Characterization of monoclonal immunoglobulin a and g against shiga toxin binding subunits produced by intranasal immunization

Prevention of Shiga toxin 1-caused colon injury by plant-derived recombinant IgA

Immunoglobulin A (IgA) is a candidate antibody for oral passive immunization against mucosal pathogens like Shiga toxin-producing Escherichia coli (STEC). We previously established a mouse IgG monoclonal antibody (mAb) neutralizing Shiga toxin 1 (Stx1), a bacterial toxin secreted by STEC. We designed cDNA encoding an anti-Stx1 antibody, in which variable regions were from the IgG mAb and all domains of the heavy chain constant region from a mouse IgA mAb. Considering oral administration, we expressed the cDNA in a plant expression system aiming at the production of enough IgA at low cost. The recombinant-IgA expressed in Arabidopsis thaliana formed the dimeric IgA, bound to the B subunit of Stx1, and neutralized Stx1 toxicity to Vero cells. Colon injury was examined by exposing BALB/c mice to Stx1 via the intrarectal route. Epithelial cell death, loss of crypt and goblet cells from the distal colon were observed by electron microscopy. A loss of secretory granules containing MUC2 mucin and activation of caspase-3 were observed by immunohistochemical methods. Pretreatment of Stx1 with the plant-based recombinant IgA completely suppressed caspase-3 activation and loss of secretory granules. The results indicate that a plant-based recombinant IgA prevented colon damage caused by Stx1 in vivo.

Hepatoprotective Mechanism of Ginsenoside Rg1 against Alcoholic Liver Damage Based on Gut Microbiota and Network Pharmacology

Alcoholic liver disease (ALD) is a major public health problem worldwide, which needs to be effective prevention. Ginsenoside Rg1 (GRg1), a bioactive ingredient extracted from ginseng, has benefit effects on health. In this study, 11 potential targets of GRg1 against ALD were firstly obtained by network pharmacology. KEGG pathway enrichment showed that GRg1-target-ALD was closely related to Toll-like receptor (TLR) and nuclear factor-kappa B (NF-κB) signaling pathways. In addition, GRg1 decreased antioxidant levels and increased oxidative levels in alcohol-treated mice, which alleviated oxidative stress-induced hepatic damage. GRg1 enhanced intestinal barrier function via upregulating the levels of tight junction protein and immunoglobulin A. GRg1 also reduced alcohol-induced inflammation by suppressing TLR4/NF-κB pathway, which was consistent with the prediction of network targets. Moreover, GRg1 altered GM population, and Verrucomicrobia, Bacteroidetes, Akkermansia, Bacteroides, Lachnospiraceae_NK4A136_group, and Alloprevotella played positive association with intestinal barrier indicators and negative correlation with hepatic inflammation biomarkers. The results suggest that GRg1 administration might be a promising strategy for protection of alcohol-induced liver damage.

Lettuce-derived secretory IgA specifically neutralizes the Shiga toxin 1 activity

MAIN CONCLUSION

An edible plant was tested as a host for the production of secretory monoclonal IgA against Shiga toxin 1 (Stx1). The lettuce-derived IgA completely protected Vero cells from Stx1. Secretory immunoglobulin A (SIgA) is thought to control mucosal infections and thus it may be applicable to oral passive immunotherapy. Edible plants are candidate hosts for producing oral formulations with SIgA against pathogenic agents. We previously established a recombinant IgA specific for the B subunit of Shiga toxin 1 (Stx1B) consisting of the Fab fragment of Stx1B-specific monoclonal IgG and the Fc region of IgA (hyIgA). Here, we developed transgenic lettuce (Lactuca sativa) that produces hyIgA in a secretory form (S-hyIgA). An Arabidopsis-derived light-harvesting complex II (LHCB) promoter was used for the expression of all four transgenes (hyIgA heavy, light and j chains, and secretory component). Agrobacterium-mediated transformation was carried out to introduce genes into lettuce leaf discs by means of a single vector harboring all four transgenes. Consistent with the tissue specificity of the LHCB promoter, the expression of hyIgA transgenes was observed in leaf and stem tissues, which contain chloroplasts, at the mRNA and protein levels. The leaves produced hyIgA in a more than tenfold higher yield as compared with stems. The lettuce-derived S-hyIgA was found to bind to Stx1B in a dose-dependent manner by means of ELISA. A leaf extract of the transgenic lettuce completely neutralized the cytotoxicity of Stx1 against Vero cells, which are highly susceptible to Stx1. In conclusion, we established a transgenic lettuce producing a secretory form of hyIgA that can bind bacterial toxin. The results indicate that edible practical plants containing S-hyIgA will provide a possible means for immunotherapy for food poisoning.

