Immunoassay methods for paralytic shellfish poisoning toxins

The current status of immunochemical techniques for analysis of paralytic shellfish poisoning (PSP) toxins is summarized. Important aspects regarding production of the biological reagents necessary for immunochemical methods, the characteristics of polyclonal and monoclonal antibodies against saxitoxin and neosaxitoxin, and the importance of test sensitivity and specificity are discussed. Applications of immunochemical techniques for PSP toxins include microtiter plate enzyme immunoasays and enzyme-linked immunofiltration assays for toxin detection, and immunoaffinity chromatography (IAC) for sample extract cleanup. A major advantage of enzyme immunoassay (EIA) is simplicity and rapidity of the test procedure, and higher sensitivity than other methods. However, quantitative agreement between EIA and mouse bioassay is dependent on antibody specificity and the toxin profile in the shellfish; thus, both over- and underestimation of total toxicity may occur. For screening purposes, however, EIAs offer major advantages over the mouse bioassay, which is criticized in Europe because of animal welfare. A major application of antibodies against PSP toxins is their use for extract cleanup by IAC, which gives highly purified extracts, thereby enhancing determination of PSP toxins by conventional physicochemical methods such as liquid chromatography. IAC can also be used to isolate PSP toxins for preparation of analytical standard solutions.

Toll-like receptors as sensors of pathogens

Initial recognition of microbes, as they enter the body, is based on germ line-encoded pattern recognition receptors that selectively bind to essential components of pathogens. This allows the body to respond immediately to the microbial invasion before the development of active immunity. The signal-transducing receptors that trigger the acute inflammatory cascade have been elusive until very recently. On the basis of their genetic similarity to the Toll signaling pathway in Drosophila, mammalian Toll-like receptors (TLRs) have been identified. By now, nine transmembrane proteins in the TLR family have been described. Mammalian TLR4 is the signal-transducing receptor activated by the bacterial lipopolysaccharide. The activation of TLR4 leads to DNA binding of the transcription factor NF-kappaB, resulting in activation of the inflammatory cascade. Activation of other TLRs is likely to have similar consequences. TLR2 mediates the host response to Gram-positive bacteria and yeast. TLR1 and TLR6 may participate in the activation of macrophages by Gram-positive bacteria, whereas TLR9 appears to respond to a specific sequence of bacterial DNA. The TLRs that control the onset of an acute inflammatory response are critical antecedents for the development of adaptive acquired immunity. Genetic and developmental variation in the expression of microbial pattern recognition receptors may affect the individual's predisposition to infections in childhood and may contribute to susceptibility to severe neonatal inflammatory diseases, allergies, and autoimmune diseases.

Anaphylactic reactions after therapeutic injection of mistletoe (Viscum album L.)

Mistletoe (Viscum album) is a plant that is semiparasitic of several trees: apple, oak, pine trees, etc. Because of the probable cytolytic action of one of the leaf's most abundant composites, in some countries mistletoe is used as a complementary medicine. Although only a few adverse reactions have been noted (cephalea, fever), cases of anaphylactic shock have been described. We present three cases of severe reaction after injection of mistletoe extract. Two of the patients had cancer. The third, whose brother had cancer, used the plant for preventive purposes. We discuss the danger of possible severe reactions due to the use of products employed in so-called alternative therapies.

Complement components as uremic toxins and their potential role as mediators of microinflammation

