Mari Ohmura

Induction of cytokines in a human colon epithelial cell line by Shiga toxin 1 (Stx1) and Stx2 but not by non-toxic mutant Stx1 which lacks N-glycosidase activity

Stx1 and Stx2 produced by Shiga toxin‐producing Escherichia coli are cytotoxic due to their N‐glycosidase activity on 28S rRNA. In this study, we have shown that proinflammatory cytokine mRNAs, especially IL‐8, were induced by Stx1 and Stx2 in Caco‐2 cells. A non‐toxic mutant of Stx1 which lacks N‐glycosidase activity did not induce cytokine mRNAs. IL‐8 production at the protein level was enhanced by Stx1 and Stx2, but not by the mutant Stx1. These results demonstrate that Shiga toxins induce expression and synthesis of cytokines in Caco‐2 cells and their N‐glycosidase activity is essential for the induction.

Typing of verotoxins by DNA colony hybridization with poly- and oligonucleotide probes, a bead-enzyme-linked immunosorbent assay, and polymerase chain reaction

To identify the type of Verotoxins (VT) produced by Verocytotoxin‐producing Escherichia coli (VTEC), a sensitive bead‐enzyme‐linked immunosorbent assay and polymerase chain reaction with common and specific primers to various VTs (VT1, VT2, VT2vha, VT2vhb, and VT2vp1) were developed. Together with colony hybridization tests with oligo‐ and polynucleotide probes, these methods were applied to VTEC isolates to type the VT produced. The toxin types of 26 of 37 strains were identified, but the reaction profiles in assays of the remaining 11 strains suggested the existence of new VT2 variants. The application of these identification procedures may be useful as a tool for clinical and epidemiological studies of VTEC infection.

Chimeras of labile toxin one and cholera toxin retain mucosal adjuvanticity and direct Th cell subsets via their B subunit.

Native cholera toxin (nCT) and the heat-labile toxin 1 (nLT) of enterotoxigenic Escherichia coli are AB5-type enterotoxins. Both nCT and nLT are effective adjuvants that promote mucosal and systemic immunity to protein Ags given by either oral or nasal routes. Previous studies have shown that nCT as mucosal adjuvant requires IL-4 and induces CD4-positive (CD4+) Th2-type responses, while nLT up-regulates Th1 cell production of IFN-γ and IL-4-independent Th2-type responses. To address the relative importance of the A or B subunits in CD4+ Th cell subset responses, chimeras of CT-A/LT-B and LT-A/CT-B were constructed. Mice nasally immunized with CT-A/LT-B or LT-A/CT-B and the weak immunogen OVA developed OVA-specific, plasma IgG Abs titers similar to those induced by either nCT or nLT. Both CT-A/LT-B and LT-A/CT-B promoted secretory IgA anti-OVA Ab, which established their retention of mucosal adjuvant activity. The CT-A/LT-B chimera, like nLT, induced OVA-specific mucosal and peripheral CD4+ T cells secreting IFN-γ and IL-4-independent Th2-type responses, with plasma IgG2a anti-OVA Abs. Further, LT-A/CT-B, like nCT, promoted plasma IgG1 more than IgG2a and IgE Abs with OVA-specific CD4+ Th2 cells secreting high levels of IL-4, but not IFN-γ. The LT-A/CT-B chimera and nCT, but not the CT-A/LT-B chimera or nLT, suppressed IL-12R expression and IFN-γ production by activated T cells. Our results show that the B subunits of enterotoxin adjuvants regulate IL-12R expression and subsequent Th cell subset responses.

Cloning and Sequencing of Two New Verotoxin 2 Variant Genes of Escherichia coli Isolated from Cases of Human and Bovine Diarrhea

We cloned and sequenced two new Verotoxin 2 (VT2) variant genes: one from an Escherichia coli strain from a case of bovine diarrhea and the other from an E. coli strain from a patient with diarrhea. The nucleotide and amino acid sequences of these two genes were highly homologous with, but distinct from those of the VT2, VT2vha, VT2vhb, SLT‐IIv (VT2vp1) and SLT‐IIva (VT2vp2) genes. Their nucleotide sequences were much more closely homologous to that of VT2vh than to that of VT2vp. Search for these two new genes in other Verocytotoxin‐producing E. coli strains resulted in the isolation of 2 strains carrying one of the new VT2 variant genes, one strain from Tokyo and the other from Canada.

Protective immunity to Streptococcus mutans induced by nasal vaccination with surface protein antigen and mutant cholera toxin adjuvant.

In this study, mice were immunized nasally with surface protein antigen of Streptococcus mutans serotype c (PAc) and a nontoxic A subunit mutant of cholera toxin (mCT) E112K, as a mucosal adjuvant. Immunization with PAc and mCT elicited significant PAc-specific secretory IgA in saliva and in nasal secretions. Antibody-forming cell (AFC) analysis confirmed the antibody (Ab) titers by revealing significant numbers of PAc-specific IgA AFCs in the submandibular gland and nasal passages. Furthermore, CD4(+) T cells from cervical lymph nodes exhibited significant proliferative responses when restimulated with PAc in vitro. Importantly, mice that were nasally immunized with PAc plus mCT E112K exhibited significantly reduced oral colonization by S. mutans. These results show that nasal administration of PAc and mCT E112K is potentially an effective mucosal vaccine against dental caries and reduces the colonization of S. mutans in the oral cavity.

