In vivo and in vitro Ah-receptor activation by commercial and fractionated pentabromodiphenylether using zebrafish (Danio rerio) and the DR-CALUX assay.

The present study addresses the toxicity of a commercial pentabrominated diphenylether (PeBDE) flame retardant mixture, DE-71, in a model aquatic vertebrate. Four weeks' exposure of juvenile zebrafish (Danio rerio) to water-borne DE-71 resulted in dose-dependent induction of CYP1A immunoreactivity, predominantly in the endocardium and the endothelium of larger blood vessels, such as ventral aorta and branchial arteries, as well as the larger hepatic and pancreatic blood vessels. To investigate the impact of possible contaminating PBDD/Fs in the DE-71 product, the study was repeated after DE-71 had been fractionated into a non-planar (cleaned PBDEs) and a planar fraction (PBDD/Fs). Zebrafish were exposed under similar conditions to the planar and cleaned DE-71 fractions, and to uncleaned DE-71. In addition, the above fractions were chemically analyzed and tested in a reporter gene assay (DR-CALUX) for their aromatic hydrocarbon-receptor (AhR) stimulating potencies. A relatively strong CALUX response was detected from the planar DE-71 fraction (19.7ng TCDD equivalent (TEQ)/g DE-71), coinciding with a strong induction of CYP1A immunoreactivity in zebrafish. CYP1A immunoreactivity in zebrafish exposed to uncleaned DE-71 was intense, although the CALUX response was 10-fold less compared to the planar fraction. Only weak CYP1A immunoreactivity was found in fish exposed to cleaned DE-71, and none in control animals; no CALUX response was detected in cleaned DE-71. The present findings indicate that chemical impurities of the commercial PeBDE product account for AhR-mediated effects. Analytical isolation of a planar fraction from the commercial product increased the in vitro (DR-CALUX) signal 10 times. Immunohistochemistry showed a strong tissue specific reaction to DE-71 in vivo at these relatively low TEQ levels regardless of chemical pretreatment of the mix, reflecting the sensitivity of CYP1A induction in juvenile zebrafish to AhR agonists.

Antitumor effect, cardiotoxicity, and nephrotoxicity of doxorubicin in the IgM solid immunocytoma-bearing LOU/M/WSL rat.

Antitumor activity, cardiotoxicity, and nephrotoxicity induced by doxorubicin were studied in LOU/M/WSL inbred rats each bearing a transplantable solid IgM immunocytoma. Animals with a tumor (diameter, 15.8 +/- 3.3 mm) were treated with iv injections of doxorubicin on 5 consecutive days, followed by 1 weekly injection for 7 weeks (dose range, 0.015-4.0 mg/kg body wt). Tumor regression was observed with 0.5 mg doxorubicin/kg. Complete disappearance of the tumor was induced with 1.0 mg doxorubicin/kg. Histologic evidence of cardiotoxicity scored as grade III was only observed at a dose of 1.0 mg doxorubicin/kg. Light microscopic evidence of renal damage was seen above a dose of 0.5 mg doxorubicin/kg, which resulted in albuminuria and very low serum albumin levels. In the group that received 1.0 mg doxorubicin/kg, the serum albumin level decreased from 33.6 +/- 4.1 to 1.5 +/- 0.5 g/liter. Ascites and hydrothorax were observed simultaneously. The same experiments were performed with non-tumor-bearing rats, in which no major differences were observed. In conclusion, antitumor activity, cardiotoxicity, and nephrotoxicity were studied simultaneously in the same LOU/M/WSL rat. Albuminuria due to renal damage led to extremely low serum albumin levels, so ascites and hydrothorax were not necessarily a consequence of the observed cardiomyopathy.

Time-course study on doxorubicin-induced nephropathy and cardiomyopathy in male and female LOU/M/Wsl rats: lack of evidence for a causal relationship.

