Experimental studies on immunosuppression: how do they predict for man?

Comparative anti-arthritic investigation of iridoid glycosides and crocetin derivatives from Gardenia jasminoides Ellis in Freund's complete adjuvant-induced arthritis in rats

BACKGROUND

Discovering novel compounds with higher activities is a key aim of natural products research. Gardenia jasminoides Ellis is a herb with anti-inflammatory properties. Iridoid glycosides (mainly geniposide) and crocetin derivatives (crocins) are the two major active constituents in this herb and are considered its active ingredients. However, which components are responsible for the anti-inflammatory properties of gardenia have remained to be investigated.

PURPOSE

Here, we prepared total iridoid glycocides (TIG) and total crocins (TC) from G. jasminoides Ellis, determined their main chemical constituents, and performed animal studies to evaluate their anti-adjuvant arthritis activities, thus, proposing a reasonable mechenism to explain the anti-inflammatory activities of the active components in this herbal remedy.

STUDY DESIGN

TIG and TC were prepared by using HPD-100 macroporous resin, and characterized by UHPLC-DAD-MS and UV-Vis spectrophotometer. Then, freund's complete adjuvant-injected rats underwent drug treatments with TIG (160 mg/kg) and TC (160 mg/kg) for 14 days, and their ankle diameters were measured. Moreover, X-ray radiographs of the adjuvant injected hind paws were evaluated. Finally, histopathological examinations of the ankle joints, spleens and thymus were carried out to evaluate inflammatory reactions, and immunohistochemical measurements were conducted to evaluate TNF-α and TGF-β1 expression in the ankle joint of the rats.

RESULTS

The chemical composition determination of the current study showed that TIG was mainly composed of geniposide and TC was a fraction predominantly with crocin-1, crocin-2 and crocin-3. Calculation of results showed that TIG and TC contained 58.2% total iridoid glycosides and 54.7% total crocins, respectively. Our study suggested TIG and TC treatments markedly decreased paw swelling and ankle diameters of AA rats (both p < 0.05). The radiological analysis showed that administration of TIG and TC ameliorated bone destruction, and reduced the radiological bone destruction scores (TIG p < 0.05, TC p>0.05). Moreover, data from histological assessment demonstrated considerable mitigation of inflammation in the joints (both p < 0.01), spleen and thymus of AA rats treated with TIG and TC. TNF-α and TGF-β1 protein expression according to immunohistochemistry staining also supported the anti-arthritis activities of TIG and TC (TNF-α: TIG p < 0.01 and TC p < 0.05, TGF-β1: TIG p < 0.01 and TC p>0.05).

CONCLUSION

In the current study, fractionation of gardenia prior to further in vivo investigation has for the first time provided reasonable explanation for the anti-inflammatory activity of this herbal remedy. Our study showed that both TIG and TC from gardenia have anti-inflammatory properties. Overall, these experimental findings suggest that gardenia could be regarded as a potential therapeutic target for arthritis. However, as geniposide has a higher content than crocins in this herbal drug, TIG (mainly geniposide) seems to be primarily responsible for the anti-inflammatory properties of gardenia. Taken together, this maiden attempt demonstrated that TIG (mainly geniposide) is more important in evaluating the anti-inflammatory activity of G. jasminoides Ellis.

Bee Venom and Hesperidin Effectively Mitigate Complete Freund's Adjuvant-Induced Arthritis Via Immunomodulation and Enhancement of Antioxidant Defense System

Objectives

This study aims to assess the antirheumatic activity of bee venom (BV) and/or hesperidin as natural products in complete Freund's adjuvant (CFA)-induced arthritis in male Wistar rats.

Material and methods

Rheumatoid arthritis was induced in 30 male Wistar rats (weight 130 g to 150 g; age 10 to 12 weeks) by subcutaneous injection of CFA into the right hind paw of the rats. The rats were divided into five groups of six rats in each and administered the following regimens for 21 days: Normal group (given the equivalent volume of saline and carboxymethylcellulose), arthritic group (given the equivalent volume of saline and carboxymethylcellulose), arthritic group treated with BV (treated with BV along with carboxymethylcellulose), arthritic group treated with hesperidin (treated with hesperidin along with saline), and arthritic group treated with BV and hesperidin (treated with BV and hesperidin concurrently).

