New approach methodologies to enhance human health risk assessment of immunotoxic properties of chemicals - a PARC (Partnership for the Assessment of Risk from Chemicals) project

As a complex system governing and interconnecting numerous functions within the human body, the immune system is unsurprisingly susceptible to the impact of toxic chemicals. Toxicants can influence the immune system through a multitude of mechanisms, resulting in immunosuppression, hypersensitivity, increased risk of autoimmune diseases and cancer development. At present, the regulatory assessment of the immunotoxicity of chemicals relies heavily on rodent models and a limited number of Organisation for Economic Co-operation and Development (OECD) test guidelines, which only capture a fraction of potential toxic properties. Due to this limitation, various authorities, including the World Health Organization and the European Food Safety Authority have highlighted the need for the development of novel approaches without the use of animals for immunotoxicity testing of chemicals. In this paper, we present a concise overview of ongoing efforts dedicated to developing and standardizing methodologies for a comprehensive characterization of the immunotoxic effects of chemicals, which are performed under the EU-funded Partnership for the Assessment of Risk from Chemicals (PARC).

Impact of chemical mixtures from wastewater treatment plant effluents on human immune cell activation: An effect-based analysis

BACKGROUND

Humans are exposed to many different chemicals on a daily basis, mostly as chemical mixtures, usually from food, consumer products and the environment. Wastewater treatment plant effluent contains mixtures of chemicals that have been discarded or excreted by humans and not removed by water treatment. These effluents contribute directly to water pollution, they are used in agriculture and may affect human health. The possible effect of such chemical mixtures on the immune system has not been characterized.

OBJECTIVE

The aim of this study was to investigate the effect of extracts obtained from four European wastewater treatment plant effluents on human primary immune cell activation.

METHODS

Immune cells were exposed to the effluent extracts and modulation of cell activation was performed by multi-parameter flow cytometry. Messenger-RNA (mRNA) expression of genes related to immune system and hormone receptors was measured by RT-PCR.

RESULTS

The exposure of immune cells to these extracts, containing 339 detected chemicals, significantly reduced the activation of human lymphocytes, mainly affecting T helper and mucosal-associated invariant T cells. In addition, basophil activation was also altered upon mixture exposure. Concerning mRNA expression, we observed that 12 transcripts were down-regulated by at least one extract while 11 were up-regulated. Correlation analyses between the analyzed immune parameters and the concentration of chemicals in the WWTP extracts, highlighted the most immunomodulatory chemicals.

DISCUSSION

Our results suggest that the mixture of chemicals present in the effluents of wastewater treatment plants could be considered as immunosuppressive, due to their ability to interfere with the activation of immune cells, a process of utmost importance for the functionality of the immune system. The combined approach of immune effect-based analysis and chemical content analysis used in our study provides a useful tool for investigating the effect of environmental mixtures on the human immune response.

In Vitro Effects of Cypermethrin and Glyphosate on LPS-Induced Immune Cell Activation

(1) Background: The insecticide cypermethrin (Cypm) and the herbicide glyphosate (Glyp) are among the most widely used pesticides. While the two pesticides have been considered to have low toxicity in mammals, some indication of potential immunotoxicity has emerged. The aim of this work was to investigate in vitro the effects of Cypm and Glyp on bacteria lipopolysaccharide (LPS)-induced immune cell activation and of Cypm on 2-mercaptobenzothiazole (MBT)-induced maturation of dendritic cells (DCs). (2) Methods: The release of the inflammatory cytokines TNF-α and IL-8, the expression of the surface markers CD54 and CD86 in human primary peripheral blood mononuclear cells (PBMC), and THP-1 cells were investigated together with CD83, HLA-DR, IL-6, and IL-18 in DCs. (3) Results: While no significant modulation on LPS-induced immune cell activation was observed following Glyp exposure, with only a trend toward an increase at the highest concentration tested, Cypm reduced the responses to LPS and to MBT, supporting a direct immunosuppressive effect. Overall, the present study contributes to our understanding of pesticide-induced immunotoxicity, and the results obtained support evidence showing the immunosuppressive effects of Cypm.