In a previous study on doxorubicin-induced cardiotoxicity in LOU/M/Wsl rats, severe nephropathy has been observed; therefore, the question was raised whether nephropathy adds to or even might be responsible for doxorubicin-induced cardiomyopathy in rats. For elucidation of this question, the temporal relationship between the onset of doxorubicin-induced cardiomyopathy and nephropathy was studied. In addition, examination was made of whether modifications of the treatment schedule could circumvent nephrotoxicity. Because preliminary studies had shown that female LOU/M/Wsl rats developed less doxorubicin-induced albuminuria, both male and female LOU/M/Wsl rats were treated with an iv dose of 1 mg doxorubicin/kg (body wt)/rat on five consecutive days and then weekly. Saline-treated animals served as controls. Albuminuria, serum albumin, and serum creatine levels were assessed weekly. For histologic examination, 5 male and 5 female rats were killed weekly. At day 14 and thereafter, doxorubicin-treated male rats showed albuminuria greater than or equal to 10 g/liter. Albuminuria of greater than or equal to 10 g/liter was not avoided by modifications of the treatment schedule. Female rats had on day 14 a urinary albumin level of 1.0-3.0 g/liter, yet reaching the level of greater than or equal to 10 g/liter at day 49. In male rats serum albumin levels decreased to levels below 10 g/liter (p less than .001 vs. finding for day 0); in contrast female rats maintained constant serum albumin levels till day 49. Serum creatine levels showed a tendency to rise, the values of male rats not being measured after day 28 due to hyperlipidemia; the levels of female rats increased from 37.8 +/- 3.0 mumol/liter to 53.7 +/- 2.5 mumol/liter on day 49 (P less than .001). At day 10 in male and female rats a grade 1-1.5 cardiomyopathy score, assessed according to the modified Billingham scoring system, was found, gradually increasing to grade 2.5-3 cardiomyopathy, both in males and females, on day 49. In male LOU/M rats the nephropathy developed steadily from day 14 and thereafter, whereas in females the rate of development of kidney damage was slower and at the end point of the study the severity of kidney lesions was less in comparison to that of the males. The onset of cardiomyopathy and nephropathy was simultaneous. It was concluded that cardiomyopathy observed in LOU/M rats is a phenomenon independent of nephropathy.

Antitumor activity, induction of cross-resistance, and nephrotoxicity of a new platinum analogue, cis-1,1-diaminomethylcyclohexaneplatinum(II) sulfate, and of cis-diamminedichloroplatinum(II) in an immunocytoma model in the LOU/M rat.

A newly synthesized platinum analogue, cis-1,1-diaminomethylcyclohexaneplatinum(II) sulfate (TNO-6), was compared with cis-diamminedichloroplatinum(II) (cis-DDP) for antitumor activity and nephrotoxicity. Antitumor activity was determined in an IgM immunocytoma model in the LOU/M rat. Tumor cells were inoculated on the left flank, and therapy was started when a tumor diameter of 10 to 30 mm was reached. At the start of the therapy, the primary tumor had already metastasized to the draining lymph node and liver. Both platinum compounds, dissolved in 5% glucose water, induced an almost complete tumor regression within 10 to 14 days (average, 84% tumor load reduction) and prolonged survival, compared to that of nontreated animals. The antitumor activity induced by repeated i.p. administration of cis-DDP and TNO-6 reached its maximum at a dose of 1.0 mg/kg body weight (twice a week for 7 weeks). This treatment regimen resulted in a highest tolerable dose for cis-DDP of 1.0 mg/kg and for TNO-6 of 2.0 mg/kg. However, when rats were treated with a 2.0-mg/kg dose of TNO-6, no increase in antitumor activity was obtained. For both platinum compounds, tumor recurrence occurred in almost all animals within 2 to 7 days after the maximum tumor load reduction. Tumors that recurred were found to be cross-resistant to both platinum compounds tested but were sensitive to treatment with doxorubicin (Adriamycin). With regard to toxicity, repeated administration of TNO-6 (1.0 mg/kg twice a week for 7 weeks) induced less decrease of body weight than did cis-DDP. For TNO-6, even in the highest dose investigated (2.0 mg/kg twice a week for 7 weeks), no nephrotoxicity was observed on histological examination of kidney and blood urea and creatinine values, whereas for cis-DDP nephrotoxicity was still present in the lowest dose investigated (0.5 mg/kg). From the comparison of the antitumor activity and nephrotoxicity of TNO-6 and cis-DDP, administered i.p. in 5% glucose solution, it is concluded that both drugs have comparable antitumor activity and potency. In contrast to the effects of cis-DDP, no nephrotoxicity was observed with TNO-6; thus, TNO-6 might be a good alternative to cis-DDP in avoiding nephrotoxicity during platinum therapy.

