Bärbel Raupach

Increased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis bacille Calmette-Guérin mutants that secrete listeriolysin

The tuberculosis vaccine Mycobacterium bovis bacille Calmette-Guérin (BCG) was equipped with the membrane-perforating listeriolysin (Hly) of Listeria monocytogenes, which was shown to improve protection against Mycobacterium tuberculosis. Following aerosol challenge, the Hly-secreting recombinant BCG (hly+ rBCG) vaccine was shown to protect significantly better against aerosol infection with M. tuberculosis than did the parental BCG strain. The isogenic, urease C-deficient hly+ rBCG (DeltaureC hly+ rBCG) vaccine, providing an intraphagosomal pH closer to the acidic pH optimum for Hly activity, exhibited still higher vaccine efficacy than parental BCG. DeltaureC hly+ rBCG also induced profound protection against a member of the M. tuberculosis Beijing/W genotype family while parental BCG failed to do so consistently. Hly not only promoted antigen translocation into the cytoplasm but also apoptosis of infected macrophages. We concluded that superior vaccine efficacy of DeltaureC hly+ rBCG as compared with parental BCG is primarily based on improved cross-priming, which causes enhanced T cell-mediated immunity.

Comparative proteome analysis of Mycobacterium tuberculosis and Mycobacterium bovis BCG strains: towards functional genomics of microbial pathogens

In 1993, the WHO declared tuberculosis a global emergency on the basis that there are 8 million new cases per year. The complete genome of the strain H37Rv of the causative microorganism, Mycobacterium tuberculosis, comprising 3924 genes has been sequenced. We compared the proteomes of two non‐virulent vaccine strains of M. bovis BCG (Chicago and Copenhagen) with two virulent strains of M. tuberculosis (H37Rv and Erdman) to identify protein candidates of value for the development of vaccines, diagnostics and therapeutics. The mycobacterial strains were analysed by two‐dimensional electrophoresis (2‐DE) combining non‐equilibrium pH gradient electrophoresis (NEPHGE) with SDS–PAGE. Distinct and characteristic proteins were identified by mass spectrometry and introduced into a dynamic 2‐DE database (http://www.mpiib‐berlin.mpg.de/2D‐PAGE). Silver‐stained 2‐DE patterns of mycobacterial cell proteins or culture supernatants contained 1800 or 800 spots, respectively, from which 263 were identified. Of these, 54 belong to the culture supernatant. Sixteen and 25 proteins differing in intensity or position between M. tuberculosis H37Rv and Erdman, and H37Rv and M. bovis BCG Chicago, respectively, were identified and categorized into protein classes. It is to be hoped that the availability of the mycobacterial proteome will facilitate the design of novel measures for prevention and therapy of one of the great health threats, tuberculosis.

Toll-like receptors are temporally involved in host defense

Toll-like receptors (TLRs) are evolutionarily conserved proteins that recognize microbial molecules and initiate host defense. To investigate how TLRs work together to fight infections, we tested the role of TLRs in host defense against the Gram-negative bacterial pathogen, Salmonella. We show that TLR4 is critical for early cytokine production and killing of bacteria by murine macrophages. Interestingly, later on, TLR2, but not TLR4, is required for macrophage responses. Myeloid differentiation factor 88, an adaptor protein directly downstream of TLRs, is required for both early and late responses. TLR4, TLR2, and myeloid differentiation factor 88 are involved in murine host defense against Salmonella in vivo, which correlates with the defects in host defense observed in vitro. We propose a model where the sequential activation of TLRs tailors the immune response to different microbes.

