Helicobacter pylori Adapts to Chronic Infection and Gastric Disease via pH-Responsive BabA-Mediated Adherence.

The BabA adhesin mediates high-affinity binding of Helicobacter pylori to the ABO blood group antigen-glycosylated gastric mucosa. Here we show that BabA is acid responsive-binding is reduced at low pH and restored by acid neutralization. Acid responsiveness differs among strains; often correlates with different intragastric regions and evolves during chronic infection and disease progression; and depends on pH sensor sequences in BabA and on pH reversible formation of high-affinity binding BabA multimers. We propose that BabA's extraordinary reversible acid responsiveness enables tight mucosal bacterial adherence while also allowing an effective escape from epithelial cells and mucus that are shed into the acidic bactericidal lumen and that bio-selection and changes in BabA binding properties through mutation and recombination with babA-related genes are selected by differences among individuals and by changes in gastric acidity over time. These processes generate diverse H. pylori subpopulations, in which BabA's adaptive evolution contributes to H. pylori persistence and overt gastric disease.

A human domain antibody and Lewis b glycoconjugate that inhibit binding of Helicobacter pylori to Lewis b receptor and adhesion to human gastric epithelium.

Increasing antibiotic resistance has prompted development of alternative approaches to antimicrobial therapy, including blocking microbial adhesion to host receptors. The BabA adhesin of Helicobacter pylori binds to fucosylated blood group antigens, such as the Lewis(b) antigens in human primate gastric mucosa. We have isolated a human domain antibody specific for BabA that inhibits binding of BabA to Lewis(b) and prevents adhesion of H. pylori to human gastric epithelium. In addition, Lewis(b) oligosaccharides covalently linked to poly-D-lysine inhibited BabA binding to Le(b). The poly-D-lysine-Le(b) hexasaccharide and an Le(b) human serum albumin conjugate not only inhibited adherence of H. pylori to gastric epithelium but also displaced adherent bacteria when added to human stomach sections. Combinations of Le(b) and sialyl Le(x) or domain antibody 25 and sialyl Le(x) acted synergistically. Domain antibody 25 inhibitor may have potential for prophylactic use and, in combination with Le(b) glycoconjugates, therapeutic use in treatment of drug-resistant H. pylori infection.

Pertussis toxin and its binding unit inhibit HIV-1 infection of human cervical tissue and macrophages involving a CD14 pathway.

Pertussis toxin (PTX) and its binding unit (PTX-B) have been shown to inhibit human immunodeficiency virus (HIV)-1 infection of primary cells. However, the anti-HIV mechanisms have yet to be defined. We demonstrate that PTX inhibits HIV-1 infection of human cervical tissue independently of viral tropism. PTX-B showed a similar pattern of HIV-1 inhibition. Further investigation in macrophages demonstrated that PTX/PTX-B inhibited HIV-1 expression but that other G protein inhibitors and activators had no effect on HIV-1 replication. Unlike the anti-HIV bacterial lipopolysaccharide, the anti-HIV effects of PTX/PTX-B were not due to beta -chemokine production or coreceptor down-modulation, but they were dependent on interaction with cell-surface receptors. Antibody blocking studies suggested that cell-surface CD14 is very likely to be the principal receptor involved in the anti-HIV effects of PTX/PTX-B. This was further strengthened by the results of surface plasmon resonance analyses. Further definition of the mechanisms of such inhibition may lead to the development of novel HIV-1 prevention strategies.

Interaction between the CCR5 chemokine receptors and microbial HSP70.

