Dose Of Ricin Research Articles

Short- and long-term outcomes of pulmonary exposure to a sublethal dose of ricin in mice

Ricin, an extremely potent toxin produced from the seeds of castor plant, Ricinus communis, is ribosome-inactivating protein that blocks cell-protein synthesis. It is considered a biological threat due to worldwide availability of castor beans, massive quantities as a by-product of castor oil production, high stability and ease of production. The consequence of exposure to lethal dose of ricin was extensively described in various animal models. However, it is assumed that in case of aerosolized ricin bioterror attack, the majority of individuals would be exposed to sublethal doses rather than to lethal ones. Therefore, the purpose of current study was to assess short- and long-term effects on physiological parameters and function following sublethal pulmonary exposure. We show that in the short-term, sublethal exposure of mice to ricin resulted in acute lung injury, including interstitial pneumonia, cytokine storm, neutrophil influx, edema and cellular death. This damage was manifested in reduced lung performance and physiological function. Interestingly, although in the long-term, mice recovered from acute lung damage and restored pulmonary and physiological functionality, the reparative process was associated with lasting fibrotic lesions. Therefore, restriction of short-term acute phase of the disease and management of long-term pulmonary fibrosis by medical countermeasures is expected to facilitate the quality of life of exposed survivors.

Transcriptome Analysis of Lungs in a Mouse Model of Severe COVID-19

Severe manifestations of coronavirus disease 2019 (COVID-19) are mostly restricted to distinct groups of people who have preexisting morbidities. Most COVID-19 animal models develop a mild pathology that resolves within a relatively short period of time, reflecting the more prevalent asymptomatic-to-mild performance of the disease observed in humans. Mice are normally unaffected by SARS coronavirus-2 infection, because of the inability of the virus to bind effectively to the murine angiotensin-converting enzyme 2 (ACE2) receptor. We have previously demonstrated that induction of mild and transient pulmonary morbidity, by application of low doses of ricin, rendered CD1 mice to be susceptible to this virus, which was displayed by sustained body weight loss and mortality rates >50%. In the present study, we performed transcriptomic analyses charting the major alterations in gene expression of mice that were pre-exposed to low doses of ricin and then subjected to SARS-CoV-2 infection compared to mice that were solely exposed to ricin or infected with SARS-CoV-2. Mice intoxicated and infected with ricin and SARS-CoV-2 demonstrated a marked stimulation of essential immunity genes and biological pathways involved in the activation of natural-killer response, cell death receptors, cytotoxic T-cells, Toll-like receptor signaling and the NLRP3 inflammasome pathway. At the protein level, an induced early and transient interferon response was recorded which was subsequently suppressed. The activation of this array of genes predicts clinical manifestations that are consistent with severe COVID-19 in humans, thereby establishing the suitability of this unique animal model for the study of severe COVID-19 disease.

An intranasally administered monoclonal antibody cocktail abrogates ricin toxin-induced pulmonary tissue damage and inflammation

ABSTRACT Ricin toxin, a plant-derived, mannosylated glycoprotein, elicits an incapacitating and potentially lethal inflammatory response in the airways following inhalation. Uptake of ricin by alveolar macrophages (AM) and other pulmonary cell types occurs via two parallel pathways: one mediated by ricin’s B subunit (RTB), a galactose-specific lectin, and one mediated by the mannose receptor (MR;CD206). Ricin’s A subunit (RTA) is a ribosome-inactivating protein that triggers apoptosis in mammalian cells. It was recently reported that a single monoclonal antibody (MAb), PB10, directed against an immunodominant epitope on RTA and administered intravenously, was able to rescue Rhesus macaques from lethal aerosol dose of ricin. In this study, we now demonstrate in mice that the effectiveness PB10 is significantly improved when combined with a second MAb, SylH3, against RTB. Mice treated with PB10 alone survived lethal-dose intranasal ricin challenge, but experienced significant weight loss, moderate pulmonary inflammation (e.g., elevated IL-1 and IL-6 levels, PMN influx), and apoptosis of lung macrophages. In contrast, mice treated with the PB10/SylH3 cocktail were essentially impervious to pulmonary ricin toxin exposure, as evidenced by no weight loss, no change in local IL-1 and IL-6 levels, retention of lung macrophages, and a significant dampening of PMN recruitment into the bronchoalveolar lavage (BAL) fluids. The PB10/SylH3 cocktail only marginally reduced ricin binding to target cells in the BAL, suggesting that the antibody mixture neutralizes ricin by interfering with one or more steps in the RTB- and MR-dependent uptake pathways.

