Immunotoxicity Studies Research Articles

Assessment of the Effects of ISIS 2302, an Anti-Sense Inhibitor of Human ICAM-1, on Cellular and Humoral Immunity in Mice

ISIS 2302 is a phosphorothioate oligonucleotide designed to inhibit human ICAM-1 and is intended for treatment of inflammatory diseases. Molecules of this class are known to elicit pro-inflammatory effects, and immunotoxicity studies were performed in mice to elucidate the nature of effects of ISIS 2302 on mammalian immune function. ISIS 2302 (1, 5, 20, or 50 mg/kg/dose) was administered intravenously every other day for 27 days. The pro-inflammatory properties of the drug were observed at doses ≥ 20 mg/kg. A dose-dependent increase in spleen weight was associated with increased absolute splenocyte and B-lymphocyte counts after the 50 mg/kg/dose regimen. The mitogenic response of B-lymphocytes to bacterial lipopolysaccharide was increased after the 20 and 50 mg/kg/doses but antibody-forming cell activities remained unchanged. Total serum IgG concentration was decreased after the 20 and 50 mg/kg/dose regimens but IgM titers were unchanged. Increases in IL-6, IL-12, and MCP-1 as well as NK cell activity were observed after administration of 20 and 50 mg/kg/dose. Cytotoxic T-lymphocyte activity was decreased by the 50 mg/kg/dose regimen. Other changes in immune function were not observed in ISIS 2302-dosed mice. ISIS 3082, a murine active ICAM-1 inhibitor, was used to demonstrate the anti-inflammatory activity of ICAM-1 inhibition in the 2,4-dinitrofluorobenzene-induced contact sensitization model. Intravenous administration of 1 mg/kg of ISIS 3082 every other day for 27 days was unequivocally anti-inflammatory in the contact sensitization test. The results of these experiments support the conclusion that the prophlogistic effects of ISIS 2302 in mice are observed only at suprapharmacologic doses.

Developmental immunotoxicity investigations in the SD rat following pre- and post-natal exposure to cyclosporin

The development and function of the immune system was assessed in juvenile SD rats following pre- or post-natal exposure to cyclosporin. The main objective was to assess the feasibility of the methods available for the detection of adverse effects on the development of the immune system for use in the safety assessment of medicines. In a pre-natal experiment, 15 pregnant rats were given 10 mg/kg/day of cyclosporin by gavage from day 6 of gestation until 4 days after parturition. A control group received olive oil. In a post-natal experiment, the pups from 35 litters were given 10 mg/kg/day of cyclosporin by gavage from 4 to 28 days of age. Half of the pups in each litter were given water and acted as controls. Immune endpoints were determined in the pups in both experiments from two to 10 weeks of age, including: lymphocyte subsets, serum immunoglobulin titres, serum autoantibodies, primary antibody response to sheep red blood cells (SRBC), delayed-type hypersensitivity response, humoral response to keyhole limpet haemocyanin, spleen cellularity, immune organ weights, and histopathology. Pre-natal exposure caused no effects on immune function. Post-natal exposure caused immune depression during the treatment period and a persistent impairment of the immune system characterised by lymphoid hyperplasia in the spleen and a reduced primary antibody response to SRBC at 10 weeks of age. These results demonstrate the importance of a post-treatment follow-up period in developmental immunotoxicity studies, in order to distinguish between the transient effects of immune modulation and the persistent consequences of developmental toxicity.

Harmonization of immunotoxicity guidelines in the ICH process – pathology considerations from the Guideline Committee of the European Society of Toxicological Pathology (ESTP)

As part of the ICH process of harmonization of testing guidelines for immunotoxicity, the European Society of Toxicologic Pathology (ESTP) has contributed to the scientific discussion on methods and evaluation of immunotoxicity studies with technical and scientific recommendations on toxicologic pathology. The weighing and sampling of immune organs is discussed taking into consideration specifically the value of lymph node weighing and the selection of appropriate lymph nodes for the detection of local and systemic effects. The different techniques of bone marrow preparation are considered for routine and extended investigations. Criteria are given for the gross and histopathological detection of effects in Peyer's patches. For the histopathological evaluation it is strongly recommended that each compartment within the different lymphoid organs is investigated separately and semiquantitatively since this approach has shown to increase the sensitivity and specificity of immunohistopathology.