Probiotic effects of Lactobacillus casei on DSS-induced ulcerative colitis in mice.

We tested the effect of Lactobacillus casei strain Shirota (LcS) on the murine model of ulcerative colitis induced by dextran sodium sulphate. The effect of LcS was tested either as a prophylactic 10 days before the onset of the disease, simultaneously with ulcerative colitis induction or continued 10 days after the disease was induced. LcS was not able to prevent the disease induction in any of the experiments. However, important clinical parameters including blood anemia indicators, body weight, and organ weight were improved in the animals receiving LcS as compared with the ulcerative colitis-induced controls. Increased colonic epithelial regeneration in the LcS treated animals was observed in the chronic stage. The results seemed better for the simultaneous short LcS treatment where some parameters remained similar to the PBS controls, including disease activity scores measured in the acute stage. We can conclude that although LcS alone cannot prevent the induction of ulcerative colitis by dextran sodium sulphate, it can improve the clinical condition of the mice. This could imply important biological consequences for the human situation. Further studies including LcS or other probiotic bacteria together with the available treatment are encouraged.

The use of tannic acid fixation for the electron microscope visualization of fluorochrome-labelled antibodies attached to cell surface antigens.

Tannic acid as a prefixative for EM purposes was introduced by Futaesaku et al. (1972). The fixative creates conditions for enhancing electron density of different protein materials. By using a mixture of tannic acid and glutaraldehyde as prefixative, followed by a routine procedure of postfixation (OsO4) and poststaining (uranylacetate and lead citrate), membrane bound antibodies not conjugated with electron dense markers are made visible under the electron microscope.

Use of the enzyme-linked immunosorbent assay (ELISA) in immunotoxicity testing.

Based on an earlier described macromethod for the routine measurement of IgM and IgG in rat sera, a mechanized micro enzyme-linked immunosorbent assay (ELISA) was developed. The assay was performed in the wells of microtiter plate thus minimizing the quantities of reagents and antisera needed. Data on reproducibility of the assay and calculation of IgM and IgG levels are provided. For the functional assessment of the humoral immunity of the rat, ELISA is a powerful tool. In an earlier report, assays for the titration of thymus-independent IgM antibodies to E. coli LPS and the IgM and IgG response to the thymus-dependent antigen tetanus toxoid were described. More recently it was shown that the antigen ovalbumin elicits a thymus-dependent IgM, IgG and IgE response which could be readily measured with the enzyme immunoassay, as well as a delayed-type hypersensitivity reaction. As the optimum ovalbumin concentration for both types of reactions was the same, it is concluded that the ovalbumin model offers the advantage that both humoral and cellular immunity can be studies simultaneously in the same animal.

The role of the immune system in hexachlorobenzene-induced toxicity.

Hexachlorobenzene (HCB) is a persistent environmental pollutant. The toxicity of HCB has been extensively studied after an accidental human poisoning in Turkey and more recently it has been shown that HCB has immunotoxic properties in laboratory animals and probably also in man. Oral exposure of rats to HCB showed stimulatory effects on spleen and lymph node weights and histology, increased serum IgM levels, and an enhancement of several parameters of immune function. Moreover, more recent studies indicate that HCB-induced effects in the rat may be related to autoimmunity. In Wistar rats exposed to HCB, IgM antibodies against several autoantigens were elevated; in the Lewis rat, HCB differently modulated two experimental models of autoimmune disease. Oral exposure of rats to HCB induces skin and lung pathology in the rat. Recently several studies have been conducted to investigate whether these skin and lung lesions can be related to HCB-induced immunomodulation, and these studies will be discussed in this review. HCB-induced skin and lung lesions probably have a different etiology; pronounced strain differences and correlation of skin lesions with immune parameters suggest a specific involvement of the immune system in HCB-induced skin lesions. The induction of lung lesions by HCB was thymus independent. Thymus-dependent T cells were not likely to be required for the induction of skin lesions, although T cells enhanced the rate of induction and the progression of the skin lesions. No deposition of autoantibodies was observed in nonlesional or lesional skin of HCB-treated rats. Therefore, we concluded that it is unlikely that the mechanism by which most allergic or autoimmunogenic chemicals work, i.e., by binding to macromolecules of the body and subsequent T- and B-cell activation, is involved in the HCB-induced immunopathology in the rat. Such a thymus-independent immunopathology is remarkable, as HCB strongly modulates T-cell-mediated immune parameters. This points at a very complex mechanism and possible involvement of multiple factors in the immunopathology of HCB.