Impact of endocrine disruptors on peripheral blood mononuclear cells in vitro: role of gender

Humans can be exposed to endocrine disruptors (EDs) in numerous ways. EDs can interfere with endogenous hormones at different levels, resulting in numerous adverse human health outcomes, including immunotoxicity. In this regard, this study aimed to investigate in vitro the possible effects of EDs on immune cells and possible gender differences. Peripheral blood mononuclear cells from healthy humans, both males and females, were exposed to 6 different EDs, namely atrazine (herbicide), cypermethrin (insecticide), diethyl phthalate (plasticizer), 17α-ethynylestradiol (contraceptive drug), perfluorooctanesulfonic acid (persistent organic pollutant), and vinclozolin (fungicide). We evaluated the effect of EDs on RACK1 (receptor for activated C kinase 1) expression, considering it as a bridge between the endocrine and the immune system, and putatively used as screening tool of immunotoxic effects of EDs. The exposure to EDs resulted at different extent in alteration in RACK1 expression, pro-inflammatory activity, natural killer lytic ability, and lymphocyte differentiation, with sex-related differences. In particular, diethyl phthalate and perfluorooctanesulfonic acid resulted the most active EDs tested, with gender differences in terms of effects and magnitude. The results from our study evidenced the ability of EDs to directly affect immune cells.

Role of miR-24-3p and miR-146a-5p in dendritic cells' maturation process induced by contact sensitizers

MiRNAs are non-coding RNA molecules that regulate gene expression at the post-transcriptional level. Although allergic contact dermatitis has been studied extensively, few studies addressed miRNA expression and their role in dendritic cell activation. The main aim of this work was to investigate the role of miRNAs in the underlying mechanism of dendritic cell maturation induced by contact sensitizers of different potency. Experiments were conducted using THP-1-derived immature DCs (iDCs). Contact allergens of different potency were used: p-benzoquinone, Bandrowski's base, and 2,4-dinitrochlorobenzene as extreme; nickel sulfate hexahydrate, diethyl maleate and 2-mercaptobenzothiazole as moderate; and α-hexyl cinnamaldehyde, eugenol, and imidazolidinyl urea as weak. Selective inhibitor and mimic miRNAs were then used and several cell surface markers was evaluated as targets. Also, patients patch tested with nickel were analyzed to determine miRNAs expression. Results indicate an important role of miR-24-3p and miR-146a-5p in DCs activation. miR-24-3p was up-regulated by extreme and weak contact allergens, while miR-146a-5p was up-regulated by weak and moderate contact allergens and down-regulated only by the extreme ones. Also, the involvement of PKCβ in contact allergen-induced miR-24-3p and miR-146a-5p expression was demonstrated. Furthermore, the expression of the two miRNAs maintains the same trend of expression in both in vitro and in human conditions after nickel exposure. Results obtained suggest the involvement of miR-24 and miR-146a in DCs maturation process in the proposed in vitro model, supported also by human evidences.

Mixtures of per- and poly-fluoroalkyl substances (PFAS) reduce the in vitro activation of human T cells and basophils

In the last decades, per- and poly-fluoroalkyl substances (PFAS), widely used industrial chemicals, have been in the center of attention because of their omnipotent presence in water and soils worldwide. Although efforts have been made to substitute long-chain PFAS towards safer alternatives, their persistence in humans still leads to exposure to these compounds. PFAS immunotoxicity is poorly understood as no comprehensive analyses on certain immune cell subtypes exist. Furthermore, mainly single entities and not PFAS mixtures have been assessed. In the present study we aimed to investigate the effect of PFAS (short-chain, long-chain and a mixture of both) on the in vitro activation of primary human immune cells. Our results show the ability of PFAS to reduce T cells activation. In particular, exposure to PFAS affected T helper cells, cytotoxic T cells, Natural Killer T cells, and Mucosal associated invariant T (MAIT) cells, as assessed by multi-parameter flow cytometry. Furthermore, the exposure to PFAS reduced the expression of several genes involved in MAIT cells activation, including chemokine receptors, and typical proteins of MAIT cells, such as GZMB, IFNG and TNFSF15 and transcription factors. These changes were mainly induced by the mixture of both short- and long-chain PFAS. In addition, PFAS were able to reduce basophil activation induced by anti-FcεR1α, as assessed by the decreased expression of CD63. Our data clearly show that the exposure of immune cells to a mixture of PFAS at concentrations mimicking real-life human exposure resulted in reduced cell activation and functional changes of primary innate and adaptive human immune cells.