Cardiovascular disease is the major cause of death in end-stage renal disease (ESRD) patients. There is growing evidence that atherogenesis is an inflammatory rather than a purely degenerative process leading to a state of microinflammation. This raises the issue of whether treatment modalities of ESRD contribute to the microinflammatory state. One potential candidate in this context is the complement system. Here we consider three potential pathways linking complement activation to progression of atherosclerosis: (1) complement activation on artificial surfaces depends on their physicochemical characteristics, the effect of which is amplified because of the accumulation of complement factor D; (2) the exposure of ESRD patients to endotoxin creates a microinflammatory state, and this may amplify complement-induced damage; exposure to endotoxin may result from frequent infections because of the impairment of host-defense mechanisms or from transfer of bacterial contaminants across dialysis membranes into the blood stream; and (3) direct transduction of proinflammatory signals from blood-material interactions to the vascular system. We conclude that the complement system is an important candidate system in the genesis of microinflammation and accelerated atherogenesis in ESRD. We advance the hypothesis that the generation of proinflammatory signals, in which the complement system appears to be involved--both through systemic and local activation--plays a role in the development of late complications of uremia, including coronary heart disease. This hypothesis provides a rationale to maximize the biocompatibility of the dialysis procedure, that is, selection of nonactivating materials, use of ultrapure dialysis fluid, and--still theoretical--high-flux dialysis to remove factor D.

The identification of plant lectins with mucosal adjuvant activity

To date, the most potent mucosal vaccine adjuvants to be identified have been bacterial toxins. The present data demonstrate that the type 2 ribosome-inactivating protein (type 2 RIP), mistletoe lectin I (ML-I) is a strong mucosal adjuvant of plant origin. A number of plant lectins were investigated as intranasal (i.n.) coadjuvants for a bystander protein, ovalbumin (OVA). As a positive control, a potent mucosal adjuvant, cholera toxin (CT), was used. Co-administration of ML-I or CT with OVA stimulated high titres of OVA-specific serum immunoglobulin G (IgG) in addition to OVA-specific IgA in mucosal secretions. CT and ML-I were also strongly immunogenic, inducing high titres of specific serum IgG and specific IgA at mucosal sites. None of the other plant lectins investigated significantly boosted the response to co-administered OVA. Immunization with phytohaemagglutinin (PHA) plus OVA elicited a lectin-specific response but did not stimulate an enhanced response to OVA compared with the antigen alone. Intranasal delivery of tomato lectin (LEA) elicited a strong lectin-specific systemic and mucosal antibody response but only weakly potentiated the response to co-delivered OVA. In contrast, administration of wheatgerm agglutinin (WGA) or Ulex europaeus lectin 1 (UEA-I) with OVA stimulated a serum IgG response to OVA while the lectin-specific responses (particularly for WGA) were relatively low. Thus, there was not a direct correlation between immunogenicity and adjuvanticity although the strongest adjuvants (CT, ML-I) were also highly immunogenic.

The removal of viruses during the purification of equine antisera using filtration aids Hyflo Super-Cel and Fulmon Super A

The manufacturing process in Australia for equine antisera against various venoms/toxins is based primarily on ammonium sulphate precipitation of pepsin-digested IgG, whereby Fc and F(ab')(2)fragments are separated. The capacity of the process to remove non-enveloped and enveloped model viruses was assessed using a scaled-down process. Each virus was added to mid-process samples from equine plasma before the material was applied to Hyflo Super-Celtrade mark filtration followed by Fulmonttrade mark Super A filtration. Samples were analysed pre- and post-filtration and the log clearance of the viruses calculated. The mean clearance factors for viral load of canine adenovirus type II (CAV(2)), poliovirus type 1 (PV1), infectious bovine rhinotracheitis virus (IBR) and canine distemper virus (CDV) were 5.3 logs, 4.2 logs, 5.7 logs and 4. 0 logs respectively. Clearance results as virus is adsorbed to the filtration aids which are removed from the process, thereby demonstrating improved viral safety of equine antisera produced by CSL.

Structure of the Malpha2-3 toxin alpha antibody-antigen complex: combination of modelling with functional mapping experimental results

Modelled structures of the acetylcholine receptor-mimicking antibody, Malpha2-3, both free and bound to its antigen, toxin alpha, are assessed in the light of new experimental mutational data from functional mapping of the paratopic region of Malpha2-3. The experimental results are consistent with the previously-predicted structure of the free antibody, and also demonstrate that structural particularities of the Malpha2-3 combining site that were identified in the models play a role in the protein association. The modelled conformations of the hypervariable loops are discussed in the context of recent new data and analyses. The new mutational data allow several previously-considered modelled structures of the complex to be rejected. Two quite similar models now remain.

