US FDA "Redbook II" immunotoxicity testing guidelines and research in immunotoxicity evaluations of food chemicals and new food proteins

Workshop report: A study roadmap to evaluate the safety of recombinant human lactoferrin expressed in Komagataella phaffii intended as an ingredient in conventional foods - Recommendations of a scientific expert panel

Human milk lactoferrin (hmLF) is a glycoprotein with well-known effects on immune function. Helaina Inc. has used a glycoengineered yeast, Komatagaella phaffii, to produce recombinant human lactoferrin (Helaina rhLF, Effera™) that is structurally similar to hmLF with intended uses as a food ingredient. However, earlier FDA reviews of rhLF were withdrawn due to insufficient safety data and unanswered safety questions the experts and FDA raised about the immunogenicity/immunotoxicity risks of orally ingested rhLF. Helaina organized a panel of leading scientists to build and vet a safety study roadmap containing the studies and safety endpoints needed to address these questions. Panelists participated in a one-day virtual workshop in June 2023 and ensuing discussions through July 2023. Relevant workshop topics included physicochemical properties of LF, regulatory history of bovine LF and rhLF as food ingredients in the FDA's generally recognized as safe (GRAS) program, and synopses of publicly available studies on the immunogenicity/alloimmunization, immunotoxicology, iron homeostasis, and absorption, distribution, metabolism, and excretion of rhLF. Panelists concluded that the safety study roadmap addresses the unanswered safety questions and the intended safe use of rhLF as a food ingredient for adults and agreed on broad applications of the roadmap to assess the safety and support GRAS of other recombinant milk proteins with immunomodulatory functions.

[International trend regarding immunotoxicity evaluation with New Approach Methods (NAMs)]

We have ongoing projects that are developing New Approach Methods (NAMs) for systematic toxicology. One NAM is to develop the immunotoxicity evaluation with non-animal test methods for the Organisation for Economic Co-operation and Development (OECD)Test Guideline (TG). The development of this evaluation includes the following steps: 1) adverse outcome pathway (AOP), 2) detailed review paper, 3) test methods based on AOP, 4) validation study of test methods for developing TGs, and 5) integrated approaches to testing and assessment (IATA). I believe that the NAMs developed on these steps may enable risk assessment of a chemical with non-animal test methods in near future.

Immunotoxic Effects Induced by Microcystins and Cylindrospermopsin: A Review

Cyanotoxin occurrence is gaining importance due to anthropogenic activities, climate change and eutrophication. Among them, Microcystins (MCs) and Cylindrospermopsin (CYN) are the most frequently studied due to their ubiquity and toxicity. Although MCs are primary classified as hepatotoxins and CYN as a cytotoxin, they have been shown to induce deleterious effects in a wide range of organs. However, their effects on the immune system are as yet scarcely investigated. Thus, to know the impact of cyanotoxins on the immune system, due to its importance in organisms’ homeostasis, is considered of interest. A review of the scientific literature dealing with the immunotoxicity of MCs and CYN has been performed, and both in vitro and in vivo studies have been considered. Results have confirmed the scarcity of reports on the topic, particularly for CYN. Decreased cell viability, apoptosis or altered functions of immune cells, and changed levels and mRNA expression of cytokines are among the most common effects reported. Underlying mechanisms, however, are still not yet fully elucidated. Further research is needed in order to have a full picture of cyanotoxin immunotoxicity.

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.

