The Use of In Vitro Systems for Evaluating Immunotoxicity: The Report and Recommendations of an ECVAM Workshop

Evaluation of THP-1 and Jurkat Cell Lines Coculture for the In Vitro Assessment of the Effects of Immunosuppressive Substances

The strong appeal to reduce animal testing calls for the development and validation of in vitro, in chemico and in silico models that would replace the need for in vivo testing and ex vivo materials. A category that requires such new approach methods is the assessment of immunosuppression that can be induced by chemicals including environmental pollutants. To assess the immunosuppressive action on monocytes and lymphocytes, we mimicked the whole-blood cytokine-release assay by preparing an in vitro coculture of THP-1 and Jurkat cell lines. We optimised its activation and investigated the effects of known immunosuppressive drugs with different mechanisms of action on the release of proinflammatory cytokines. Decreased secretion of IL-8 was achieved by several immunosuppressive mechanisms and was therefore selected as an appropriate marker of immunosuppression. A set of environmentally occurring bisphenols, BPA, BPAP, BPP, BPZ, BPE, TCBPA and BPS-MAE, were then applied to the model and BPP and BPZ were found to act as potent immunosuppressants at micromolar concentrations.

Immunotoxicity of cynobacterial toxin Microcystin-LR is mitigated by Quercitin and himalaya tonic Liv52

Microcystin-LR (MC-LR) has received worldwide concern for its hepatotoxicity with maximum acceptable daily intake of 0.0015 mg/L (1.5 μg/L) [Federal-Provinicial-Territorial-Committee-on-drinking-water-2002]. Comprehensive immunotoxicity data is still deficient with MC-LR. To curb the menace of MC-LR, Quercitin (QE), himalaya made hepatotonic Liv52 were studied. To investigate the immunotoxic properties of MC-LR, QE and Liv52, primary splenocyte cells prepared, cultured, and immunoproliferation assay with mitogens lipopolysaccharide (LPS) or concanavalin A, (Con A) was done for, immunophenotyping, cell cycle and apoptotic studies. In current study, we have divided the splenocytes into 4 groups, i.e., Group I: Normal saline, Group II: MC-LR (0.1 μM), Group III: MC-LR (0.1 μM) + QE (20 μM), and Group IV: MC-LR (0.1 μM) + Liv52 (25 μg/ml) and treated with maximum < CC50 concentration. MC-LR enhanced proliferation of Con A and LPS stirred splenocytes at 24 h, whereas QE and Liv52 both act as antimitogenic. With combined mixture of MC-LR + QE, a significant increase in proliferation compared to mitogen or MC-LR was observed. MC-LR down-regulated expression of CD19+, CD3e+, CD4+, CD8+, (1.05%), (18.9%), (8.9%), and (7.8%) respectively in comparison to Group I. Down-regulation of 10% and 28% is observed in CD19+ and CD4+ populations with MC-LR and QE. The Liv52 addition concealed MC-LR adverse properties in most effective way. MC-LR induced G1-phase significant declined cell cycle arrest at S phase (9.26%) and G2/M phase (26.31%) was observed. QE and Liv52 mask the activity of MC-LR. Further apoptotic study revealed that MC-LR treatment decreases late apoptotic cells compared to control with no significant change in live and early apoptotic cells. Although QE increased live cells and Liv52 significantly increased late apoptotic cells, these results suggest that a Collapse

Key Words

• Cynobacterial toxin
• FACS analysis
• Immunomodulation
• Immunophenotyping
• MC-LR

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MESH Headings

• Lipopolysaccharides
• Microcystins/toxicity
• Cell Cycle

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Grants Collapse

Affiliation(s)

Kriti Shrinet School of Biotechnology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, 221005, India; School of Biotechnology, IFTM University, Moradabad, Uttar Pradesh, 244102, India
Arvind Kumar School of Biotechnology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, 221005, India.

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Development of a transcriptome-based determination of innate immune suppressor (TDIS) assay as an in vitro test for immunotoxicity

Immunotoxicity has been an important topic in toxicology since inadvertent exposures to xenobiotics were found to alter immune functions in humans. While rodent toxicity tests can reveal some levels of immunotoxicity, alternative methods must be developed to identify the detailed mechanisms. In this study, a method of in vitro prediction of innate immune suppression by substances was developed using a genomics approach. The primary selection of immune suppressors was based on their ability to downregulate MCP-1, CCL3, TNF, IL-8, and IL-12p40 expression levels in lipopolysaccharide (LPS)-stimulated THP-1 cells. Among 11 substances classified as potent immune suppressors, six including dexamethasone, tacrolimus, tofacitinib, prednisolone, sodium lauryl sulfate, and benzoic acid were used to create a dataset by transcriptomics of chemical-treated THP-1 cells using bulk RNA sequencing. We selected genes that were significantly upregulated by suppressor treatment while filtering out genes also upregulated in LPS-treated THP-1 cells. We identified a 226-gene immunosuppressive gene set (ISG). Innate immune suppressor signature scores were calculated as the median expression of the ISG. In a validation dataset, the signature score predicted acyclovir, cyclosporine, and mercuric chloride as immune suppressors, while selecting genistein as a non-immune suppressor. Although more dataset integration is needed in the future, our results demonstrated the possibility and utility of a novel genomics-based approach, the transcriptome-based determination of innate immune suppressor (TDIS) assay, to evaluate innate immune suppression by different substances. This provides insight into the development of future alternative testing methods because it reflects a comprehensive genetic signature derived from multiple substances rather than one cytokine.