Cutting Edge: Role of B Lymphocytes in Protective Immunity Against Salmonella typhimurium Infection

Infection of mice with Salmonella typhimurium gives rise to a disease similar to human typhoid fever caused by S. typhi. Since S. typhimurium is a facultative intracellular bacterium, the requirement of B cells in the immune response against S. typhimurium is a longstanding matter of debate. By infecting mice on a susceptible background and deficient in B cells (Igμ−/− mice) with different strains of S. typhimurium, we could for the first time formally clarify the role of B cells in the response against S. typhimurium. Compared with Igμ+/+ mice, LD50 values in Igμ−/− mice were reduced during primary, and particularly secondary, oral infection with virulent S. typhimurium. After systemic infection, Igμ−/− mice cleared attenuated aroA− S. typhimurium, but vaccine-induced protection against systemic infection with virulent S. typhimurium involved both B cell-dependent and -independent effector mechanisms. Thus, B cell-mediated immunity plays a distinct role in control of S. typhimurium in susceptible mice.

Caspase-1-Mediated Activation of Interleukin-1β (IL-1β) and IL-18 Contributes to Innate Immune Defenses against Salmonella enterica Serovar Typhimurium Infection

ABSTRACT Caspase-1 (Casp-1) mediates the processing of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 to their mature forms. Casp-1-deficient mice succumb more rapidly to Salmonella challenge than do wild-type animals. Both Casp-1 substrates, IL-18 and IL-1β, are relevant for control of Salmonella enterica serovar Typhimurium. We used IL-18−/− and IL-1β−/− mice in addition to administration of recombinant IL-18 to Casp-1−/− mice to demonstrate that IL-18 is important for resistance to the systemic infection but not for resistance to the intestinal phase of the infection. This suggests that IL-1β is critical for the intestinal phase of the disease. Thus, we show that Casp-1 is essential for host innate immune defense against S. enterica serovar Typhimurium and that Casp-1 substrates are required at distinct times and anatomical sites.

Escherichia coli Strain Nissle 1917 Ameliorates Experimental Colitis via Toll-Like Receptor 2- and Toll-Like Receptor 4-Dependent Pathways

ABSTRACT Toll-like receptors (TLRs) are key components of the innate immune system that trigger antimicrobial host defense responses. The aim of the present study was to analyze the effects of probiotic Escherichia coli Nissle strain 1917 in experimental colitis induced in TLR-2 and TLR-4 knockout mice. Colitis was induced in wild-type (wt), TLR-2 knockout, and TLR-4 knockout mice via administration of 5% dextran sodium sulfate (DSS). Mice were treated with either 0.9% NaCl or 107E. coli Nissle 1917 twice daily, followed by the determination of disease activity, mucosal damage, and cytokine secretion. wt and TLR-2 knockout mice exposed to DSS developed acute colitis, whereas TLR-4 knockout mice developed significantly less inflammation. In wt mice, but not TLR-2 or TLR-4 knockout mice, E. coli Nissle 1917 ameliorated colitis and decreased proinflammatory cytokine secretion. In TLR-2 knockout mice a selective reduction of gamma interferon secretion was observed after E. coli Nissle 1917 treatment. In TLR-4 knockout mice, cytokine secretion was almost undetectable and not modulated by E. coli Nissle 1917, indicating that TLR-4 knockout mice do not develop colitis similar to the wt mice. Coculture of E. coli Nissle 1917 and human T cells increased TLR-2 and TLR-4 protein expression in T cells and increased NF-κB activity via TLR-2 and TLR-4. In conclusion, our data provide evidence that E. coli Nissle 1917 ameliorates experimental induced colitis in mice via TLR-2- and TLR-4-dependent pathways.

Immune responses to intracellular bacteria

The multifaceted dialogue between intracellular bacteria and the mammalian host continues to be an exciting issue from both the scientific and public-health viewpoint. The recent year has witnessed some particularly impressive progress in knowledge about the two major culprits affecting the health of mankind, Mycobacterium tuberculosis and Salmonella typhi - the causative agents of tuberculosis and typhoid fever.

