Search

Increased expectations from a number of regulatory agencies, e.g., Environmental Protection Agency (EPA), Food and Drug Administration (FDA), European Medicines Agency (EMEA), and the Ministry of Health, Labour and Welfare (MHLW) of Japan, call for the evaluation of potential adverse effects on the immune system. As recently summarized in the ICH S8 guideline, the T-cell-dependent antibody response (TDAR) has been identified in a regulatory context as a main functional test of immunotoxicity. While the characterization of immunotoxic potential is pertinent to both the chemical and pharmaceutical industries, the use of immunotoxicology data for hazard identification and/or risk assessment in each case is different. Therefore, multiple approaches to immunotoxicity testing have evolved. The assays that evaluate TDAR function include both well-established tests, e.g., anti-sheep red blood cell plaque-forming cell (PFC) assay, and newer models, e.g., anti-keyhole limpet hemocyanin (KLH) antibody ELISA. These tests vary in the study design, antigen application and analytical methods. However, they all evaluate the same endpoint - a competent immune (e.g., antibody) response to an antigen. Numerous issues have been identified in the application of TDAR tests, including high animal to animal variability; differences in antigen source and potency; a lack of established "normal range" of the immune response and uncertainty about the degree of inhibition of the TDAR to be considered toxicologically important. As such, the need for a forum to discuss these issues was recognized by the immunotoxicology community, and was addressed at the 2006 Society of Toxicology (SOT) Workshop. A series of papers will summarize that forum with the ultimate objectives being to build a consensus among immunotoxicologists on the implications of these factors on using TDAR results in hazard identification and/or risk assessment, and to establish a criteria to classify compounds as immunotoxicants. [ABSTRACT FROM AUTHOR]

The immunotoxic potential of drug candidates is assessed through the examination of results from a variety of studies and endpoints. While the functional assessment of CD8+ cytotoxic T-lymphocytes (CTL) is well-characterized in the clinic, the lack of a robust macaque CTL functional assay has been an important hurdle in evaluating and accurately quantifying cell-mediated CD8+ T-cell effector responses in the nonclinical setting. This paper describes the development of an assay to measure CTL activity in peripheral blood mononuclear cells (PBMC) isolated from Cynomolgus macaques. A human EGFR/CD3 Bispecific T-cell Engager (BiTE®) was used to mount a robust CD8+ T-cell response in the presence of target-expressing cells. Upon target engagement, degranulation of CD107a and production of interferon (IFN)-γ both reliably indicated a robust functional response in CD8+ T-cells. The BiTE®-mediated stimulation method proved to be favorable when compared to other methods of stimulation in the absence of target cells. These studies demonstrated acceptable longitudinal variability of the functional assay and sensitivity to dexamethasone-mediated immunosuppression. Taken together, the results indicated an assay leveraging CD3-bispecific antibodies and target-expressing cells can provide a robust approach to the in vitro or ex vivo assessment of CTL function in Cynomolgus macaques. Because the impairment of CTL activity by immunomodulators is recognized to be an important contributor to decreased antiviral defense and increased carcinogenicity risk, we believe that this novel assay to be a valuable addition to the immunotoxicology assessment of therapeutic drug candidates. [ABSTRACT FROM AUTHOR]

Endocrine-disrupting chemicals (EDCs) refer to a group of chemicals that cause adverse effects in human health, impairing hormone production and regulation, resulting in alteration of homeostasis, reproductive, and developmental, and immune system impairments. The immunotoxicity of EDCs involves many mechanisms altering gene expression that depend on the activation of nuclear receptors such as the aryl hydrocarbon receptor (AHR), the estrogen receptor (ER), and the peroxisome proliferator-activated receptor (PPAR), which also results in skin and intestinal disorders, microbiota alterations and inflammatory diseases. This systematic review aims to review different mechanisms of immunotoxicity and immunomodulation of T cells, focusing on T regulatory (Treg) and Th17 subsets, B cells, and dendritic cells (DCs) caused by specific EDCs such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), bisphenols (BPs) and polyfluoroalkyl substances (PFASs). To achieve this objective, a systematic study was conducted searching various databases including PubMed and Scopus to find in-vitro, in-vivo, and biomonitoring studies that examine EDC-dependent mechanisms of immunotoxicity. While doing the systematic review, we found species- and cell-specific outcomes and a translational gap between in-vitro and in-vivo experiments. Finally, an adverse outcome pathway (AOP) framework is proposed, which explains mechanistically toxicity endpoints emerging from different EDCs having similar key events and can help to improve our understanding of EDCs mechanisms of immunotoxicity. In conclusion, this review provides insights into the mechanisms of immunotoxicity mediated by EDCs and will help to improve human health risk assessment. Overview of the mechanisms of immunotoxicity of EDCs for T, B, and Dendritic cells and the main outcomes of exposure that result in immunotoxicity: imbalance of Treg/Th17 lymphocyte populations; a decrease of antibodies production; an increase of DCs maturation. [ABSTRACT FROM AUTHOR]