Prospects for Developmental Immunotoxicity Guidance and an Update on ICH S8

Potential adverse effects of drug exposure on the developing immune system had been a relatively neglected area of toxicology until fairly recently. However, with the recent regulatory emphasis on evaluation of drugs for use in pediatric patients, juvenile animal studies have been considered in much more detail than in the past in order to enable clinical trials. Assessment of immunotoxicity potential in these juvenile animal studies has been a natural consequence of drug development for pediatric patients. Unfortunately, the efforts to evaluate developmental immunotoxicity studies have not kept pace with the writing of an immunotoxicology guidance for the International Conference on Harmonisation of Technical Requirements for Registration of Human Pharmaceuticals (ICH). This document has recently reached Step 4 in the approval process: it is thus likely that juvenile animal studies for immunotoxicity would be recommended based on considerations enumerated in the ICH Safety Number 8 (S8) guidance. Sufficient flexibility exists in this document to cover the issue of developmental immunotoxicity. ICH S8 advocates a weight-of-evidence approach, which should be interpreted to indicate that immunotoxicity testing would be conducted based on identified cause(s) for concern rather than as a routine screening method. The presentation reflecting these issues, as presented to attendees of the Pharmaceutical Education Associates workshop on Innovative Methods and Applications for Risk Assessment in Pharmaceutical Development is summarized herein.

Importance of immunotoxicity in safety assessment: a medical toxicologist’s perspective

The clinical data accumulated so far unequivocally demonstrate that immunotoxicity is associated with significant morbidity. Immunotoxic effects are divided into four categories: immunosuppression, immunostimulation, hypersensitivity and autoimmunity. Each category is associated with distinct adverse effects. Even though concern primarily focused on immunosuppression, hypersensitivity and immunostimulation are also key issues, especially with pharmaceuticals. Histology of the lymphoid organs is not sufficient to reliably predict immunosuppression and at least one immune function assay is recommended. It is not known whether function assays used to predict immunosuppression are applicable to the prediction of immunostimulation. Specific assays can be helpful. Most available animal models and assays are not valid to assess the potential for hypersensitivity, and autoimmunity is not predictable at all. Conflicting guidelines and the lack of human data contribute further to this situation. Several critical factors deserve consideration. Dose–response relationships are often atypical and this should impact on the study design. Due to the redundancy of the immune system, a single change is not necessarily sufficient evidence for immunotoxicity so that a global assessment of all preclinical findings is advisable. Genetic factors play a major role in immune responses. As wide inter-individual variability is unavoidable, sufficient numbers of animals, a cautious comparison with both study and historical controls, and the possible use of inbred or genetically modified animals are to be considered. Marked interspecies differences in the immune system should lead to use more than one animal species and to confirm animal data during clinical trials. The inclusion of certain immune endpoints applicable to animals and man is therefore essential. The optimal timing of immunotoxicity studies is debated, but early studies are recommended. Despite significant progress, quite a few issues are still pending. Nevertheless, due to the many adverse effects reported in man, the immunotoxicity potential of every new molecular entity should be systematically and specifically evaluated.

69 Improving the sensitivity and predictability of current testing strategies for immunotoxicity

The clinical data accumulated so far unequivocally demonstrate that immunotoxicity is associated with significant morbidity. Immunotoxic effects are divided into four categories: immunosuppression, immunostimulation, hypersensitivity and autoimmunity. Each category is associated with distinct adverse effects. Even though concern primarily focused on immunosuppression, hypersensitivity and immunostimulation are also key issues, especially with pharmaceuticals. Histology of the lymphoid organs is not sufficient to reliably predict immunosuppression and at least one immune function assay is recommended. It is not known whether function assays used to predict immunosuppression are applicable to the prediction of immunostimulation. Specific assays can be helpful. Most available animal models and assays are not valid to assess the potential for hypersensitivity, and autoimmunity is not predictable at all. Conflicting guidelines and the lack of human data contribute further to this situation. Several critical factors deserve consideration. Dose–response relationships are often atypical and this should impact on the study design. Due to the redundancy of the immune system, a single change is not necessarily sufficient evidence for immunotoxicity so that a global assessment of all preclinical findings is advisable. Genetic factors play a major role in immune responses. As wide inter-individual variability is unavoidable, sufficient numbers of animals, a cautious comparison with both study and historical controls, and the possible use of inbred or genetically modified animals are to be considered. Marked interspecies differences in the immune system should lead to use more than one animal species and to confirm animal data during clinical trials. The inclusion of certain immune endpoints applicable to animals and man is therefore essential. The optimal timing of immunotoxicity studies is debated, but early studies are recommended. Despite significant progress, quite a few issues are still pending. Nevertheless, due to the many adverse effects reported in man, the immunotoxicity potential of every new molecular entity should be systematically and specifically evaluated.