New approach methodologies in immunotoxicology: challenges and opportunities

To maintain the integrity of an organism, a well-functioning immune system is essential. Immunity is dynamic, with constant surveillance needed to determine whether to initiate an immune response or to not respond. Both inappropriate immunostimulation and decreased immune response can be harmful to the host. A reduced immune response can lead to high susceptibility to cancer or infections, whereas an increased immune response can be related to autoimmunity or hypersensitivity reactions. Animal testing has been the gold standard for hazard assessment in immunotoxicity but a lot of efforts are ongoing to develop non-animal-based test systems, and important successes have been achieved. The term "new approach methodologies" (NAMs) refer to the approaches which are not based on animal models. They are applied in hazard and risk assessment of chemicals and include approaches such as defined approaches for data interpretation and integrated approaches to testing and assessment. This review aims to summarize the available NAMs for immunotoxicity assessment, taking into consideration both inappropriate immunostimulation and immunosuppression, including implication for cancer development.

In Vitro Effects of Bisphenol Analogs on Immune Cells Activation and Th Differentiation

AIMS

Investigate the immunomodulatory effects of bisphenols in the THP-1 cell line and peripheral blood mononuclear cells in response to lipopolysaccharide (LPS) activation or to phorbol 12-myristate 13-acetate (PMA) and ionomycin.

BACKGROUND

We have previously demonstrated the usefulness of the evaluation of RACK1 expression as a link between endocrine disrupting activity and the immunotoxic effect of xenobiotics. We demonstrated that while BPA and BPAF reduced RACK1 expression, BPS was able to increase it.

OBJECTIVE

Bisphenol A (BPA) is one of the most commonly used chemicals in the manufacturing of polycarbonate plastics and plastic consumer products. Its endocrine disrupting (ED) potential and changes in European regulations have led to replacing BPA in many uses with structurally similar chemicals, like bisphenol AF (BPAF) and bisphenol S (BPS). However, emerging data indicated that bisphenol analogues may not be safer than BPA both in toxic effects and ED potential.

METHODS

THP-1 cell line and peripheral blood mononuclear cells were activated with lipopolysaccharide (LPS) or with phorbol 12-myristate 13-acetate (PMA) and ionomycin.

RESULTS

BPA and BPAF decreased LPS-induced expression of surface markers and the release of pro-inflammatory cytokines, while BPS increased LPS-induced expression of CD86 and cytokines. BPA, BPAF, and BPS affected PMA/ionomycin-induced T helper differentiation and cytokine release with gender-related alterations in some parameters investigated.

CONCLUSION

Data confirm that bisphenols can modulate immune cell differentiation and activation, further supporting their immunotoxic effects.

Characterization of post-vaccination SARS-CoV-2 T cell subtypes in patients with different hematologic malignancies and treatments

Background

To evaluate the benefits of SARS-CoV-2 vaccination in cancer patients it is relevant to understand the adaptive immune response elicited after vaccination. Patients affected by hematologic malignancies are frequently immune-compromised and show a decreased seroconversion rate compared to other cancer patients or controls. Therefore, vaccine-induced cellular immune responses in these patients might have an important protective role and need a detailed evaluation.

Methods

Certain T cell subtypes (CD4, CD8, Tfh, γδT), including cell functionality as indicated by cytokine secretion (IFN, TNF) and expression of activation markers (CD69, CD154) were assessed via multi-parameter flow cytometry in hematologic malignancy patients (N=12) and healthy controls (N=12) after a second SARS-CoV-2 vaccine dose. The PBMC of post-vaccination samples were stimulated with a spike-peptide pool (S-Peptides) of SARS-CoV-2, with CD3/CD28, with a pool of peptides from the cytomegalovirus, Epstein-Barr virus and influenza A virus (CEF-Peptides) or left unstimulated. Furthermore, the concentration of spike-specific antibodies has been analyzed in patients.

Results

Our results indicate that hematologic malignancy patients developed a robust cellular immune response to SARS-CoV-2 vaccination comparable to that of healthy controls, and for certain T cell subtypes even higher. The most reactive T cells to SARS-CoV-2 spike peptides belonged to the CD4 and Tfh cell compartment, being median (IQR), 3.39 (1.41-5.92) and 2.12 (0.55-4.14) as a percentage of IFN- and TNF-producing Tfh cells in patients. In this regard, the immunomodulatory treatment of patients before the vaccination period seems important as it was strongly associated with a higher percentage of activated CD4 and Tfh cells. SARS-CoV-2- and CEF-specific T cell responses significantly correlated with each other. Compared to lymphoma patients, myeloma patients had an increased percentage of SARS-CoV-2-specific Tfh cells. T-SNE analysis revealed higher frequencies of γδT cells in patients compared to controls, especially in myeloma patients. In general, after vaccination, SARS-CoV-2-specific T cells were also detectable in patients without seroconversion.