Impaired immunity in harbour seals (Phoca vitulina) exposed to bioaccumulated environmental contaminants: review of a long-term feeding study.

Mass mortalities among seals and dolphins inhabiting contaminated marine regions have led to speculation about a possible involvement of immunosuppression associated with environmental pollution. To evaluate whether contaminants at ambient environmental levels can affect immune function of seals, we carried out an immunotoxicological study under semifield conditions. Two groups of 11 harbour seals (Phoca vitulina) originating from a relatively uncontaminated area were fed herring from either the highly polluted Baltic Sea or the relatively uncontaminated Atlantic Ocean. Changes in immune function were monitored over a 2 1/2-year period. The seals that were fed contaminated Baltic herring developed significantly higher body burdens of potentially immunotoxic organochlorines and displayed impaired immune responses as demonstrated by suppression of natural killer cell activity and specific T-cell responses. During a 2-week fasting experiment performed at the end of the feeding study, mobilization of organochlorines from the blubber did not lead to a strong increase of contaminant levels in the blood, and no enhancement of the existing immunosuppression was observed. These results demonstrate that chronic exposure to environmental contaminants accumulated through the food chain affects immune function in harbour seals, whereas short-term fasting periods, which are normal for seals, do not seem to pose an additional risk. The seals of this study were not exposed perinatally to high levels of environmental chemicals, and body burdens of organochlorines measured near the end of the study were lower than those generally observed in free-ranging seals inhabiting many contaminated regions. Therefore, it may be expected that environmental contaminants adversely affect immune function of free-ranging seals inhabiting contaminated regions at least as seriously as observed in these studies.

Vaccine-induced antibody responses as parameters of the influence of endogenous and environmental factors.

In laboratory animals, an adequate way to assess effects of environmental exposures on the immune system is to study effects on antigen-specific immune responses, such as after sensitization to T-cell-dependent antigens. This probably also applies to testing effects in the human population. It has thus been suggested that antibody responses to vaccination might be useful in this context. Vaccination responses may be influenced by a variety of factors other than environmental ones. One factor is the vaccine itself; a second is the vaccination procedure used. In addition, the intrinsic capacity of the recipient to respond to a vaccine, which is determined by sex, genetic factors, and age, is important. Psychological stress, nutrition, and (infectious) diseases are also likely to have an impact. We reviewed the literature on vaccine response. With regard to exogenous factors, there is good evidence that smoking, diet, psychological stress, and certain infectious diseases affect vaccination titers, although it is difficult to determine to what extent. Genetic factors render certain individuals nonresponsive to vaccination. In general, in epidemiologic studies of adverse effects of exposure to agents in the environment in which vaccination titers are used, these additional factors need to be taken into consideration. Provided that these factors are corrected for, a study that shows an association of exposure to a given agent with diminished vaccination responses may indicate suboptimal function of the immune system and clinically relevant diminished immune response. It is quite unlikely that environmental exposures that affect responses to vaccination may in fact abrogate protection to the specific pathogen for which vaccination was performed. Only in those cases where individuals have a poor response to the vaccine may exogenous factors perhaps have a clinically significant influence on resistance to the specific pathogen. An exposure-associated inhibition of a vaccination response may, however, signify a decreased host resistance to pathogens against which no vaccination had been performed.

Contaminant-related suppression of delayed-type hypersensitivity and antibody responses in harbor seals fed herring from the Baltic Sea.

Recent mass mortalities among several marine mammal populations have led to speculation about increased susceptibility to viral infections as a result of contaminant-induced immunosuppression. In a 2.5-year study, we fed herring from either the relatively uncontaminated Atlantic Ocean or the contaminated Baltic Sea to two groups of captive harbor seals and monitored immune function in the seals. Seals fed the contaminated fish were less able to mount a specific immunological response to ovalbumin, as measured by in vivo delayed-type hypersensitivity (DTH) reactions and antibody responses. The skin reaction to this protein antigen was characterized by the appearance of mononuclear cells which peaked at 24 hr after intradermal administration, characteristic of DTH reactions in other animals studied. These DTH responses correlated well with in vitro tests of T-lymphocyte function, implicating this cell type in the reaction. Aryl-hydrocarbon (Ah) receptor-dependent toxic equivalent (TEQ) profiles in blubber biopsies taken from the seals implicated polychlorinated biphenyls rather than dioxins or furans in the observed immunosuppression. Marine mammal populations currently inhabiting polluted coastal environments in Europe and North America may therefore have an increased susceptibility to infections, and pollution may have played a role in recent virus-induced mass mortalities.