Results

Bee venom and/or hesperidin successfully reversed the CFA-arthritis-induced increases in right hind leg paw swelling, leukocytes' count, liver lipid peroxidation, serum inflammatory cytokine interleukin (IL-2 and IL-12) levels and spleen tumor necrosis factor-alpha messenger ribonucleic acid expression. Moreover, the CFA-induced down-regulation in serum IL-10 level and spleen IL-4 messenger ribonucleic acid expression as well as the deterioration in the antioxidant defense system were significantly improved as a result of BV and hesperidin administration. Both treatments also markedly counteracted the severe inflammatory changes and leukocytic infiltration in the periarticular tissue of the ankle joints. In addition, BV and hesperidin obviously amended the lymphoid hyperplasia in white pulps of spleen as well as the widening of the medulla and mononuclear cell infiltration found in thymus.

Conclusion

Bee venom and hesperidin administration produced their ameliorative effects on rheumatoid arthritis via their antioxidant, antiinflammatory and immunomodulatory potentials. BV plus hesperidin particularly seemed to be the most potent in improving rheumatoid arthritis in Wistar rats.

In vivo anti-inflammatory activities of the essential oil from Radix Angelicae dahuricae

Although Radix Angelicae dahuricae (Angelica) has been traditionally used in patients with rheumatism arthralgia, its bioactive ingredients remain to be determined. In this study, the essential oil extract of Radix Angelicae dahuricae (EOAD) was assessed for its anti-inflammatory activities against xylene-induced acute ear swelling and carrageenan-induced acute paw edema in mice as well as its anti-inflammatory and immunomodulating properties in Freund's complete adjuvant (FCA)-induced arthritis in rats. We found that EOAD at 100 mg/kg significantly alleviated xylene-induced ear swelling and carrageenan-induced paw edema in mice. Moreover, in the FCA-induced rat arthritis model, EOAD significantly improved hind paw swelling, lowered the adjuvant arthritis score, mitigated synovial hyperplasia, inflammatory cell infiltration, and cartilage destruction in the ankle joint, and reduced the serum levels of inflammatory mediators such as nitric oxide, tumor necrosis factor-α, and prostaglandin E2 as well as serum nitric oxide synthase activity. These findings support the fact that the essential oil extract of Angelica contains important active constituents responsible for its anti-inflammatory activities and therefore help to understand the phytotherapeutic effects of Angelica in the treatment of aseptic inflammation.

Immunotoxicology and its application in risk assessment

Immunotoxicology is the study of undesired modulation of the immune system by extrinsic factors. Toxicological assessments have demonstrated that the immune system is a target following exposure to a diverse group of xenobiotics including ultraviolet radiation, chemical pollutants, therapeutics, and recreational drugs. There is a well-established cause and effect relationship between suppression of the immune response and reduced resistance to infections and certain types of neoplasia. In humans, mild-to-moderate suppression of the immune response is linked to reduced resistance to common community-acquired infections, whereas opportunistic infections, which are very rare in the general population, are common in individuals with severe suppression. Xenobiotic exposure may also result in unintended stimulation of immune function. Although a cause and effect relationship between unintended stimulation of the immune response and adverse consequences has yet to be established, evidence does suggest that hypersensitivity, autoimmunity, and pathological inflammation may be exacerbated in susceptible populations exposed to certain xenobiotics. Xenobiotics can act as allergens and elicit hypersensitivity responses, or they can modulate hypersensitivity responses to other allergens such as pollen or dust mite by acting as adjuvants, enhancing the development or expression of hypersensitivity. Allergic contact dermatitis, allergic rhinitis, and asthma are the most commonly encountered types of hypersensitivity reactions resulting from chemical exposure. The immunologic effectors and mechanisms involved in autoimmune reactions are the same as those associated with responses to foreign antigens; however, the reactions are directed against the host's own cells. Thus, chemicals that induce immune suppression, nonspecific immunostimulation, or hypersensitivity may also impact autoimmunity. Risk assessment for immunotoxicity should be performed using the same approaches and principles for other noncancer effects. However, since xenobiotics may have effects on more than one aspect of immune function, immunotoxicity data should be evaluated separately for evidence of suppression, stimulation, hypersensitivity, and autoimmunity.