Intramuscular Ricin Poisoning of Mice Leads to Widespread Damage in the Heart, Spleen, and Bone Marrow.

Ricin, a lethal toxin derived from castor oil beans, is a potential bio-threat due to its high availability and simplicity of preparation. Ricin is prepared according to simple recipes available on the internet, and was recently considered in terrorist, suicide, or homicide attempts involving the parenteral route of exposure. In-depth study of the morbidity developing from parenteral ricin poisoning is mandatory for tailoring appropriate therapeutic measures to mitigate ricin toxicity in such instances. The present study applies various biochemical, hematological, histopathological, molecular, and functional approaches to broadly investigate the systemic effects of parenteral intoxication by a lethal dose of ricin in a murine model. Along with prompt coagulopathy, multi-organ hemorrhages, and thrombocytopenia, ricin induced profound morpho-pathological and functional damage in the spleen, bone marrow, and cardiovascular system. In the heart, diffuse hemorrhages, myocyte necrosis, collagen deposition, and induction in fibrinogen were observed. Severe functional impairment was manifested by marked thickening of the left ventricular wall, decreased ventricular volume, and a significant reduction in stroke volume and cardiac output. Unexpectedly, the differential severity of the ricin-induced damage did not correlate with the respective ricin-dependent catalytic activity measured in the various organs. These findings emphasize the complexity of ricin toxicity and stress the importance of developing novel therapeutic strategies that will combine not only anti-ricin specific therapy, but also will target ricin-induced indirect disturbances.

An Intranasally Administered Antibody Cocktail Prevents Ricin Toxin-Induced Lung Inflammation and Alveolar Macrophage Death

Abstract Ricin toxin, a plant-derived, mannosylated glycoprotein, elicits an incapacitating and potentially lethal, pulmonary inflammatory response in the airways following inhalation. Uptake by alveolar macrophages (AM) and other pulmonary cell types occurs via ricin’s B subunit (RTB), a galactose-specific lectin, and the mannose receptor (MR; CD206). Ricin’s A subunit (RTA) is a ribosome-inactivating protein capable of inducing apoptosis in all mammalian cell types. It was recently reported that a single monoclonal antibody (MAb), PB10, directed against an immunodominant epitope on RTA, is able rescue Rhesus macaques against lethal dose of ricin administered by aerosol. In this study, we now demonstrate in mice that the effectiveness PB10 is significantly improved when combined with a second MAb, SylH3, against RTB. Mice treated with PB10 alone survived lethal-dose intranasal ricin challenge, but experienced significant weight loss, moderate pulmonary inflammation (e.g., elevated IL-1 and IL-6 levels, PMN influx), and apoptosis of alveolar and tissue macrophages. In contrast, mice treated with the PB10/SylH3 cocktail were essentially impervious to pulmonary ricin toxin exposure, as evidenced by no weight loss, no change in local IL-1 and IL-6 levels, retention of alveolar and tissue macrophage numbers, and a significant dampening of PMN recruitment to the bronchoalveolar lavage (BAL) fluids. The PB10/SylH3 cocktail only marginally reduced ricin binding to target cells in the BAL, suggesting that the antibody mixture neutralizes ricin by interfering with one or more steps in the RTB- and MR-dependent uptake pathways.

Clinical manifestations following intramuscular exposure of mice to a lethal dose of ricin

Abstract Ricin a plant toxin derived from seeds of Ricinus communis, irreversibly inactivates ribosomes by site-specific depurination, thereby arresting cell protein synthesis, while its clinical manifestations following intramuscular exposure have not yet been investigated in depth. Here we report an extensive pathological study of intramuscular intoxication with a lethal dose of ricin in a murine model. Ricin injection caused neutrophilia, thrombocytopenia and coagulopathy. Although histopathological alternations including hemorrhages, vessel congestion and focal necrosis were observed in various organs, major insults were limited to the spleen, bone marrow (BM) and cardiovascular system. Intensive atrophy, evident in the BM and splenic white pulps, were accompanied be severe depletion of megakaryocytes in both organs. Moreover, splenic T and B lymphocytes, NK cells, macrophages and dendritic cells decreased significantly. The most striking damage was in the heart, where we observed diffuse hemorrhages, myocyte disconnection, loss of striation, interstitial edema, collagen deposition and elevated levels of serum cardiac troponin. Finally, echocardiography revealed marked thickening of the walls, along with sequential decrease in left ventricular volume. These were accompanied by a significant reduction in stroke volume and cardiac output, while the ejection fraction remained unaltered. Measurements of the toxin direct catalytic performance in the spleen, BM and heart of the ricin-intoxicated mice revealed no substantial 28S rRNA depurination. The lack of measurable ricin catalytic activity in conjunction with the striking clinical disorders observed, suggests that ricin affects these organs in an indirect manner.

