Sensitivity and predictivity in immunotoxicity testing: immune endpoints and disease resistance

Development of a transcriptome-based determination of innate immune suppressor (TDIS) assay as an in vitro test for immunotoxicity

Immunotoxicity has been an important topic in toxicology since inadvertent exposures to xenobiotics were found to alter immune functions in humans. While rodent toxicity tests can reveal some levels of immunotoxicity, alternative methods must be developed to identify the detailed mechanisms. In this study, a method of in vitro prediction of innate immune suppression by substances was developed using a genomics approach. The primary selection of immune suppressors was based on their ability to downregulate MCP-1, CCL3, TNF, IL-8, and IL-12p40 expression levels in lipopolysaccharide (LPS)-stimulated THP-1 cells. Among 11 substances classified as potent immune suppressors, six including dexamethasone, tacrolimus, tofacitinib, prednisolone, sodium lauryl sulfate, and benzoic acid were used to create a dataset by transcriptomics of chemical-treated THP-1 cells using bulk RNA sequencing. We selected genes that were significantly upregulated by suppressor treatment while filtering out genes also upregulated in LPS-treated THP-1 cells. We identified a 226-gene immunosuppressive gene set (ISG). Innate immune suppressor signature scores were calculated as the median expression of the ISG. In a validation dataset, the signature score predicted acyclovir, cyclosporine, and mercuric chloride as immune suppressors, while selecting genistein as a non-immune suppressor. Although more dataset integration is needed in the future, our results demonstrated the possibility and utility of a novel genomics-based approach, the transcriptome-based determination of innate immune suppressor (TDIS) assay, to evaluate innate immune suppression by different substances. This provides insight into the development of future alternative testing methods because it reflects a comprehensive genetic signature derived from multiple substances rather than one cytokine.

Impact of an immunosuppressive human pharmaceutical on the interaction of a bacterial parasite and its invertebrate host

The interaction of pollutants and pathogens may result in altered and often enhanced effects of the chemical, the biotic stressor or both. These interaction effects cannot be reliably predicted from the toxicity of the chemical or the virulence of the pathogen alone. While standardized detection methods for immunotoxic effects of chemicals exist with regard to human health, employing host-resistance assays with vertebrates, such standardized test systems are completely lacking for invertebrate species and no guidance is available on how immunotoxic effects of a chemical in invertebrates could be definitively identified. In the present study, we investigated the impact of the immunosuppressive pharmaceutical cyclosporine A (CsA) on the invertebrate host-pathogen system Daphnia magna - Pasteuria ramosa. CsA is a calcineurin-inhibitor in vertebrates and also known to have antibiotic as well as antifungal properties. Juvenile D. magna were exposed to CsA for 21 days with or without additional pathogen challenge during the first 72 h of exposure. Long-term survival of the host D. magna was synergistically impacted by co-exposure to the chemical and the pathogen, expressed e.g. in significantly enhanced hazard ratios. Additionally, enhanced virulence of the pathogen upon chemical co-exposure was expressed in an increased proportion of infected hosts and an increased speed of Pasteuria-induced host sterilization. In contrast, effects on reproduction were additive in Pasteuria-challenged, but finally non-infected D. magna. The enhancing effects of CsA occurred at and below 3 μg/L, which was in the absence of the pathogen the lowest concentration significantly impacting the standard toxicity endpoint 'reproduction' in D. magna. Hence, the present study provides evidence that a pharmaceutical intended to suppress the human immune system can also suppress disease resistance of an aquatic invertebrate organism at otherwise non-toxic concentrations. Plausible ways of direct interactions of CsA with the host's immune system are discussed, e.g. interference with phagocytosis or Toll-like receptors. Experimental verification of such a direct interference would be warranted to support the strong evidence for immunotoxic activity of CsA in invertebrates. While it remains open whether CsA concentrations in the environment are high enough to trigger adverse effects in environmental organisms, our findings highlight the need to consider immunotoxicity in an environmental risk assessment, and to develop suitable standardized methods for this purpose.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