Therapeutic effects of standardized Vitex negundo seeds extract on complete Freund's adjuvant induced arthritis in rats

The seeds of Vitex negundo L. (Verbenaceae) have been commonly used as a folk remedy for the treatment of rheumatism and joint inflammation in Traditional Chinese Medicine. This study aimed to evaluate the anti-arthritic activity of the extract of V. negundo seeds (EVNS) using Freund's complete adjuvant (CFA) induced arthritis (AA) in rat model. As a result, EVNS, with abundant phenylnaphthalene-type lignans, significantly inhibited the paw edema, decreased the arthritis score and spleen index, and reversed the weight loss of CFA-injected rats. Histopathological studies showed a marked decrease of synovial inflammatory infiltration and synovial lining hyperplasia in the joints of EVNS-treated animals. The remarkable decrement of serum inflammatory factors (TNF-α, IL-1β and IL-6) were observed in EVNS-treated rats, whereas, IL-10, an anti-inflammatory cytokine, was found to be significantly increased by EVNS. The expressions of COX-2 and 5-LOX in PBMC were also inhibited by administration of EVNS. Our results demonstrated that V. negundo seeds possessed potential therapeutic effect on adjuvant induced arthritis in rats by decreasing the levels of TNF-α, IL-1β and IL-6 and increasing that of IL-10 in serum as well as down-regulating the levels of COX-2 and 5-LOX, and therefore may be an effective cure for the treatment of human rheumatoid arthritis.

Developmental Immunotoxicity, Perinatal Programming, and Noncommunicable Diseases: Focus on Human Studies

Developmental immunotoxicity (DIT) is a term given to encompass the environmentally induced disruption of normal immune development resulting in adverse outcomes. A myriad of chemical, physical, and psychological factors can all contribute to DIT. As a core component of the developmental origins of adult disease, DIT is interlinked with three important concepts surrounding health risks across a lifetime: (1) the Barker Hypothesis, which connects prenatal development to later-life diseases, (2) the hygiene hypothesis, which connects newborns and infants to risk of later-life diseases and, (3) fetal programming and epigenetic alterations, which may exert effects both in later life and across future generations. This review of DIT considers: (1) the history and context of DIT research, (2) the fundamental features of DIT, (3) the emerging role of DIT in risk of noncommunicable diseases (NCDs) and (4) the range of risk factors that have been investigated through human research. The emphasis on the human DIT-related literature is significant since most prior reviews of DIT have largely focused on animal research and considerations of specific categories of risk factors (e.g., heavy metals). Risk factors considered in this review include air pollution, aluminum, antibiotics, arsenic, bisphenol A, ethanol, lead (Pb), maternal smoking and environmental tobacco smoke, paracetamol (acetaminophen), pesticides, polychlorinated biphenyls, and polyfluorinated compounds.

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.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated disruption of the CD40 ligand-induced activation of primary human B cells

Suppression of the primary antibody response is particularly sensitive to suppression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice; however, surprisingly little is known concerning the effects of TCDD on humoral immunity or B cell function in humans. Results from a limited number of previous studies, primarily employing in vitro activation models, suggested that human B cell effector function is suppressed by TCDD. The present study sought to extend these findings by investigating, in primary human B cells, the effects of TCDD on several critical stages leading to antibody secretion including activation and plasmacytic differentiation using an in vitro CD40 ligand activation model. These studies revealed important differences in the response of human and mouse B cells to TCDD, the most striking being altered expression of plasmacytic differentiation regulators, B lymphocyte-induced maturation protein 1 and paired box protein 5, in mouse but not human B cells. The activation of human B cells was profoundly impaired by TCDD, as evidenced by decreased expression of activation markers CD80, CD86, and CD69. The impaired activation correlated with decreased cell viability, which prevented the progression of human B cells toward plasmacytic differentiation. TCDD treatment also attenuated the early activation of mitogen-activated protein kinases (MAPK) and Akt signaling in human B cells. Collectively, the present study provided experimental evidence for novel mechanisms by which TCDD impairs the effector function of primary human B cells.