Immunotoxicity In Vitro Assays for Environmental Pollutants under Paradigm Shift in Toxicity Tests

With the outbreak of COVID-19, increasingly more attention has been paid to the effects of environmental factors on the immune system of organisms, because environmental pollutants may act in synergy with viruses by affecting the immunity of organisms. The immune system is a developing defense system formed by all metazoans in the course of struggling with various internal and external factors, whose damage may lead to increased susceptibility to pathogens and diseases. Due to a greater vulnerability of the immune system, immunotoxicity has the potential to be the early event of other toxic effects, and should be incorporated into environmental risk assessment. However, compared with other toxicity endpoints, e.g., genotoxicity, endocrine toxicity, or developmental toxicity, there are many challenges for the immunotoxicity test of environmental pollutants; this is due to the lack of detailed mechanisms of action and reliable assay methods. In addition, with the strong appeal for animal-free experiments, there has been a significant shift in the toxicity test paradigm, from traditional animal experiments to high-throughput in vitro assays that rely on cell lines. Therefore, there is an urgent need to build high-though put immunotoxicity test methods to screen massive environmental pollutants. This paper reviews the common methods of immunotoxicity assays, including assays for direct immunotoxicity and skin sensitization. Direct immunotoxicity mainly refers to immunosuppression, for which the assays mostly use mixed immune cells or isolated single cells from animals with obvious problems, such as high cost, complex experimental operation, strong variability and so on. Meanwhile, there have been no stable and standard cell lines targeting immune functions developed for high-throughput tests. Compared with direct immunotoxicity, skin sensitizer screening has developed relatively mature in vitro assay methods based on an adverse outcome pathway (AOP), which points out the way forward for the paradigm shift in toxicity tests. According to the experience of skin sensitizer screening, this paper proposes that we also should seek appropriate nodes and establish more complete AOPs for immunosuppression and other immune-mediated diseases. Then, effective in vitro immunotoxicity assay methods can be developed targeting key events, simultaneously coordinating the studies of the chemical immunotoxicity mechanism, and further promoting the paradigm shift in the immunotoxicity test.

Translatability and transferability of in silico models: Context of use switching to predict the effects of environmental chemicals on the immune system

Immunotoxicity hazard identification of chemicals aims to evaluate the potential for unintended effects of chemical exposure on the immune system. Perfluorinated alkylate substances (PFAS), such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), are persistent, globally disseminated environmental contaminants known to be immunotoxic. Elevated PFAS exposure is associated with lower antibody responses to vaccinations in children and in adults. In addition, some studies have reported a correlation between PFAS levels in the body and lower resistance to disease, in other words an increased risk of infections or cancers. In this context, modelling and simulation platforms could be used to simulate the human immune system with the aim to evaluate the adverse effects that immunotoxicants may have. Here, we show the conditions under which a mathematical model developed for one purpose and application (e.g., in the pharmaceutical domain) can be successfully translated and transferred to another (e.g., in the chemicals domain) without undergoing significant adaptation. In particular, we demonstrate that the Universal Immune System Simulator was able to simulate the effects of PFAS on the immune system, introducing entities and new interactions that are biologically involved in the phenomenon. This also revealed a potentially exploitable pathway for assessing immunotoxicity through a computational model.

Assessing Fish Immunotoxicity by Means of In Vitro Assays: Are We There Yet?

There is growing awareness that a range of environmental chemicals target the immune system of fish and may compromise the resistance towards infectious pathogens. Existing concepts to assess chemical hazards to fish, however, do not consider immunotoxicity. Over recent years, the application of in vitro assays for ecotoxicological hazard assessment has gained momentum, what leads to the question whether in vitro assays using piscine immune cells might be suitable to evaluate immunotoxic potentials of environmental chemicals to fish. In vitro systems using primary immune cells or immune cells lines have been established from a wide array of fish species and basically from all immune tissues, and in principal these assays should be able to detect chemical impacts on diverse immune functions. In fact, in vitro assays were found to be a valuable tool in investigating the mechanisms and modes of action through which environmental agents interfere with immune cell functions. However, at the current state of knowledge the usefulness of these assays for immunotoxicity screening in the context of chemical hazard assessment appears questionable. This is mainly due to a lack of assay standardization, and an insufficient knowledge of assay performance with respect to false positive or false negative signals for the different toxicant groups and different immune functions. Also the predictivity of the in vitro immunotoxicity assays for the in vivo immunotoxic response of fishes is uncertain. In conclusion, the currently available database is too limited to support the routine application of piscine in vitro assays as screening tool for assessing immunotoxic potentials of environmental chemicals to fish.