Associating Changes in the Immune System with Clinical Diseases for Interpretation in Risk Assessment

This overview is an update of the unit originally published in 2004. While the basic tenets of immunotoxicity have not changed in the past 10 years, several publications have explored the application of immunotoxicological data to the risk assessment process. Therefore, the goal of this unit is still to highlight relationships between xenobiotic-induced immunosuppression and risk of clinical diseases progression. In immunotoxicology, this may require development of models to equate moderate changes in markers of immune functions to potential changes in incidence or severity of infectious diseases. For most xenobiotics, exposure levels and disease incidence data are rarely available, and safe exposure levels must be estimated based on observations from experimental models or human biomarker studies. Thus, it is important to establish a scientifically sound framework that allows accurate and quantitative interpretation of experimental or biomarker data in the risk assessment process.

Chemical compounds from anthropogenic environment and immune evasion mechanisms: potential interactions

An increasing number of studies suggest an important role of host immunity as a barrier to tumor formation and progression. Complex mechanisms and multiple pathways are involved in evading innate and adaptive immune responses, with a broad spectrum of chemicals displaying the potential to adversely influence immunosurveillance. The evaluation of the cumulative effects of low-dose exposures from the occupational and natural environment, especially if multiple chemicals target the same gene(s) or pathway(s), is a challenge. We reviewed common environmental chemicals and discussed their potential effects on immunosurveillance. Our overarching objective was to review related signaling pathways influencing immune surveillance such as the pathways involving PI3K/Akt, chemokines, TGF-β, FAK, IGF-1, HIF-1α, IL-6, IL-1α, CTLA-4 and PD-1/PDL-1 could individually or collectively impact immunosurveillance. A number of chemicals that are common in the anthropogenic environment such as fungicides (maneb, fluoxastrobin and pyroclostrobin), herbicides (atrazine), insecticides (pyridaben and azamethiphos), the components of personal care products (triclosan and bisphenol A) and diethylhexylphthalate with pathways critical to tumor immunosurveillance. At this time, these chemicals are not recognized as human carcinogens; however, it is known that they these chemicalscan simultaneously persist in the environment and appear to have some potential interfere with the host immune response, therefore potentially contributing to promotion interacting with of immune evasion mechanisms, and promoting subsequent tumor growth and progression.

Assessment of drug-induced immunotoxicity in animal models

With the growing understanding that drugs might induce immune-mediated adverse reactions in patients, immunotoxicity testing of new pharmaceuticals has become an important topic in drug development. The nonclinical assessment of unexpected immune suppression is based on relatively well-standardized and validated assays and animal models. For the evaluation of direct immune stimulation few animal models are available, whilst the development of animal models to assess drug-induced hypersensitivity and in particular autoimmunity is in its infancy.:

Perfluorinated compounds: emerging POPs with potential immunotoxicity

Perfluorinated compounds (PFCs) have been recognized as an important class of environmental contaminants commonly detected in blood samples of both wildlife and humans. These compounds have been in use for more than 60 years as surface treatment chemicals, polymerization aids, and surfactants. They possess a strong carbon-fluorine bond, which leads to their environmental persistence. There is evidence from both epidemiology and laboratory studies that PFCs may be immunotoxic, affecting both cell-mediated and humoral immunity. Reported effects of PFCs include decreased spleen and thymus weights and cellularity, reduced specific antibody production, reduced survival after influenza infection, and altered cytokine production. Immunosuppression is a critical effect associated with exposure to PFCs, as it has been reported to reduce antibody responses to vaccination in children. Mounting evidence suggests that immunotoxicity in experimental animals can occur at serum concentrations below, within, or just above the reported range for highly exposed humans and wildlife. Considering bioaccumulation and exposure to multiple PFCs, the risk of immunotoxicity for humans and wildlife cannot be discounted. This review will discuss current and recently published work exploring the immunomodulatory effects of PFCs in experimental animals and humans.