Immunotoxicity of epicutaneously applied anticoagulant rodenticide warfarin: evaluation by contact hypersensitivity to DNCB in rats

The immunotoxicity of epicutaneously administered anticoagulant rodenticide warfarin (WF) was examined in this work by using experimental contact hypersensitivity (CHS) reaction to hapten dinitrochlorobenzene (DNCB). WF (0.05 and 0.5 mg/kg) administration 24 h before the induction of CHS does not change expression of CHS evaluated by ear swelling assay. Regional draining lymph node response during sensitization phase was characterized by decreased cellularity but increased spontaneous and IL-2 stimulated proliferation of draining lymph node cells (DLC). No changes in IL-2 production and in numbers of CD25 + cells were noted and even decreased proliferative index (ratio of IL-2 stimulated to unstimulated DLC proliferation) was detected. Increase in granulocyte activity (MTT reduction and adhesion to plastic) was noted following application of WF solely with further increase following subsequent application of DNCB, when granulocyte activation (NBT reduction) was noted also. Access of WF into general circulation might be responsible for observed changes, what was supported by ex vivo changes in DLC and granulocyte functions assessed before initiation of sensitization and by in vitro effect of exogenous WF as well. Differential effects of WF on lymphocytes and granulocytes noted in this study highlight the need for simultaneous testing of both cell type activity what might constitute a more integrated approach in immunotoxicity studies.

Chemistry and safety of triclosan, and its use as an antimicrobial coating on Coated VICRYL* Plus Antibacterial Suture (coated polyglactin 910 suture with triclosan).

The safety of the antimicrobial agent triclosan was reviewed, and the biocompatibility of coated polyglactin 910 suture with triclosan was evaluated. Acute single exposure LD(50) values for triclosan were determined in multiple species by several routes of administration. Subacute to chronic toxicity for dermal and oral exposure to triclosan was determined in multiple species in studies of up to one year's duration. Chronic oral toxicity/carcinogenicity potential was determined in 2-year studies in rodents and non-rodents. The genotoxicity potential of triclosan was determined using a battery of standard assays. Reproductive toxicity and teratology studies were conducted in rodents and non-rodents. Immunotoxicity studies in guinea pigs and the repeat-insult patch test in humans were conducted to assess the potential for sensitization reactions. Pharmacokinetic studies were conducted in animals and humans to understand the metabolic profile of triclosan. Preclinical biocompatibility studies conducted on coated polyglactin 910 suture with triclosan included in vitro cytotoxicity, in vivo intracutaneous reactivity, material-mediated pyrogenicity, and intramuscular tissue reaction/absorption studies. The oral LD(50) values for triclosan ranged from 3,750 to 5,000 mg/kg, whereas the LD(50) after subcutaneous injection was >14,600 mg/kg. Safety factors calculated from repeated daily dosing studies ranged from 1,000 to 25,000 times the no-observed-effect levels. There was no evidence of carcinogenic potential in either species, and genotoxicity studies were negative. Reproductive toxicity studies did not reveal any evidence of teratogenic potential. There was no evidence of skin sensitization potential in controlled studies. Pharmacokinetic studies in animals and humans have shown that triclosan is rapidly absorbed, well distributed in the body, metabolized in the liver, and excreted by the kidneys, with no indication of accumulation over time. Biocompatibility studies showed that coated polyglactin 910 suture with triclosan was non-cytotoxic, non-irritating, and not a chemical pyrogen. In addition, an intramuscular implantation study demonstrated a tissue reaction, a healing response, and an absorption profile comparable to current polyglactin 910 suture. The extensive toxicology database supporting the safety of triclosan and the biocompatibility studies conducted on coated polyglactin 910 suture with triclosan demonstrate the safety of this suture for clinical use. Considering the clinical relevance of surgical site infections and the relatively low level of triclosan required to inhibit bacterial colonization of the suture, the use of this antimicrobial technology is well suited to this application.