Delayed-type hypersensitivity (DTH) is a T-cell-mediated immune response that may be used for immunotoxicity testing in non-clinical species. However, in some cases DTH assays using T-dependent antigens may be confounded by the production of antibodies to the antigen. The authors have previously modified a DTH assay, initially validated in the mouse, for use in juvenile rats to assess the effect of immunosuppressive drugs on the developing rat immune system. The assay measures footpad swelling induced by subcutaneous footpad injection ofCandida albicans(C. albicans) derived-chitosan in rats previously sensitized withC. albicans. Antibodies to chitosan are not produced in this model. However, considerable inter-animal variability inherent in the footpad swelling assay can make it difficult to precisely quantify the magnitude of the immune response and inhibition by immunosuppressants, particularly if complete suppression is not observed. This report describes the development of anex vivoassay to assess DTH in rats using interferon (IFN)-γ production by splenocytes, obtained from rats sensitized withC. albicans, as the quantifiable measure of the DTH response. Adult and neonatal rats administered dexamethasone (DEX), a known immunosuppressant, exhibited immunosuppression as evidenced by a reduction inex vivoIFNγ production from splenocytes challenged withC. albicans-derived chitosan. Current data indicate that theex vivobased DTH assay is more sensitive than the conventional footpad swelling assay due to a lower background response and the ability to detect a response as early as post-natal day (PND) 12. Theex vivobased rat DTH assay offers a highly sensitive and quantitative alternative to the footpad swelling assay for the assessment of the immunotoxic potential of drugs. The increased sensitivity of theex vivoDTH assay may be useful for identifying smaller changes in response to immunotoxic drugs, as well as detecting responses earlier in animal development. [ABSTRACT FROM PUBLISHER]

Deoxynivalenol (DON) is one of the most abundant mycotoxins worldwide and mostly detected in cereals and grains. As such, DON poses a risk for many adverse health effects to human and animals. In particular, immune cells are very sensitive to DON, with the initiating step leading to toxicity being a binding to the eukaryotic 60S ribosomal subunit and induction of ribotoxic stress. The present study aimed to: (1) extend insight into the mechanism of action (MOA) of DON in immune cells; and (2) understand why immune cells are more sensitive to DON than most other cell types. Previously published microarray studies have described the effects of DON on immune cells. To build upon these findings, here, immunocytological and biochemical studies were performed using human T-lymphocyte Jurkat cells that were exposed for 3 h to 0.5 µM DON. Induction of ER stress by DON was confirmed by immunocytology demonstrating increased protein expression of two major ER stress markers ATF3 and DDIT3. T-cell activation was confirmed by induction of phosphorylation of protein kinases JNK and AKT, activation of NF- κB (p65), and increased expression of NFAT target gene NUR77; each of these are known inducers of the T-cell activation response. Induction of an oxidative stress response was also confirmed by monitoring the nuclear translocation of major oxidative stress markers NRF2 and KEAP1, as well as by changes (i.e. decreases) in cell levels of reduced glutathione. Lastly, this study showed that DON induced cleavage of caspase-3, an event known to mediate apoptosis. Taken together, these results allowed us to formulate a potential mechanism of action of DON in immune cells, i.e. binding to eukaryotic 60S ribosomal subunit → ribotoxic stress → ER stress → calcium release from the ER into cytoplasm → T-cell activation and oxidative stress → apoptosis. It is proposed that immune cells are more sensitive to DON than other cell types due to the induction of a T-cell activation response by increased intracellular calcium levels. [ABSTRACT FROM AUTHOR]

