Identification of immunotoxic effects of chemicals and assessment of their relevance to man

Non-Clinical Safety Evaluation of Exosomes Derived from Human Umbilical Cord Mesenchymal Stem Cells in Cynomolgus Monkeys

Purpose

In recent years, exosomes have been proved to be used to treat many diseases. However, due to the lack of uniform quality control standards for exosomes, the safety of exosomes is still a problem to be solved, especially now more and more exosomes are used in clinical trials, and its non-clinical safety evaluation is particularly important. However, there is no safety evaluation standard for exosomes at present. Therefore, this study will refer to the evaluation criteria of therapeutic biological products, adopt non-human primates to evaluate the non-clinical safety of human umbilical cord mesenchymal stem cell exosomes from the general pharmacology and immunotoxicity, aiming at establishing a safety evaluation system of exosomes and providing reference for the clinical application of exosomes in the future.

Methods

3.85 × 1012 exosomes derived from human umbilical cord mesenchymal stem cells were injected into cynomolgus monkeys intravenously. The changes of general clinical conditions, hematology, immunoglobulin, Th1/Th2 cytokines, T lymphocytes and B lymphocytes, and immune organs were observed before and within 14 days after injection.

Results

The results showed that exosomes did not have obvious pathological effects on the general clinical conditions, blood, coagulation function, organ coefficient, immunoglobulin, Th1/Th2 cytokines, lymphocytes, major organs, and major immune organs (spleen, thymus, bone marrow) of cynomolgus monkeys. However, the number of granulocyte-macrophage colonies in exosomes group was significantly higher than that in control group.

Conclusion

To sum up, the general pharmacological results and immunotoxicity results showed that the injection of 3.85 × 1012 exosomes may have no obvious adverse reactions to cynomolgus monkeys. This dose of exosomes is relatively safe for treatment, which provides basis research for non-clinical safety evaluation of exosomes and provides reliable research basis for future clinical application of exosomes.

Environmental Toxicology: Children at Risk

Children today live in a world that is vastly different from a few generations ago. While industrialization has maximized (for many) children’s opportunities to survive, develop and enjoy high levels of health, education, recreation, and fulfillment, it has also added significant challenges to their development.

SLE in a United States-Mexico border community

This report describes the results of a clinic-based study conducted to verify a community-reported excess prevalence of systemic lupus erythematosus (SLE) and a possible connection between ethnicity and environmental factors in the reporting of SLE in the United States-Mexico border town of Nogales, Arizona. A community group in Nogales reported 37 cases of SLE in its community, suggesting a prevalence rate of 200 per 100,000. This report describes 19 definite and 7 probable cases of SLE using the 1982 American College of Rheumatology criteria. All definite and probable cases were self-identified, Mexican-American females. This yields a prevalence rate of 94 per 100,000, among the highest reported to date. The majority of cases resided within 3 miles of the United States-Mexico border and within 1 mile of the polluted Nogales Wash or ground wells with documented toxins. It remains to be determined whether this confirms that SLE is more common in Mexican-Americans or whether environmental factors, especially pollutants, are predominantly responsible. In addition to the need to be aware about the apparent increased risk of SLE in many Latin-Americans, clinicians should ask about possible environmental factors.

Use of SRBC antibody responses for immunotoxicity testing

The production of antigen-specific antibodies represents a major defense mechanism of humoral immune responses and involves the cooperation and interaction of several immune cell types: antigen presenting cells, T helper cells, and B cells. Thus, there are several cells or cell products (e.g., interleukins) that may be altered following xenobiotic exposure, making assays that evaluate the production of antigen specific antibody a relatively comprehensive and sensitive assessment of immune function. Data suggest that the primary antibody response to SRBC may be one of the most sensitive endpoints available to assess chemical-induced alterations to the immune system. As a result, this endpoint has become the cornerstone of several recently established guidelines for assessing the potential immunotoxicity of xenobiotics. Five types of antibody may be produced in a humoral immune response (i.e., IgGs of various subtypes, IgM, IgD, IgA, or IgE). For immunotoxicity assessment, the focus has primarily been on assays that assess production of IgM antibodies. Although a number of assays have been developed to evaluate antibody production, the antibody forming cell (AFC) assay and enzyme-linked immunosorbent assay (ELISA) are the two most frequently employed to evaluate the potential immunotoxicity of a xenobiotic. In this manuscript, background information, as well as the pros and cons of each of these assays are discussed and detailed methods on conducting each assay are provided.