Bio-detoxification of ricin in castor bean (Ricinus communis L.) seeds

Ricin is a highly toxic ribosome-inactivating lectin occurring in the seeds of castor bean (Ricinus communis L.). Castor bean grows throughout tropical and sub-tropical regions and is a very important crop due to its high seed content of ricinoleic acid, an unusual fatty acid, which has several industrial applications. However, due to the presence of the toxin, castor bean can cause death after the exposure of animals to low doses of ricin through skin contact, injection, inhalation or oral routes. Aiming to generate a detoxified genotype, we explored the RNAi concept in order to silence the ricin coding genes in the endosperm of castor bean seeds. Results indicated that ricin genes were effectively silenced in genetically modified (GM) plants, and ricin proteins were not detected by ELISA. Hemagglutination activity was not observed with proteins isolated from GM seeds. In addition, we demonstrated that seed proteins from GM plants were not toxic to rat intestine epithelial cells or to Swiss Webster mice. After oil extraction, bio-detoxified castor bean cake, which is very rich in valuable proteins, can be used for animal feeding. Gene silencing would make castor bean cultivation safer for farmers, industrial workers and society.

Potent Antiedematous and Protective Effects of Ciprofloxacin in Pulmonary Ricinosis.

The plant toxin ricin is considered a biological threat agent of concern and is most toxic when inhaled. Pulmonary exposure to a lethal dose of ricin can be redressed by treatment with antiricin antibodies; however, late antitoxin intervention is of limited efficacy. This limitation is associated with overt lung damage, clinically manifested as severe pulmonary inflammation, which develops over time. Increased evidence indicates that ciprofloxacin, a broad-spectrum antimicrobial agent, possesses immunomodulatory properties. Here we demonstrate that while antiricin antibody administration at late hours after intranasal exposure to ricin confers limited protection to mice, highly efficient protection can be achieved by adding ciprofloxacin to the antibody treatment. We further demonstrate that parameters associated with lung injury, in particular, pulmonary proinflammatory cytokine production, neutrophil migration, and edema, are sharply reduced in ricin-intoxicated mice that were treated with ciprofloxacin. The presented data highlight the potential clinical application of ciprofloxacin as a beneficial immunomodulatory agent in the course of ricin intoxication.

Humanized Monoclonal Antibody That Passively Protects Mice against Systemic and Intranasal Ricin Toxin Challenge.

PB10 is a murine monoclonal antibody against an immunodominant epitope on ricin toxin's enzymatic subunit. Here, we characterize a fully humanized version of PB10 IgG1 (hPB10) and demonstrate that it has potent in vitro and in vivo toxin-neutralizing activities. We also report the minimum serum concentrations of hPB10 required to protect mice against 10 times the 50% lethal dose of ricin when delivered by injection and inhalation.

Monoclonal antibody, mAb 4C13, an effective detoxicant antibody against ricin poisoning

Ricin is a glycoprotein produced in castor seeds and consists of two polypeptide chains named Ricin Toxin A Chain (RTA) and Ricin Toxin B Chain (RTB), linked via a disulfide bridge. Due to its high toxicity, ricin is regarded as a high terrorist risk for the public. However, antibodies can play a pivotal role in neutralizing the toxin. In this research, the anti-toxicant effect of mAb 4C13, a monoclonal antibody (mAb) established using detoxicated ricin as the immunized antigen, was evaluated. Compared with mAb 4F2 and mAb 5G6, the effective mechanism of mAb 4C13 was analyzed by experiments relating to its cytotoxicity, epitope on ricin, binding kinetics with the toxin, its blockage on the protein synthesis inhibition induced by ricin and the intracelluar tracing of its complex with ricin. Our result indicated that mAb 4C13 could recognize and bind to RTA, RTB and exert its high affinity to the holotoxin. Both cytotoxicity and animal toxicity of ricin were well blocked by pre-incubating the toxin with mAb 4C13. By intravenous injection, mAb 4C13 could rescue the mouse intraperitoneally (ip) injected with a lethal dose of ricin (20μg/kg) even at 6h after the intoxication and its efficacy was dependent on its dosage. This research indicated that mAb 4C13 could be an excellent candidate for therapeutic antibodies. Its potent antitoxic efficiency was related to its recognition on the specific epitope with very high affinity and its blockage of protein synthesis inhibition in cytoplasm followed by cellular internalization with ricin.