Nasal immunization with E. coli verotoxin 1 (VT1)-B subunit and a nontoxic mutant of cholera toxin elicits serum neutralizing antibodies

Escherichia coli O157:H7 produces two forms of verotoxin (VT), VT1 and VT2, which cause hemorrhagic colitis with development, in some cases, of hemolytic uremic syndrome. These toxins consist of an enzymatically active A subunit and pentamers of B subunit responsible for their binding to host cells. We used the secretion-expression system of Bacillus brevis to produce recombinant VT1B and VT2B. The secreted B subunits were purified and sequenced to verify their structure. Receptor-binding showed that rVT1B but not rVT2B bound to Gb3-receptor. When mice were nasally immunized with rVT1B or rVT2B together with a nontoxic mutant of cholera toxin (mCT) or native cholera toxin (nCT) as adjuvants, serum IgG and mucosal IgA antibody responses to VT1B were induced. The VT1B-specific antibodies prevented VT1B binding to its Gb3 receptor. In contrast, poor serum and no mucosal VT2B-specific antibodies but brisk CTB-specific antibody responses were induced by nasal immunization with rVT2B in the presence of mCT or nCT. These results show that nasal immunization with rVTB and mCT as a nontoxic mucosal adjuvant is an effective regimen for the induction of VT1B but not VT2B antibody responses which inhibit VT1B binding to Gb3 receptor.

Nontoxic Shiga Toxin Derivatives from Escherichia coli Possess Adjuvant Activity for the Augmentation of Antigen-Specific Immune Responses via Dendritic Cell Activation

ABSTRACT Shiga toxin (Stx) derivatives, such as the Stx1 B subunit (StxB1), which mediates toxin binding to the membrane, and mutant Stx1 (mStx1), which is a nontoxic doubly mutated Stx1 harboring amino acid substitutions in the A subunit, possess adjuvant activity via the activation of dendritic cells (DCs). Our results showed that StxB1 and mStx1, but not native Stx1 (nStx1), resulted in enhanced expression of CD86, CD40, and major histocompatibility complex (MHC) class II molecules and, to some extent, also enhanced the expression of CD80 on bone marrow-derived DCs. StxB1-treated DCs exhibited an increase in tumor necrosis factor alpha and interleukin-12 (IL-12) production, a stimulation of DO11.10 T-cell proliferation, and the production of both Th1 and Th2 cytokines, including gamma interferon (IFN-γ), IL-4, IL-5, IL-6, and IL-10. When mice were given StxB1 subcutaneously, the levels of CD80, CD86, and CD40, as well as MHC class II expression by splenic DCs, were enhanced. The subcutaneous immunization of mice with ovalbumin (OVA) plus mStx1 or StxB1 induced high titers of OVA-specific immunoglobulin M (IgM), IgG1, and IgG2a in serum. OVA-specific CD4+ T cells isolated from mice immunized with OVA plus mStx1 or StxB1 produced IFN-γ, IL-4, IL-5, IL-6, and IL-10, indicating that mStx1 and StxB1 elicit both Th1- and Th2-type responses. Importantly, mice immunized subcutaneously with tetanus toxoid plus mStx1 or StxB1 were protected from a lethal challenge with tetanus toxin. These results suggest that nontoxic Stx derivatives, including both StxB1 and mStx1, could be effective adjuvants for the induction of mixed Th-type CD4+ T-cell-mediated antigen-specific antibody responses via the activation of DCs.

Highly purified mutant E112K of cholera toxin elicits protective lung mucosal immunity to diphtheria toxin

We demonstrated that the mutant of cholera toxin (mCT) E112K which was LPS-free supported the induction of protective immunity in mucosal (e.g. lung lavage) and systemic (e.g. serum) compartments when given nasally with vaccine-grade diphtheria toxoid (DT) to mice. Significant DT-specific mucosal IgA antibody (Ab) and serum IgG, IgA and IgM Ab responses were induced when LPS-depleted mCT E112K or native CT (nCT) was co-administered nasally with DT. The analysis of DT-specific Ab-forming cell (AFC) responses supported the Ab titers and significant numbers of DT-specific IgA AFC were present in the lungs, nasal passages and submandibular glands. Furthermore, DT-specific IgG AFC in cervical lymph nodes (CLN) and the spleen were induced in mice administered with DT nasally with either mCT or nCT. The analysis of antigen-specific T cell responses revealed that increased DT-specific CD4+ T cell proliferative and Th2-type cytokine responses were induced in mice nasally-immunized with DT and the LPS-free form of mCT. The neutralization of diphtheria toxin by Abs showed that DT-specific IgG Ab responses in serum and lung lavages of mice immunized with DT and mCT were protective. Furthermore, it was shown that an IgA-enriched fraction of lung lavages possessed diphtheria toxin-specific neutralizing activity. These results are the first demonstration that nasally co-administered mCT E112K can induce DT-specific protective Ab responses in mucosal compartments (e.g. lung lavages and the lungs).