Methodological Approaches To Assess Innate Immunity and Innate Memory in Marine Invertebrates and Humans

Assessing the impact of drugs and contaminants on immune responses requires methodological approaches able to represent real-life conditions and predict long-term effects. Innate immunity/inflammation is the evolutionarily most widespread and conserved defensive mechanism in living organisms, and therefore we will focus here on immunotoxicological methods that specifically target such processes. By exploiting the conserved mechanisms of innate immunity, we have examined the most representative immunotoxicity methodological approaches across living species, to identify common features and human proxy models/assays. Three marine invertebrate organisms are examined in comparison with humans, i.e., bivalve molluscs, tunicates and sea urchins. In vivo and in vitro approaches are compared, highlighting common mechanisms and species-specific endpoints, to be applied in predictive human and environmental immunotoxicity assessment. Emphasis is given to the 3R principle of Replacement, Refinement and Reduction of Animals in Research and to the application of the ARRIVE guidelines on reporting animal research, in order to strengthen the quality and usability of immunotoxicology research data.

Optimization of the IL-2 Luc assay for immunosuppressive drugs: a novel in vitro immunotoxicity test with high sensitivity and predictivity

We have reported that the IL-2 Luc assay can detect the effects of chemicals on IL-2 promoter activity by using a dual reporter cell line, 2H4 cells that measure IL-2 promoter-driven luciferase activity (IL2LA) and GAPDH promoter-driven luciferase activity (GAPLA). Since the IL-2 Luc assay cannot detect immunosuppressive drugs that are antimitotic towards rapidly proliferating cells, we attempted to establish a new assay to detect these chemicals by taking advantage of the dual reporter cell properties of 2H4 cells. We first determined the optimal incubation time with drugs and the seeding cell density, and confirmed that the change in GAPLA and IL2LA levels reflects the change in cell count and IL-2 production of 2H4 cells after drug treatment. We designed the IL-2 luciferase lymphotoxicity test (IL-2 Luc LTT) to detect the antimitotic effects of chemicals by modifying the protocol and criteria of the IL-2 Luc assay. To determine the performance of the IL-2 Luc LTT and that of the combination of the IL-2 Luc LTT and the IL-2 Luc assay, we examined 46 drugs: 19 immunosuppressive drugs with different mechanisms of action, 12 anti-cancer drugs, and 15 non-immunosuppressive drugs. The performances of the IL-2 Luc LTT, the IL-2 Luc assay and their combination were 43.3%, 61.3%, and 93.3%, respectively, for sensitivity, 84.6%, 53.3%, and 50.0%, respectively, for specificity, and 55.8%, 58.7%, and 79.5%, respectively, for accuracy. These results demonstrated that the combination of these two assays is promising for the detection of immunosuppressive drugs with different mechanisms of action.

Oxidative Properties of Polystyrene Nanoparticles with Different Diameters in Human Peripheral Blood Mononuclear Cells (In Vitro Study)

With the ongoing commercialization, human exposure to plastic nanoparticles will dramatically increase, and evaluation of their potential toxicity is essential. There is an ongoing discussion on the human health effects induced by plastic particles. For this reason, in our work, we assessed the effect of polystyrene nanoparticles (PS-NPs) of various diameters (29, 44 and 72 nm) on selected parameters of oxidative stress and the viability of human peripheral blood mononuclear cells (PBMCs) in the in vitro system. Cells were incubated with PS-NPs for 24 h in the concentration range of 0.001 to 100 µg/mL and then labeled: formation of reactive oxygen species (ROS) (including hydroxyl radical), protein and lipid oxidation and cell viability. We showed that PS-NPs disturbed the redox balance in PBMCs. They increased ROS levels and induced lipid and protein oxidation, and, finally, the tested nanoparticles induced a decrease in PBMCs viability. The earliest changes in the PBMCs were observed in cells incubated with the smallest PS-NPs, at a concentration of 0.01 μg/mL. A comparison of the action of the studied nanoparticles showed that PS-NPs (29 nm) exhibited a stronger oxidative potential in PBMCs. We concluded that the toxicity and oxidative properties of the PS-NPs examined depended to significant degree on their diameter.