Antibody/doxycycline combined therapy for pulmonary ricinosis: Attenuation of inflammation improves survival of ricin-intoxicated mice

Ricin, a highly toxic plant-derived toxin, is considered a potential weapon in biological warfare due to its high availability and ease of preparation. Pulmonary exposure to ricin results in the generation of an acute edematous inflammation followed by respiratory insufficiency and death. Passive immunization with polyclonal anti-ricin antibodies conferred protection against pulmonary ricinosis, however, at clinically-relevant time points for treatment, survival rates were limited. In this study, intranasal instillation of a lethal dose of ricin to mice, served as a lung challenge model for the evaluation and comparison of different therapeutic modalities against pulmonary ricinosis. We show that treatment with doxycycline resulted in a significant reduction of pro-inflammatory cytokines, markers of oxidative stress and capillary permeability in the lungs of the mice. Moreover, survival rates of mice intoxicated with ricin and treated 24 h later with anti-ricin antibody were significantly improved by co-administration of doxycycline. In contrast, co-administration of the steroid drug dexamethasone with anti-ricin antibodies did not increase survival rates when administered at late hours after intoxication, however dexamethasone did exert a positive effect on survival when applied in conjunction with the doxycycline treatment. These studies strongly suggest that combined therapy, comprised of neutralizing anti-ricin antibodies and an appropriate anti-inflammatory agent, can promote high-level protection against pulmonary ricinosis at clinically-relevant time points post-exposure.

Pathology of Lethal and Sublethal Doses of Aerosolized Ricin in Rhesus Macaques

Ricin toxin, a type 2 ribosome-inactivating protein and a category B bioterrorism agent, is produced from the seeds of castor oil plant (Ricinus communis). Chronic pathological changes in survivors of aerosolized ricin exposure have not been reported in primates. Here we compare and contrast the pathological changes manifested between rhesus macaques (RM) that succumbed to lethal dose of ricin (group I) and survivor RM exposed to low dose of ricin (group II). All animals in group I exhibited severe diffuse, necrotizing bronchiolitis and alveolitis with fibrinopurulent bronchointerstitial pneumonia, massive alveolar, perivascular and peribronchial/bronchiolar edema with hemorrhage, and necropurulent and hemorrhagic tracheobronchial lymphadenitis. All animals from group II had multifocal, fibrosing interstitial pneumonia with prominent alveolar histiocytosis and type II pneumocyte hyperplasia. Subacute changes like infiltration by lymphocytes and plasma cells and persistence of edematous fluid were occasionally present in lung and tracheobronchial lymph nodes. The changes appear to be a continuum wherein the inflammatory response shifts from an acute to subacute/chronic reparative process if the animals can survive the initial insult.

Stabilization of a recombinant ricin toxin A subunit vaccine through lyophilization

Lyophilization was used to prepare dry, glassy solid vaccine formulations of recombinant ricin toxin A-chain containing suspensions of colloidal aluminum hydroxide adjuvant. Four lyophilized formulations were prepared by using combinations of rapid or slow cooling during lyophilization and one of two buffers, histidine or ammonium acetate. Trehalose was used as the stabilizing excipient. Aggregation of the colloidal aluminum hydroxide suspension was reduced in formulations processed with a rapid cooling rate. Aluminum hydroxide particle size distributions, glass transition temperatures, water contents, and immunogenicities of lyophilized vaccines were independent of incubation time at 40°C for up to 15weeks. Mice immunized with reconstituted ricin toxin subunit A (RTA) vaccines produced RTA-specific antibodies and toxin-neutralizing antibodies (TNAs) regardless of the length of high temperature vaccine storage or the degree of aluminum adjuvant aggregation that occurred during lyophilization. In murine studies, lyophilized formulations of vaccines conferred protection against exposure to lethal doses of ricin, even after the lyophilized formulations had been stored at 40°C for 4weeks. A corresponding liquid formulation of vaccine stored at 40°C elicited RTA-specific antibody titers but failed to confer immunity during a ricin challenge.