Acute Suppression of Serum IgM and IgA in Tank Workers Exposed to Benzene

We investigated associations between benzene exposure and alterations of proteins and cells of the immune system among workers maintaining cargo tanks containing crude oil residues. Individual exposure to benzene, benzene in blood and urine, peripheral blood lymphocytes (total lymphocytes, lymphocytes in subpopulations CD3, CD4, CD8, CD19, CD56 and CD4/CD8 ratio), complement factors C3 and C4 and serum concentration of immunoglobulins (IgG, IgA, IgM and IgE) were analysed among 13 tank workers and nine unexposed referents (catering section). Benzene exposure was measured during three consecutive 12-h work days. Blood and urine samples were collected pre-shift on the first day (baseline), post-shift on the third day, and pre-next shift on the following morning. The time spent in the cargo tank was logged. The individual geometric mean benzene exposure in the breathing zone of tank workers over 3 days was 0.15 p.p.m. (range 0.01-0.62 p.p.m.) (n = 26). The geometric mean benzene concentration in blood post-shift was 12.3 nmol/l among tank workers versus 0.7 nmol/l among the referents. Tank workers showed a decline (versus referents) in IgM from baseline to post-shift (t-test, P = 0.04) and IgA from baseline to pre-next shift (t-test, P = 0.01). They also showed a decline in CD4 T cells from baseline to post-shift (t-test, P = 0.04). Suppression correlated with benzene exposure, benzene concentrations in blood and urine and time spent in the tank. The groups did not differ significantly in the change in other immune parameters. The clinical significance is unknown and warrants further studies.

Inflammatory cytokines reaction elicited by root-end filling materials

Cytokines are inflammation in the list of tissue reactions that cytokines control of cell and tissue growth, development, and differentiation. Root-end filling materials often contact with existing periapical tissue, and they need to be biocompatible with remnant periapical tissue. The aim of this study was to focus the effects of the root end filling materials on bone cell viability and expression of inflammatory cytokines and their role in maintaining health and stability of the restored dental tissues. Calcium hydroxide-based (Life), zinc oxide eugenol-based (Super EBA), and mineral trioxide aggregate-based (MTA) root-end filling materials were used to investigate their effect on a human osteosarcoma cell line (U2OS). The cell attachment assay was observed microscopically, and the expression of interleukin-2, -4, and -10 were quantified by enzyme-linked immunosorbent assay. Any resultant difference between the root-end filling material was analyzed statistically by one-way analysis of variance. The results showed that the best cell attachment to root-end filling material occurred with MTA. The IL-4 (0.824 +/- 0.396) and IL-10 (2.06 +/- 1.24) levels were greater for the MTA group, whereas IL-2 expression for the three kinds of root-end filling materials was similar. All materials were able to induce expression of inflammatory cytokines from cultured bone cells.

Immune responses: adverse versus non-adverse effects

The adaptive immune system in vertebrates has evolved to provide host resistance to infectious microorganisms and malignant disease. Normal immune function and the induction of specific immune responses require the orchestrated interaction between cells and molecules both within and outside the lymphoid system. Immunotoxicology can be defined as the study of adverse health effects that may result from the interaction of xenobiotics with the immune system. In general terms such effects can take one of two forms. The first of these is immunotoxicity (or immunosuppression) where there is a perturbation of, or damage to, one or more components of the immune system resulting in impaired immune function and reduced host resistance. The design and interpretation of experimental immunotoxicity studies and the investigation of clinical immunosuppression require consideration of the relationship between changes in the structure and/or function of discrete components of the immune system and holistic changes in the susceptibility to infectious and malignant disease. The other main way in which chemicals may cause adverse health effects secondary to interaction with the immune system is through stimulation of specific immune responses that result in allergic disease. Allergy to chemicals and proteins can take many forms, including allergic contact dermatitis, allergic sensitization of the respiratory tract (associated with rhinitis and/or asthma), systemic allergic reactions (associated frequently with drug treatment), and gastrointestinal disease. Here there is a need to distinguish between immunogenic responses per se and those immune responses that are of sufficient vigor and of the quality necessary to provoke allergic sensitization. The purpose of this article is to explore the extent to which distinctions can be drawn between adverse and nonadverse effects in the context of immunotoxicity and allergy.