Evaluation of an in vitro assay to screen for the immunotoxic potential of chemicals to fish

A wide variety of environmental contaminants has been shown to disrupt immune functions of fish and may compromise their defense capability against pathogens. Immunotoxic effects, however, are rarely considered in ecotoxicological testing strategies. The aim of this study was to systematically evaluate the suitability of an in vitro immuno-assay using selected fish immune parameters to screen for chemicals with known immunotoxic potential and to differentiate them from non-immunotoxicants. Non-stimulated and lipopolysaccharide-stimulated head kidney leukocytes of rainbow trout (Oncorhynchus mykiss) were exposed for 3 h or 19 h to chemicals with different modes of action. As immune parameters, phagocytosis activity, oxidative burst activity and cytokine transcription (IL-1β, TNFα, IL-10) were examined, accompanied by in silico modelling. The immunotoxicants dexamethasone, benzo(a)pyrene, ethinylestradiol and bisphenol A significantly altered the immune parameters at non-cytotoxic concentrations whereas diclofenac had only weak effects. However, the two baseline chemicals with no known immunotoxic potential, butanol and ethylene glycol, caused significant effects, too. From our results it appears that the in vitro fish leukocyte assay as performed in the present study has only a limited capacity for discriminating between immunotoxicants and non-immunotoxicants.

An international validation study of the IL-2 Luc assay for evaluating the potential immunotoxic effects of chemicals on T cells and a proposal for reference data for immunotoxic chemicals

To evaluate the immunotoxic effects of xenobiotics, we have established the Multi-ImmunoTox assay, in which three stable reporter cell lines are used to evaluate the effects of chemicals on the IL-2, IFN-γ, IL-1β and IL-8 promoters. Here, we report the official validation study of the IL-2 luciferase assay (IL-2 Luc assay). In the Phase I study that evaluated five coded chemicals in three sets of experiments, the average within-laboratory reproducibility was 86.7%. In the Phase II study, 20 coded chemicals were evaluated at multiple laboratories. In the combined results of the Phase I and II studies, the between-laboratory reproducibility was 80.0%. These results suggested that the IL-2 Luc assay was reproducible both between and within laboratories. To determine the predictivity, we collected immunotoxicological information and constructed the reference data by classifying the chemical into immunotoxic compounds targeting T cells or others according to previously reported criteria. When compared with the reference data, the average predictivity of the Phase I and II studies was 75.0%, while that of additional 60 chemicals examined by the lead laboratory was 82.5%. Although the IL-2 Luc assay alone is not sufficient to predict immunotoxicity, it will be a useful tool when combined with other immune tests.

Development and utilization of a unique in vitro antigen presentation co-culture model for detection of immunomodulating substances

Current regulatory immunotoxicity studies require the use of animal models. However, evolving regulatory requirements, the need to evaluate large numbers of chemicals efficiently and societal pressures are driving the development and utilization of alternative in vitro methods for identifying potential immunotoxicants. In line with these efforts, we developed a novel in vitro cell-based assay to evaluate effects on antigen presentation - a key step in successful immunization. In this assay, Ch27 B cells acquire and present hen egg lysozyme peptides to antigen-restricted 3A9 T cells, causing them to produce and secrete IL-2. IL-2 levels in the culture medium may be monitored to identify effects of immunotoxicant exposure on antigen uptake, processing or presentation by the Ch27 cells and on antigen recognition and IL-2 production and secretion by the 3A9 cells. IL-2 production was reduced in response to treatment with well-known immunotoxicants cyclosporin A (CYA), dexamethasone (DEX), azathioprine (AZPR), methotrexate (MOT) and benzo(a)pyrene (BAP) but was not affected by treatment with cyclophosphamide (CYPH). A negative control compound mannitol (MANN) altered neither cell viability nor IL-2 levels whereas the lysosomotrophic compound ammonium chloride (AMCL) reduced IL-2 production. This novel in vitro assay of immune function may be suitable for integration into a tiered testing battery for screening and prioritization of potential immunosuppressants.

Profiling the immunotoxicity of chemicals based on in vitro evaluation by a combination of the Multi-ImmunoTox assay and the IL-8 Luc assay