Four-week inhalation toxicity, mutagenicity and immunotoxicity studies of Keum-Yeon-Cho (NosmoQ), tobacco substitute composition, in mice

Safety of Keum-Yeon-Cho (NosmoQ), a tobacco substitute composition, was evaluated in terms of acute- and 4 weeks repeated-inhalation toxicity, mutagenicity, and immunotoxicity using Balb/c mice. The air inside the inhalation chamber was collected and analyzed by GC–MS. In acute inhalation toxicity test, male and female mice were exposed to 40 Keum-Yeon-Cho cigarettes. The 50% lethal concentration (LC 50) of NosmoQ was considered to be much higher than 40 cigarettes in both sexes. In 4-week repeated inhalation toxicity test, male and female mice were exposed for 6 h/day, 5 days/week for 4 weeks to 10 and 20 cigarettes per day, while control mice were exposed to filtered air. Our data indicated that no observed adverse effect level (NOAEL) of Keum-Yeon-Cho should be over 20 cigarettes per day. Results of Salmonella typhimurium reversion assay with/without histidine moiety, in vivo chromosomal aberration and in vivo micronucleus assays using mouse bone marrow cells revealed that Keum-Yeon-Cho has no mutagenicity. Evaluation of peripheral cellular immunity of mice treated with Keum-Yeon-Cho using in vitro lymphocyte proliferation assay showed no significant difference in mean stimulation index (SI) between mice exposed to Keum-Yeon-Cho and control mice. Mean CO concentrations and total particulate matter contents of 10 and 20 cigarettes were 21.1±1.23 and 40.7±1.21 ppm (mean±S.D., n=5), and 25.7±3.09 and 59.0±4.0 mg dry weight (mean±S.D., n=5), respectively. Although at negligible concentration (less than ppb level) several polycyclic aromatic hydrocarbons (PAHs) were also detected, these results indicate that NosmoQ has no toxic effect on mice.

The mouse as a model for developmental immunotoxicology.

The laboratory mouse has been the most extensively used model system for demonstrating postnatal immune deficits following perinatal immunotoxicant exposure. Assays utilized have historically been those developed for adult mice. Clear gaps in the available database exist, however, regarding the predictive strength of adult mouse immune screens for detecting either transient or long-lasting postnatal immune suppression. Limited information is also available regarding postnatal ages when various immune assays can be first employed to detect developmental immunotoxicity in mice. Furthermore, difficulties and expense inherent with breeding of in-bred mice, as used for adult immunotoxicity studies, raise questions regarding the feasibility of an in-bred mouse model as a standard, widely available developmental immunotoxicity testing system. These and additional concerns will need to be addressed as a model system with utility for studying developmental immunotoxicants is produced.

Effect of cyclosporin A in Lewis rats in vivo and HeLa cells in vitro.

The aim of this study was to compare the effect of cyclosporin A (CsA) in inbred Lewis rats with published assessment of immunotoxicity in 'classical' outbred Wistar rats. A second purpose was to consider the contribution of a panel of in vitro assays in cell cultures when added to an immunotoxicity study in vivo. The in vivo effect of CsA was investigated in a 28-day subacute immunotoxicity study in male Lewis rats at three different concentrations: 1.25, 5 and 20 mg kg(-1). The highest dose of CsA exceeded the maximum tolerated dose. A drop in body, spleen and popliteal lymph node weight of exposed animals displayed symptoms of toxicity. At a high toxic dose, haematological changes showed a decrease in the leucocyte count and in the percentage of lymphocytes, and an increase in the percentage of polymorphonuclear leucocytes. The haematocrit was significantly dose-dependently suppressed in all rats exposed to CsA. A similar dose-dependent depression of the mean cell volume of erythrocytes was found in rats given high and middle doses of CsA. The phagocytic activity of polymorphonuclear leucocytes and monocytes also was significantly dose-dependently suppressed. No significant changes in primary antibody response to sheep erythrocytes or in vitro proliferative response of spleen lymphocytes to mitogens were found in those rats.A battery of in vitro cytotoxicity methods was selected for the evaluation of metabolic and functional activity of subcellular organelles (mitochondria, lysosomes) and for the detection of drug-induced superoxide-mediated damage in HeLa cells. This cell line was chosen because it has a lower activity of superoxide dismutase (SOD) than normal cells and is sufficiently sensitive for the detection of the induction of oxygen radicals. The in vitro results indicated a direct relationship between CsA cytotoxicity and a change in the mitochondrial enzyme activity, as well as an induction of superoxide production. The results of the study indicated that a combination of selected in vivo and in vitro methods is an inexpensive way to obtain more complex information on cell status affected by xenobiotics.