Threshold of toxicological concern for chemical substances present in the diet: a practical tool for assessing the need for toxicity testing

The de minimis concept acknowledges a human exposure threshold value for chemicals below which there is no significant risk to human health. It is the underlying principle for the US Food and Drug Administration (FDA) regulation on substances used in food-contact articles. Further to this, the principle of Threshold of Toxicological Concern (TTC) has been developed and is now used by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in their evaluations. Establishing an accepted TTC would benefit consumers, industry and regulators, since it would preclude extensive toxicity evaluations when human intakes are below such threshold, and direct considerable time and cost resources towards testing substances with the highest potential risk to human health. It was questioned, however, whether specific endpoints that may potentially give rise to low-dose effects would be covered by such threshold. In this review, the possibility of defining a TTC for chemical substances present in the diet was examined for general toxicity endpoints (including carcinogenicity), as well as for specific endpoints, namely neurotoxicity and developmental neurotoxicity, immunotoxicity and developmental toxicity. For each of these endpoints, a database of specific no-observed-effect levels (NOELs) was compiled by screening oral toxicity studies. The substances recorded in each specific database were selected on the basis of their demonstrated adverse effects. For the neurotoxicity and developmental neurotoxicity databases, it was intended to cover all classes of compounds reported to have either a demonstrated neurotoxic or developmentally neurotoxic effect, or at least, on a biochemical or pharmacological basis were considered to have a potential for displaying such effects. For the immunotoxicity endpoint, it was ensured that only immunotoxicants were included in the database by selecting most of the substances from the Luster et al. database, provided that they satisfied the criteria for immunotoxicity defined by Luster. For the developmental toxicity database, substances were selected from the Munro et al. database that contained the lowest NOELs retrieved from the literature for more than 600 compounds. After screening these, substances showing any effect which could point to developmental toxicity as broadly defined by the US were recorded in the database. Additionally, endocrine toxicity and allergenicity were addressed as two separate cases, using different approaches and methodology. The distributions of NOELs for the neurotoxicity, developmental neurotoxicity and developmental toxicity endpoints were compared with the distribution of NOELs for non-specific carcinogenic endpoints. As the immunotoxicity database was too limited to draw such a distribution of immune NOELs, the immunotoxicity endpoint was evaluated by comparing immune NOELs (or LOELs-lowest-observed-effect levels-when NOELs were not available) with non-immune NOELs (or LOELs), in order to compare the sensitivity of this endpoint with non-specific endpoints. A different methodology was adopted for the evaluation of the endocrine toxicity endpoint since data currently available do not permit the establishment of a clear causal link between endocrine active chemicals and adverse effects in humans. Therefore, this endpoint was analysed by estimating the human exposure to oestrogenic environmental chemicals and evaluating their potential impact on human health, based on their contribution to the overall exposure, and their estrogenic potency relative to endogenous hormones. The allergenicity endpoint was not analysed as such. It was addressed in a separate section because this issue is not relevant to the overall population but rather to subsets of susceptible individuals, and allergic risks are usually controlled by other means (i.e. labelling) than the Threshold of Toxicological Concern approach. (ABSTRACT TRUNCATED)

Immunotoxicological examination of repeated dose combined exposure by dimethoate and two heavy metals in rats

The immunotoxicity of 28 days combined oral exposure by dimethoate (DM) and two heavy metals (Pb or Cd) was investigated in male Wistar rats. Immunotoxic and no-effect doses of DM (28.2 and 7.04 mg/kg) were combined with immunotoxic and no-effect doses of CdCl2 (6.43 and 1.61 mg/kg) or lead acetate (80.0 and 20.0 mg/kg) in such a way that the high dose of each substance was given in combination with the no-effect dose of the other. To examine the interactions of these agents, general toxicological (body weight gain, organ weights), haematological (absolute and differential WBC, RBC, MCV, Ht. cell content of the femoral bone marrow), and immune function (splenic PFC number. DTH reaction) parameters were measured. Treatment with the combination of Pb or Cd and DM did not result in a reduction of humoral (PFC) and cellular (DTH) immune responses, whereas treatment with the substances alone did result in immune suppression. This protecting effect can probably be attributed to an effect on the kinetics of the compounds tested rather than on the immune system itself. Further interactions were found in both combinations, DM-Cd and DM-Pb, in the body weight gain and in the relative liver weight; the DM-Pb combination also affected the relative thymus weight and the MCV value. These findings show that the immunotoxic effects of the investigated materials, including their detectability and health consequences, can be modified in case of combined exposure.