Plant-derived secretory component forms secretory IgA with shiga toxin 1-specific dimeric IgA produced by mouse cells and whole plants

A key module, secretory component (SC), was efficiently expressed in Arabidopsis thaliana. The plant-based SC and immunoglobulin A of animal or plant origin formed secretory IgA that maintains antigen-binding activity. Plant expression systems are suitable for scalable and cost-effective production of biologics. Secretory immunoglobulin A (SIgA) will be useful as a therapeutic antibody against mucosal pathogens. SIgA is equipped with a secretory component (SC), which assists the performance of SIgA on the mucosal surface. Here we produced SC using a plant expression system and formed SIgA with dimeric IgAs produced by mouse cells as well as by whole plants. To increase the expression level, an endoplasmic reticulum retention signal peptide, KDEL (Lys-Asp-Glu-Leu), was added to mouse SC (SC-KDEL). The SC-KDEL cDNA was inserted into a binary vector with a translational enhancer and an efficient terminator. The SC-KDEL transgenic Arabidopsis thaliana produced SC-KDEL at the level of 2.7% of total leaf proteins. In vitro reaction of the plant-derived SC-KDEL with mouse dimeric monoclonal IgAs resulted in the formation of SIgA. When reacted with Shiga toxin 1 (Stx1)-specific ones, the antigen-binding activity was maintained. When an A. thaliana plant expressing SC-KDEL was crossed with one expressing dimeric IgA specific for Stx1, the plant-based SIgA exhibited antigen-binding activity. Leaf extracts of the crossbred transgenic plants neutralized Stx1 cytotoxicity against Stx1-sensitive cells. These results suggest that transgenic plants expressing SC-KDEL will provide a versatile means of SIgA production.

Human Cell Line-Derived Monoclonal IgA Antibodies for Cancer Immunotherapy

IgA antibodies have great potential to improve the functional diversity of current IgG antibody-based cancer immunotherapy options. However, IgA production and purification is not well established, which can at least in part be attributed to the more complex glycosylation as compared to IgG antibodies. IgA antibodies possess up to five N-glycosylation sites within their constant region of the heavy chain as compared to one site for IgG antibodies. The human GlycoExpress expression system was developed to produce biotherapeutics with optimized glycosylation and used here to generate a panel of IgA isotype antibodies directed against targets for solid (TA-mucin 1, Her2, EGFR, Thomsen–Friedenreich) and hematological (CD20) cancer indications. The feasibility of good manufacturing practice was shown by the production of 11 g IgA within 35 days in a one liter perfusion bioreactor, and IgA antibodies in high purity were obtained after purification. The monoclonal IgA antibodies possessed a high sialylation degree, and no non-human glycan structures were detected. Kinetic analysis revealed increased avidity antigen binding for IgA dimers as compared to monomeric antibodies. The IgA antibodies exhibited potent Fab- and Fc-mediated functionalities against cancer cell lines, whereby especially granulocytes are recruited. Therefore, for patients who do not sufficiently benefit from therapeutic IgG antibodies, IgA antibodies may complement current regiment options and represent a promising strategy for cancer immunotherapy. In conclusion, a panel of novel biofunctional IgA antibodies with human glycosylation was successfully generated.

Protection of Human Colon Cells from Shiga Toxin by Plant-based Recombinant Secretory IgA

Shiga toxin is a major virulence factor of food-poisoning caused by Escherichia coli such as O157:H7. Secretory immunoglobulin (Ig) A (SIgA) is supposed to prevent infection of the mucosal surface and is a candidate agent for oral immunotherapy. We previously established a recombinant monoclonal antibody (mAb) consisting of variable regions from a mouse IgG mAb specific for the binding subunit of Shiga toxin 1 (Stx1) and the Fc region of mouse IgA. Here we produced a secretory form of the recombinant IgA (S-hyIgA) with transgenic Arabidopsis thaliana plant. All the S-hyIgA cDNAs (heavy, light, J chain and secretory component) were expressed under the control of a bidirectional promoter of a chlorophyll a/b-binding protein of A. thaliana without using a viral promoter. The plant-based S-hyIgA exhibited antigen binding, and was modified with plant-specific N-linked sugar chains. The Ig heavy chain and secretory components were observed in an intracellular protein body-like structure of the transgenic leaves on immuno-electron microscopy. An extract of the transgenic leaves neutralized the cytotoxicity of Stx1 toward butyrate-treated Caco-2 cells, a human colon carcinoma cell line. These results will contribute to the development of edible therapeutic antibodies such as those for the treatment of mucosal infection.

