Evaluation of mercury exposure reduction through a fish consumption advisory program for Anishinaabe tribal members in Northern Wisconsin, Michigan, and Minnesota.

The Great Lakes Indian Fish and Wildlife Commission has an extensive program to inform Anishinaabe tribal members from northern Wisconsin, Michigan, and Minnesota who harvest and consume walleye about the health risks of consuming these fish, and to encourage harvest and consumption practices that reduce exposure to MeHg. We report here the results of a probabilistic analysis of exposure to methyl mercury (MeHg) among tribal members who consume walleye. The model predicts that the potential for greatest exposures to MeHg occur among women of child-bearing age and children who consume large walleye from lakes that contain heavily contaminated (MeHg concentration >0.5 mg/kg) fish. The analysis allows GLIFWC to evaluate, focus, and fine-tune its initiatives to protect the health of tribal members in ways that result in exposure and risk reduction for tribal harvesters, women of child-bearing age, and children, while maintaining important tribal lifeways, which include the harvest and consumption of walleye.

Methods to identify and characterize developmental neurotoxicity for human health risk assessment. I: behavioral effects.

Alterations in nervous system function after exposure to a developmental neurotoxicant may be identified and characterized using neurobehavioral methods. A number of methods can evaluate alterations in sensory, motor, and cognitive functions in laboratory animals exposed to toxicants during nervous system development. Fundamental issues underlying proper use and interpretation of these methods include a) consideration of the scientific goal in experimental design, b) selection of an appropriate animal model, c) expertise of the investigator, d) adequate statistical analysis, and e) proper data interpretation. Strengths and weaknesses of the assessment methods include sensitivity, selectivity, practicality, and variability. Research could improve current behavioral methods by providing a better understanding of the relationship between alterations in motor function and changes in the underlying structure of these systems. Research is also needed to develop simple and sensitive assays for use in screening assessments of sensory and cognitive function. Assessment methods are being developed to examine other nervous system functions, including social behavior, autonomic processes, and biologic rhythms. Social behaviors are modified by many classes of developmental neurotoxicants and hormonally active compounds that may act either through neuroendocrine mechanisms or by directly influencing brain morphology or neurochemistry. Autonomic and thermoregulatory functions have been the province of physiologists and neurobiologists rather than toxicologists, but this may change as developmental neurotoxicology progresses and toxicologists apply techniques developed by other disciplines to examine changes in function after toxicant exposure.

Topics in cancer risk assessment.

The estimation of carcinogenic risks from exposure to chemicals has become an integral part of the regulatory process in the United States within the past decade. With it have come considerable controversy and debate over the scientific merits and shortcomings of the methods and their impact on risk management decisions. In this paper we highlight selected topics of current interest in the debate. As an indication of the level of public concern, we note the major recent reports on risk assessment from the National Academy of Sciences and the U.S Environmental Protection Agency's proposed substantial revisions to its Guidelines for Carcinogen Risk Assessment. We identify and briefly frame several key scientific issues in cancer risk assessment, including the growing recognition of the importance of understanding the mode of action of carcinogenesis in experimental animals and in humans, the methodologies and challenges in quantitative extrapolation of cancer risks, and the question of how to assess and account for human variability in susceptibility to carcinogens. In addition, we discuss initiatives in progress that may fundamentally alter the carcinogenesis testing paradigm.

Principles for the selection of doses in chronic rodent bioassays. ILSI Risk Science Working Group on Dose Selection.

Dose selection in chronic rodent bioassays has been one of the most debated issues in risk assessment. The Committee on Risk Assessment Methods of the National Research Council attempted, but failed, in 1993 to reach consensus on how to select doses for chronic rodent bioassays. However, a more recent effort conducted by the ILSI Risk Science Institute has resulted in a consensus set of principles for dose selection, including selection of the highest dose for chronic rodent bioassays. The principles encourage a move away from sole reliance on a maximum tolerated dose (MTD), as it has been traditionally defined (primarily by body weight and histopathology), and toward the use of sound scientific and toxicologic principles for the selection of all doses in the chronic bioassay. Specifically, the principles recommend that dose selection for chronic studies must be based on sound toxicologic principles; dose selection should consider human exposure; dose selection should be based on a variety of endpoints and effects derived from prechronic studies; and dose selection should consider physicochemical and other factors. Implementation of the principles internationally will have two important benefits; improvement in the quality and consistency of the rodent bioassay and international harmonization of dose selection procedures.

Chemical mixtures: current risk assessment methodologies and future directions.

Some of the most challenging problems that toxicologists confront are determining how biological effects of components in a complex mixture may interact, determining how these interactions affect the overall toxicity of the mixture, and determining how to incorporate this information into risk assessments of chemical mixtures. There has been considerable effort in this area since the publication of the U.S. Environmental Protection Agency's guidelines for risk assessment of chemical mixtures in 1986. This paper reviews the terminology used to describe chemical interactions and the methodologies that have been developed for conducting risk assessments of chemical mixtures. Particular attention is directed towards an examination of the applicability and validity of the methods for the assessment of risk posed by exposure to environmentally relevant concentrations of chemical mixtures. Limited, yet compelling, data are reviewed that suggest that for noncancer endpoints, adverse effects are unlikely to occur when the individual components in the mixture are present at levels well below their respective thresholds. Synergistic or antagonistic effects, not readily predicted from the mechanisms of action of the individual components, are possible when the mixture components are present at levels equal to or above their individual thresholds. Finally, synergistic carcinogenic effects have been observed in animal studies of mixtures, even at relatively low doses.