Epidemiology studies in immunotoxicity evaluations

Studies in humans designed to detect immunomodulation from exposure to xenobiotics present challenging problems to epidemiologists and immunotoxicologists. Exposed and control groups must be carefully selected, exposure to the xenobiotic must be sufficiently high and well-documented, and the referent group should be as similar as possible to the exposed. Immune markers/functional tests in an individual may be influenced by sunlight exposure, medication, illness and use of recreational drugs; all of these potential confounding factors must be addressed. Sample acquisition is usually performed at sites geographically distant from the controlled environment of an investigator's laboratory, yielding an assortment of new problems that would not occur in clinical or hospital situations. Regulations and guidelines concerning the transport of biological samples and potential hazards of HIV and HBV exposures to personnel must be adapted to field conditions. Since the application of immunotoxicological techniques to populations exposed to xenobiotics is relatively new, and the ability to measure an increasing number of immune biomarkers of activation, suppression, autoimmunity or hypersensitivity is rapidly expanding, there are difficulties in the interpretation of statistically positive results (sometimes within the normal range) and their potential health significance. Finally, both biological and methodological factors complicate the assessment of dose-response/concentration effect relationships in human immunotoxicity studies, and traditional dose-response relationships may not always be present.

Further evaluation of the incorporation of an immunotoxicological functional assay for assessing humoral immunity for hazard identification purposes in rats in a standard toxicology study

A previous study (Ladics et al., 1995) conducted in our laboratory using the known immunosuppressant agent, cyclophosphamide, indicated that a functional assay for assessment of humoral immunity may be conducted in rats in a standard toxicology study. The objective of this study was to further examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats in a standard toxicology study using a chemical, carbon tetrachloride (CCl4), whose principal target organ of toxicity is not the immune system. Specifically, the previous study and this study were done to determine whether the conduct of an assay for assessing humoral immune function would affect standard toxicological endpoints. Male CD rats were untreated or dosed orally for 30 or 90 days, excluding weekends, with vehicle or 12.5 or 25 mg/kg CCl4. Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC) for assessment of humoral immune function. One day prior to necropsy, blood for hematological and clinical chemical measurements was collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and later examined microscopically. One-half of each spleen was used to assess spleen cell numbers and quantitate lymphocyte subsets (Thelper; Tcyt/sup; total T- and B-cells) by flow cytometry. Serum was analyzed for anti-SRBC IgM antibody by using an enzyme-linked immunosorbent assay. Administration of 12.5 and 25 mg/kg CCl4 for 30 days decreased SRBC-specific serum IgM levels 42 and 45%, respectively, while 25 mg/kg CCl4 for 90 days increased SRBC-specific IgM levels by 50%. CCl4 did not alter splenic lymphocyte subset numbers nor the weight nor morphology of lymphoid organs. Exposure to 25 mg/kg CCl4 did increase liver weight and serum sorbitol dehydrogenase levels, as well as produce centrilobular fatty change. SRBC administration did not alter any hematological or clinical chemistry parameters, nor lymphocyte subset numbers. With the expected exception of the spleen (slight increase in number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the rather mild hepatotoxic effects of CCL4 exposure observed in this study. Based on these and previous findings, it appears that a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study without altering standard toxicological endpoints.