Assessment of the Immunotoxic Potential of Human Pharmaceuticals: A Workshop Report

The assessment of the immunotoxic potential of human pharmaceuticals has drawn considerable attention worldwide in the past few years. In Europe, the Committee for Proprietary Medicinal Products released its immunotoxicity guidance documents. The Food and Drug Administration's Center for Drug Evaluation and Research in the United States and the Japanese Ministry of Health, Labor, and Welfare are in the process of finalizing similar guidance documents. This report summarizes the discussions on drug immunotoxicity assessment held at a November 2001 DIA workshop held in Noordwijk, The Netherlands. This workshop revealed that an important issue for company attendees was the timing of the immunotoxicity studies during the drug development process. The Committee for Proprietary Medicinal Products requires that immunotoxicity endpoints be monitored for all new compounds. Industry has interpreted this requirement, and the expectation that these endpoints be studied in a 28-day repeated dose study in rats, as obligatory immunotoxicity testing for all new compounds, regardless of the stage of development. The Committee for Propietary Medicinal Products requirements, however, are applicable only at the stage of the marketing application. Workshop participants agreed that immunotoxicity screening should preferably be carried out prior or parallel to Phase 2 development. This will substantially reduce the number of compounds that require enhanced tesitng for immunotoxicity (approximately 80% of the compounds are dropped from development after Phase 1) and reduce the use of animals. Presentations and discussions at the worshop also demonstrated that there is a strong scientific basis for European requirements as included in the Revised Note for Guidance on Repeated Dose Toxicity Testing. For example, not evaluating the response to a T-cell-dependent antigen would have missed the immunotoxicological effects of several compounds. This is probably due to the dynamic nature of the immune system whereby immune effects are best demonstrated using an immune function assay, as opposed to reliance on an essentially static analysis such as histopathology.

EFFECT OF MURINE RECOMBINANT IL-2 ON THE COURSE OF LUPUS-LIKE DISEASE IN (NZB×NZW) F1 Female Mice

ABSTRACTThe exacerbation of pre-existing autoimmune diseases is a potential toxic effect of immunoactive drugs. An increase in the incidence of autoimmune thyroiditis has been noted in patients treated with human recombinant interleukin-2 (rIL-2). In contrast, human rIL-2 tends to protect mice from autoimmunity. As the effects of murine rIL-2 on autoimmunity have not been reported in mice, lupus-prone female (NZB×NZW) F1 mice were treated with 20,000 IU murine rIL-2 intraperitoneally, twice weekly for 13 weeks, beginning at 15 weeks of age. No evidence of an exacerbating effect of murine IL-2 on the lupus disease of (NZB×NZW) F1 mice was observed as no change in the following parameters were seen, namely mean survival time, mean body weight, anti-DNA and antinuclear antibody production. These results show that: 1) like human rIL-2, murine rIL-2 does not exacerbate autoimmunity in mice; 2) the biological effects of human as well as murine rIL-2 in mice differ from those seen with human rIL-2 in man. These latter findings suggest that the selection of the relevant animal species for immunotoxicity studies with recombinant cytokines and derivatives may be less straightforward than previously thought.

Immune responses: adverse versus non-adverse effects.