Determination and Comparative Study of Sugars and Synthetic Colorants in Commercial Branded Fruit Juice Products

Fruit juice-based products are potentially high demanded products in Sri Lanka. The research was conducted to estimate the total sugar content in commercially available fruit juice products and to compare the suitability and efficiency of analytical methods: Lane and Eynon titration method and UV-Visible spectrophotometric methods. Further synthetic colorants in the products were identified and compared with the label information. A consumer survey was conducted to elicit information on consumer preference and knowledge on sugar content of the products. Based on the survey, consumers were more concerned about taste (37%), brand name (28%), price (28%), and nutrition value (7%), respectively. Awareness about the Recommended Dietary Allowance (RDA) of sugar, added sugar consumption, and risk of chronic diseases was 49%. Awareness on the color coding system of the products was 68%. The total sugar content of the fruit nectars was determined using both methods. The maximum total sugar level (18.38 g/100 mL) was observed by the titration method, while the maximum total sugar level (18.31 g/100 mL) was measured by the spectrophotometric method in wood apple (Limonia acidissima) nectar in brand No. “1.” The maximum sucrose content (10.57 g/100 mL) was observed in mango (Mangifera indica L.) nectar in the brand No. “1.” Total sugar contents of both tested methods were compared using SAS 9.0 (Randomized Complete Block Design, RCBD). There is no significant difference (P>0.05) between the two testing methods. In conclusion, the Lane and Eynon titration method was identified as the most effective method for analysis of the total sugar in fruit juice-based products. Based on the analysis of thin-layer chromatography (TLC), a majority of fruit nectar samples (57.14%) contained natural colorants, while 42.86% of total samples contained synthetic colorants. Labelling violation was done by the manufacturers, and the consumer awareness was high with the color-coding system. Continuous surveillance is recommended to minimize health risk related to high sugar consumption of the population.

Hyperlipidemia-induced lipotoxicity and immune activation in rats are prevented by curcumin and rutin

We assessed the effects of curcumin, rutin, and the association of rutin and curcumin in organs of hyperlipidemic rats. Rutin and curcumin have notable antioxidant and anti-inflammatory actions, so we hypothesized that their association would enhance their beneficial effects. Hyperlipidemia results in lipotoxicity and affects several organs. Lipotoxicity is not only an outcome of lipid accumulation in non-adipose tissues but also a result of the hyperlipidemia-associated inflammation and oxidative stress. Wistar rats were treated with rutin and curcumin for 30 days before the induction of acute hyperlipidemia by Poloxamer-407. After 36 h, the animals were euthanized for collection of blood and organs. Untreated hyperlipidemic rats showed higher uric acid and albumin levels in the serum and increased spleen size and ADA activity. Rutin, curcumin and the association reduced the spleen size by 20% and ADA activity by 23, 28, and 27%, respectively. Rats pretreated with rutin showed reduced lipid damage in the liver (40%) and the kidney (44%), and the protein damage was also reduced in the liver (75%). The lipid damage was decreased by 40% in the liver, and 56% in the kidney of rats pretreated with curcumin. The association reduced lipid damage by 50% and 36%, and protein damage by 77% and 64% in the liver and kidney, respectively. Rutin better prevented the decrease in the antioxidant defenses, increasing SOD by 34%, CAT by 246% and GST by 84% in the liver, as well as SOD by 119% and GST by 190% in the kidney. Also, analyses of blood and spleen parameters of untreated and pretreated non-hyperlipidemic rats showed no signs of immunotoxicity. Despite showing protective effects, the association did not perform better than the isolated compounds. Here, we showed that rutin and/or curcumin reestablished the immune homeostasis and redox balance disrupted by hyperlipidemia in peripheral organs of rats.

Dietary Safety Assessment of Flk1-Transgenic Fish

Genetic engineering, also called genetic modification, is facing with growing demands of aquaculture and aquatic products. Although various genetically modified (GM) aquatics have been generated, it is important to evaluate biosafety of GM organisms on the human health before entering into our food chain. For this purpose, we establish a zebrafish wild adult feeding Flk1-transgenic larvae model to examine the predatory fish's histology in multiple tissues, and the global gene expression profile in the liver. 180 days of feeding trial show that there are no significantly morphological changes in intestine, liver, kidney, and sex gonads between fish fed with Flk1 transgenic fish diet (TFD) and fish fed with regular food meal (RFM). However, a characteristic skin spot and autofluorescence increase in the theca of follicle are observed in F1 generation of TFD fish. Liver RNA-sequencing analyses demonstrate that 53 out of 56712 genes or isoforms are differentially transcribed, and mostly involved in proteolysis in extracellular region. According to GO enrichment terms these deregulated genes function in catalytic activity, steroid storing, lipid metabolic process and N-Glycan biosynthesis. These results suggest that a long term of Flk1-transgenic fish diet could alter certain metabolic pathways and possibly cause related tissue deformation. Compared to the previous reports, our feasible transgenic dietary assess system could evaluate subchronic and potential health impact of transgenic fish diet by combining multi-tissue histology and liver transcriptome analyses.

