Fundamentals of clinical immunotoxicology

CD4+ T lymphocyte responses to viruses and virus-relevant stimuli in teleost fish

Fish diseases caused by viruses are a major threat to aquaculture. Development of disease protection strategies for sustainable fish aquaculture requires a better understanding of the immune mechanisms involved in antiviral defence. The innate and adaptive arms of the vertebrate immune system collaborate to mount an effective defence against viral pathogens. The T lymphocyte components of the adaptive immune system, comprising two major classes (helper T, Th or CD4+ and cytotoxic T lymphocytes, CTLs or CD8+ T cells), are responsible for cell-mediated immune responses. In particular, CD4+ T cells and their different subsets orchestrate the actions of various other immune cells during immune responses, making CD4+ T cells central drivers of responses to pathogens and vaccines. CD4+ T cells are also present in teleost fish. Here we review the literature that reported the use of antibodies against CD4 in a few teleost fish species and transcription profiling of Th cell-relevant genes in the context of viral infections and virus-relevant immunomodulation. Studies reveal massive CD4+ T cell proliferation and expression of key cytokines, transcription factors, and effector molecules that evoke mammalian Th cell responses. We also discuss gaps in the current understanding and evaluation of teleost CD4+ T cell responses and how development and application of novel tools and approaches to interrogate such responses could bridge these gaps. A greater understanding of fish Th cell responses will further illuminate the evolution of vertebrate adaptive immunity, inform strategies to address viral infections in aquaculture, and could further foster fish as model organisms.

Suppression of Th2 cytokines as a potential mechanism for reduced antibody response following PFOA exposure in female B6C3F1 mice

Perfluorooctanoic acid (PFOA), a member of the Per- and polyfluoroalkyl substances, is a highly persistent "forever" chemicals with increasing concern for its potential health effects. However, the mechanisms of PFOA immunotoxic effects are poorly understood. We assessed the antibody response to a physiological antigen stimulation and associated cytokine response upon PFOA exposure. The significant decrease in the IgM antibody response to the T cell dependent antigen keyhole limpet hemocyanin (KLH) at a dose lower than the previously documented LOAEL was accompanied by a significant reduction of the Th2 serum cytokines IL-5 and IL-13, a non-significant dose-response reduction of IL-4, a significant reduction of the Th1 cytokine IL-12, and a non-significant dose-response increase in IL-2 and IFNγ. PFOA significantly decreased the pro-inflammatory cytokines IL-17α and IL-1α, decreased (non-significantly but dose-response) IL-6, and a significantly increased TNFα. Overall, the modulation of serum Th1/Th2 cytokines could explain the reduction in antibody response, pointing to a potential role for T helper cells in the immunotoxicity of PFOA. Further, the higher than anticipated weight loss and increased liver weight, compared to previous studies using similar doses, highlight the potential importance of the route and duration of exposure, contributing to the total accumulated dose, in assessing the toxicity of PFOA.

Exposure, health effects, sensing, and remediation of the emerging PFAS contaminants - Scientific challenges and potential research directions

Per- and polyfluoroalkyl substances (PFAS) make up a large group of persistent anthropogenic chemicals which are difficult to degrade and/or destroy. PFAS are an emerging class of contaminants, but little is known about the long-term health effects related to exposure. In addition, technologies to identify levels of contamination in the environment and to remediate contaminated sites are currently inadequate. In this opinion-type discussion paper, a team of researchers from the University of Connecticut and the University at Albany discuss the scientific challenges in their specific but intertwined PFAS research areas, including rapid and low-cost detection, energy-saving remediation, the role of T helper cells in immunotoxicity, and the biochemical and molecular effects of PFAS among community residents with measurable PFAS concentrations. Potential research directions that may be employed to address those challenges and improve the understanding of sensing, remediation, exposure to, and health effects of PFAS are then presented. We hope our account of emerging problems related to PFAS contamination will encourage a broad range of scientific experts to bring these research initiatives addressing PFAS into play on a national scale.

Investigative Immunotoxicology

Immunotoxicology is the study of immune system dysfunction that can result from occupational, inadvertent, or therapeutic exposure to a variety of chemical or biologic agents that alter the immune system and affect human health. Immunotoxicology can manifest in a variety of ways, with one of the most prominent effects being immunosuppression. Immunosuppression can be defined as a reduced ability of the immune system to respond to a challenge from a level considered normal, regardless of whether clinical disease results. Although immunosuppression can lead to an increased incidence and severity of infectious and neoplastic disease, interpreting data from experimental immunotoxicology studies, or even epidemiologic studies, for quantitative risk assessment has been a persistent challenge. Decades of research has resulted in the development of specific assays and the identification of sensitive endpoints that measure effects on the immune response, from which many regulatory agencies have developed specific immunotoxicity testing guidelines. However, establishing a direct link between exposure and disease manifestations for immunosuppression in humans is an ongoing challenge due to inherent limitations of epidemiological studies to draw causal conclusions. Efforts have been made to examine the relationships between laboratory measures of immune response and disease resistance in experimental animal models and also in human studies. The identification of sensitive endpoints and the development of experimental assays to identify suspect immunotoxicants are a primary focus of the field of immunotoxicology. This chapter is organized around sections discussing the impact and scientific basis of immunotoxicity testing, predictive immunotoxicity testing strategies, examples of immunotoxicity testing, and key considerations and recent developments related to effective testing strategies for health risk reduction.

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.

Keyhole limpet haemocyanin - a model antigen for human immunotoxicological studies

Immunization with a T-cell dependent antigen has been promoted as a reliable and sensitive tool for assessing the influence of putative immunotoxic exposures or agents on immune function. Keyhole limpet haemocyanin (KLH) is a very large, copper-containing protein molecule derived from the haemolymph of the inedible mollusc, Megathura crenulata. KLH is a highly immunogenic T-cell dependent antigen that is used increasingly in immunotoxicological studies, particularly in those involving animals. This report systematically reviews the human clinical studies that have used trans-cutaneous KLH immunization for assessment of the influence of various physiological and disease states and exposures on immune function over the last 20 years (1994-2013). These studies varied in their immunization protocols, formulation of KLH, dose, site and route of administration and immunoassay platforms developed to assess KLH-specific responses. KLH immunization has been well tolerated with only mild to moderate adverse effects reported. Though very promising as a model antigen candidate in immunotoxicology research, more work on standardizing immunization and immunoassay protocols is required.

Environmental risk factors for autism

Autism is a devastating childhood condition that has emerged as an increasing social concern just as it has increased in prevalence in recent decades. Autism and the broader category of autism spectrum disorders are among the increasingly seen examples in which there is a fetal basis for later disease or disorder. Environmental, genetic, and epigenetic factors all play a role in determining the risk of autism and some of these effects appear to be transgenerational. Identification of the most critical windows of developmental vulnerability is paramount to understanding when and under what circumstances a child is at elevated risk for autism. No single environmental factor explains the increased prevalence of autism. While a handful of environmental risk factors have been suggested based on data from human studies and animal research, it is clear that many more, and perhaps the most significant risk factors, remain to be identified. The most promising risk factors identified to date fall within the categories of drugs, environmental chemicals, infectious agents, dietary factors, and other physical/psychological stressors. However, the rate at which environmental risk factors for autism have been identified via research and safety testing has not kept pace with the emerging health threat posed by this condition. For the way forward, it seems clear that additional focused research is needed. But more importantly, successful risk reduction strategies for autism will require more extensive and relevant developmental safety testing of drugs and chemicals.