[Analysis of major antigenic determinants in Mistletoe lectin I]

Antigenic determinants of Mistletoe Lectin I, a toxin from Viscum album were predicted on the basis of the primary amino acid sequence of the protein. Based on the results of analysis, the peptide FPGGSTRTQARS, which corresponds to the 144-155 segment of the viscumin A-chain, was synthesized. The peptide was tested in enzyme-linked immunosorbent assay with monoclonal antibodies against the viscumin A-chain obtained previously. The peptide reacted with antibodies with a low affinity and did not inhibit the binding of viscumin molecule to any of the antibodies. Analysis of the peptide by 1H-NMR spectroscopy in aqueous solution was performed. The three-dimensional structure of the 144-155 segment in the native protein globule was shown.

Epidermal HLA-DR and the enhancement of cutaneous reactivity to superantigenic toxins in psoriasis

Streptococcal and staphylococcal superantigens (SAg's) have been implicated in the pathogenesis of inflammatory skin diseases, but the mechanisms by which these toxins act are unknown. The present study assessed the ability of nanogram quantities of topically applied purified toxic shock syndrome toxin-1 (TSST-1), staphylococcal enterotoxin type B, and streptococcal pyrogenic enterotoxin types A and C to induce inflammatory reactions in clinically uninvolved skin of normal controls and subjects with psoriasis, atopic dermatitis, and lichen planus. These SAg's triggered a significantly greater inflammatory skin response in psoriatics than in normal control subjects or in subjects with atopic dermatitis or lichen planus. Surprisingly, skin biopsies did not exhibit the T-cell receptor Vbeta stimulatory properties predicted for SAg-induced skin reactions. By 6 hours after patch testing with SAg's, TNF-alpha mRNA had increased in the epidermis (but not the dermis) in biopsies from psoriatics, compared with controls. Immunohistochemical studies revealed significantly higher HLA-DR expression in keratinocytes from psoriatics than from controls. However, a mutant TSST-1 protein that fails to bind HLA-DR did not elicit an inflammatory skin reaction. These results indicate that keratinocyte expression of HLA-DR enhances inflammatory skin responses to SAg's. They may also account for previous studies failing to demonstrate selective expansion of T-cell receptor Vbetas in psoriatics colonized with SAg-producing Staphylococcus aureus, and they identify a novel T cell-independent mechanism by which SAg's contribute to the pathogenesis of inflammatory skin diseases.

Mistletoe lectin dissociates into catalytic and binding subunits before translocation across the membrane to the cytoplasm

Hybridomas producing monoclonal antibodies (mAbs) against the mistletoe lectin A-chain (MLA) were obtained to investigate the intracellular routing and translocation of ribosome-inactivating proteins. Anti-MLA mAb MNA5 did not bind the holotoxin but interacted with isolated MLA. This epitope was not recognized upon MLA denaturation or conjugation of MLA with the ricin binding subunit (RTB). Furthermore, the mAbs did not appreciably react with a panel of MLA synthetic octapeptides linked to the surface of polyethylene pins. A study of the cytotoxicity of mistletoe lectin, ricin, and chimeric toxin MLA/RTB for the hybridomas revealed that interchain disulfide bond reduction and subunit dissociation are required for cytotoxic activity of mistletoe lectin.

Protein toxins produced by pathogenic vibrios

Genus Vibrio includes some pathogenic species which are classified into two groups: a gastrointestinal infection group and an extraintestinal infection group. The vibrios produce various toxic proteins. Cholera toxin (CT) produced by V. cholerae O1 and O139 is a factor causing diarrhea with severe dehydration by ADP-ribosylation of the alpha subunit of the GTP-binding protein which stimulates adenylate cyclase activity. CT-like toxins are found in some strains of V. cholerae non-O1 or V. mimicus, but not in V. parahaemolyticus, another major diarrheagenic vibrio species. A thermostable direct hemolysin (TDH) is thought to be the pathogenic factor causing diarrhea in the vibrio. Hemolysin is the most widely distributed toxin in the pathogenic vibrios and plays various roles in the infection process. Protease activity is also common in the vibrios. Many of the proteases produced by the vibrios are a metalloprotease having a zinc atom immunologically cross reactive to each other. The proteases act not only for processing and activation of protein toxins but also direct toxic factors causing edematous or hemorrhagic skin lesions or disturbance of host defense system.