Immunotoxicology: A Brief History

Immunotoxicological research and testing have evolved from early studies of anaphylaxis to the robust and diverse field of immunotoxicology as we know it today. Early studies connecting immune dysfunction with exposure to exogenous agents focused on adverse reactions to immunogenic agents present in vaccines. Over time, work done by immunologists and pathologists leads to descriptions of characteristics of immunogenic agents as well as mechanisms by which anaphylaxis occurs and an understanding of the concept of immunosuppression. These myriad achievements greatly improved public health and led the field of immunotoxicology, which addresses all aspects of adverse immunological responses following exposure to exogenous agents as well as the development of testing paradigms to understand immunological responses of designed agents such as drugs and biologics.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

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.

Perturbation of physiological systems by nanoparticles

Nanotechnology is having a tremendous impact on our society. However, societal concerns about human safety under nanoparticle exposure may derail the broad application of this promising technology. Nanoparticles may enter the human body via various routes, including respiratory pathways, the digestive tract, skin contact, intravenous injection, and implantation. After absorption, nanoparticles are carried to distal organs by the bloodstream and the lymphatic system. During this process, they interact with biological molecules and perturb physiological systems. Although some ingested or absorbed nanoparticles are eliminated, others remain in the body for a long time. The human body is composed of multiple systems that work together to maintain physiological homeostasis. The unexpected invasion of these systems by nanoparticles disturbs normal cell signaling, impairs cell and organ functions, and may even cause pathological disorders. This review examines the comprehensive health risks of exposure to nanoparticles by discussing how nanoparticles perturb various physiological systems as revealed by animal studies. The potential toxicity of nanoparticles to each physiological system and the implications of disrupting the balance among systems are emphasized.

Immunotoxic effects of environmental toxicants in fish - how to assess them?

Numerous environmental chemicals, both long-known toxicants such as persistent organic pollutants as well as emerging contaminants such as pharmaceuticals, are known to modulate immune parameters of wildlife species, what can have adverse consequences for the fitness of individuals including their capability to resist pathogen infections. Despite frequent field observations of impaired immunocompetence and increased disease incidence in contaminant-exposed wildlife populations, the potential relevance of immunotoxic effects for the ecological impact of chemicals is rarely considered in ecotoxicological risk assessment. A limiting factor in the assessment of immunotoxic effects might be the complexity of the immune system what makes it difficult (1) to select appropriate exposure and effect parameters out of the many immune parameters which could be measured, and (2) to evaluate the significance of the selected parameters for the overall fitness and immunocompetence of the organism. Here, we present - on the example of teleost fishes - a brief discussion of how to assess chemical impact on the immune system using parameters at different levels of complexity and integration: immune mediators, humoral immune effectors, cellular immune defenses, macroscopical and microscopical responses of lymphoid tissues and organs, and host resistance to pathogens. Importantly, adverse effects of chemicals on immunocompetence may be detectable only after immune system activation, e.g., after pathogen challenge, but not in the resting immune system of non-infected fish. Current limitations to further development and implementation of immunotoxicity assays and parameters in ecotoxicological risk assessment are not primarily due to technological constraints, but are related from insufficient knowledge of (1) possible modes of action in the immune system, (2) the importance of intra- and inter-species immune system variability for the response against chemical stressors, and (3) deficits in conceptual and mechanistic assessment of combination effects of chemicals and pathogens.