Monoclonal antibodies against the ricin toxin B subunit: Evidence for extracellular and intracellular mechanisms of toxin neutralization. (53.2)

Abstract Antibodies are remarkable in their capacity to inactivate even the most potent protein toxins, including anthrax, botulinum, diphtheria, and ricin. However, the underlying mechanisms by which this occurs are poorly understood. In this study, we have produced and characterized a collection of monoclonal antibodies (mAbs) directed against the B subunit (RTB) of ricin toxin. RTB plays two roles in ricin cytotoxicity; it promotes toxin attachment to host cell surfaces, and it mediates the intracellular trafficking of the toxin from the plasma membrane to the endoplasmic reticulum (ER). We screened ~2,000 RTB-specific murine B cell hybridomas, and identified 4 mAbs with toxin neutralizing activity. Two of these mAbs, SylH3 and 24B11, passively protected mice against a 5xLD50 dose of ricin, but only partially prevented ricin binding to cell surfaces, indicating that they must neutralize ricin by a mechanism other than simply interfering with receptor attachment. Using a modified Vero cell cytotoxicity assay we found that both SylH3 and 24B11 were able to completely neutralize ricin in vitro even after the toxin had bound to cell surfaces. These data reveal that SylH3 and 24B11 neutralize ricin downstream of attachment, perhaps by interfering with the ability of the toxin to traffic to the ER. We are currently using biochemical and microscopic techniques to localize where in the cell these mAbs interfere with ricin toxicity.

Detection of Ricin Contamination in Liquid Egg by Electrochemiluminescence Immunosorbent Assay

A monoclonal antibody-based electrochemical luminescence method was developed for detecting and quantifying ricin in liquid egg, with a limit of detection of 0.2 ng/mL. Because this highly toxic protein, present in the seeds of Ricinus communis (castor), has been used for intentional poisoning in the past, it is important to have sensitive and reliable analytical methodology to detect ricin in food matrices such as liquid egg. The detection of this quantity of pure or crude ricin spiked into commercial samples of liquid egg provides approximately 50000-fold greater sensitivity than required to detect a toxic dose of ricin (>1 mg) in a 100 g sample. Because ricin has been used for intentional poisoning, there is a need for analytical methodology to detect ricin in food matrices to assure a safe food supply. Using monoclonal antibodies to ricin developed in our laboratory, we explored an assay readout system known as electrochemiluminescence. This technique afforded sensitive and specific analysis of ricin intentionally added to liquid egg and could potentially be used to monitor egg-based vaccine production.

Protective immunity to ricin toxin conferred by antibodies against the toxin's binding subunit (RTB)

The B subunit (RTB) of ricin toxin is a galactose-/N-acetyl galactosamine-specific lectin that promotes attachment and entry of ricin into host cells. RTB is also the archetype of the so-called R-type lectin family, whose members include haemagglutinins of botulinum neurotoxin (BoNT) progenitor toxins, as well as the binding subunits of cytolethal distending toxins. Although RTB is an appealing subunit vaccine candidate, as well as a potential target for immunotherapeutics, the degree to which RTB immunization elicits protective antibodies against ricin toxin remains unresolved. To address this issue, groups of mice were immunized with RTB and then challenged with 5×LD(50)s of ricin administered intraperitoneally. Despite high RTB-specific serum antibody titers, groups of RTB immunized mice were only partially immune to ricin challenge. Analysis of a collection of RTB-specific B cell hybridomas suggested that only a small fraction of antibodies against RTB have demonstrable neutralizing activity. Two RTB-specific neutralizing monoclonal IgG(1) antibodies, 24B11 and SylH3, when passively administered to mice, were sufficient to protect the animals against a 5×LD(50) dose of ricin. Both 24B11 and SylH3 blocked ricin attachment to terminal galactose residues and prevented toxin binding to the surfaces of bone marrow-derived macrophages (BMM), suggesting that they function by steric hindrance and recognize epitopes located on RTB's carbohydrate recognition sub-domains (1α or 2γ). These data raise the possibility of using specific RTB sub-domains, rather than RTB itself, as antigens to more efficiently elicit neutralizing antibodies and protective immunity against ricin.