Quantification of total IgM and IgG and specific IgM and IgG to a thymus-independent (LPS) and a thymus-dependent (tetanus toxoid) antigen in the rat by enzyme-linked immunosorbent assay (ELISA).

Rat IgM and IgG was determined by mechanized "sandwich" enzyme-linked immunosorbent assay (ELISA) using peroxidase labeled anti-rat-IgM and -IgG. Linear ranges in standard curves of a reference rat serum had a slope similar to the slopes found with sera of 25 rats of various age. IgM and IgG measurements by ELISA in these sera correlated well with results obtained by single radial immuno-diffusion (SRID). In addition, the precision of the enzyme immunoassay was the same as obtained with the SRID. Compared with SRID, ELISA is less time consuming and the amount of antiserum used in the macro-ELISA is one order of magnitude lower; and again 10 times lower in the mechanized micro-ELISA that is currently being developed. In conclusion, the ELISA is a specific, reliable, sensitive, and economic method for routine measurement of rat serum IgG and IgM e.g. in toxicity studies. In the second part of this study, ELISA and the passive hemagglutination test were compared to determine the primary and secondary antibody response to E. coli lipopolysaccharide (LPS) and tetanus toxoid in rats. In the ELISA, the antigens were bound to the wells of polystyrene microplates. Tetanus toxoid was coated directly, LPS after complexing with methylated bovine serum albumin. After incubation with dilutions of the rat sera, the amount of antibody bound to the solid phase was quantified by means of peroxidase-labeled antiimmunoglobulin. The specificity of the enzyme immunoassay was tested by absorption of the sera with the respective antigens. ELISA proved to be more sensitive than the hemagglution reaction, except when titers were determined during the secondary response to tetanus toxoid. Besides its specificity and sensitivity, ELISA is a convenient method for measuring both IgM and IgG antibodies. Finally, evidence is presented that in the rat, the humoral immune response to LPS is a thymus-independent phenomenon. Thus, by using the antibody response to LPS and tetanus toxoid in function studies of the immune system of the rat, insight can be obtained in the thymus-independent and thymus-dependent humoral immune response.

Hexachlorobenzene-induced stimulation of the humoral immune response in rats.

Rats were fed diets containing 0, 500, 1000, and 2000 mg HCB/kg during a 3-week period. Marked weight increases of spleen, popliteal and mesenteric lymph nodes and of the liver were found. Histologically, the white pulp in the spleen was enlarged because of an increase in size of marginal zones and follicles. In addition, there was an increase of extramedullary hemopoiesis. In the lymph nodes, the number of high endothelial venules was increased at all dose levels. The number of neutrophils, basophils and monocytes in the peripheral blood was significantly increased, whereas peripheral lymphocyte counts were slightly higher. Total serum IgM levels were markedly increased, but IgG concentrations were unaltered. On the basis of this experiment, the 1000 mg HCB/kg diet level was chosen for the different function studies that were carried out after a 3-weeks dietary regimen. Regarding the humoral immunity, IgM antibodies to LPS were unaltered, whereas primary and secondary IgM and IgG antibody titers to tetanus toxoid were increased approximately three-fold. HCB did not significantly alter the cell-mediated immunity, as shown by the following parameters: resistance to Listeria monocytogenes infection, rejection of skin transplants, and delayed-type hypersensitivity to tuberculin. The phagocytizing capacity of macrophages was studied by measuring the blood clearance of carbon particles. HCB did slightly depress the phagocytic index, but the difference with control animals was statistically not significant. The in vitro responsiveness of thymus cells to the mitogens PHA, Con A, and PWM was not changed by in vivo HCB-treatment. On a cell-for-cell basis, the responsiveness of spleen cells was increased when cultured in the presence of LPS. On a whole organ basis, the response to PHA, Con A, PWM, and LPS was markedly enhanced because of an increase in the number of nucleated spleen cells. Regarding peripheral lymphocytes, only the response to the mitogen Con A was higher. On the basis of these studies it is concluded that HCB stimulates the humoral immune response in the rat, enhances the in vitro responsiveness of spleen cells to the different mitogens mainly as a result of an increase in the number of splenic lymphocytes, but does not alter the cell-mediated immunity as shown with in vivo tests. This result contrasts with data in the literature that show that HCB suppresses the humoral and cell-mediated immunity in mice. Finally, HCB pretreatment only marginally increased the susceptibility of rats to endotoxin, whereas mice have been shown to be 20-fold more susceptible to the lethal effects of bacterial endotoxin.