Evidence is presented that the microbial 70-kD heat shock protein (HSP70) binds to CCR5 chemokine receptors in CCR5-transfected cell lines and in primary human cells. Significant CCR5-mediated calcium mobilization was stimulated by HSP70 and inhibited with TAK 779, which is a specific CCR5 antagonist. HSP70-mediated activation of the p38 MAPK phosphorylation signaling pathway was also demonstrated in CCR5-transfected HEK 293 cells. Direct binding of three extracellular peptides of CCR5 to HSP70 was demonstrated by surface plasmon resonance. Functional evidence of an interaction between HSP70, CCR5 and CD40 was shown by enhanced production of CCL5 by HEK 293 cells transfected with both CD40 and CCR5. Primary monocyte-derived immature DC stimulated with HSP70 produced IL-12 p40, which showed dose-dependent inhibition of >90% on treatment with both TAK 779 and anti-CD40 mAb. Stimulation of IL-12 p40 or TNF-alpha by HSP70 was related to the differential cell surface expression of CCR5 in primary human immature and mature DC, and those with the homozygous triangle DeltaDelta32 CCR5 mutation. These findings may be of significance in the interaction between HSP70 and immune responses of CCR5+ T cells in HIV-1 infection, as well as in inflammatory bowel disease.

Identification of stimulating and inhibitory epitopes within the heat shock protein 70 molecule that modulate cytokine production and maturation of dendritic cells.

The 70-kDa microbial heat shock protein (mHSP70) has a profound effect on the immune system, interacting with the CD40 receptor on DC and monocytes to produce cytokines and chemokines. The mHSP70 also induces maturation of dendritic cells (DC) and thus acts as an alternative ligand to CD40L on T cells. In this investigation, we have identified a cytokine-stimulating epitope (peptide 407-426), by activating DC with overlapping synthetic peptides (20-mers) derived from the sequence of mHSP70. This peptide also significantly enhances maturation of DC stimulated by mHSP70 or CD40L. The epitope is located at the base of the peptide-binding groove of HSP70 and has five critical residues. Furthermore, an inhibitory epitope (p457-496) was identified downstream from the peptide-binding groove that inhibits cytokine production and maturation of DC stimulated by HSP70 or CD40L. The p38 MAP kinase phosphorylation is critical in the alternative CD40-HSP70 pathway and is inhibited by p457-496 but enhanced by p407-426.

Expression of a functional single-chain Fv antibody on the surface of Streptococcus gordonii.

Gram-positive bacterium Streptococcus gordonii, a human oral commensal, was engineered to display a single-chain Fv (scFv) antibody fragment at the cell surface. The previously developed host-vector system allowed expression of the Guy's 13 scFv as a fusion with the streptococcal surface protein M6. Surface expression of the 515-amino acid M6/scFv fusion protein was confirmed by Western blot analysis on cellular fractions and flow cytometric analysis. Guy's 13 scFv was derived from the Guy's 13 monoclonal antibody, which was raised against streptococcal antigen I/II (SA I/II), the major adhesin of the caries-producing bacterium Streptococcus mutans. Surface plasmon resonance was used to test binding of scFv-expressing S. gordonii to SA I/II. Whole cells of recombinant S. gordonii were found to specifically bind to immobilised SA I/II and binding was inhibited by fluid-phase SA I/II in a dose-dependent manner. Production of a functional scFv in S. gordonii is the first step towards the development of genetically engineered commensal bacteria that, by colonizing mucosal surfaces, may provide the host with sustained delivery of recombinant antibodies.

The rational design of an anti-caries peptide against Streptococcus mutans.

The cariogenic bacterium Streptococcus mutans attaches to tooth surfaces via a cell surface adhesin termed streptococcal antigen I/II (SA I/II). Mapping studies identified an adhesion epitope within residues 1025-1044. A synthetic peptide (p1025) spanning these residues inhibited adhesion of S. mutans in vitro and was tested in an in vivo human streptococcal adhesion model. Direct application of p1025 to the teeth prevented recolonisation of the oral cavity by S. mutans but not Actinomyces naeslundii. This review also describes various other adhesion-inhibiting peptides have been identified in vitro. We suggest that adhesion-blocking synthetic peptides may provide novel anti-infective agents. Topical application of such peptides at mucosal surfaces does not provide sustained selective pressure and in contrast to antibiotics, may not induce resistance.