Assessment of possible immunotoxicity of the antipsychotic drug clozapine

OBJECTIVES

The immunomodulatory effects of clozapine (CLZ), antipsychotic drug, were investigated in vivo using female Balb/c mice. The main aim of this study was to evaluate the immunomodulatory effects of CLZ, antipsychotic drug, following daily intraperitoneal injection to female Balb/c mice over a period of 21 days.

METHODS

Mice were divided into five groups, eight animals per group. Group I, served as a control group, received only the vehicle. Groups II-V received a daily intraperitoneal dose of CLZ (1, 5, 10 and 20 mg/kg, respectively) over a period of 21 days.

KEY FINDINGS

CLZ has shown a significant decrease in the animal body weight, and it showed a significant decrease in the percentage of circulating neutrophils and lymphocytes while circulating monocytes were increased. The immunotoxicity has been also assessed by evaluating spleen cellularity, humoral immune response to a foreign antigen using sheep red blood cells and delayed-type hypersensitivity reaction. The results showed a marked suppression in these responses in CLZ-treated mice compared with the control group. Detectable changes have also been noticed in the histology of the footpad tissue and spleen.

CONCLUSIONS

Results showed significant immunomodulatory effects of CLZ when used in Balb/c mice.

Pesticide induced immunotoxicity in humans: a comprehensive review of the existing evidence

The immune system can be the target of many chemicals, with potentially severe adverse effects on the host's health. In Western countries pesticides, together with new and modified patterns of exposure to chemicals, have been implicated in the increasing prevalence of diseases associated with alterations of the immune response, such as hypersensitivity reactions, certain autoimmune diseases and cancers. Xenobiotics may initiate, facilitate or exacerbate pathological immune processes, resulting in immunotoxicity by induction of mutations in genes coding for immunoregulatory factors, modifying immune tolerance and activation pathways. The purpose of this article is to update the evidence of pesticide immunotoxicity. Even if experimental data as well as sporadic human studies indicate that some pesticides can affect the immune system, overall, existing epidemiological studies are inadequate to raise conclusions on the immunotoxic risk associated to pesticide exposure. The available studies on the effects of pesticides on human immune system have several limitations including poor indication on exposure levels, multiple chemical exposures, heterogeneity of the approach, and difficulty in giving a prognostic significance to the slight changes often observed. Further studies are necessary, and they should be preferably carried out through comparison of pre and post-exposure findings in the same group of subjects with a matched control group. Attempt should be made to define the prognostic significance of slight changes often observed. Animal and in vitro studies are also important and necessary to scientifically support epidemiological evidences on pesticide-induced immunotoxicity.

Host resistance assays including bacterial challenge models

Immunotoxicity testing is used to provide safety assessment with the major objective being the avoidance of unacceptable risk of infectious or neoplastic disease. To this end, immunotoxicity testing has employed a variety of host resistance challenge models for measuring both host resistance to disease as well as immune function. This chapter provides an overview of those viral, bacterial, fungal, and parasitic host resistance models that are most commonly used in safety assessment. It also describes in more detail the bacterial challenge models that are employed to address specific host resistance and immune function issues.

Parasite challenge as host resistance models for immunotoxicity testing

Identification of potentially immunosuppressive compounds typically involves assessing a combination of observational endpoints as surrogates for functional endpoints and functional endpoints as surrogates for resistance to infectious or neoplastic disease. Host resistance assays are considered to be the "gold standard" against which suppression of immune function at the molecular or cellular level can be judged, because resistance to infection, regardless of the actual pathogen, involves multiple pathways of effector function to neutralize or eliminate pathogens. Resistance to infection with the parasitic nematode Trichinella spiralis has been used to assess immune function following exposure to a variety of immunotoxicants at the whole animal level. The various immunological mechanisms that are responsible for resistance to different phases of the life cycle are well documented, as are the effects of immunosuppression on the outcome of infection. This chapter describes methods to assess elimination of adult parasites from the small intestine, body burdens of larvae, as well as antibody responses and lymphocyte responses to parasite antigens.