What’s So Special about the Developing Immune System?

The evolution of the subdiscipline of developmental immunotoxicology (DIT) as it exists today has been shaped by significant regulatory pressures as well as key scientific advances. This review considers the role played by legislation to protect children’s health, and on the emergence of immunotoxcity and developmental immunotoxicity guidelines, as well as providing some context to the need for special attention on DIT by considering the evidence that the developing immune system may have unique susceptibilities when compared to the adult immune system. Understanding the full extent of this potential has been complicated by a paucity of data detailing the development of the immune system during critical life stages as well as by the complexities of comparisons across species. Notably, there are differences between humans and nonhuman species used in toxicity testing that include specific differences relative to the timing of the development of the immune system as well as more general anatomic differences, and these differences must be factored into the interpretation of DIT studies. Likewise, understanding how the timing of the immune development impacts on various immune parameters is critical to the design of DIT studies, parameters most extensively characterized to date in young adult animals. Other factors important to DIT, which are considered in this review, are the recognition that effects other than suppression (e.g., allergy and autoimmunity) are important; the need to improve our understanding of how to assess the potential for DIT in humans; and the role that pathology has played in DIT studies in test animals. The latter point receives special emphasis in this review because pathology evaluations have been a major component of standard nonclinical toxicology studies, and could serve an important role in studies to evaluate DIT. This possibility is very consistent with recommendations to incorporate a DIT evaluation into standard developmental and reproductive toxicology (DART) protocols. The overall objective of this review is to provide a ‘snapshot’ of the current state-of-the-science of DIT. Despite significant progress, DIT is still evolving and it is our hope that this review will advance the science.

Methods of evaluating immunotoxicity

Immunotoxicology is an important aspect of the safety evaluation of drugs and chemicals. Immunosuppression, (unspecific) immunostimulation, hypersensitivity and autoimmunity are the four types of immune-mediated adverse effects. However, the nonclinical assessment of immunotoxicity is at present often restricted to animal models and assays to predict unexpected immunosuppression. There is, however, no general consensus that a variety of assays can be considered depending on the compound to be tested. A major issue is whether histological examination of the thymus, spleen, lymphoid organs and Peyer's patches is a reliable predictor of immunosuppression or whether immune function should also be assessed. A T-dependent antibody response assay, either the plaque-forming cell assay or anti-keyhole limpet haemocyanin enzyme-linked immunosorbant assay, is recommended as a first-line assay. A variety of assays, including lymphocyte subset analysis, natural killer-cell activity, lymphocyte proliferation, delayed-type hypersensitivity, cytotoxic T-lymphocyte activity and macrophage/neutrophil function assays, can also be used. In certain circumstances, host resistance assays can be considered. With the exception of contact sensitisation, very few animal models and assays can reliably predict the potential for (unspecific) immunostimulation, hypersensitivity or autoimmunity. A major limitation of immunotoxicity risk assessment is the lack of human data. Immunological end points and clinical criteria to be included in clinical trials and epidemiological studies have to be carefully standardised and validated.

Regulatory aspects of immunotoxicology

Since years, differences among the regulatory requirements on preclinical immunotoxicity testing for pharmaceuticals in the EU, Japan and US indicated a need for an internationally accepted approach. Requests for immunotoxicity investigations are also addressed by guidelines in non-drug areas. While some contain more detailed information in their requirements, other regulations comprise only vague descriptions for consideration of (non-intended) effects on the immune effects. Since 2002, the International Conference on Harmonisation (ICH) of Technical Requirements for Registration of Pharmaceuticals for Human Use put effort in the development of a harmonised approach for testing of immunosuppression and immunoenhancement. Consensus on the ICH S8 guideline on immunotoxicity testing for pharmaceuticals was achieved which now can be implemented into national regulations. The new concept contains in-depth testing, e.g., by functional tests in a concern/weight of evidence approach if the standard toxicity studies or other causes of concern give evidence of an immunotoxic potential or when the target populations are specifically vulnerable. It is expected that the progress on immunotoxicity testing reached by the ICH process will also have an impact on other regulatory areas. Additionally, the regulatory differences in testing requirements on immunotoxicity in other pharmaceutical areas including biotechnology-derived drugs, medicinal products and vaccines and in non-drug areas consisting of chemicals, agrochemicals or food additives are briefly highlighted.

