrax, a lethal zoonotic disease during the early infection stages, entail restricting the resilient infectious form, i.e., the spores from proliferating to replicating bacilli in the host. The extractible antigen (EA1), a major S-layer protein present on the vegetative cells and spores of Bacillus anthracis, is highly immunogenic and protects mice against lethal challenge upon immunization. In the present study, mice were immunized with r-EA1C, the C terminal crystallization domain of EA1, to generate a neutralizing monoclonal antibody EA752–862, that was evaluated for its anti-spore and anti-bacterial properties. The monoclonal antibody EA752–862 had a minimum inhibitory concentration of 0.08 mg/ml, was bactericidal at a concentration of 0.1 mg/ml and resulted in 100% survival of mice against challenge with B. anthracis vegetative cells. Bacterial cell lysis as observed by scanning electron microscopy and nucleic acid leakage assay could be attributed as a possible mechanism for the bactericidal property. The association of mAb EA752–862 with spores inhibits their subsequent germination to vegetative cells in vitro, enhances phagocytosis of the spores and killing of the vegetative cells within the macrophage, and subsequently resulted in 90% survival of mice upon B. anthracis Ames spore challenge. Therefore, owing to its anti-spore and bactericidal properties, the present study demonstrates mAb EA752–862 as an efficient neutralizing antibody that hinders the establishment of early infection before massive multiplication and toxin release takes place.

Maternal vaccination against group B Streptococcus (GBS) might provide protection against invasive GBS disease in infants. We investigated the kinetics of transplacentally transferred GBS serotype-specific capsular antibodies in the infants and their immune response to diphtheria toxoid and pneumococcal vaccination. This phase 1b/2, observer-blind, single-center study (NCT01193920) enrolled infants born to women previously randomized (1:1:1:1) to receive either GBS vaccine at dosages of 0.5, 2.5, or 5.0 μg of each of 3 CRM197-glycoconjugates (serotypes Ia, Ib, and III), or placebo. Infants received routine immunization: combination diphtheria vaccine (diphtheria-tetanus-acellular pertussis-inactivated poliovirus/Haemophilus influenzae type b vaccine; age 6/10/ 14 weeks) and 13-valent pneumococcal CRM197-conjugate vaccine (PCV13; age 6/14 weeks and 9 months). Antibody levels were assessed at birth, day (D) 43, and D91 for GBS serotypes; 1 month postdose 3 (D127) for diphtheria; and 1 month postprimary (D127) and postbooster (D301) doses for pneumococcal serotypes. Of 317 infants enrolled, 295 completed the study. In infants of GBS vaccine recipients, GBS serotype-specific antibody geometric mean concentrations were significantly higher than in the placebo group at all timepoints and predictably decreased to 41%-61% and 26%-76% of birth levels by D43 and D91, respectively. Across all groups, ≥95% of infants were seroprotected against diphtheria at D127 and ≥91% of infants had seroprotective antibody levels against each PCV13 pneumococcal serotype at D301. Maternal vaccination with an investigational CRM197-glycoconjugate GBS vaccine elicited higher GBS serotype-specific antibody levels in infants until 90 days of age, compared with a placebo group, and did not affect infant immune responses to diphtheria toxoid and pneumococcal vaccination. NCT01193920.