We established a luciferase reporter assay system, the Multi-ImmunoTox Assay (MITA), which can evaluate the effects of chemicals on the promoter activities of four cytokines: IL-2, IFN-γ, IL-1β, and IL-8. We previously reported that MITA correctly reflected the change in mRNA of human whole-blood cells treated with dexamethasone, cyclosporine, FK506, or several other immunosuppressive drugs. In this study, we combined MITA with the IL-8 Luc assay to detect skin sensitization chemicals (OECD 442E) (modified MITA: mMITA) and established a data set of 60 chemicals examined by mMITA. Using the mMITA results, chemicals can be classified based on the lowest observed effect level (LOEL) of chemicals in suppressing or augmenting the promoter activities of the four cytokines. Moreover, we demonstrated that K-means clustering and hierarchical clustering of the 60 chemicals based on the LOEL for their effects on IL-2 and IL-8 promoter activities and the judgment by the IL-8 Luc assay resulted in the same 6-cluster solution: cluster 1 with preferential suppression of IL-8, cluster 2 with suppression of IL-2 and a positive IL-8 Luc assay result, cluster 3 with suppression of both IL-2 and IL-8, cluster 4 with no effects on IL-2 or IL-8 and a negative IL-8 Luc assay result, cluster 5 with suppression of both IL-2 and IL-8 and a negative IL-8 Luc assay result, and cluster 6 with preferential suppression of IL-8. These data suggest that mMITA is a promising novel high-throughput approach for detecting unrecognized immunological effects of chemicals and for profiling their immunotoxic effects.

In vitro assessment of silver nanoparticles immunotoxicity

This study aimed to characterize unwanted immune effects of nanoparticles (NP) using THP-1 cells, human whole blood and enriched peripheral blood monocytes. Commercially available silver NP (AgNP < 100 nm, also confirmed by Single Particle Extinction and Scattering) were used as prototypical NP. Cells were treated with AgNP alone or in combination with classical immune stimuli (i.e. LPS, PHA, PWM) and cytokine assessed; in addition, CD54 and CD86 expression was evaluated in THP-1 cells. AgNP alone induced dose-related IL-8 production in all models, with higher response observed in THP-1 cells, possibly connected to different protein corona formation in bovine versus human serum. AgNP potentiated LPS-induced IL-8 and TNF-α, but not LPS-induced IL-10. AgNP alone induced slight increase in IL-4, and no change in IFN-γ production. While responses to PHA in term of IL-4 and IFN-γ production were not affected, increased PWM-induced IL-4 and IFN-γ production were observed, suggesting potentiation of humoral response. Reduction in PHA-induced IL-10 was observed. Overall, results indicate immunostimulatory effects. THP-1 cells work as well as primary cells, representing a useful and practical alternative, with the awareness that from a physiological point of view the whole blood assay is the one that comes closest to reality.

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.

Review of various molecular targets on mast cells and its relation to obesity: A future perspective

Mast cells are stimulatory factors in prognosis of various immunogenic and allergic diseases in human body. These cells play an important role in various immunological and metabolic diseases. The aim of present article is to explore the molecular targets to suppress the over expression of mast cells in obesity. The last 20 years literature were searched by various bibliographic data bases like Pubmed, google Scholar, Scopus and web of Science. The data were collected by keywords like "Mast Cell" "obesity" and "role of mast cell or role in obesity". Articles and their abstract were reviewed with a counting of 827 publications, in which 87 publications were considered for study and remaining was excluded because of its specificity to the subject. This review explains the characteristics, molecular targets and role of mast cells in obesity and existing research with mast cells to the area of metabolic diseases.

Immunotoxicity, genotoxicity and epigenetic toxicity of nanomaterials: New strategies for toxicity testing?

The unique properties of nanomaterials (NMs) are beneficial in numerous industrial and medical applications. However, they could also induce unintended effects. Thus, a proper strategy for toxicity testing is essential in human hazard and risk assessment. Toxicity can be tested in vivo and in vitro; in compliance with the 3Rs, alternative strategies for in vitro testing should be further developed for NMs. Robust, standardized methods are of great importance in nanotoxicology, with comprehensive material characterization and uptake as an integral part of the testing strategy. Oxidative stress has been shown to be an underlying mechanism of possible toxicity of NMs, causing both immunotoxicity and genotoxicity. For testing NMs in vitro, a battery of tests should be performed on cells of human origin, either cell lines or primary cells, in conditions as close as possible to an in vivo situation. Novel toxicity pathways, particularly epigenetic modification, should be assessed along with conventional toxicity testing methods. However, to initiate epigenetic toxicity screens for NM exposure, there is a need to better understand their adverse effects on the epigenome, to identify robust and reproducible causal links between exposure, epigenetic changes and adverse phenotypic endpoints, and to develop improved assays to monitor epigenetic toxicity.