The minipig in toxicology

The use of pigs (Sus scrofa) in biomedical research is well established in particular in surgical and physiological research. For years both pigs and minipigs have been used in pharmacology and toxicology to answer specific questions when the more conventional species have been found unsuitable. The development of minipigs has resulted in strains of more manageable size than the domestic pig. Because of their well-accepted physiological and other similarities to humans, minipigs are becoming increasingly attractive toxicological and pharmacological models. There are several strains of minipigs (Göttingen, Yucatan, Sinclair, Hanford and other). This presentation is based on experience primarily with the Göttingen minipigs. In toxicology in Europe minipigs have become very popular for pharmaceutical studies in place of dogs and primates. Minipigs have been shown to be sensitive to a wide variety of drugs and chemicals. It has become obvious that minipigs can be used for all routes of administration, and in many cases are preferable to dogs or primates for metabolic or pharmacological reasons. There are advantages over the traditional non-rodent species in relation to specific responses to particular drug classes. Their use in general toxicology testing employing the continuous intravenous infusion, dermal or inhalation route has been described in detail in the literature. Background data on toxicological endpoints (ophthalmology, clinical pathology, ECG, organ weight, histopathology and reproduction parameters) have been well-established allowing studies to be interpreted. In the context of this conference, histopathology and toxicopathology data of spontaneous or drug-induced origin are available in the scientific literature. Now there is good supply of high-quality minipigs of known disease status. There are advantages over the traditional non-rodent species in relation to the ethical difficulties of use of animals in biomedical research. Consequently, there are scientific, economic and sociological reasons that make minipigs good toxicological and pharmacological models. The principal disadvantage is that toxicity testing in minipigs may require more test compound than the traditional species.

Perinatal immunotoxicity: why adult exposure assessment fails to predict risk

Recent research has pointed to the developing immune system as a remarkably sensitive toxicologic target for environmental chemicals and drugs. In fact, the perinatal period before and just after birth is replete with dynamic immune changes, many of which do not occur in adults. These include not only the basic maturation and distribution of immune cell types and selection against autoreactive lymphocytes but also changes designed specifically to protect the pregnancy against immune-mediated miscarriage. The newborn is then faced with critical immune maturational adjustments to achieve an immune balance necessary to combat myriad childhood and later-life diseases. All these processes set the fetus and neonate completely apart from the adult regarding immunotoxicologic risk. Yet for decades, safety evaluation has relied almost exclusively upon exposure of the adult immune system to predict perinatal immune risk. Recent workshops and forums have suggested a benefit in employing alternative exposures that include exposure throughout early life stages. However, issues remain concerning when and where such applications might be required. In this review we discuss the reasons why immunotoxic assessment is important for current childhood diseases and why adult exposure assessment cannot predict the effect of xenobiotics on the developing immune system. It also provides examples of developmental immunotoxicants where age-based risk appears to differ. Finally, it stresses the need to replace adult exposure assessment for immune evaluation with protocols that can protect the developing immune system.

Harmonization of immunotoxicity guidelines in the ICH process--pathology considerations from the guideline Committee of the European Society of Toxicological Pathology (ESTP)

As part of the ICH process of harmonization of testing guidelines for immunotoxicity, the European Society of Toxicologic Pathology (ESTP) has contributed to the scientific discussion on methods and evaluation of immunotoxicity studies with technical and scientific recommendations on toxicologic pathology. The weighing and sampling of immune organs is discussed taking into consideration specifically the value of lymph node weighing and the selection of appropriate lymph nodes for the detection of local and systemic effects. The different techniques of bone marrow preparation are considered for routine and extended investigations. Criteria are given for the gross and histopathological detection of effects in Peyer's patches. For the histopathological evaluation it is strongly recommended that each compartment within the different lymphoid organs is investigated separately and semiquantitatively since this approach has shown to increase the sensitivity and specificity of immunohistopathology.