Rapid Neutrophil Response Controls Fast-Replicating Intracellular Bacteria but Not Slow-Replicating Mycobacterium tuberculosis

Being one of the first cells to invade the site of infection, neutrophils play an important role in the control of various bacterial and viral infections. In the present work, the contribution of neutrophils to the control of infection with different intracellular bacteria was investigated. Mice were treated with the neutrophil-depleting monoclonal antibody RB6-8C5, and the time course of infection in treated and untreated mice was compared by using intracellular bacterial species and strains varying in virulence and replication rate. The results indicate that neutrophils are crucial for the control of fast-replicating intracellular bacteria, whereas early neutrophil effector mechanisms are dispensable for the control of the slow-replicating Mycobacterium tuberculosis.

Escherichia coli Nissle 1917 Distinctively Modulates T-Cell Cycling and Expansion via Toll-Like Receptor 2 Signaling

ABSTRACT Although the probiotic Escherichia coli strain Nissle 1917 has been proven to be efficacious for the treatment of inflammatory bowel diseases, the underlying mechanisms of action still remain elusive. The aim of the present study was to analyze the effects of E. coli Nissle 1917 on cell cycling and apoptosis of peripheral blood and lamina propria T cells (PBT and LPT, respectively). Anti-CD3-stimulated PBT and LPT were treated with E. coli Nissle 1917-conditioned medium (E. coli Nissle 1917-CM) or heat-inactivated E. coli Nissle 1917. Cyclin B1, DNA content, and caspase 3 expression were measured by flow cytometry to assess cell cycle kinetics and apoptosis. Protein levels of several cell cycle and apoptosis modulators were determined by immunoblotting, and cytokine profiles were determined by cytometric bead array. E. coli Nissle 1917-CM inhibits cell cycling and expansion of peripheral blood but not mucosal T cells. Bacterial lipoproteins mimicked the effect of E. coli Nissle 1917-CM; in contrast, heat-inactivated E. coli Nissle 1917, lipopolysaccharide, or CpG DNA did not alter PBT cell cycling. E. coli Nissle 1917-CM decreased cyclin D2, B1, and retinoblastoma protein expression, contributing to the reduction of T-cell proliferation. E. coli Nissle 1917 significantly inhibited the expression of interleukin-2 (IL-2), tumor necrosis factor α, and gamma interferon but increased IL-10 production in PBT. Using Toll-like receptor 2 (TLR-2) knockout mice, we further demonstrate that the inhibition of PBT proliferation by E. coli Nissle 1917-CM is TLR-2 dependent. The differential reaction of circulating and tissue-bound T cells towards E. coli Nissle 1917 may explain the beneficial effect of E. coli Nissle 1917 in intestinal inflammation. E. coli Nissle 1917 may downregulate the expansion of newly recruited T cells into the mucosa and limit intestinal inflammation, while already activated tissue-bound T cells may eliminate deleterious antigens in order to maintain immunological homeostasis.

A role for IL-18 in protective immunity against Mycobacterium tuberculosis.

Tuberculosis remains the most hazardous bacterial infection worldwide. The causative agent, Mycobacterium tuberculosis, is a facultative intracellular pathogen of resting MΦ. IFN‐γ secreted by natural killer, CD4 Th 1 and CD8 T cells upon instruction by IL‐12 and ‐18 activates MΦ to restrict mycobacterial growth. Production of both cytokines is induced by TLR signalling in DC and MΦ. Mice deficient for the TLR adaptor, MyD88, are highly susceptible to M. tuberculosis infection. Shared usage of MyD88 by signalling cascades for TLR and receptors for IL‐1 and IL‐18 prompted us to revisit the role of IL‐18 during experimental infection with M. tuberculosis. We show that mice deficient for IL‐18 and MyD88 but not for IL‐18 receptor promptly succumbed to M. tuberculosis infection in contrast to WT or TLR‐2/‐4 double KO mice indicating that lack of IL‐18 contributes to the high susceptibility of MyD88 KO mice to M. tuberculosis. Without IL‐18, the protective Th1 response was decreased and hence, mycobacterial propagation was favoured. Neutrophil‐driven lung immunopathology concomitant with unrestrained growth of tubercle bacilli are most likely responsible for the premature death of IL‐18 KO mice. Thus, IL‐18 plays a decisive role in protective immunity against tuberculosis.