Shiga toxin-induced apoptosis is more efficiently inhibited by dimeric recombinant hybrid-IgG/IgA immunoglobulins than by the parental IgG monoclonal antibodies

Shiga toxin 1 (Stx1) is a virulence factor of enterohaemorrhagic Escherichia coli strains such as O157:H7 and Shigella dysenteriae. To prevent entry of Stx1 from the mucosal surface, an immunoglobulin A (IgA) specific for Stx1 would be useful. Due to the difficulty of producing IgA monoclonal antibodies (mAb) against the binding subunit of Stx1 (Stx1B) in mice, we took advantage of recombinant technology that combines the heavy chain variable region from Stx1B-specific IgG1 mAb and the Fc region from IgA. The resulting hybrid IgG/IgA was stably expressed in Chinese hamster ovary cells as a dimeric hybrid IgG/IgA. We separated the dimeric hybrid IgG/IgA from the monomeric one by size-exclusion chromatography. The dimer fraction, confirmed by immunoblot analyses, was used for toxin neutralization assays. The dimeric IgG/IgA was shown to neutralize Stx1 toxicity toward Vero cells by assaying their viability. To compare the relative effectiveness of the dimeric hybrid IgG/IgA and parental IgG1 mAb, Stx1-induced apoptosis was examined using 2 different cell lines, Ramos and Vero cells. The hybrid IgG/IgA inhibited apoptosis more efficiently than the parental IgG1 mAb in both cases. The results indicated that the use of high affinity binding sites as variable regions of IgA would increase the utility of IgA specific for virulence factors.

Recombinant immunoglobulin A specific for influenza A virus hemagglutinin: production, functional analysis, and formation of secretory immunoglobulin A

Secretory immunoglobulin (Ig) A (SIgA), comprised of dimeric IgA and secretory component (SC), is believed to provide a defense mechanism on the mucosal surface. Influenza A virus (IAV) hemagglutinin (HA)-specific SIgA is thought to play an important role in the prevention of IAV infection. However, the topical application of preformed IAV-specific SIgA has not been shown to prevent IAV infection. This is due to the difficulty in the production of antigen-specific IgA monoclonal antibodies (mAbs) and monoclonal SIgA. Here, a recombinant hybrid IgA (HIgA) was established that utilizes variable regions of an HA-specific mouse IgG mAb and the heavy chain constant region of a mouse IgA mAb. We expressed the dimeric HIgA in Chinese hamster ovary-K1 (CHO-K1) cells. When in vitro IAV infection of Madin-Darby canine kidney (MDCK) cells was tested, 10 times lower concentrations of HIgA were able to inhibit it as compared with an HA-specific IgG with the same variable regions. A functional hybrid secretory IgA (HSIgA) was also produced through incubation of the dimeric HIgA with recombinant mouse SC in vitro. It was demonstrated that HSIgA could be separated from the dimeric HIgA on size exclusion chromatography. This study provides a basic strategy for investigating the role of SIgA upon IAV infection on the mucosal surface.

Stable expression and characterization of monomeric and dimeric recombinant hybrid-IgG/IgA immunoglobulins specific for Shiga toxin