The toxic effects of highly carcinogenic mycotoxins, especially aflatoxins (AF), on key antigen-presenting cells, such as dendritic cells (DC), are largely unknown. To elucidate the effect of AF on DC function, porcine monocyte-derived DC (MoDC) were treated with a mixture of several AF (i.e., AFB1, AFB2, AFG1, and AFG2) and the phagocytic capacity, the membrane expression level of several DC activation markers, the T-cell proliferation-inducing capacity, and the cytokine secretion pattern were assessed. As compared to untreated MoDC, AF significantly up-regulated the expression of the co-stimulatory molecules CD25 and CD80/86. However, the phagocytic activity of MoDC was not affected by AF treatment. While the cytokine secretion pattern of AF-treated MoDC was similar to control MoDC, the T-cell proliferation-inducing capacity of MoDC was increased upon aflatoxin treatment. The results indicate that a mixture of naturally occurring AF enhances the antigen-presenting capacity of DC, which could explain the observed immunotoxicity of AF by breaking down tolerance and further emphasizes the need to reduce the admissible level of AF in agricultural commodities. [ABSTRACT FROM AUTHOR]

The potential for immunotoxicological effects of ethyl tertiary butyl ether (ETBE, CAS RN 637-92-3) was studied in young adult female Crl:CD(SD) rats following subchronic oral exposures. Rats were exposed by gavage once daily for 28 consecutive days to 0, 250, 500, or 1000 mg ETBE/kg body weight (BW)/day; a concurrent positive control group received four intraperitoneal injections of at 50 mg cyclophosphamide monohydrate (CPS)/kg/day on study Days 24-27. Immunotoxicity was evaluated using a splenic antibody-forming cell (AFC) assay to assess T-cell-dependent antibody responses in rats sensitized with sheep red blood cells (SRBC). All rats survived to the scheduled necropsy. There were no effects on clinical observations, body weights, feed or water consumption, or macroscopic pathology findings in the ETBE-treated rats. No ETBE-related effects were observed on absolute or relative (to final body weight) spleen or thymus weights, spleen cellularity, or on the specific (AFC/106 spleen cells) or total activity (AFC/spleen) of splenic IgM AFC to the T-cell-dependent antigen SRBC. CPS produced expected effects consistent with its known immunosuppressive properties and validated the appropriateness of the AFC assay. Based on the results of this study, ETBE did not suppress the humoral component of the immune system in female rats. The no-observed-effect level for immunotoxicity was the highest dosage tested at 1000 mg/kg/day. [ABSTRACT FROM AUTHOR]

This study has evaluated the effects of three industrially relevant multi-walled carbon nanotubes (MWNTs) on human Jurkat T cells and compared them to those of crocidolite asbestos. No overt acute toxicity was observed for all MWNTs tested although signs of oxidative stress were evident. MWNTs did not activate resting Jurkat cells and only slightly stimulated the release of the cytokine interleukin-2 (IL-2) in activated cells. Similar to MWNTs, crocidolite had little toxic effects on Jurkat cells but neither induced the formation of reactive oxygen species nor changes in IL-2 signaling. These findings suggest that, in contrast to many other cell types, T cells are relatively resistant to stress induced by high-aspect ratio particles. [ABSTRACT FROM AUTHOR]

Previously, we showed that in utero exposure to mercury induced phenotypic changes in fetal immune cells. Here, we sought to determine whether the effects of in utero exposure on immune cells persisted in the adult. After overnight breeding to DBA/1 males, pregnant BALB/c dams were given either mercuric chloride in drinking water at 10 mg/L ad libitum for the duration of gestation or plain water. At the time of parturition, all dams were placed on regular drinking water. The pups (DBF1) were weaned and thymic and splenic tissues were harvested at 10 wk-of-age to assess T-cell phenotypes and function. Significant changes in the CD4/CD8 subsets in the thymus and spleen among mercury-exposed male and female mice were not observed. However, there was a significant reduction in splenic CD4+CD25+ cells in mercury-exposed female, but not in male, mice. ConA-stimulated splenocytes from mercury-exposed mice showed significant increases in proliferative responses relative to cells from control mice, regardless of sex. Cytokine secretion was also modulated in the mercury-exposed mice. In particular, the production of IL-4 and IFN by ConA-stimulated splenocytes from mercury-exposed male and female mice was significantly increased, while IL-2 and IL-10 levels were unaffected. The results of our study revealed that exposure of the developing immune system to relatively low levels of inorganic mercury could lead to persistent alterations in adult immune cell phenotypes and functions. These changes could pose a relevant health risk, if they contribute to impaired responses to pathogens and/or an increased risk for the development of atopy, asthma or possibly autoimmune diseases. [ABSTRACT FROM AUTHOR]