Immune modulator studies in primates: the utility of flow cytometry and immunohistochemistry in the identification and characterization of immunotoxicity

Exposure to natural environmental products, biopharmaceuticals, or investigational adjuvants has the potential to negatively impact the immune system, resulting in either up- or downregulation of immune function (immunomodulation). Many current protocols for primate toxicologic testing call for the evaluation of changes in immune cell number (peripheral blood or tissue), alterations in the weights of immune system organs (lymph nodes, spleen, thymus), and/or increases in the overall incidence of infections or neoplasms; these data are relied upon to suggest altered immune function. However, these are informative only when clear differences in frequency and/or severity of effects can be distinguished across control and dosed groups. In the absence of such distinct morphologic or clinical pathologic changes, the identification of potential immunomodulatory effects can present a much greater challenge. Additional evaluations may be needed to detect altered immune system integrity; these are based on in vivo assessments in primates of cellular or humoral responsiveness. Immunomodulatory effects can be characterized by in vitro or in vivo immune function tests: these tests require prestudy planning to integrate assessments into ongoing toxicology programs. These methods also involve specialized training and equipment, particularly if the intent is to evaluate parameters in a GLP laboratory setting. In primate toxicology, the added costs required to perform a complete functional analysis of the immune system can be substantial, but may be warranted depending on the clinical development plans. Two analytical methods that are easily incorporated into the standard toxicology profile in primates are flow cytometry and immunohistochemistry. Flow cytometry (FC) is used to assess changes in the relative distribution of immune cell marker expression, and where marker expression is known to fluctuate with the state of cell activation, can also provide information on functional attributes of immune cells. Immunohistochemistry (IHC) provides a means to evaluate similar characteristics of immune cells within tissue sections. Used together, FC and IHC can aid in the identification of changes in immune system that may not be apparent by traditional testing procedures (such as H&E staining), thus aiding in the characterization of immune system alterations. This presentation focused on the utility of flow cytometry and immunohistochemistry in a standard primate toxicology evaluation, with representative examples showing the benefits of these technologies in the diagnosis of potential immunomodulatory effects.

The functions of cytokines and their uses in toxicology

Cytokines are critical controllers of cell, and hence tissue, growth, migration, development and differentiation. The family includes the inflammatory cytokines such as the interleukins and interferons, growth factors such as epidermal and hepatocyte growth factor and chemokines such as the macrophage inflammatory proteins, MIP-1alpha and MIP-1beta. They do not include the peptide and steroid hormones of the endocrine system. Cytokines have important roles in chemically induced tissue damage repair, in cancer development and progression, in the control of cell replication and apoptosis, and in the modulation of immune reactions such as sensitization. They have the potential for being sensitive markers of chemically induced perturbations in function but from a toxicological point of view, the detection of cytokine changes in the whole animal is limited by the fact that they are locally released, with plasma measures being generally unreliable or irrelevant, and they have short half lives which require precise timing to detect. Even where methodology is adequate the interpretation of the downstream effects of high, local concentrations of a particular cytokine is problematic because of their interdependence and the pleiotropism of their action. A range of techniques exist for their measurement including those dependent upon antibodies specific for the respective cytokines, but with the introduction of genomic and proteomic technology, a more complete study of cytokine changes occurring under the influence of chemical toxicity should be possible. Their further study, as markers of chemical toxicity, will undoubtedly lead to a greater understanding of how synthetic molecules perturb normal cell biology and if, and how, this can be avoided by more intuitive molecular design in the future.