Immunotoxicological effects of benzene inhalation in male Sprague-Dawley rats

The inhalation of benzene is toxic to various components of the immunologic system in rodents. Spleen and thymus weights, total spleen and femur marrow cell counts, enumeration of spleen B- and T-lymphocytes, and an assessment of humoral immunocompetence, were used to evaluate the immunotoxicity of benzene in male Sprague-Dawley rats. Rats were exposed to 0, 30, 200 or 400 ppm benzene for 6 h/day, 5 days/week for 2 or 4 weeks. An early indicator of immunotoxicity was a reduction in the number of B-lymphocytes after 2 weeks of 400 ppm. After 4 weeks of 400 ppm, there was a reduction in thymus weight and spleen B-, CD4+/CD5+ and CD5+ T-lymphocytes. Rats exposed to 30, 200 or 400 ppm benzene for 2 or 4 weeks and challenged with sheep red blood cells developed a humoral response comparable to that of the control (0 ppm) animals. Enumeration of spleen T- and B-lymphocytes in rats exposed to benzene and challenged with SRBC showed only a transient reduction in spleen B-lymphocytes after 2 weeks of exposure to 400 ppm. These data suggest that there are no immunotoxicological effects of exposure to 200 ppm benzene or less, in rats exposed for 6 h/day, 5 days/week for 2 or 4 weeks.

An immunotoxicity screening study on salmeterol in rats

Salmeterol, a long-acting beta 2-adrenoreceptor agonist without known immunotoxicity, was studied in a 28-day repeated dose toxicity test in Wistar rats. Several immunotoxicity screening parameters were incorporated in the study protocol to investigate the immunotoxic potential of the compound. Male rats were orally treated with 0, 0.2, 2 and 20 mg salmeterol/kg body weight/day. At the 20 mg/kg/day dose level, intubation errors occurred because the animals tried to resist intubation. Some of these animals died intercurrently. Therefore, the magnitude of the dose was lowered to 10 mg/kg/day at day 9 of treatment. Body weight and bone marrow cellularity were not affected. Hematological parameters were not altered either, except for platelet counts, that were decreased at all dose levels. Also liver weights were decreased at all dose levels tested. Absolute thymic weights were decreased at the 2 and 20/10 mg/kg/day dose levels. No treatment-related (histo)pathological lesions were seen in the (non)lymphoid organs. Serum IgM levels were increased at the 0.2, and IgG at the 2 and 20/10 mg/kg/day dose levels, respectively. B cell numbers in the spleen were decreased at all dose levels tested. The data indicate that the test battery applied to salmeterol is able to detect low immunotoxic potential. Further research is needed to elucidate whether salmeterol interferes with immune responses in rats upon antigenic challenge.

Pathology considerations for, and subsequent risk assessment of, chemicals identified as immunosuppressive in routine toxicology

Several proposals have been made with the aim of assisting in the early identification of chemicals with immunotoxic potential. The Organisation for Economic Cooperation and Development is now likely to incorporate enhanced immunopathology into the test guideline for the 28-day rat study, which may be regarded as a Tier I investigation. However, no guidelines have yet been proposed either for how the new data generated will be evaluated, or for how a subsequent risk assessment will be made. In this paper, considerations for the immunopathological assessment of the thymus, spleen, lymph nodes and bone marrow are described, together with comments on haematological and organ weight changes that may be associated with immunotoxicity. Their interpretation will depend on the doses at which changes are manifest, the quantity and quality of the effects observed and the presence and severity of other forms of toxicity. Lastly, risk assessment and the approach to Tier II testing in immunotoxicity is discussed. It is concluded that much of this work must be on a case-by-case basis, but should not in principle differ from the approach adopted for any other type of toxicity identified ina 28-day study.

Possible incorporation of an immunotoxicological functional assay for assessing humoral immunity for hazard identification purposes in rats on standard toxicology study

The objective of this study was to examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats on standard toxicology study. Male CD rats were untreated or dosed intraperitoneally daily for 30 or 90 days, excluding weekends, with vehicle or 2 mg/kg cyclophosphamide (CY). Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC). One day prior to necropsy, blood samples for hematological and clinical chemical measurements were collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and examined microscopically. One-half of each spleen was used to prepare a single cell suspension in order to assess spleen cell numbers. Serum was analyzed for anti-SRBC IgM antibody using an enzyme-linked immunosorbent assay. A second set of studies was performed to examine further the effect of SRBC administration on lymphoid organ weights using 30- and 90-day study age-equivalent naive male CD rats. Exposure of animals to 2 mg/kg CY for 30 or 90 days resulted in a 28% and 61% decrease, respectively, in SRBC-specific serum IgM levels. CY treatment also caused mild alterations in some leukocytic parameters, with significant decreases of 35% and 33% in white blood cell and lymphocyte counts, respectively, observed in 30-day CY-treated animals receiving SRBC. Injection of SRBC alone did not alter hematological or clinical chemistry parameters. With the expected exception of the spleen (increased number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the immunosuppressive effects of CY treatment under the conditions of this study. Based on our preliminary findings, a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study.