Immunomodulatory effects of domoic acid differ between in vivo and in vitro exposure in mice

The immunotoxic potential of domoic acid (DA), a well-characterized neurotoxin, has not been fully investigated. Phagocytosis and lymphocyte proliferation were evaluated following in vitro and in vivo exposure to assay direct vs indirect effects. Mice were injected intraperitoneally with a single dose of DA (2.5 μg/g b.w.) and sampled after 12, 24, or 48 hr. In a separate experiment, leukocytes and splenocytes were exposed in vitro to 0, 1, 10, or 100 μM DA. In vivo exposure resulted in a significant increase in monocyte phagocytosis (12-hr), a significant decrease in neutrophil phagocytosis (24-hr), a significant decrease in monocyte phagocytosis (48-hr), and a significant reduction in T-cell mitogen-induced lymphocyte proliferation (24-hr). In vitro exposure significantly reduced neutrophil and monocyte phagocytosis at 1 μM. B- and T-cell mitogen-induced lymphocyte proliferation were both significantly increased at 1 and 10 μM, and significantly decreased at 100 μM. Differences between in vitro and in vivo results suggest that DA may exert its immunotoxic effects both directly and indirectly. Modulation of cytosolic calcium suggests that DA exerts its effects through ionotropic glutamate subtype surface receptors at least on monocytes. This study is the first to identify DA as an immunotoxic chemical in a mammalian species.

Determination of immunomodulatory effects: focus on functional analysis of phagocytes as representatives of the innate immune system

The evaluation of the effects of drugs or chemicals on the functions of the immune system is an increasingly important task. Due to the accessibility of primary cells and cell lines, in vitro cellular functional tests are frequently being performed with cells representing the innate immune system, in particular those with phagocytotic activities, such as neutrophils and macrophages. Suitable functional parameters are the efficiency of phagocytosis, the efficiency with which viable pathogens are killed, the production of reactive oxygen and nitrogen species (ROS and RNS) and that of cytokines. Corresponding analytical procedures are available, but standardization is required, as varying the procedure may influence the outcomes of the assays.

Ingestion of deoxynivalenol (DON) contaminated feed alters the pig vaccinal immune responses

Deoxynivalenol (DON), a mycotoxin produced by some Fusarium species, is a frequent contaminant of cereals. This toxin is known to modulate the immune function but only few studies have investigated the effect of DON on the vaccinal immune response. In the present experiment, 24 pigs received for 9 weeks either control feed or feed naturally contaminated with 2.2-2.5 mgDON/kg feed. At days 4 and 15 of the experiment, the animals were subcutaneously immunized with ovalbumin. Consumption of DON-contaminated diet does not have a major effect on the hematological and biochemical blood parameters. By contrast, ingestion of DON significantly affects the global and the specific immune response of the pigs. In the serum, DON increases the concentration of total IgA and, in vaccinated animals, DON also increases the concentration of ovalbumin-specific IgA and IgG. DON does not modulate lymphocytes proliferation after mitogenic stimulation but the toxin had a biphasic effect on lymphocyte proliferation after antigenic stimulation (up-regulation at day 21 and down-regulation at day 35-49). Because cytokines play a key role in immunity, the expression levels of TGF-beta, IFN-gamma, IL-4 and IL-6 were measured, by RT-PCR in the spleen, the ileum and the mesenteric lymph node of the animals at the end of the experiment. In the mesenteric lymph node, a significantly lower expression of both TGF-beta and IFN-gamma mRNA expression levels is observed in animals feed with DON when compared with control piglets. Taken together, our data indicate that DON alters the vaccinal immune response. These results may have implications for humans and animals consuming DON-contaminated food or feed as breakdown in vaccinal immunity may lead to the occurrence of disease even in properly vaccinated populations.