The adaptive immune system in vertebrates has evolved to provide host resistance to infectious microorganisms and malignant disease. Normal immune function and the induction of specific immune responses require the orchestrated interaction between cells and molecules both within and outside the lymphoid system. Immunotoxicology can be defined as the study of adverse health effects that may result from the interaction of xenobiotics with the immune system. In general terms such effects can take one of two forms. The first of these is immunotoxicity (or immunosuppression) where there is a perturbation of, or damage to, one or more components of the immune system resulting in impaired immune function and reduced host resistance. The design and interpretation of experimental immunotoxicity studies and the investigation of clinical immunosuppression require consideration of the relationship between changes in the structure and/or function of discrete components of the immune system and holistic changes in the susceptibility to infectious and malignant disease. The other main way in which chemicals may cause adverse health effects secondary to interaction with the immune system is through stimulation of specific immune responses that result in allergic disease. Allergy to chemicals and proteins can take many forms, including allergic contact dermatitis, allergic sensitization of the respiratory tract (associated with rhinitis and/or asthma), systemic allergic reactions (associated frequently with drug treatment), and gastrointestinal disease. Here there is a need to distinguish between immunogenic responses per se and those immune responses that are of sufficient vigor and of the quality necessary to provoke allergic sensitization. The purpose of this article is to explore the extent to which distinctions can be drawn between adverse and nonadverse effects in the context of immunotoxicity and allergy.

Recent developments in regulatory requirements for developmental toxicology

A number of legislative and regulatory changes have occurred over the past 5 years to prompt the re-evaluation of the regulatory requirements for developmental toxicity testing and use of the data for risk assessment. In particular, passage of the 1996 Food Quality Protection Act (FQPA) in the United States required the USEPA to evaluate children's health risks in a more rigorous fashion, and to apply an additional 10-fold safety factor if data were inadequate or children appeared to be more sensitive than adults. A review of the testing protocols required by USEPA led to extension of the dosing period to term in the prenatal developmental toxicity study and the addition of endpoints to the 2-generation reproduction study protocol as indicators of possible neurologic, reproductive, or immune alterations. Revised testing guidelines for pesticides and toxic substances were published by USEPA in 1998, including a developmental neurotoxicity testing protocol. Further review for FQPA implementation resulted in the proposal for a core set of required toxicology studies, including routine developmental neurotoxicity, adult neurotoxicity, and adult immunotoxicity studies. In addition, development of new testing guidelines in several areas was recommended, these guidelines to be used in conjunction with or as follow-up when indicated from standard testing: developmental immunotoxicity, carcinogenesis, specialized neurotoxicity studies, endocrine disruptor studies, pharmacokinetics, and direct dosing of neonates. The impact of these efforts on the policies for toxicity testing of pesticides are discussed, and these issues are currently being reviewed on a broader scale, in particular, by evaluating the adequacy of the methods used for reference values (e.g. chronic RfD, RfC). Three major areas of focus for this review include life stages evaluated, endpoints assessed, and the duration of exposure used in various studies. A major focus of these efforts is to ensure that children's health risks are being adequately addressed in the risk assessment process.

Histopathologic approaches to detect changes indicative of immunotoxicity.

Toxicologic pathology is crucial in the identification and characterization of health effects following exposure to xenobiotics, mainly in toxicity experiments in rodents. Regarding regulatory toxicology, histopathology of lymphoid organs and tissues is a cornerstone in the identification of immunotoxic compounds. A 2-tier testing system is usually employed in which the first tier is a general screen for (immuno)toxicity and the second tier consists of specific immune function studies, including host resistance tests or mechanistic studies. The role attributed to histopathology of lymphoid organs in the updated Organisation for Economic Cooperation and Development and Food and Drug Administration guidelines requires improvement and standardization of the histopathology procedures. Optimalization and standardization was started in an international collaborative immunotoxicity study (ICICIS). However, several problems were left unaddressed, mostly because of the few compounds tested in this study. Based on the results of the ICICIS study and the morphologic changes induced by immunotoxic/immunomodulatory compounds observed in other investigations, suggestions are given to further improve the identification and (semi)quantification of histopathologic changes in lymphoid organs and tissues.

Preclinical development of keliximab, a Primatized anti-CD4 monoclonal antibody, in human CD4 transgenic mice: characterization of the model and safety studies.