Recognition of different antigens of mistletoe extracts by anti-mistletoe lectin antibodies

Anti-mistletoe lectin-1 (ML-1) antibodies are produced during treatment of cancer patients with mistletoe extracts. However, little is known about their ability to recognise distinct epitopes present in mistletoe extracts. To estimate this, ML-1, ML-2 and ML-3 were analysed by Western blot analysis using high titred anti-ML antibody positive sera from cancer patients treated with different mistletoe extracts. In these experiments we could clearly demonstrate that anti-ML antibodies bind to ML-1 A- and B-chains and, in addition, that they recognised a spectrum of other antigens. This kind of immunological response varied from one individual to another and was not influenced by the different mistletoe extracts. Elution studies showed that anti-ML-1 A-chain or B-chain specific antibodies cross-reacted with A- or B-chains of the other lectins indicating homologies between these molecules (probably in the glycosylated side chain). However, the unglycosylated ML-3 A-chain was only detectable by antibodies specific for the ML-3 A-chain. From our data it has to be concluded that different epitopes of the mistletoe extracts are involved in the induction of the humoral immune response during mistletoe therapy and also that cross-reactivity between the different ML exist.

Detection of ALMB-toxin in the larval body of Myrmeleon bore by anti-N-terminus peptide antibodies

Antibodies were raised against a synthetic antigen carrying the N-terminus peptide of ALMB-toxin, which had been isolated from the antlion, Myrmeleon bore, that exhibited high specificity to the toxin. Analyses with the antibodies showed the toxin to be present mainly at the larval stage and localized in a region from the thorax to abdomen of the larval body.

Elapid venom toxins: multiple recruitments of ancient scaffolds

Nigroxins A and B, two myotoxic phospholipases A2 (PLA2s) from the venom of the American elapid Micrurus nigrocinctus, belong to a new PLA2 subclass. Their primary structures were established and compared with those of PLA2s that have already been studied with respect to myotoxic activity. The combination of amino acid residues Arg15, Ala100, Asn108 and a hydrophobic residue at position 109 is present exclusively in class I PLA2s that display myotoxic activity. These residues cluster within a surface region rich in positive charges and are suggested to play a role in the interaction with the target membrane of the muscle fibers. It is concluded that the myotoxic PLA2s resulted from recruitment of an ancient scaffold. Dendrotoxins and alpha-neurotoxins are similarly derived from other old structures, which are, however, now also present in nontoxic proteins that are widely distributed throughout the animal kingdom. The evolutionary pathways by which elapid PLA2s acquired myotoxicity and dendrotoxins acquired K+-channel blocker activity are traced. They demonstrate how existing scaffolds were adapted stepwise to serve toxic functions by exchange of a few surface-exposed residues.

The neglected saliva: medically important toxins in the saliva of human lice

Although there has been a great deal of research effort within the last two decades on identifying the active components of the saliva of blood-sucking ticks, mosquitoes, biting flies, fleas and bugs, essentially neglected have been the human lice. Despite initial reports in the early part of this century suggestive of vasodilatory, anticoagulant and immunosuppressive properties of the saliva, for the next 50 years there were no biochemical studies on the active principles. Very recently, anatomical and biochemical studies have begun to characterize the bioactive molecules in lice saliva. The louse stocks a salivary vasodilator in excess over what is needed for a single bite, and injects similar amounts at each successive bite. The vasodilator in lice saliva appears to have different pharmacological properties than peroxidative, oxidative and maxidilan types of vasodilators reported from other blood-sucking insects. Possible anticoagulant activities have also been characterized. This belated, but welcome, interest comes at a time of resurgence of lice-born disease in certain parts of Africa, and of resistance to chemical control in Europe and North America.