Expression of Th1/Th2 cytokines in human blood after in vitro treatment with chlorpyrifos, and its metabolites, in combination with endotoxin LPS and allergen Der p1

Exposure to organophosphate (OP) pesticides has been associated with respiratory symptoms and may be related to asthma; however, few studies have examined the molecular basis for these associations. Asthma and allergic disorders are characterized by elevated Th2 cytokines (IL-4, IL-5, IL-13), whereas the chronic inflammatory response in asthmatic airways is maintained by Th1 cytokine IFN-gamma. The goal of this in vitro study was to examine the effects of OP chlorpyrifos (CPF), and its metabolites chlorpyrifos-oxon (CPO) and 3,5,6-trichloro-2-pyridinol (TCP), singly, and in combination with endotoxin lipopolysaccharide (LPS) or house dust mite Dermatophagoides pteronyssinus (Der p1) allergen, on expression of IFN-gamma and IL-4, Th1 and Th2 signature cytokines, respectively. Cytokine expression was measured by ELISA and flow cytometry. Human blood cultures were treated with CPF/CPO/TCP (1-1000 microg ml(-1)) and LPS (1.5-2.5 microg ml(-1)) or Der p1 (200 AU ml(-1)) and supernatants were collected at 48 h. Pesticides CPF, CPO and TCP did not induce cytokine expression in vitro, while LPS and Der p1 induced IFN-gamma and IL-4 expression, respectively. Whole blood cultures treated with low doses of CPO (1 and 10 microg ml(-1)), in combination with LPS, expressed higher levels of IFN-gamma than LPS alone (P < 0.05). While CPO increased LPS-dependent induction of IFN-gamma, CPO treatment did not alter Der p1 induction of IL-4. The interaction between CPO and LPS, which results in an increased type 1 immune response, should be investigated further, particularly since the combination of OP pesticides and endotoxin is common in rural, agricultural communities.

Influenza virus host resistance model

Host resistance (HR) models are used to evaluate the effect of a test article on clearance of an infectious microorganism in order to assess total immunocompetence. HR models serve as biomarkers of net immunological health or immunological well-being. Immunotoxicity can result either in an impaired clearance of an infectious agent, increased susceptibility to an opportunistic microorganism, prevention of immunization, or exacerbation of latent viral infections. The purpose of immunotoxicity testing is to obtain data that is meaningful for safety assessment, and for immunosuppression the major objective is to determine the significance with respect to increased susceptibility to infectious disease. Host resistance models provide the only sure method of examining the influence of test articles on the functional integrity of the immune system and its ability to eliminate pathogenic microorganisms and tumor cells. They provide the means to directly assess the functional reserve of the immune system. Clearance of influenza virus requires an intact and functional immune system that incorporates a cascade of immune responses. Mechanistic studies can be included in the influenza virus host resistance model by measuring the effect of a test article on innate immunity (cytokine and interferon production, macrophage function, and natural killer (NK) cell function) and acquired or adaptive immunity (cytotoxic T lymphocyte (CTL) activity as well as influenza-specific IgM and/or IgG antibody).

Cell-based assays for profiling activity and safety properties of cancer drugs

INTRODUCTION

Our goal was to establish versatile and high capacity assays to characterize activity and toxicity of chemotherapeutics. The major anti-cancer activity indicators of these agents included inhibition of proliferation and induction of apoptosis to cancer cells. In addition, cytotoxicity and myelosuppressive activity to normal cells were parameters to evaluate toxicity of these drugs.

METHODS

Using a panel of cell-based assay systems, we investigated activity and toxicity properties of selected cancer drugs. Drug effects on a number of normal and cancer cell types from human origin were evaluated.

RESULTS

Topoisomerase inhibitors (camptothecin, doxorubicin and etoposide) and microtubule inhibitors (colchicine and paclitaxel) showed anti-proliferation activity and induced apoptosis in MDA-231 cancer cells. Except for doxorubicin, these drugs had relatively low toxicity to normal cells because the dosage required for cytotoxicity EC(50) was >200-folds higher than the dosage for anti-proliferation EC(50) in cancer cells (MDA-231, HL60). However, these drugs were potent inducers of myelotoxicity in human bone marrow progenitor cells. In comparison, the DNA alkylating agents (cisplatin and carboplatin) were less potent proliferation inhibitors (EC(50)>10 microM) in MDA-231 cells and they were also less myelosuppressive.