The preclinical safety assessment of biopharmaceuticals necessitates that studies be conducted in species in which the products are pharmacologically active. Monoclonal antibodies are a promising class of biopharmaceuticals for many disease indications; however, by design, these agents tend to have limited species cross-reactivity and tend to only be active in primates. Keliximab is a human-cynomolgus monkey chimeric (Primatized) monoclonal antibody with specificity for human and chimpanzee CD4. In order to conduct a comprehensive preclinical safety assessment of this antibody to support chronic treatment of rheumatoid arthritis in patients, a human CD4 transgenic mouse was used for chronic and reproductive toxicity studies and for genotoxic studies. In addition, immunotoxicity studies were conducted in these mice with Candida albicans, Pneumocystis carinii and B16 melanoma cells to assess the effects of keliximab on host resistance to infection and immunosurveillance to neoplasia. The results of these studies found keliximab to be well tolerated with the only effects observed being related to its pharmacologic activity on CD4+ T lymphocytes. The use of transgenic mice expressing human proteins provides a useful alternative to studies in chimpanzees with biopharmaceutical agents having limited species cross-reactivity.

IMMUNOMODULATION BY FUNGAL TOXINS

The availability of immunotoxicity data for fungal toxins varies considerably for different toxins. The following is a comprehensive review of the most recent literature on the immunotoxicity of aflatoxins, fumonisins, gliotoxin, ochratoxins, patulin, and trichothecenes. Aflatoxin is an immunomodulating agent that acts primarily on cell-mediated immunity and phagocytic cell function. In addition to further characterization of aflatoxininduced immunotoxicity in various species, some recent studies have focused on ameliorating the effects of aflatoxin by supplementing or amending the diet. The immunomodulatory effects of ochratoxins have also been considered for many years. Notably, recent studies have examined immune function in the offspring of rats and mice exposed to ochratoxin pre- and perinatally. Fumonisin toxicity has been characterized relatively recently in comparison to aflatoxin and ochratoxin, and fumonisin-induced immunotoxicity is an area of active research. As these studies progress, they may also clarify the role of sphingolipid metabolism in immune function. The most recent study of patulin immunotoxicity in mice indicates that exposure to levels found in foods and feeds would not likely result in immunotoxicity. Exposure to gliotoxin would most likely be by infection with gliotoxin-producing fungi. Although the toxin is immunosuppressive in vitro, the link between immunosuppression and the presence of gliotoxin in infected tissues in vivo has yet to be made. The trichothecenes can both suppress and stimulate immune function. By comparison, more information is available on the molecular events associated with trichothecene-induced immunomodulation than for any other fungal toxins. The molecular basis of immune function modulation by fungal toxins remains a frontier for future research.

Biomarkers for TBT Immunotoxicity Studies on the Cultivated Clam Tapes philippinarum (Adams and Reeve, 1850)

The aim of this investigation was to quantify the effects of tributyltin (TBT) on the immune reactivity of haemocytes from the cultivated clam Tapes philippinarum (Adams and Reeve, 1850) using a series of in vitro bioassays. It is known that TBT has adverse effects on cellular immune functions like mobility, phagocytosis and lysosomal enzyme activity. As defining TBT-sensitive immunologic biomarkers in sentinel organisms is important in the field of ecotoxicology, the authors propose three indexes, amoebocytic (A.I.), phagocytic (P.I.), and lysosomal activity (L.A.I.), as sensitive and useful biomarkers to assess environmental risks due to TBT contamination.

Epidemiology studies in immunotoxicity evaluations

Studies in humans designed to detect immunomodulation from exposure to xenobiotics present challenging problems to epidemiologists and immunotoxicologists. Exposed and control groups must be carefully selected, exposure to the xenobiotic must be sufficiently high and well-documented, and the referent group should be as similar as possible to the exposed. Immune markers/functional tests in an individual may be influenced by sunlight exposure, medication, illness and use of recreational drugs; all of these potential confounding factors must be addressed. Sample acquisition is usually performed at sites geographically distant from the controlled environment of an investigator’s laboratory, yielding an assortment of new problems that would not occur in clinical or hospital situations. Regulations and guidelines concerning the transport of biological samples and potential hazards of HIV and HBV exposures to personnel must be adapted to field conditions. Since the application of immunotoxicological techniques to populations exposed to xenobiotics is relatively new, and the ability to measure an increasing number of immune biomarkers of activation, suppression, autoimmunity or hypersensitivity is rapidly expanding, there are difficulties in the interpretation of statistically positive results (sometimes within the normal range) and their potential health significance. Finally, both biological and methodological factors complicate the assessment of dose–response/concentration–effect relationships in human immunotoxicity studies, and traditional dose–response relationships may not always be present.