In vitro immunotoxicity assessment of culture-derived extracellular vesicles in human monocytes

The potential to engineer extracellular vesicles (EV) that target specific cells and deliver a therapeutic payload has propelled a growing interest in their development as promising therapeutics. These EV are often produced from cultured cells. Very little is known about the interaction of cell culture-derived EV with cells of the immune system and their potential immunomodulatory effects. The present study evaluated potential immunotoxic effects of HEK293T-derived EV on the human monocytic cell lines THP-1 and U937. Incubation of cells with different doses of EV for 16-24 h was followed by assessment of cytotoxicity and cell function by flow cytometry. Changes in cell functionality were evaluated by the capacity of cells to phagocytize fluorescent microspheres. In addition, the internalization of labeled EV in THP-1 and U937 cells was evaluated. Exposure to EV did not affect the viability of THP-1 or U937 cells. Although lower doses of the EV increased phagocytic capacity in both cell lines, phagocytic efficiency of individual cells was not affected by EV exposure at any of the doses evaluated. This study also demonstrated that THP-1 and U937 monocytic cells are highly permissive to EV entry in a dose-response manner. These results suggest that, although HEK293T-derived EV are efficiently internalized by human monocytic cells, they do not exert a cytotoxic effect or alter phagocytic efficiency on the cell lines evaluated.

Sodium benzoate, a food preservative, affects the functional and activation status of splenocytes at non cytotoxic dose

Sodium benzoate (SB) is a widely used food preservative due to its bacteriostatic and fungistatic properties. The acceptable daily intake of SB is 5 mg/kg-bw, however, it has been found to be used in the food commodities at relatively high levels (2119 mg/kg). Earlier studies on SB have shown its immunosuppressive properties, but comprehensive immunotoxicity data is lacking. Our studies have shown that SB was non cytotoxic in splenocytes up to 1000 μg/ml for 72 h, however at 2500 μg/ml it was found to be cytotoxic. Thus, 1000 μg/ml dose of SB was chosen for the subsequent experiments. SB significantly suppresses the proliferation of Con A and LPS stimulated splenocytes at 72 h, while allogenic response of T cells was significantly decreased after 96 h. SB did not affect the relative expression of CD3e or CD4 molecules following 72 h exposure, however, it downregulated the relative expression of CD8 co-receptor. Further, exposure of splenocytes to SB for 72 h led to reduced expression of CD28 and CD95, which play a vital role in T cell activation. SB also suppresses the relative expression of CD19, CD40 and CD95 receptors on B cells after 72 h. In addition to the functional responses, SB lowered the expression of IL4, IL6, IFNγ and IL17 cytokines in Con A stimulated splenocytes; and IL6, IFNγ and TNFα in LPS stimulated splenocytes following 48 h of exposure. Taken together, the present study is suggestive of the immunomodulatory potential of SB.

Application of cellular biosensors for detection of atypical toxic bioactivity in microcystin-containing cyanobacterial extracts

Despite the focus of most ecotoxicological studies on cyanobacteria on a select group of cyanotoxins, especially microcystins, a growing body of evidence points to the involvement of other cyanobacterial metabolites in deleterious health effects. In the present study, original, self-developed reporter gene-based cellular biosensors, detecting activation of the main human xenobiotic stress response pathways, PXR and NFkappaB, were applied to detect novel potentially toxic bioactivities in extracts from freshwater microcystin-producing cyanobacterial blooms. Crude and purified extracts from cyanobacteria containing varying levels of microcystins, and standard microcystin-LR were tested. Two cellular biosensor types applied in this study, called NHRTOX (detecting PXR activation) and OXIBIOS (detecting NFkappaB activation), successfully detected potentially toxic or immunomodulating bioactivities in cyanobacterial extracts. The level of biosensor activation was comparable to control cognate environmental toxins. Despite the fact that extracts were derived from microcystin-producing cyanobacterial blooms and contained active microcystins, biosensor-detected bioactivities were shown to be unrelated to microcystin levels. Experimental results suggest the involvement of environmental toxins (causing a response in NHRTOX) and lipopolysaccharides (LPS) or other cell wall components (causing a response in OXIBIOS) in the potentially harmful bioactivity of investigated extracts. These results demonstrate the need for further identification of cyanobacterial metabolites other than commonly studied cyanotoxins as sources of health risk, show the usefulness of cellular biosensors for this purpose and suggest a novel, more holistic approach to environmental monitoring.

Evaluation of the Multi-ImmunoTox Assay composed of 3 human cytokine reporter cells by examining immunological effects of drugs

We established a luciferase reporter assay system, the Multi-ImmunoTox Assay (MITA), to evaluate the effects on key predictivein vitro components of the human immune system. The system is composed of 3 stable reporter cell lines transfected with 3 luciferase genes, SLG, SLO, and SLR, under the control of 4 cytokine promoters, IL-2, IFN-γ, IL-1β, and IL-8, and the G3PDH promoter. We first compared the effects of dexamethasone, cyclosporine, and tacrolimus on these cell lines stimulated with phorbol 12-myristate 13-acetate and ionomycin, or lipopolysaccharides, with those on mRNA expression by the mother cell lines and human whole blood cells after stimulation. The results demonstrated that MITA correctly reflected the change of mRNA of the mother cell lines and whole blood cells. Next, we evaluated other immunosuppressive drugs, off-label immunosuppressive drugs, and non-immunomodulatory drugs. Although MITA did not detect immunosuppressive effects of either alkylating agents or antimetabolites, it could demonstrate those of the off-label immunosuppressive drugs, sulfasalazine, chloroquine, minocycline, and nicotinamide. Compared with the published immunological effects of the drugs, these data suggest that MITA can present a novel high-throughput approach to detect immunological effects of chemicals other than those that induce immunosuppressive effects through their inhibitory action on cell division.