DISCUSSION

Using marketed drugs as examples, our study established a multiple assay platform for profiling in vitro properties of cancer drugs. In drug discovery, such a platform will help to expedite lead selection at early stage.

Fatty acids as modulators of the immune response

Research describing fatty acids as modulators of inflammation and immune responses abounds. Many of these studies have focused on one particular group of fatty acids, omega-3. The data from animal studies have shown that these fatty acids can have powerful anti-inflammatory and immunomodulatory activities in a wide array of diseases (e.g., autoimmunity, arthritis, and infection). However, the evidence from human trials is more equivocal. In this review, a historical framework for understanding how and why fatty acids may affect the immune system is provided. Second, highlights of two recent landmark reports from the Agency for Healthcare Research and Quality are presented. These reports critically evaluate the evidence from human clinical trials of omega-3 fatty acids and rheumatoid arthritis, asthma, and a few other immune-mediated diseases. Third, the data from human clinical trials investigating the impact of various bioactive fatty acids on ex vivo and in vivo immune response are reviewed. Limitations in experimental design and immune assays commonly used are discussed. The discordance between expectation and evidence in this field has been a disappointment. Recommendations for improving both animal-based and human studies are provided.

Gene Expression Alterations in Immune System Pathways following Exposure to Immunosuppressive Chemicals

Exposure to environmental agents can affect a number of adverse immunological outcomes, including changes in the incidence of infectious disease. Diethylstilbestrol (DES), dexamethasone (DEX), cyclophosphamide, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are immunosuppressive chemicals that can induce similar pathophysiological end points in the thymus; however, the mechanism of toxicity is different for each compound. We examined differential gene expression in the spleen and thymus following chemical exposure and correlated these changes with alterations in functional immune end points and our knowledge of the known mechanisms of action. RNA from the spleen and thymus has been analyzed using Illumina Sentrix arrays and BeadStudio software. Preliminary data suggest that DES induced the greatest number of gene changes in the spleen, while DEX induced the most changes in the thymus. In both spleen and thymus, genomic analysis revealed gene expression changes that were common to multiple chemicals and that may be associated with xenobiotic-induced immune system perturbations, including alterations in genes associated with apoptosis, antigen processing and presentation, and response to biotic stimulus. This was particularly evident in the thymus, where there were many similarities in the expression profiles, as well as gene alterations unique to a single compound. In contrast, expression profiles in spleen were more distinct. The category of genes most profoundly affected by all four chemicals was response to biotic stimulus: there were both clusters of genes modulated by multiple chemicals and genes altered by a single chemical. The distinct gene profiles may specifically relate to cellular targets and mechanism of action.

Design and evaluation of immunotoxicity studies

The evaluation of potential adverse effects of pharmaceuticals on the immune system is part of the standard drug development procedures and needs to be available prior to the start of phase III clinical trials. Although the histopathological assessment of lymphoid organs/tissues is considered fundamental for the identification and characterization of immunotoxic reactions, additional investigations are now recommended by the European guidelines for repeated-dose toxicity testing of medicinal products in order to achieve an accurate assessment of immune system functionality with regard to immunomodulation. In the present paper, we describe and discuss a study design which permits the investigation of the immune function in a 4-week study in rats following immunization by subcutaneous administration of the T-dependent antigen Keyhole Limpet Hemocynin (KLH). This includes assessment of hematology parameters, titration of KLH-specific antibodies in serum, lymphocyte immunophenotyping in blood, thymus, spleen and lymph nodes, macroscopic pathology and histopathological evaluation of the lymphatic organs/tissues and of the injection sites.