A natural immunity-activating plant lectin, Viscum album agglutinin-I, induces apoptosis in human lymphocytes, monocytes, monocytic THP-1 cells and murine thymocytes

A galactoside-specific plant lectin, Viscum album agglutinin-I (VAA-I) with protein synthesis-inhibiting properties, has been shown to be cytotoxic in various eukaryotic cells, in vitro above a 10 ng/ml concentration. Noncytotoxic concentrations of VAA-I induced mRNA expression and enhanced secretion of proinflammatory cytokines in cultures of human peripheral blood mononuclear cells. In an animal model VAA-I has been shown to stimulate natural killer cells and granulocytes. In this study, human peripheral blood lymphocytes (PBL), human peripheral blood monocytes (PBM), murine thymocytes and human monocytic THP-1 cells were incubated for 24 h in the presence of various concentrations of VAA-I. The apoptotic effect of VAA-I was analyzed by flow cytometry following staining of the apoptotic nuclei in the cells with PI in hypotonic buffer and quantitative detection of DNA breaks were analyzed by the terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) assay. In cultures of all types of investigated cells, a dose-dependent VAA-I concentrations above 10 ng/ml in PBL and at 1 ng/ml VAA-I concentration in PBM, thymocytes and THP-1 cells, a lectin-induced increase of the apoptotic nuclei was observed. In 24-hour cultures of PBL and thymocytes, the ratios between apoptotic and nonapoptotic cells were enhanced 10 times and 8 times, respectively, by 100 ng/ml VAA-I compared to the negative control. The concentration of 100 micrograms/ml VAA-I only caused necrosis. The isolated A chain of the VAA-I induced apoptosis in PBL and thymocytes. In the culture of PBL the isolated B chain of the VAA-I was not effective indicating that cytokine induction by VAA-I is probably not involved in its apoptotic effect. On CD4+8+ thymocytes, VAA-I resulted in a reduced expression of CD8+ molecules that could be related to a loss of volume and increase of density, both characteristic features of apoptosis.

Localization of intravenously administered verocytotoxins (Shiga-like toxins) 1 and 2 in rabbits immunized with homologous and heterologous toxoids and toxin subunits

Rabbits challenged intravenously with Shiga toxin or with Escherichia coli verocytotoxin 1 or 2 (VT1 or VT2) are known to develop diarrhea, paralysis, and death, which can be prevented by immunization with a toxoid. The pathological effects of VT1 in the central nervous system and the gastrointestinal tract of unimmunized rabbits correlate with the localization of 125I-VT1 in these tissues, whereas in immunized animals, localization of 125I-VT1 in target tissues is inhibited and labeled toxin is cleared by the liver and spleen. By using the approach described above in this study, rabbits immunized with VT1 toxoid, VT2 toxoid, or with the A or B subunit of each toxin were challenged with intravenous 125I-VT1 or 125I-VT2. After 2 h, the animals were sacrificed, and selected tissues were analyzed for uptake of labeled toxin. It was found that animals immunized with either VT1 toxoid or VT2 toxoid were protected from target tissue uptake of both 125I-VT1 and 125I-VT2. Rabbits immunized with either the VT1 A or VT2 A subunit were also protected from target tissue uptake of both the homologous and heterologous 125I-labeled holotoxins. In contrast, in animals immunized with the toxin B subunits, protection extended only against challenge by the homologous toxin. These results provide evidence of VT1 and VT2 cross-neutralization in vivo in the rabbit model and indicate that the in vivo cross-neutralization is a function, mainly, of antibodies directed to the VT A subunits. This suggests that the VT1 A or VT2 A subunit may be a suitable immunogen for immunizing humans against systemic VT-mediated disease.