Sport fish consumption advisories and projected cancer risks in the Great Lakes basin.

Because Great Lakes sport fish are contaminated with several toxicants, the Great Lakes states individually issue advisories, principally based on Food and Drug Administration (FDA) action levels, that suggest limiting or eliminating consumption of contaminated fish. We describe the procedures the states use to determine when to issue consumption advisories and we evaluate the associated cancer risks using EPA-IARC-OSTP risk assessment procedures. Projected cancer risks are high for consumers of small quantities of sport fish contaminated with DDT or dieldrin at their respective action levels. Projected risks at concentrations that are common but below the action levels are also substantial. We propose that sport fish with tissue concentrations of DDT or dieldrin one-fifth and one-third of the action levels should be covered by consumption advisories to warn consumers of the potential adverse health impacts.

Functional analysis of a cytoplasmic domain-deleted mutant of the CD4 molecule.

The CD4 molecule is a receptor found on a subset of T lymphocytes. It has been proposed that, upon binding MHC class II molecules expressed on APC, the CD4 molecule enhances the responsiveness of the T cell by increasing intercellular avidity and/or by transducing an intracellular signal. We have analyzed the effect of removing the cytoplasmic domain of the CD4 molecule on the ability of the CD4 molecule to enhance T cell responsiveness. The cytoplasmic domain-deleted mutant of the CD4 molecule (CD4 delta) was found to be as efficient as the CD4 molecule at enhancing responsiveness to cells bearing the appropriate Ag. If subcellular Ag in the form of purified Ag incorporated into liposomes was used, the CD4 molecule was found to be much more efficient than the CD4 delta molecule at enhancing responsiveness. However, the defect in the ability of the CD4 delta molecule to enhance responsiveness could be compensated for by increasing the level of expression of the CD4 delta molecule.

Expression and function of CD4 in a murine T-cell hybridoma.

The CD4 (T4) antigen was originally described as a phenotypic marker specific for helper T cells, and has recently been shown to be the receptor for the human immunodeficiency virus (HIV). Functional studies using monoclonal antibodies directed at CD4 and major histocompatibility complex (MHC) class II molecules led to the suggestion that CD4 binds to the MHC class II molecules expressed on stimulator cells, enhancing T-cell responsiveness by increasing the avidity of T cell-stimulator cell interaction and/or by transmitting a positive intracellular signal. But recent evidence that antibodies to CD4 inhibit T-cell responsiveness in the absence of any putative ligand for CD4 has been interpreted as suggesting that antibody-mediated inhibition may involve the transmission of a negative signal via the CD4 molecule instead. We have infected a murine T-cell hybridoma that produces interleukin 2 (IL-2) in response to human class II HLA-DR antigens with a retroviral vector containing CD4 cDNA. The resulting CD4-expressing hybridoma cell lines produce 6- to 20-fold more IL-2 in response to HLA-DR antigens than control cell lines. Furthermore, when antigen levels are suboptimal, the response of the cell lines is entirely CD4-dependent. The data presented here clearly demonstrate that CD4 can enhance T-cell responsiveness and may be crucial in the response to suboptimal levels of antigen.

Immunochemically purified DR antigens in liposomes stimulate xenogeneic cytolytic T cells in secondary in vitro cultures.

A monoclonal antibody directed against the human class II major histocompatibility antigen DR was generated. Use of this antibody, LB3.1, allowed isolation of large amounts of highly purified DR by immunoaffinity chromatography. The DR was reconstituted into liposomes and shown to stimulate secondary xenogeneic cytolytic T lymphocytes (CTL) specific for targets expressing DR antigens. DR digested with neuraminidase was equally as effective as native DR at stimulating CTL, while denatured DR and other purified membrane proteins were much less effective. The DR liposome-induced CTL lysed only target cells expressing class II antigens. Cytolysis of targets bearing class II antigens was blocked by DR-specific antisera.

The role of T cell accessory molecules in the generation of class II-specific xenogeneic cytolytic T cells.

In the generation of allogeneic, hapten-modified and virus-specific cytotoxic T cell (CTL) responses there is usually a requirement for T-T interaction between the T helper cell (TH) and the precursor CTL (CTL). We have investigated the role of a TH signal in the induction of a xenogeneic mouse antihuman CTL response by using membranes and liposomes bearing the xenogeneic antigen to stimulate primed responders. The TH signal can be achieved by either an Ia-restricted, L3T4+ DR-specific T cell or by the addition of nonspecific T helper factors(s). This signal is delivered to an Lyt-2+, L3T4-DR-specific CTL to generate active xenogeneic (xeno-) CTL. The roles of the T cell accessory molecules L3T4, Lyt-2, and LFA-1 in the generation of and target cell lysis by xeno-CTL are investigated.

New rapid technique for counting microorganisms directly on membrane filters.

The proposed technique is a modification of classical procedures for counting micoorganisms directly on membrane filters. The technique consists of clearing the filter with immersion oil, paraffin oil or cedar oil prior to staining with crystal violet, carbol fuchsin or malachite green. Millipore filters (0.1 micron pore size, VC type) were found to be superior to other filters with regard to the contrast between microorganisms and filter surface.

Immobilization of baboons (Papio anubis) using ketamine and diazepam.

Ketamine (10mg/kg body weight) was administered intramuscularly in 10 baboons (Papio anubis). Subsequently, a combination of ketamine (10mg/kg body weight) and diazepam (7.5 mg) was administered intramuscularly. Results indicated that using diazepam concurrently with ketamine suppressed or eliminated the epileptoid movements characteristic of anesthesia with ketamine used alone.