T-2 toxin impairment of enteric reovirus clearance in the mouse associated with suppressed immunoglobulin and IFN-gamma responses

Trichothecenes are exquisitely toxic to the gastrointestinal (GI) tract and leukocytes and thus are likely to impair gut immunity. The purpose of this research was to test the hypothesis that the Type A trichothecene T-2 toxin interferes with the gut mucosal immune response to enteric reovirus infection. Mice were exposed i.p. first to 1.75 mg/kg bw T-2 and then 2 h later with 3 × 10⁷ plaque-forming units of reovirus serotype 1, strain Lang (T1/L). As compared to vehicle-treated control, T-2-treated mice had dramatically elevated intestinal plaque-forming viral titers after 5 days and failed to completely clear the virus from intestine by 10 days. Levels of reovirus λ2 core spike (L2 gene) RNA in feces in T-2-treated mice were significantly higher at 1, 3, 5, and 7 days than controls. T-2 potentiated L2 mRNA expression in a dose-dependent manner with as little as 50 μg/kg of the toxin having a potentiative effect. T-2 exposure transiently suppressed induction of reovirus-specific IgA in feces (6 and 8 days) as well as specific IgA and IgG_2a in serum (5 days). This suppression corresponded to decreased secretion of reovirus-specific IgA and IgG_2a in Peyer's patch (PP) and lamina propria fragment cultures prepared 5 days after infection. T-2 suppressed IFN-γ responses in PP to reovirus at 3 and 7 days as compared to infected controls whereas IL-2 mRNA concentrations were unaffected. PP IL-6 mRNA levels were increased 2-fold 2 h after T-2 treatment, but no differences between infected T-2-exposed and infected vehicle-treated mice were detectable over the next 7 days. Overall, the results suggest that T-2 toxin increased both the extent of GI tract reovirus infection and fecal shedding which corresponded to both suppressed immunoglobulin and IFN-γ responses.

Modulation of Murine Host Response to Enteric Reovirus Infection by the Trichothecene Deoxynivalenol

Based on the known capacity of deoxynivalenol (DON) to target gut lymphoid tissue and IgA production, it was hypothesized that this mycotoxin interferes with the immune response to enteric reovirus infection. When mice were orally gavaged, first with 25 mg/kg bw DON, and then with reovirus serotype 1, strain Lang (T1/L) 2 or 12 h later, viral titers in the GI tract were 10-fold higher than control mice after 5 days. Virus was almost completely cleared in both treatment and control groups from intestinal tissue after 10 days. Real-time PCR indicated that, in infected control mice, reovirus lambda2 core spike (L2 gene) RNA per g feces in infected mice that were pretreated with DON was significantly higher at 1, 3, and 5 days than in infected mice only. In reovirus-infected mice, DON at doses of 10 and 25 mg/kg bw but not 2 and 5 mg/kg bw increased fecal L2 RNA, whereas DON doses as low as 2 mg/kg potentiated L2 RNA levels in Peyer's patches (PP). Reovirus-specific IgA levels in feces of mice treated with DON were significantly elevated, as were specific IgA responses in lamina propria and PP fragment cultures. Similar effects were observed for serum IgA and IgG. DON suppressed IFN-gamma responses in PP to reovirus at 3 and 5 days as compared to infected controls, while IL-2 mRNA concentrations were unaffected. Although reovirus alone did not induce Th2 cytokine mRNAs in PP, DON exposure significantly elevated IL-4, IL-6, and IL-10 mRNA expression at various times during the infection. ELISPOT revealed that mRNA expression data corresponded to suppression of IFN-gamma- and enhancement of IL-4-producing cell responses in PP cultures from DON-treated mice. Taken together, these data suggest that DON transiently increased both severity of the reovirus infection and shedding in feces as well as elevated reovirus IgA responses. These effects corresponded to suppressed Th1 and enhanced Th2 cytokine expression.

Associating changes in the immune system with clinical diseases for interpretation in risk assessment

This overview unit discusses the relationship between immunosuppression, a potential consequence of immunotoxicity, and disease progression. It also discusses other factors, such as stress and age, that affect disease susceptibility. These factors play an important role in risk assessment for exposures to environmental factors.