Immunologic analyses of peripheral leukocytes from workers at an ethical narcotics manufacturing facility

Little information exists about possible adverse health effects associated with workplace exposure to opiate compounds. We have previously reported opiate-specific IgG antibodies, positive epicutaneous tests, and pulmonary function decrements in workers exposed occupationally to opiates. In the present work, we extended these findings to investigate the effect of occupational opiate exposure on lymphocyte subpopulations and mitogen-induced lymphoblastogenesis. Thirty-three opiate-exposed workers and 8 nonexposed control workers were evaluated for lymphocyte subpopulation absolute numbers and percentages, by evaluating cell surface antigen expression with flow cytometry. A complete blood count with differential, common clinical chemistry parameters, and serum immunoglobulin levels were also evaluated. Opiate-exposed workers showed significantly (p < .05) increased absolute numbers and percentages of HLA-DR+ cells (MHC class II histocompatibility antigen), significantly (p < .01) decreased percentages of T helper-inducer (CD4+) cells, and significantly (p < .05) decreased numbers of basophils, compared with nonexposed opiate workers from the same factory. A trend toward reduction in the T helper-inducer (CD4+)/T cytotoxic-suppressor (CD8+) lymphocyte ratio was also evident. There was also a significant decrease in lymphocyte activity stimulated by pokeweed mitogen (p < .05) in opiate-exposed workers. These data indicate that occupational opiate exposure may change the number and types of circulating peripheral blood leukocytes, or alternatively, alter the expression of receptors on the surface of these cells. In addition, occupational opiate exposure appears to decrease the sensitivity of B-cells to pokeweed mitogen stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of smoking and high experimental exposure to environmental tobacco smoke (ETS) on the immune system

Controversial results have been published on the immune response to cigarette smoking while the effects of exposure to environmental tobacco smoke (ETS) have not yet been reported. In a controlled study, acute effects of smoking and of a high environmental exposure to ETS on immunological parameters have been investigated. The study consisted of four experimental days, two control and two exposure days. On control days, 1 and 3, smokers (n = 5) and nonsmokers (n = 5) sat in an unventilated 45 m3 room for 8 h. On the exposure days, 2 and 4, each of the smokers smoked 24 cigarettes in 8 h, while the nonsmokers were exposed to the ETS generated by the smoking volunteers. Blood was drawn before and after each exposure session on all four experimental days for dosimetry of tobacco smoke exposure and determination of the immune response. Flow cytometry using monoclonal antibodies was used to determine CD3+ cells (whole T cells), CD19+ cells (B lymphocytes), CD16+ and CD56+ cells (natural killer cells), CD4+ cells (T-helper cells), CD8+ cells (T-suppressor cells), the CD4+/CD8+ (helper/suppressor ratio), and Fc receptors on granulocytes. Serum was analyzed for soluble CD14 receptors (sCD14), interleukin 1, interleukin 6 and prostaglandin E2 (PGE2). Functional stimulation assays were performed to determine the basal and induced level of reactive oxygen intermediate (ROI) production by polymorphic neutrophils. Exposure to tobacco smoke in both groups was confirmed by dosimetry of carboxyhemoglobin, plasma nicotine, and cotinine levels. In comparison to nonsmokers, smokers had elevated granulocyte cell counts, increased CD16+ and CD56+ cell levels and decreased CD3+ and CD19+ levels. Acute smoking, but not exposure to ETS, resulted in a slight decrease in the number of CD19+ cells and an increase in the number of granulocytes; the latter was restricted to one subject. Acute smoking and exposure to high experimental concentrations of ETS resulted in a slight increase in CD16+ and CD56+ cells. None of the changes determined in immunological parameters after either acute smoking or exposure to ETS reached statistical significance. Serum sCD14, cytokine and PGE2, functional stimulation of in vitro ROI production, and changes in Fc receptors were not affected by acute smoking or exposure to ETS. Although no clear guidelines exist to assess immunotoxicity in man, our data do not favor immunosuppression and the possibility of increased risk of infection in nonsmokers exposed to ETS under real-life conditions.