Detection of Ricin Contamination in Ground Beef by Electrochemiluminescence Immunosorbent Assay

Ricin is a highly toxic protein present in the seeds of Ricinus communis (castor), grown principally as a source of high quality industrial lubricant and as an ornamental. Because ricin has been used for intentional poisoning in the past and could be used to contaminate food, there is a need for analytical methodology to detect ricin in food matrices. A monoclonal antibody-based method was developed for detecting and quantifying ricin in ground beef, a complex, fatty matrix. The limit of detection was 0.5 ng/g for the electrochemiluminescence (ECL) method and 1.5 ng/g for enzyme-linked immunosorbent assay (ELISA). The detection of nanogram per gram quantities of ricin spiked into retail samples of ground beef provides approximately 10,000-fold greater sensitivity than required to detect a toxic dose of ricin (>1 mg) in a 100 g sample.

The B-subunit of ricin toxin is involved in eliciting protective antibodies (106.18)

Abstract The ricin toxin B subunit (RTB) is a galactose-specific lectin that promotes attachment and entry of the ricin enzymatic subunit (RTA) into host cells. RTB is an appealing alternative to RTA-based vaccines, because it is non-toxic and inherently antigenic. However, the degree to which RTB elicits protective immunity against ricin remains unresolved. Here we report that parenteral immunization of mice with RTB elicited high ricin-specific serum antibody titers, yet conferred only partial protection against systemic ricin challenge. Analysis of ~2000 RTB-specific B cell hybridomas identified only a handful of neutralizing monoclonal antibodies (mAbs). Two neutralizing mAbs, 24B11 and SylH3, were shown by passive immunization to be sufficient to protect mice against a 5xLD50 dose of ricin. Both 24B11 and SylH3 blocked ricin attachment to terminal galactose residues and prevented toxin binding to primary macrophages, suggesting that they function by steric hindrance and recognize epitopes located on RTB’s galactose binding sub-domains, 1α or 2γ. By contrast, analysis of four non-neutralizing mAbs revealed that they recognized epitopes situated within sub-domains of RTB not involved in galactose recognition (i.e., 1β, 2α). Based on these data, we propose using specific RTB sub-domains as antigens, rather than RTB itself, as a means to more efficiently elicit neutralizing antibodies and protective immunity against ricin.

Lethal Ricin Intoxication in Two Adult Dogs: Toxicologic and Histopathologic Findings

Two adult dogs with the same owner were intoxicated by ingestion of fertilizer composed of residual plant material of the castor bean plant (Ricinus communis L.). Both dogs died within 2 and 3 days, respectively, after the first signs of vomiting and abundant hemorrhagic diarrhea. Toxicologic and histopathologic examinations were performed on different organs. Histopathologic examination of the kidneys revealed tubular degeneration and necrosis and membranous glomerulonephritis. Additionally, myocardial degeneration with localized inflammation, lymphoid necrosis, and depletion in the spleen and mesenteric lymph nodes and hemorrhagic ulcerative gastroenteritis were found. The 2 cases could be used to elucidate the lethal dose of ricin and the histopathologic lesions in dogs.

A mouse model for ricin poisoning and for evaluating protective effects of antiricin antibodies

Background. Ricin is a potential bioterrorism agent and no specific antidote or treatment exists for ricin poisoning. For this reason, we developed ricin-specific antibodies that were tested in a murine model of ricin poisoning for use as antidotes against symptoms of ricin poisoning. Methods. Mice were poisoned with a lethal dose of ricin (5 μg) and their temperature and general condition were monitored for determination of a surrogate and humane end point. Mice were then treated with injections of ricin and different combinations of polyclonal anti-ricin antibodies. Antibody effect was evaluated for various doses and using various time points from ricin to antibody injection. Also, the effect of adjuvant symptomatic treatment was examined. Brain, heart, intestines, kidney, liver, lung, pancreas, spleen, and stomach tissues were sampled for histopathological analysis. Results. The mouse model was reproducible and easy to use. A clear protective effect of both anti-ricin A-chain and anti-ricin B-chain antibodies–but not of irrelevant antibodies–was demonstrated with no added effect of symptomatic treatment. Conclusions. These data suggest that specific polyclonal antibodies against ricin A- and B-chain may reproducibly protect mice against ricin poisoning, even when the antibodies are administered up to 1.5 h after poisoning.