Conclusion

Hematologic malignancy patients are capable of developing a SARS-CoV-2-specific CD4 and Tfh cellular immune response after vaccination, and certain immunomodulatory therapies in the period before vaccination might increase the antigen-specific immune response. A proper response to recall antigens (e.g., CEF-Peptides) reflects immune cellular functionality and might be predictive for generating a newly induced antigen-specific immune response as is expected after SARS-CoV-2 vaccination.

Air Pollution: Possible Interaction between the Immune and Nervous System?

Exposure to environmental pollutants is a serious and common public health concern associated with growing morbidity and mortality worldwide, as well as economic burden. In recent years, the toxic effects associated with air pollution have been intensively studied, with a particular focus on the lung and cardiovascular system, mainly associated with particulate matter exposure. However, epidemiological and mechanistic studies suggest that air pollution can also influence skin integrity and may have a significant adverse impact on the immune and nervous system. Air pollution exposure already starts in utero before birth, potentially causing delayed chronic diseases arising later in life. There are, indeed, time windows during the life of individuals who are more susceptible to air pollution exposure, which may result in more severe outcomes. In this review paper, we provide an overview of findings that have established the effects of air pollutants on the immune and nervous system, and speculate on the possible interaction between them, based on mechanistic data.

Effects of endocrine active contaminating pesticides on RACK1 expression and immunological consequences in THP-1 cells

We have previously demonstrated that RACK1, which expression is under steroid hormone control, plays an important role in the activation of immune cells and its expression can be useful to evaluate the immunotoxic profile of endocrine disrupting chemicals (EDCs). Hence, we investigated the effects of three contaminating and persistent pesticides: the fungicide vinclozolin (VIN), the herbicide atrazine (ATR) and the insecticide cypermethrin (CYP) on RACK1 expression and on innate immune response. VIN resulted in modest alteration of RACK1 while ATR and CYP reduced in a dose dependent manner RACK1 expression, ultimately leading to the decrease in lipopolysaccharide-induced IL-8 and TNF-α release and CD86 and CD54 surface marker expression. Moreover, our data indicate that, after exposure to EDCs, alterations of RACK1 expression can also occur with mechanisms not directly mediated by an interaction with a nuclear or membrane steroid receptors. Therefore, RACK1 could represent a useful EDCs screening tool to evaluate their immunotoxic potential and to dissect their mechanisms of action.

Effects of endocrine disrupting chemicals on the expression of RACK1 and LPS-induced THP-1 cell activation

The existence of a complex hormonal balance among glucocorticoids, androgens and estrogens involved in the regulation of Receptor for Activated C Kinase 1 (RACK1) expression and its related immune cells activation, highlights the possibility to employ this protein as screening tool for the evaluation of the immunotoxic profile of endocrine disrupting chemicals (EDCs), hormone-active substances capable of interfering with the physiologic hormonal signaling. Hence, the aim of this work was to investigate the effect of the exposure of EDCS 17α-ethynylestradiol (EE), diethyl phthalate (DEP) and perfluorooctanesulfonic acid (PFOS) on RACK1 expression and on lipopolysaccharide (LPS)-induced activation of the human monocytic cell line THP-1, a validated model for this investigation. In line with our previous results with estrogen-active compounds, EE treatment significantly induced RACK1 promoter transcriptional activity, mRNA expression, and protein levels, which paralleled an increase in LPS-induced IL-8, TNF-α production and CD86 expression, previously demonstrated to be dependent on RACK1/PKCβ activation. EE mediates its effect on RACK1 expression through G-protein-coupled estrogen receptor (GPER) and androgen receptor (AR) ligand-independent cascade, as also suggested by in silico molecular docking simulation. Conversely, DEP and PFOS induced a dose-dependent downregulation of RACK1 promoter transcriptional activity, mRNA expression, and protein levels, which was mirrored by a reduction of IL-8, TNF-α production and CD86 expression. Mifepristone pre-treatments abolish DEP and PFOS effects, confirming their GR agonist profile, also corroborated by molecular docking. Altogether, our data confirm that RACK1 represents an interesting target of steroid active compounds, which expression offers the opportunity to screen the immunotoxic potential of different hormone-active substances of concerns due to their human exposure and environmental persistence.