The identification of chemicals with sensitizing or immunosuppressive properties in routine toxicology

In the context of this paper, immunotoxicity is taken to encompass immunosuppression/immunopotentiation and allergy. Over the last 10 to 15 years, well characterized methods for the assessment of altered immune competence have been reported. This has led to proposals for tiered testing schemes. This review examines the suitability of immunotoxicity parameters for inclusion in routine 28-day studies and comments on methods that have been proposed for incorporation within the guidelines issued by the US FDA and US EPA and OECD. It is recommended that the existing OECD Guideline 407 is modified to incorporate total and differential blood cell counts, spleen and thymus weight and histopathology, and draining and distal lymph node histopathology for Tier I level testing. Data so generated will provide a reliable and accurate means of identifying at an early stage potential immunotoxic effects. Tier II testing should be carried out on a case by case basis and only assuming positive results are obtained at Tier I. An increasingly sophisticated understanding of the nature of immune responses to chemical allergens has facilitated the design of novel predictive methods for the identification of sensitizing activity. Opportunities which arise from these new developments in allergy testing such as the local lymph node assay, mouse ear swelling test, and the mouse IgE test should be monitored closely.

Human immune toxicity

This review examines xenobiotic toxicity to the immune system, stressing in particular those aspects of most relevance to humans. Immunotoxicity is examined especially from three points of view: by what immunological component is affected, by classes of foreign agents that adversely affect the human immune system and by critical evaluation of human case reports and epidemics. Mechanisms by which xenobiotics interrupt cytokine networks are emphasized. The concept that microbial agents, both environmental as well as infectious, may act as immunotoxicants, either alone or in synergism with conventional agents is introduced. Instances of human immunotoxicology are critically evaluated in terms of clinical relevance, i.e. whether increased susceptibility to opportunistic infections or tumor emergence takes place in the affected individuals.

Methyl mercury exposure via placenta and milk impairs natural killer (NK) cell function in newborn rats

The effect of methyl mercury (MeHg) exposure (3.9 micrograms/g diet) on the development of immune function was studied in the newborn Sprague-Dawley rat after MeHg exposure via placenta and/or milk. No consistent alterations were observed between control and treated offspring (at the age of 15 days) on the following parameters: body weights, lymphoid organ weights or cell number, and the lymphoproliferative response to B-cell mitogen. The lymphoproliferative response to T-cell mitogen was increased in thymocytes (by 30-48%), but decreased in splenocytes (by 30-32%). This decreased activity was only observed in the groups exposed during lactation. White blood cell counts (WBC) were increased in all groups. Natural killer (NK) cell activity was reduced (by 42%, P less than 0.01) in the group that was exposed both via placenta and milk. These results indicate that placental and lactational transfer of MeHg does adversely affect the developing immune system of the rat.

Immunotoxic effects of hexachlorobenzene on the pathogenesis of systemic, pneumonic and hepatic virus infections in the mouse

A quantitative histopathological method has been developed for the evaluation of the effects of hexachlorobenzene (HCB) on the pathogenesis of three virus infections in the mouse. Hexachlorobenzene was selected because a substantial amount of immunotoxicological data already exists with which we could compare our results. To establish the validity of the method a systemic virus infection (mouse cytomegalovirus, MCMV), a pneumonia causing virus (pneumonia virus of mice, PVM) and a hepatitis virus (mouse hepatitis virus, MHV) were used. We have compared the existing data with the actual pathological effects of hexachlorobenzene on virus disease processes, to gain a more realistic idea of the value of the risk assessment to be derived from extrapolating the in-vitro data in particular, to the in-vivo situation. The results show that the data derived from previous studies on the immunotoxicity of HCB were accurate in predicting the exacerbation of the viral hepatitis, especially in immunodeficient athymic 'nude' mice. It is proposed that this histopathological technique could be a useful technique in the evaluation of host resistance changes following exposure to potentially immunotoxic compounds, but caution will have to be exercised in interpretation in relation to human disease.