Chemical-specific properties co-determine the type of adverse immune response

Assessing cumulative health risks from exposure to environmental mixtures - three fundamental questions

Differential exposure to mixtures of environmental agents, including biological, chemical, physical, and psychosocial stressors, can contribute to increased vulnerability of human populations and ecologic systems. Cumulative risk assessment is a tool for organizing and analyzing information to evaluate the probability and seriousness of harmful effects caused by either simultaneous and/or sequential exposure to multiple environmental stressors. In this article we focus on elucidating key challenges that must be addressed to determine whether and to what degree differential exposure to environmental mixtures contributes to increased vulnerability of exposed populations. In particular, the emphasis is on examining three fundamental and interrelated questions that must be addressed as part of the process to assess cumulative risk: a) Which mixtures are most important from a public health perspective? and b) What is the nature (i.e., duration, frequency, timing) and magnitude (i.e., exposure concentration and dose) of relevant cumulative exposures for the population of interest? c) What is the mechanism (e.g., toxicokinetic or toxicodynamic) and consequence (e.g., additive, less than additive, more than additive) of the mixture's interactive effects on exposed populations? The focus is primarily on human health effects from chemical mixtures, and the goal is to reinforce the need for improved assessment of cumulative exposure and better understanding of the biological mechanisms that determine toxicologic interactions among mixture constituents.

Immunological principles of T-cell-mediated adverse drug reactions in skin

Drug hypersensitivity reactions in skin are an immune-mediated phenomenon associated with significant patient mortality and morbidity. Antigen-specific T cells, which have been isolated from the peripheral circulation and target organs of hypersensitive patients, are thought to propagate and regulate the development of clinical symptoms. The investigation of clinical cases with respect to the basic cellular and chemical mechanisms that underpin drug hypersensitivity has resulted in: i) the need to redress some aspects of present immunological dogma; and ii) additional fundamental immunological questions. Thus, the aim of this review article is to summarise present opinion on how and why drugs initiate a pathogenic T-cell response in a small section of the population and subsequently reflect on gaps in basic immunology and where future research might lead.

Multiorgan autoimmune inflammation, enhanced lymphoproliferation, and impaired homeostasis of reactive oxygen species in mice lacking the antioxidant-activated transcription factor Nrf2

Nuclear factor erythroid 2-related factor 2 (Nrf2) is an antioxidant-activated cap "n" collar basic leucine zipper transcription factor. To assess the function of Nrf2 in the antioxidant response, we examined mice with targeted disruption of the Nrf2 gene. Nrf2-null mice developed complex disease manifestations, with a majority exhibiting a lupus-like autoimmune syndrome characterized by multiorgan inflammatory lesions with a marked female predominance, appearance of anti-double-stranded DNA antibodies in young adulthood, intravascular deposition of immunoglobulin complexes in blood vessels, and premature death due to rapidly progressing membranoproliferative glomerular nephritis. Mechanistic analyses revealed that the null mice showed enhanced proliferative response of CD4+ T cells, altered ratios of CD4+ and CD8+ cells, and increased oxidative lesions in tissues. Analyses of antioxidant-induced gene expression showed that the knockout mice were devoid of the basal and inducible expression of certain phase 2 detoxification enzymes and antioxidant genes in hepatic and lymphoid cells in vivo. Our findings suggest that Nrf2 mediates important antioxidant functions involved in the control of peripheral lymphocyte homeostasis and autoimmune surveillance.

Free radical theory of autoimmunity

Background

Despite great advances in clinical oncology, the molecular mechanisms underlying the failure of chemotherapeutic intervention in treating lymphoproliferative and related disorders are not well understood.

Hypothesis

A hypothetical scheme to explain the damage induced by chemotherapy and associated chronic oxidative stress is proposed on the basis of published literature, experimental data and anecdotal observations. Brief accounts of multidrug resistance, lymphoid malignancy, the cellular and molecular basis of autoimmunity and chronic oxidative stress are assembled to form a basis for the hypothesis and to indicate the likelihood that it is valid in vivo.

Conclusion

The argument set forward in this article suggests a possible mechanism for the development of autoimmunity. According to this view, the various sorts of damage induced by chemotherapy have a role in the pattern of drug resistance, which is associated with the initiation of autoimmunity.

Cytokine release does not improve the sensitivity and specificity of the direct popliteal lymph node assay

The popliteal lymph node assay (PLNA) is being considered as a tool to predict the potential of drugs for inducing systemic autoimmune and hypersensitivity reactions. Despite the use of different technical approaches and the evaluation of over 130 compounds, the sensitivity and specificity of the PLNA are still debatable due to many false positive and negative responses. In this study, cytokine production was assessed as a possible endpoint to improve the direct (primary) PLNA. Diclofenac, imipramine, hydralazine, glafenin and minocycline were tested using the classical procedure. TH1 cytokines (IL-2 and IFN-gamma), TH2 cytokines (IL-4 and IL-5) and pro-inflammatory cytokines (IL-6, TNF-alpha, monocyte chemoattractant protein-1 (MCP-1), IL-12p70 and IL-10) were measured in the serum and in suspensions of popliteal lymph node cells of female Balb/c mice by flow cytometry 7 days after drug administration. Only diclofenac and imipramine induced a cellularity index above 5 (considered as a positive response). Of the five tested drugs, only diclofenac induced a slight increase in TH1 cytokines, but there were no effects on TH2 cytokine production whatever the drug tested. Diclofenac increased the production of pro-inflammatory cytokines, whereas the production of MCP-1 was increased by minocycline and decreased by imipramine. No changes in serum cytokine levels were evident. These results suggest that measuring cytokine release is unlikely to improve the sensitivity and specificity of the direct PLNA.