Developments of immunotoxicology methods in the rat and applications to the study of environmental pollutants

Ecological Risks Due to Immunotoxicological Effects on Aquatic Organisms

The immunotoxic effects of some anthropogenic pollutants on aquatic organisms are among the causes of concern over the presence of these pollutants in the marine environment. The immune system is part of an organism's biological defense necessarily for homeostasis. Thus, the immunotoxicological impacts on aquatic organisms are important to understand the effects of pollutant chemicals in the aquatic ecosystem. When aquatic organisms are exposed to pollutant chemicals with immunotoxicity, it results in poor health. In addition, aquatic organisms are exposed to pathogenic bacteria, viruses, parasites, and fungi. Exposure to pollutant chemicals has reportedly caused aquatic organisms to show various immunotoxic symptoms such as histological changes of lymphoid tissue, changes of immune functionality and the distribution of immune cells, and changes in the resistance of organisms to infection by pathogens. Alterations of immune systems by contaminants can therefore lead to the deaths of individual organisms, increase the general risk of infections by pathogens, and probably decrease the populations of some species. This review introduced the immunotoxicological impact of pollutant chemicals in aquatic organisms, including invertebrates, fish, amphibians, and marine mammals; described typical biomarkers used in aquatic immunotoxicological studies; and then, discussed the current issues on ecological risk assessment and how to address ecological risk assessment through immunotoxicology. Moreover, the usefulness of the population growth rate to estimate the immunotoxicological impact of pollution chemicals was proposed.

Immunotoxic effects of environmental pollutants in marine mammals

Due to their marine ecology and life-history, marine mammals accumulate some of the highest levels of environmental contaminants of all wildlife. Given the increasing prevalence and severity of diseases in marine wildlife, it is imperative to understand how pollutants affect the immune system and consequently disease susceptibility. Advancements and adaptations of analytical techniques have facilitated marine mammal immunotoxicology research. Field studies, captive-feeding experiments and in vitro laboratory studies with marine mammals have associated exposure to environmental pollutants, most notable polychlorinated biphenyls (PCBs), organochlorine pesticides and heavy metals, to alterations of both the innate and adaptive arms of immune systems, which include aspects of cellular and humoral immunity. For marine mammals, reported immunotoxicology endpoints fell into several major categories: immune tissue histopathology, haematology/circulating immune cell populations, functional immune assays (lymphocyte proliferation, phagocytosis, respiratory burst, and natural killer cell activity), immunoglobulin production, and cytokine gene expression. Lymphocyte proliferation is by far the most commonly used immune assay, with studies using different organic pollutants and metals predominantly reporting immunosuppressive effects despite the many differences in study design and animal life history. Using combined field and laboratory data, we determined effect threshold levels for suppression of lymphocyte proliferation to be between b0.001-10 ppm for PCBs, 0.002-1.3 ppm for Hg, 0.009-0.06 for MeHg, and 0.1-2.4 for cadmium in polar bears and several pinniped and cetacean species. Similarly, thresholds for suppression of phagocytosis were 0.6-1.4 and 0.08-1.9 ppm for PCBs and mercury, respectively. Although data are lacking for many important immune endpoints and mechanisms of specific immune alterations are not well understood, this review revealed a systemic suppression of immune function in marine mammals exposed to environmental contaminants. Exposure to immunotoxic contaminants may have significant population level consequences as a contributing factor to increasing anthropogenic stress in wildlife and infectious disease outbreaks.

The Use of In Vitro Systems for Evaluating Immunotoxicity: The Report and Recommendations of an ECVAM Workshop

This is the report of a workshop organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods that are of importance to the biosciences and which replace, reduce or refine the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures that would enable it to become well informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organization of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (Anonymous, 1994). The workshop on "The use of in vitro systems for evaluating Immunotoxicity" was held at ECVAM (Ispra), Italy, on 24th-26th November 2003. The participants represented academia, national organizations, international regulatory bodies and industry. The aim of the workshop was to review the state-of-the-art in the field of in vitro immunotoxicology, and to develop strategies towards the replacement of in vivo testing. At the end of this report are listed the recommendations that should be considered for prevalidation and validation of relevant and reliable procedures, that could replace the use of animals in chemical and cosmetics toxicity testing.