Antigen-specific immunoglobulin A (IgA) may be useful for preventing infectious diseases through passive immunization on the mucosal surface. We previously established mouse IgA and IgG monoclonal antibodies (mAbs) specific for the binding subunit of Shiga toxin 1 (Stx1B). We also developed a recombinant hybrid-IgG/IgA, in which variable regions from the IgG mAb were present. The binding activity of recombinant hybrid-IgG/IgA was verified by transient expression. Aiming at a constant supply, we established Chinese hamster ovary cells stably expressing monomeric or dimeric hybrid-IgG/IgA. The cDNAs encoding heavy and light chains were co-expressed for the monomeric hybrid-IgG/IgA, while those encoding heavy, light, and joining chains were co-expressed for the dimeric one. Serum-free culture supernatants of the cloned transfectants were subjected to size-exclusion chromatography. The elution patterns showed that the binding to immobilized Stx1B and the immunoblot signals of assembled immunoglobulins were correlated. In the transfectant for the dimeric hybrid-IgG/IgA, both monomers and dimers were observed. Size-exclusion chromatography enabled us to prepare a sample of the dimeric hybrid-IgG/IgA devoid of the monomeric one. The monomeric and dimeric forms of hybrid-IgG/IgA were prepared from the respective transfectants to examine the neutralization of Stx1. After pretreatment with monomeric or dimeric hybrid-IgG/IgA, the cytotoxicity of Stx1 toward Vero cells was abolished. Furthermore, the dimeric form was more than 10-fold more effective than the monomeric one in terms of toxin neutralization. These results suggest that the tetravalent feature of the binding sites of the dimeric hybrid-IgG/IgA contributes to the efficacy of toxin neutralization.

Production of hybrid-IgG/IgA plantibodies with neutralizing activity against Shiga toxin 1

Shiga toxin 1 (Stx1) is a virulence factor of enterohemorrhagic Escherichia coli, such as the O157:H7 strain. In the intestines, secretory IgA (SIgA) is a major component of the immune defense against pathogens and toxins. To form SIgA, the production of dimeric IgA that retains biological activity is an important step. We previously established hybrid-IgG/IgA having variable regions of the IgG specific for the binding subunit of Stx1 (Stx1B) and the heavy chain constant region of IgA. If hybrid-IgG/IgA cDNAs can be expressed in plants, therapeutic or preventive effects may be expected in people eating those plants containing a “plantibody”. Here, we established transgenic Arabidopsis thaliana expressing dimeric hybrid-IgG/IgA. The heavy and light chain genes were placed under the control of a bidirectional promoter and terminator of the chlorophyll a/b-binding protein of Arabidopsis thaliana (expression cassette). This expression cassette and the J chain gene were subcloned into a single binary vector, which was then introduced into A. thaliana by means of the Agrobacterium method. Expression and assembly of the dimeric hybrid-IgG/IgA in plants were revealed by ELISA and immunoblotting. The hybrid-IgG/IgA bound to Stx1B and inhibited Stx1B binding to Gb₃, as demonstrated by ELISA. When Stx1 holotoxin was pre-treated with the resulting plantibody, the cytotoxicity of Stx1 was inhibited. The toxin neutralization was also demonstrated by means of several assays including Stx1-induced phosphatidylserine translocation on the plasma membrane, caspase-3 activation and 180 base-pair DNA ladder formation due to inter-nucleosomal cleavage. These results indicate that edible plants containing hybrid-IgG/IgA against Stx1B have the potential to be used for immunotherapy against Stx1-caused food poisoning.

Phagocytic entry of Legionella pneumophila into macrophages through phosphatidylinositol 3,4,5-trisphosphate-independent pathway

Legionella pneumophila, a causative agent of Legionnaire's disease, is an intracellular pathogen. It intervenes in the signal transduction of macrophages by secreting effector molecules through the Icm/Dot type IV secretion system (T4SS). There is a connection between signaling cascades that regulate phagocytosis and the production of reactive oxygen species (ROS). Class I phosphatidylinositol 3-kinase (PI3-K) and its product phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) play key roles in the reorganization of cytoskeleton (phagocytosis) and activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (ROS production). We investigated the production of PI(3,4,5)P3 and recruitment of class I PI3-K and Rac1 during phagocytosis of L. pneumophila by macrophages. Transient recruitment of class I PI3-K as well as PI(3,4,5)P3 production was observed around a phagocytosed T4SS mutant LELA3118 or avirulent mutant 25D in an early stage of infection. In contrast, class I PI3-K was recruited while accumulation of PI(3,4,5)P3 was not observed around wild type JR32. Immunoglobulin G (IgG)-opsonized live JR32, which would activate class I PI3-K through the Fcγ receptor pathway, did not induce PI(3,4,5)P3 production. Regardless of whether wild type or mutants were used, transient Rac1 accumulation was observed around bacteria. These results indicate that the phagocytosis of wild type L. pneumophila occurs via a special mechanism in which PI(3,4,5)P3 production is absent. This suggests that L. pneumophila may inhibit the production of PI(3,4,5)P3, but not the recruitment of class I PI3-K and Rac1, in a T4SS-dependent manner. L. pneumophila may start the modulation of host signaling cascade immediately after contact with host cells to evade the ROS-dependent bactericidal system while completing entry into macrophages.