Using Immunotoxicity Information to Improve Cancer Risk Assessment for Polycyclic Aromatic Hydrocarbon Mixtures

Estimating cancer risk from environmental mixtures containing polycyclic aromatic hydrocarbons (PAHs) is challenging. Ideally, each mixture would undergo toxicity testing to derive a cancer slope factor (CSF) for use in site-specific cancer risk assessments. However, this whole mixture approach is extremely costly in terms of finances, time, and animal usage. Alternatively, if an untested mixture is “sufficiently similar” to a well-characterized mixture with a CSF, the “surrogate” CSF can be used in risk assessments. We propose that similarity between 2 mixtures could be established using an in vitro battery of genotoxic and nongenotoxic tests. An observed association between carcinogenicity and immunosuppression of PAHs suggests that the addition of immune suppression assays may improve this battery. First, using published studies of benzo[a]pyrene (BaP) and other PAHs, we demonstrated a correlation between the derived immune suppression relative potency factors (RPFs) for 9 PAHs and their respective cancer RPFs, confirming observations published previously. Second, we constructed an integrated knowledge map for immune suppression by BaP based on the available mechanistic information. The map illustrates the mechanistic complexities involved in BaP immunosuppression, suggesting that multiple in vitro tests of immune suppression involving different processes, cell types, and tissues will have greater predictive value for immune suppression in vivo than a single test. Based on these observations, research strategies are recommended to validate a battery of in vitro immune suppression tests that, along with tests for genotoxic and other nongenotoxic modes of cancer action, could be used to establish “sufficient similarity” of 2 mixtures for site-specific cancer risk assessments.

Translational immunologic safety evaluation: a perspective

Although translational research is a rapidly evolving area of biomedical sciences, translational immunologic safety evaluation has so far attracted only very limited attention. Assays and animal models have been developed to identify immunotoxic hazards related to immunosuppression, but less attention has been paid to immunostimulation, hypersensitivity, and autoimmunity. Some of these assays and models are recommended by regulatory bodies, even though it is as yet unsure to what extent they can predict the potential of, or lack of, new chemical entities and drug candidates for inducing significant immunotoxic effects. A translational approach should attempt to standardize and validate those models, assays, and biomarkers that could be used in regulatory non-clinical safety studies as well as clinical studies. Beyond translational immunologic safety, immune monitoring during clinical studies is intended to identify and evaluate potential immune safety issues not seen in non-clinical studies. Based on this overview of the current knowledge, it can be concluded that much remains to be done to conduct translational studies helpful to enhance the immunologic safety of drugs and chemicals.

Alternative in vitro assays in nanomaterial toxicology

Nanomaterials are acclaimed for their novel properties, for which broad new uses are being discovered with increasing frequency. It is obvious that, as the properties change, unwanted properties (toxicity) are to be expected as well. Current toxicology, however, is already overwhelmed with the challenge of addressing new chemicals, not to mention the enormous number of old chemicals never properly assessed. Limitations of traditional approaches range from animal welfare issues, which were a strong driving force for alternative approaches (the 3Rs concept) over the last two decades, to aspects of throughput and accuracy of the predicted toxicities. The latter has prompted discussion about a revolutionary change in chemical safety assessment, now known as Toxicology for the 21st Century (Tox-21c). The multitude of possible formulations of nanomaterials to be assessed for novel toxic properties makes these alternative approaches especially attractive, given the well recognized limitations of traditional animal-based approaches--limitations that might be even more pronounced for nanomaterials, which have notably altered biokinetics.

In vitro cytokine release from human peripheral blood mononuclear cells in the assessment of the immunotoxic potential of chemicals

Alternative methods to the use of animals in testing of chemicals are needed. We investigated if the immunotoxic potential of 12 dietary toxicants could be predicted from effects on cytokine release from human peripheral blood mononuclear cells (PBMC) after in vitro exposure. Nine cytokines were selected to reflect different types of immune responses. The toxicants were classified as immunotoxic or non-immunotoxic substances according to the published in vivo data. Isolated human PBMC were exposed for 20 h to three concentrations of each of the 12 substances in the presence of human liver S9 fraction. After further incubation of PBMC in fresh medium containing the mitogen phytohemagglutinin (PHA, 10 μg/ml) for 48 h, release of the nine selected cytokines into the supernatant as well as cell proliferation were measured by Luminex technology™ and the BrdU incorporation assay, respectively. All 12 substances investigated affected the release of one or more cytokines, and each of the substances showed different cytokine release patterns. Within the limitations of the study design, the present study suggests that the effect of the substances on mitogen-induced cytokine release from PBMC cannot predict their immunotoxic potential, but may be useful in mechanistic studies.