Induction of the aryl hydrocarbon receptor-responsive genes and modulation of the immunoglobulin M response by 2,3,7,8-tetrachlorodibenzo-p-dioxin in primary human B cells

Past studies in rodent models identified the suppression of primary humoral immune responses as one of the most sensitive sequela associated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. Yet, the sensitivity of humoral immunity to TCDD in humans represents an important toxicological data gap. Therefore, the objectives of this investigation were two-fold. The first was to assess the induction of known aryl hydrocarbon receptor (AHR)-responsive genes in primary human B cells as a measure of early biological responses to TCDD. The second was to evaluate the direct effect of TCDD on CD40 ligand-induced immunoglobulin M (IgM) secretion by human primary B cells. The effects of TCDD on induction of AHR-responsive genes and suppression of the IgM response were also compared with B cells from a TCDD-responsive mouse strain, C57BL/6. AHR-responsive genes in human B cells exhibited slower kinetics and reduced magnitude of induction by TCDD when compared with mouse B cells. Evaluation of B-cell function from 12 donors identified two general phenotypes; the majority of donors exhibited similar sensitivity to suppression by TCDD of the IgM response as mouse B cells, which was not attributable to decreased B-cell proliferation. In a minority of donors, no suppression of the IgM response by TCDD was observed. Although donor-to-donor variation in sensitivity to TCDD was observed, human B cells from the majority of donors evaluated showed impairment of effector function by TCDD. Collectively, data presented in this series of studies demonstrate that TCDD impairs the humoral immunity of humans by directly targeting B cells.

Establishment of an immunoglobulin m antibody-forming cell response model for characterizing immunotoxicity in primary human B cells

Rodent models have been extensively utilized to identify putative human immunotoxicants; however, even when immunotoxicity is established, uncertainty remains whether the effects are predictive of human risk. Therefore, the objective of this study was to establish a polyclonal immunoglobulin M (IgM) antibody-forming cell (AFC) response model to directly characterize immunotoxicity in primary mouse or human B cells. CD40 ligand (CD40L) was selected to activate B cells because it effectively drives both primary human and mouse B cells in vitro to AFC in a physiologically relevant manner to mimic T-cell-dependent antibody responses in vivo. In this model, the IgM AFC response is induced by cell surface-expressed CD40L and promoted by recombinant cytokines. Reported here are the conditions required to induce IgM AFC responses using mouse splenic B cells or human peripheral blood B cells, allowing for species comparisons. Moreover, less than one order of magnitude difference was observed in the CD40L-induced B-cell AFC responses based on data from multiple donors. In addition to antibody production, proliferation and phenotypic changes characteristic of B-cell activation as well as the plasma cell phenotype were also significantly induced. Finally, two well-characterized immunotoxicants, arsenic and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide, using the CD40L-induced IgM AFC response were compared in both mouse and human B cells. Collectively, an IgM AFC response model is described that can be applied to assess the sensitivity of antibody responses to modulation by xenobiotics using mouse as well as human primary B cells.

Xenobiotic-induced alterations in thymocyte development

The thymus is a very sensitive target for environmental pollutants, which can affect this organ as well as thymocyte differentiation. A failure in thymocyte development can be due to the exacerbation of apoptosis, arrest of thymocyte maturation, generation of autoreactive T cells, and inhibition or stimulation of the output of recent thymic emigrants to the periphery. Recent data demonstrate that the immune system has the potential to maintain homeostasis under conditions of elevated risk, and the thymus plays a crucial role in this process. Environmental xenobiotics can exert their effects through receptor-mediated interactions or independently on receptor involvement. Under natural conditions organisms are exposed to a variety of xenobiotics. The final effect of such exposure is not related to the action of a single chemical, but to the action of a mixture of chemicals. The toxic effect of environmental xenobiotics on the generation and functions of immune cells may result in suppression or stimulation of the immune response. The most intensive studies have been done on halogenated aromatic hydrocarbons, heavy metals and various chemicals acting as endocrine disrupters. Recently, special interest has focused on the action of air particulate matter.

Immune Function Tests for Hazard Identification: A Paradigm Shift in Drug Development