Interaction between Shiga toxin and monoclonal antibodies: binding characteristics and in vitro neutralizing abilities

Monoclonal antibodies (MAbs) have been employed either for diagnosis or treatment of infections caused by different pathogens. Specifically for Shiga toxin-producing Escherichia coli (STEC), numerous immunoassays have been developed for STEC diagnosis, showing variability in sensitivity and specificity when evaluated by reference laboratories, and no therapy or vaccines are currently approved. Thus, the aim of this work was the characterization of the interaction between MAbs against Stx1 and Stx2 toxins and their neutralizing abilities to enable their use as tools for diagnosis and therapy. The selected clones designated 3E2 (anti-Stx1) and 2E11 (anti-Stx2) were classified as IgG1. 3E2 recognized the B subunit of Stx1 with an affinity constant of 2.5 × 10⁻¹⁰ M, detected as little as 6.2 ng of Stx1 and was stable up to 50 ºC. In contrast, 2E11 recognized the A subunit of Stx2, was stable up to 70 ºC, had a high dissociation constant of 6.1 × 10⁻¹⁰ M, and detected as little as 12.5 ng of Stx2. Neutralization tests showed that 160 ng of 3E2 MAb inhibited 80% of Stx1 activity and 500 µg 2E11 MAb were required for 60% inhibition of Stx2 activity. These MAb amounts reversed 25 to 80% of the cytotoxicity triggered by different STEC isolates. In conclusion, these MAbs show suitable characteristics for their use in STEC diagnosis and encourage future studies to investigate their protective efficacy.

Monoclonal antibodies and toxins--a perspective on function and isotype

Antibody therapy remains the only effective treatment for toxin-mediated diseases. The development of hybridoma technology has allowed the isolation of monoclonal antibodies (mAbs) with high specificity and defined properties, and numerous mAbs have been purified and characterized for their protective efficacy against different toxins. This review summarizes the mAb studies for 6 toxins—Shiga toxin, pertussis toxin, anthrax toxin, ricin toxin, botulinum toxin, and Staphylococcal enterotoxin B (SEB)—and analyzes the prevalence of mAb functions and their isotypes. Here we show that most toxin-binding mAbs resulted from immunization are non-protective and that mAbs with potential therapeutic use are preferably characterized. Various common practices and caveats of protection studies are discussed, with the goal of providing insights for the design of future research on antibody-toxin interactions.

Establishment of recombinant hybrid-IgG/IgA immunoglobulin specific for Shiga toxin

Shiga toxin 1 produced by enterohaemorrhagic Escherichia coli is an AB(5) toxin that is involved in the life-threatening haemolytic-uraemic syndrome. The B subunits (Stx1B) are cell-binding subunits. We previously established mouse hybridoma cell line producing IgA and IgG monoclonal antibodies (mAbs) against Stx1B. Here, we cloned cDNAs encoding each of the heavy, light and joining (J) chains from the hybridoma cell lines by means of the 5' rapid amplification of cDNA ends (RACE) PCR method. Upon assignment of the variable regions of the heavy and light chains to known germline sequences, we found substantial somatic hypermutation in the complementarity-determining regions in both the IgA and IgG mAbs. We also established a hybrid-IgG/IgA heavy chain having variable regions of the IgG mAb by means of recombinant PCR methods. Upon transient expression of the hybrid-IgG/IgA heavy, IgG-associated light and J chains in COS-1 cells, the translated dimeric hybrid-IgG/IgA bound to immobilized Stx1B, as revealed on ELISA. The production of dimeric hybrid-IgG/IgA was revealed on immunoblot analysis. The dimeric hybrid-IgG/IgA inhibited the binding of digoxigenin-conjugated Stx1B to natural ligands (CD77) displayed on Burkitt's lymphoma cell line Ramos. These results indicate that the replacement of variable regions resulted in the production of more useful recombinant dimeric IgA against Stx1B.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.