Changes in cellular immunity among workers occupationally exposed to styrene in a plastics lamination plant

BACKGROUND

Styrene is a widely used industrial chemical. Immune and hematological parameters were examined in 29 hand laminators and sprayers exposed to styrene for an average of 14 years and in 19 in-factory unexposed controls. The workers performed hand lamination procedures in a production area with an average area airborne styrene level of 139.5 mg/m(3). Mean concentration of styrene in the blood of exposed workers was 945.7 microg/L and the mean styrene in exhaled air was 38.8 microg/L.

METHODS

Parameters of internal and external exposure, immune function assays, immunoglobulins, acute phase reactants and hematology were evaluated in exposed and non-exposed populations.

RESULTS

Using multifactorial analysis of variance we found a significant decrease in proliferation of lymphocytes stimulated by Concanavalin A but not by pokeweed mitogen (PWM) in workers occupationally exposed to styrene. Proliferative response to PWM was significantly correlated with the levels of styrene in blood. Phagocytic activity of monocytes, levels of IgG, IgA, IgM, IgE and alpha-2-macroglobulin in serum were indistinguishable in the two groups. The population exposed to styrene had increased levels of C4-component of complement. Levels of C3-component of complement were positively correlated with duration of exposure. A significant elevation in the percentage and number of monocytes and a significantly decreased number of lymphocytes were seen in exposed workers. Styrene concentrations in both blood and exhaled air were associated with decreased percentage of large granular lymphocytes.

CONCLUSIONS

These results suggest immune alterations of cell-mediated immune response of T-lymphocytes and imbalance in leucocyte subsets in peripheral blood of workers exposed to styrene.

Effects of prolonged exposure to morphine and methadone on in vivo parameters of immune function in rats

In rats, two 6-week repeated dose oral toxicity studies were performed with morphine (250 and 500 mg/kg food) and methadone (200 and 400 mg/kg food), respectively. Alterations in immune function were studied by assessing primary and secondary immune responses to sheep red blood cells. In addition, the ability to resist challenge with infectious agents was measured in host resistance models employing the parasite Trichinella spiralis and the bacterium Listeria monocytogenes. The primary and secondary antibody responses to sheep red blood cells were not affected by treatment with either morphine or methadone. The clearance of L. monocytogenes bacteria in the spleen was not affected either. Prolonged treatment with morphine, however, resulted in a decrease in host resistance to T. spiralis infection, as indicated by a 1.5-fold increase in numbers of muscle larvae counted in the carcass, but did not affect the T. spiralis-specific IgM, IgG and IgE antibody responses. In contrast to morphine, the methadone-treated animals did not show a significant change in host resistance to T. spiralis. Total serum IgG levels, however, were increased in high-dose methadone-treated animals. Apparently, prolonged administration of morphine to rats resulted in immune suppression, mediating a slight, though biologically relevant, exacerbation of the T. spiralis infection, whereas methadone did not.

An immunotoxicity screening study on salmeterol in rats

Salmeterol, a long-acting beta 2-adrenoreceptor agonist without known immunotoxicity, was studied in a 28-day repeated dose toxicity test in Wistar rats. Several immunotoxicity screening parameters were incorporated in the study protocol to investigate the immunotoxic potential of the compound. Male rats were orally treated with 0, 0.2, 2 and 20 mg salmeterol/kg body weight/day. At the 20 mg/kg/day dose level, intubation errors occurred because the animals tried to resist intubation. Some of these animals died intercurrently. Therefore, the magnitude of the dose was lowered to 10 mg/kg/day at day 9 of treatment. Body weight and bone marrow cellularity were not affected. Hematological parameters were not altered either, except for platelet counts, that were decreased at all dose levels. Also liver weights were decreased at all dose levels tested. Absolute thymic weights were decreased at the 2 and 20/10 mg/kg/day dose levels. No treatment-related (histo)pathological lesions were seen in the (non)lymphoid organs. Serum IgM levels were increased at the 0.2, and IgG at the 2 and 20/10 mg/kg/day dose levels, respectively. B cell numbers in the spleen were decreased at all dose levels tested. The data indicate that the test battery applied to salmeterol is able to detect low immunotoxic potential. Further research is needed to elucidate whether salmeterol interferes with immune responses in rats upon antigenic challenge.