Induction of anti-mistletoe lectin antibodies in relation to different mistletoe-extracts

Mistletoe extracts are frequently applied in adjuvant cancer treatment. The mistletoe lectins are especially suggested to mediate an antitumorous effect. During treatment with mistletoe lectin-rich extracts, anti-mistletoe lectin antibodies preferentially of the immunoglobulin G type are produced against mistletoe lectin (ML)-1. Interestingly, after application of mistletoe extracts containing natural micelles, anti-mistletoe lectin antibodies of the immunoglobulin G as well as one of the immunoglobulin E type were induced in parallel, suggesting that the nature and preparation of the antigens within the extract modifies immune responses. Anti-mistletoe lectin antibodies were shown to neutralize the cytotoxic effect of mistletoe lectin on peripheral blood mononuclear cells in vitro. Thus, the mode of application of these extracts seems to be of importance with respect to the therapeutic effect.

Structural model of the anti-snake-toxin antibody, M alpha 2,3

We present results of structural modeling of the variable fragment of M alpha 2,3, an antibody capable of neutralizing all short snake toxins. Three different methods were used to model the hypervariable loops: the conformational search algorithm CONGEN (Bruccoleri and Karplus, Biopolymers 26:137-168, 1987), high-temperature molecular dynamics (Bruccoleri and Karplus, Biopolymers 29:1847-1862, 1990), and a combined knowledge-based and energy-based algorithm (Martin et al., Proc. Natl. Acad. Sci. USA 86:9268-9272, 1989). Ninety plausible conformations were generated and were clustered into 13 classes. The clustering results indicate that there was little overlap of the conformational space explored by the different methods. Canonical loop structures were found by all methods for two of the loops, in agreement with previously established empirical modeling criteria. Nine of the 13 classes of structure were rejected on the ground of their lacking common features of antibody combining-site structure. The remaining four models were refined using restrained molecular dynamics. It was found that interconversion between the four resulting structures is possible with no significant energy barriers, suggesting that they are in thermodynamic equilibrium at 300 K. Features of the combining-site structure likely to be particularly important for antigen binding are discussed.

Killer factor interference in mixed opportunistic yeast cultures

The interaction of the killer yeast Pichia anomala UP 25F with the killer toxin-sensitive clinical isolate Candida albicans UCSC 10S and its natural toxin-resistant mutant derivative C. albicans UCSC 10R were studied under various conditions. A differential inhibition was shown to occur in vitro at pH and temperature values, which are not encountered in vivo, only by using preformed killer toxin, since antagonism due to yeast growth proved to be predominant on the killer effect. Under adverse growth conditions, the P. anomala killer yeast proved to be able to produce an anatoxin antigenically related to the active or heat inactivated killer toxin. These findings suggest that killer toxins may not function as potential virulence factors in the competition between the opportunistic killer yeast P. anomala and sensitive microorganisms for colonization in the course of natural human infections.

Prospective study of toxigenic Clostridium difficile in children given amoxicillin/clavulanate for otitis media

OBJECTIVE

Evaluate antibiotic-associated diarrhea and toxigenic Clostridium difficile in stool specimens obtained from children before and after 10 days of amoxicillin/clavulanate for otitis media.

DESIGN

Children, 12 to 47 months of age, treated with amoxicillin/clavulanate for otitis media in an outpatient setting were enrolled. Stool specimens were obtained at enrollment, when diarrhea occurred and at the end of therapy. All stool specimens were tested for C. difficile toxins A and B by enzyme immunoassay.

RESULTS

Seventy-six children who had stool specimens collected at enrollment and after therapy were included in the analysis. None had C. difficile toxin in stool specimens at enrollment. Six (27%) of 22 children with diarrhea, and 4 (7%) of 54 children without diarrhea had C. difficile toxin present at completion of therapy (P = 0.03).

CONCLUSION

Toxigenic C. difficile was identified in 13% of children at the conclusion of amoxicillin/clavulanate therapy with a significantly higher frequency in children with diarrhea.