Direct Effects of Glyphosate on In Vitro T Helper Cell Differentiation and Cytokine Production

Glyphosate (G) is the active ingredient of the most used herbicides worldwide. Its use is currently very debated, as several studies indicating its hazard and toxicity are emerging. Among them, there is evidence of adverse effects on the immune system. The aim of this work was to investigate if G could directly affect immune cells. Peripheral blood mononuclear cells (PBMC) obtained from healthy donors were used as experimental model. PBMC were expose to G and stimulated with PMA/ionomycin, T helper (Th) cell differentiation and cytokine production were assessed by flow cytometry and enzyme-linked immunosorbent assay, respectively. A reduction of Th1/Th2 ratio, mainly due to a decrease in Th1 cells, was observed following G exposure. Results show an enhancement of IL-4 and IL-17A production, and a reduction of IFN-γ. Based on literature evidence that suggest G being an endocrine disruptor, we investigated the role of nuclear estrogen receptors (ER). ERα/ERβ inhibition by ICI 182,780 abolished the effects of G on IFN-γ and IL-4 release, suggesting a role of ER in the observed effects. To further characterize the mechanism of action of G, miRNAs, both in exosome and intracellular, were investigated. A statistically significant increase in miR-500a-5p was observed following G treatment. The blockage of miR-500a-5p, using a specific antagomir, prevented G-induced reduction of IFN-γ production. Finally a relationship between miR-500a-5p up-regulation and ER was observed. Overall, these results suggest that G can directly act on T cells, altering T cell differentiation and cytokines production.

The Modified THP-1 Activation Assay for the In Vitro Identification of Drug-Inducing Systemic Hypersensitivity

The development of new low molecular weight drugs has many chances of failure and is an expensive process. Currently, there are no screening methods and/or models to assess the hazard of hypersensitivity reactions to drugs (DHRs) in the preclinical phase. DHRs represent 6–15% of adverse drug reactions. Although rare, DHRs represent a serious health problem for predisposed individuals, resulting, in some cases, in life-threatening pathologies. To date, there are no in vitro or in vivo sensitive models able to predict the sensitizing potential of drugs in the preclinical tests, and these reactions are highlighted only after the drug has been placed on the market, affecting both population and public health. This article describes a novel approach methodology for the study of the sensitizing potential of drugs based on the use of the human promyelocytic cell line THP-1 as a surrogate for dendritic cells. The method is based on the upregulation of specific surface markers (CD86 and CD54) and on the production of IL-8. In our experience, the THP-1 activation assay allowed the correct identification of drugs known to induce systemic hypersensitivity in humans, including the one associated with specific HLAs. This method may help to discover possible systemic hypersensitivity reactions early in the preclinical phase of drug development.

Glyphosate-based herbicides: Evidence of immune-endocrine alteration

Glyphosate (G) is the active ingredient of the most widely used herbicide products. It targets the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which lacks in humans, suggesting to confer a low mammalian toxicity to G-based herbicides (GBHs). Despite this, the use of G is currently under intense debate. Many studies indicating its hazard and toxicity on non-target organisms are emerging, and associations between GBHs and immune-endocrine disturbances have been described. This review aims to investigate, based on recent epidemiological studies and studies performed in vitro and in vivo in animals, the possible association between GBHs and immune-endocrine alterations. Published data suggest that GBHs have endocrine disrupting potentiality targeting sex and thyroid hormones, although its relevance for humans will require further investigations. Evidence of immunotoxicity are limited compared to those on endocrine effects, but overall highlight possible noxious effects, including lung inflammation and rhinitis. An attractive hypothesis could be the one that connects microbiota dysbiosis with possible immune-endocrine outcomes. Indeed, several intestinal microorganisms express the enzyme EPSPS and, studies are emerging that highlight a possible G-induced dysbiosis. Considering the wide use of GBHs in agriculture, further studies investigating their noxious effects at levels relevant for human exposure should be performed. A critical analysis of emerging evidence of G toxicity is required to better characterize its safety profile. In addition, attention should be paid to the differences between G alone and its formulations, which, containing substances able to increase G absorption, may present a different toxicity profile.