In vitro testing for direct immunotoxicity: state of the art

Immunotoxicity is defined as the toxicological effects of xenobiotics including pharmaceuticals on the functioning of the immune system and can be induced in either direct or indirect ways. Direct immunotoxicity is caused by the effects of chemicals on the immune system, leading to immunosuppression and subsequently to reduced resistance to infectious diseases or certain forms of nongenotoxic carcinogenicity.In vitro testing has several advantages over in vivo testing, such as detailed mechanistic understanding, species extrapolation (parallelogram approach), and reduction, refinement, and replacement of animal experiments. In vitro testing for direct immunotoxicity can be done in a two-tiered approach, the first tier measuring myelotoxicity. If this type of toxicity is apparent, the compound can be designated immunotoxic. If not, the compound is tested for lymphotoxicity (second tier). Several in vitro assays for lymphotoxicity exist, each comprising specific functions of the immune system (cytokine production, cell proliferation, cytotoxic T-cell activity, natural killer cell activity, antibody production, and dendritic cell maturation). A brief description of each assay is provided. Only one assay, the human whole blood cytokine release assay, has undergone formal prevalidation, while another one, the lymphocyte proliferation assay, is progressing towards that phase.Progress in in vitro testing for direct immunotoxicity includes prevalidation of existing assays and selection of the assay (or combination of assays) that performs best. To avoid inter-species extrapolation, assays should preferably use human cells. Furthermore, the use of whole blood has the advantage of comprising multiple cell types in their natural proportion and environment. The so-called "omics" techniques provide additional mechanistic understanding and hold promise for the characterization of classes of compounds and prediction of specific toxic effects. Technical innovations such as high-content screening and high-throughput analysis will greatly expand the opportunities for in vitro testing.

Immunotoxicology: Opportunities for Non-animal Test Development

At present, several animal-based assays are used to assess immunotoxic effects such as immunosuppression and sensitisation. The use of whole animals, however, presents several secondary issues, including expense, ethical concerns and relevance to human risk assessment. There is a growing belief that non-animal approaches can eliminate these issues without impairing human safety, provided that biological markers are available to identify the immunotoxic potentials of new chemicals to which humans may be exposed. Driven by the 7th Amendment to the EU Cosmetics Directive, the new EU policy on chemicals (the REACH system), proposals to update the European legislation on the protection of animals used in research, and emerging visions and strategies for predicting toxicity, such in vitro methods are likely to play a major role in the near future. The realisation that the immune system can be the target of many chemicals, resulting in a range of adverse effects on the host's health, has raised serious concerns from the public and within the regulatory agencies. Hypersensitivity and immunosuppression are considered the primary focus for developing in vitro methods in immunotoxicology. However, in vitro assays to detect immunostimulation and autoimmunity are also needed. This review of the state-of-the-art in the field of in vitro immunotoxicity, reveals a lack of cell-based immunotoxicity assays for predicting the toxicity of xenobiotics toward the immune system in a simple, fast, economical and reliable way.

In vitro tests to evaluate immunotoxicity: A preliminary study

The implementation of Registration, Evaluation and Authorisation of new and existing Chemicals (REACH) will increase the number of laboratory animals used, if alternative methods will not be available. In the meantime, REACH promotes the use of in vitro tests and, therefore, a set of appropriated alternative testing methods and assessment strategies are needed. The immune system can be a target for many chemicals including environmental contaminants and drugs with potential adverse effects on human health. The aim of this study was to evaluate the predictivity of a set of in vitro assays to detect immunosuppression. The tests have been performed on human, rat and murine cells. Different endpoints have been assessed: cytotoxicity, cytokine release, myelotoxicity and mitogen responsiveness. For each of these endpoints IC50s values have been calculated. Six chemical substances, representative of the full range of in vivo responses and for which good human and/or animal data are available either from databases or literature, have been selected: two chemicals classified as not immunotoxic (Urethane and Furosemide), and four (tributyltin chloride (TBTC), Verapamil, Cyclosporin A, Benzo(a)pyrene) with different effect on immune system. All the tests confirmed the strong immunotoxic effect of TBTC as well as they confirmed the negative controls. For one chemical (Verapamil) the IC50 is similar through the different tests. The IC50s obtained with the other chemicals depend on the endpoints and on the animal species. The clonogenic test (CFU-GM) and the mitogen responsiveness showed similar IC50s between human and rodent cells except for Cyclosporin A and TBTC. All different tests classified the compounds analyzed in the same way.