Routine immune function testing in preclinical drug development was established as a regulatory requirement in June of 2000 under the Committee of Proprietary Medicinal Products (CPMP) Note for Guidance on Repeated Dose Toxicity (CPMP/SWP/1042/99). The purpose of the more stringent approach to immunotoxicology testing was to better identify unintended immunosuppression; however, the requirement was met with much discussion and debate. At the center of the discussion was an attempt to reconcile opposing regulatory directives from agencies outside of Europe that adhere to a more selective, weight-of-evidence approach to functional evaluations. Uncertainty over the predictive value of the recommended immune function tests relative to conventional toxicology parameters prompted an investigation by the International Committee on Harmonization (ICH). The results of a preliminary, industry-wide survey indicated that only a low percentage of pharmaceuticals adversely affect immune function without alterations to standard toxicology parameters. Expected ICH guidelines will ultimately determine to what extent and for what purpose immune function tests will be conducted. In the meantime, optimization of the recommended immune function tests is ongoing. The T-cell dependent antibody response (TDAR) by either conventional Sheep Red Blood Cell (SRBC) plaque assay or by the modified ELISA method using either SRBC or keyhole limpet hemocyanin (KLH) as antigen is being extensively evaluated to determine best practices and procedures for preclinical immunotoxicity evaluations. This review addresses some aspects of the debate concerning the appropriateness of immune function tests for hazard identification, along with recommendations for optimizing TDAR methodology to ensure adequate sensitivity and predictability in risk assessments for immunotoxicity.

Immune function testing of human pharmaceuticals: regulatory overshoot?

Suppression of the activity of the immune system can result in decreased resistance to (opportunistic) infection and cancer. Experimental animal studies have identified many immunotoxic agents, but data on unintended immuno-toxicity of human pharmaceuticals are limited. To enhance the sensitivity of the non-clinical screening of human pharmaceuticals, immunotoxicity endpoints in standard toxicity studies, as well as an immune function study, are requested by the EU, incorporating a T-cell-dependent antigen response in the first screening phase. Authorities from other areas in the world follow similar lines for immunotoxicity testing, but differ in whether or not the functional assay is seen as a primary requisite or can be secondary to other factors or observations. Based on a limited survey in the framework of the International Conference on Harmonization, the European position has been reconsidered to negotiate a broad cause-for-concern approach. The relevance of functional testing of the immune system to show effects of human pharmaceuticals is shown in this review. There is certainly a need for more in-depth testing of the integrity of the immune system and a cause-for-concern approach is, therefore, needed. A broad category is the number of compounds that might interact via binding to receptor sites at the broadly taken population of leukocytes (e.g., lymphocytes, macrophages). Criteria to differentiate among compounds in this category have yet to be ascertained.

The development of methods for immunophenotypic and lymphocyte function analyzes for assessment of Southern sea otter (Enhydra lutris nereis) health

The Southern sea otter (Enhydra lutris nereis) is listed as threatened under the Endangered Species Act. The population began a pattern of slow decline in 1995. The decline was attributed to high adult mortality rates with infectious disease being the major cause of death. Multiple pathogens were implicated in these deaths including opportunistic pathogens such as Coccidiodes immitis and Toxoplasma sp. These findings suggested that the immunological health of mature animals in this population might be compromised. The primary goal of this study was to establish techniques for assessing phenotypic and functional baseline data for peripheral blood mononuclear cells (PBMC) in free-ranging sea otters. Standard total and differential white blood cell counts were augmented by emumeration of T and B lymphocyte subsets. Lymphocyte function was determined by both mitogen-induced proliferation and expression of IL-2 receptors. In addition to establishing normal ranges for adult animals, age-related changes were identified in B lymphocyte numbers and cell-surface density of major histocompatability complex class II (MHC II) proteins. The predominant lymphocyte subpopulation in Southern sea otters is the T lymphocyte. Substantial variation among individual animals was observed within the B lymphocyte population both in cell number and density of MHC II expression. Pups had greater numbers of T and B lymphocyte, as well as, greater MHC II expression on B lymphocytes than adults. Mitogen-induced proliferation of peripheral blood mononuclear cells (PBMC) was variable among individual animals with no significant difference in cell response between age class and gender. Concanavalin (ConA) was a more effective mitogen in stimulating proliferation and interleukin (IL)-2 receptor expression than pokeweed. This data can be used to augment routine hematology profiles and aid in the identification of animals with immunologic perturbations.

Regulatory immunotoxicology: does the published evidence support mandatory nonclinical immune function screening in drug development?