In vitro identification of drugs inducing systemic hypersensitivity reactions known in vivo to be associated with specific HLA genotypes

Hypersensitivity drug reactions (HDRs) are common among drugs, despite this, there are no validated in vitro or in vivo methods for screening the sensitizing potential of drugs in the preclinical phase. We previously developed the THP-1 activation assay, based on CD86 upregulation and IL-8 production, for the in vitro identification of drugs able to induce selective dendritic cell activation. In this paper, we investigated the predictive capacity of the method toward drugs associated with HDRs for which a correlation with specific human leukocyte antigens (HLA) have been demonstrated. For that purpose, abacavir, carbamazepine and clozapine were used. Metformin was used as negative control. Dose- and time-course experiments were conducted. The surface markers CD86, CD54 and HLA-DR were evaluated by flow cytometry analysis, whereas IL-8 release by ELISA. Abacavir, carbamazepine and clozapine gave positive results with CD86 upregulation and/or IL-8 release, with abacavir also inducing HLA-DR. The test reveals the ability of drugs to induce dendritic cell activation (signals 1/2), that preceded the adaptive immune response, which will be manifested only in a minority of patients carrying the specific HLA genotypes. The idea is to integrate this simple method during drug development to identify the potential of drugs to induce hypersensitivity reactions in the pre-clinical phase.

Antiproliferative effects of chalcones on T cell acute lymphoblastic leukemia-derived cells: Role of PKCβ

In this study, a series of 20 chalcone derivatives was synthesized, and their antiproliferative activity was tested against the human T cell acute lymphoblastic leukemia-derived cell line, CCRF-CEM. On the basis of the structural features of the most active compounds, a new library of chalcone derivatives, according to the structure-activity relationship design, was synthesized, and their antiproliferative activity was tested against the same cancer cell line. Furthermore, four of these derivatives (compounds 3, 4, 8, 28), based on lower IC₅₀ values (between 6.1 and 8.9 μM), were selected for further investigation regarding the modulation of the protein expression of RACK1 (receptor for activated C kinase), protein kinase C (PKC)α and PKCβ, and their action on the cell cycle level. The cell cycle analysis indicated a block in the G0/G1 phase for all four compounds, with a statistically significant decrease in the percentage of cells in the S phase, with no indication of apoptosis (sub-G0/G1 phase). Compounds 4 and 8 showed a statistically significant reduction in the expression of PKCα and an increase in PKCβ, which together with the demonstration of an antiproliferative role of PKCβ, as assessed by treating cells with a selective PKCβ activator, indicated that the observed antiproliferative effect is likely to be mediated through PKCβ induction.

Effect of estrogen-active compounds on the expression of RACK1 and immunological implications

We previously demonstrated the existence of a balance among steroid hormones, i.e. glucocorticoids and androgens, in RACK1 (receptor for activated C kinase 1) expression and innate immunity activation, which may offer the opportunity to use RACK1 expression as marker to evaluate immunotoxicity of hormone-active substances. Because of the existence of close interconnections between the different steroid hormone receptors with overlapping ligand specificities and signaling pathways, in this study, we wanted to investigate a possible effect of estrogenic active compounds, namely 17β-estradiol, diethylstilbestrol, and zearalenone, on RACK-1 expression and innate immune responses using THP-1 cells as experimental model. All compounds increased RACK1 transcriptional activity as evaluated by reporter luciferase activity, mRNA expression as assessed by real time-PCR and protein expression by western blot analysis, which paralleled an increase in LPS-induced IL-8, TNF-α production, and CD86 expression, which we previously demonstrated to be dependent on RACK1/PKCβ activation. As the induction of RACK1 expression can be blocked by the antagonist G15, induced by the agonist G1 and by the non-cell permeable 17β-estradiol conjugated with BSA, a role of GPER (previously named GPR30) activation in estrogen-induced RACK1 expression could be demonstrated. In addition, a role of androgen receptor (AR) in RACK1 transcription was also demonstrated by the ability of flutamide, a nonsteroidal antiandrogen, to completely prevent diethylstilbestrol-induced RACK1 transcriptional activity and protein expression. Altogether, our data suggest that RACK1 may represent an interesting target of steroid-active compounds, and its evaluation may offer the opportunity to screen the immunotoxic potential of hormone-active substances.