Recent immunotoxicity guidance documents from the EU CHMP and the US FDA apply significantly different weightings to immune function testing; whereas the former mandates (as a starting point) incorporation of immune function tests (IFTs) to screen for immunotoxic potential in sub-chronic rodent toxicity studies, the more cautious 'for cause' FDA approach recommends the use of IFTs only when warranted by evidence obtained from conventional nonclinical and/or clinical studies. Conclusions from detailed evaluations of several key drugs, including salmeterol and some opioids, challenge the notion that data on these examples support the need for IFTs to detect unintended immunosuppression. Given the virtual absence of convincing pharmaceutical examples and the rarity of unintended immunosuppression, routine immune function testing of all new pharmaceuticals is not considered justified. Resources currently being employed in this manner in an attempt to detect a seemingly rare phenomenon would appear to be better applied to the development of reliable predictive assays for drug hypersensitivity, which is known to cause significant patient morbidity. Any moves towards a globally harmonised guideline that recommends the use of concern-based IFTs, need ideally to be accompanied by the establishment of appropriate historical control reference intervals and interpretation criteria to support a reliable weight-of-evidence approach to data evaluation.

Assessing immunotoxicity: guidelines

Over the last couple of years the assessment of immunotoxic potential of human pharmaceuticals has drawn considerable attention worldwide. Regulatory agencies entrusted with the registration of pharmaceuticals (or other compounds) found an increased need for guidance on this issue. This has resulted in the release of guidance documents on immunotoxicity in Europe, USA and Japan in close succession. In Europe the CPMP has released their immunotoxicity guidance documents that are now in force. The FDA and the Japanese Authorities are in the process of doing so, and will shortly enforce them. Immune suppression and stimulation, hypersensitivity, photosensitivity, drug-induced autoimmunity and developmental immunotoxicity are the focus of regulatory testing. This review discusses these kinds of immunotoxicity and their clinical implications. The three regional guidelines and screening tools for detection are discussed. Additionally, the scientific background on which these guidelines are based is briefly highlighted.

Evaluation and prevalidation of an immunotoxicity test based on human whole-blood cytokine release

Immunotoxicology is a relatively new field in toxicology, and is one of emerging importance, because immunotoxicity appears to contribute to the development of cancer, autoimmune disorders, allergies and other diseases. At present, there is a lack of human cell-based immunotoxicity assays for predicting the toxicity of xenobiotics toward the immune system in a simple, fast, economical and reliable way. Existing immunotoxicity tests are mainly performed in animals, although species differences favour human-based testing. Whole-blood cytokine release models have attracted increasing interest, and are broadly used for pharmacological in vitro and ex vivo studies, as well as for pyrogenicity testing. We have adapted those methods for immunotoxicity testing, to permit the potency testing of immunostimulants and immunosuppressants. Following stimulation with a lipopolysaccharide or staphylococcal enterotoxin B, monocytes and lymphocytes release interleukin-1beta and interleukin-4, respectively. Thirty-one pharmaceutical compounds, with known effects on the immune system, were used to optimise and standardise the method, by analysing their effects on cytokine release. The in vitro results were expressed as IC50 values for immunosuppression, and SC(4) (fourfold increase) values for immunostimulation, and compared with therapeutic serum concentrations of the compounds in patients, and in vivo LD50 values from animal studies. The in vitro results correlated well with the in vivo data, so the test appears to reflect immunomodulation. Results were reproducible (CV = 20 +/- 5%), and the method could be transferred to another laboratory (r(2) = 0.99). We therefore propose this method for further validation and for use in immunotoxicity testing strategies.

A perspective on the progression of immunotoxicology

Immunotoxicology originated in the early 1970s, when scientists began investigating chemicals. During the 1970s and early 1980s, a few investigators determined that chemicals were immunotoxic, developed and/or refined immunoassays, and began to characterize immunotoxic responses. In the 1980s, many new investigators entered the field, graduates were being trained as immunotoxicologists, the immune system was identified as a primary target organ, mechanisms of action studies proliferated, a comprehensive immunotoxicological panel was validated, the discipline gained universal credibility, and human studies emerged. The 1990s were ushered in with the concept of biological markers in immunotoxicology, a better understanding of "immune function", inclusion of immunotoxicology in risk assessment analysis, and a focus on molecular immunology. Future investigations will continue to improve and expand this foundation, pursue the relationship of immunotoxic chemicals and adverse health effects in humans, utilize genetically altered rodent models, and use gene expression technology to better understand the pathogenesis of immunotoxicological processes. Immunotoxicology has not only matured since its inception nearly 30 yr ago, but has become a prominent and respected discipline with global recognition; one that has made significant contributions to the advancement of the biomedical sciences.