Effects of small doses of dioxins on the immune system of marmosets and rats.

There is no doubt that TCDD is capable of inducing effects on a variety of components and functions of the immune system in a variety of species. In fact, such changes seem to belong to the most sensitive variables affected by TCDD. Some of the biological effects, induced at rather high doses of TCDD exhibiting general toxicity (> 3 micrograms TCDD/kg body wt), may be considered unspecific or the result of the pronounced thymus involution. However, other effects (such as that on lymphocyte subtype patterns in marmosets or a reduced resistance of mice to influenza viruses) have been reported to occur at dose levels far from those leading to thymic involution or general toxicity. It should be remembered that the pathognomonic relevance for man of subtle modifications in the pattern of lymphocyte surface receptors is largely unknown. Until now, such deviations are considered rather as biological phenomena than indications or causes of specific diseases. Nevertheless, such changes represent clear-cut biological effects induced by TCDD. Since effects of TCDD on components and defined functions of the immune system have been revealed in several species, it would be surprising if humans were largely resistant to such effects, but reliable data in humans with high exposures to defined dioxins verified by an appropriate quantification of the exposure are scarce as of now. Data published so far have not revealed pronounced alterations of such variables. However, no studies of well-defined human populations with quantified body burdens have been performed with modern methods (such as flow cytometry) analyzing a wide variety of surface receptors. Performance of such studies is essential for a better and reliable risk assessment, and the technology is available. Some of the effects observed (such as the changes in the pattern of lymphocyte subpopulations) must certainly be considered as biological effects induced by TCDD, and the situation is similar to the induction of hepatic monooxygenases, which are also observable in this dose range. However, the relevance of such changes with respect to adverse health effects in humans is presently difficult to judge in the absence of clear-cut functional deficits demonstrated so far either in vivo or in vitro.

Detection of immunotoxicity of benzo[a]pyrene in a subacute toxicity study after oral exposure in rats.

In an extended OECD 407 study protocol, including immune parameters, male Riv:Tox Wistar SPF rats were treated for 35 days with benzo[a]pyrene (B[a]p) (3, 10, 30, or 90 mg/kg body weight) by gavage. Oral administration of B[a]p in rats resulted not only in general toxicity, as indicated by the effects on body weight, but also in immunotoxicity, as indicated by the effects on bone marrow, thymus, spleen, and lymph nodes. Oral B[a]p induced a dose-related decrease in thymus weight (at 10, 30, and 90-mg/kg). Lymph node weights (popliteal, mandibular, and mesenteric) were decreased in the 90-mg/kg rats only. Histologically, indications for cortical atrophy were noted in the thymuses of the 30- and 90-mg/kg dose groups, which was confirmed by morphometric analysis. Nucleated spleen and bone marrow cell counts were decreased in the 90-mg/kg group. Both the absolute number (90 mg/kg) and relative number (10, 30, and 90 mg/kg) of B cells in the spleen were decreased. Red blood cell (RBC) and white blood cell (WBC) counts were significantly decreased; for the WBC at 90 mg/kg, and for the RBC at 10, 30, and 90 mg/kg. The absolute number of lymphocytes and eosinophilic granulocytes was decreased in the 90-mg/kg group, while the absolute number of monocytes was increased in the 10- and 30-mg/kg dose groups. Serum immunoglobulin levels showed a decrease of IgM and IgA after treatment of the animals with 30 and 90 mg/kg, respectively. The highest dose of B[a]p treatment (90 mg/kg) resulted in a significant decrease of natural killer (NK)-cell activity in the spleen. Most toxic effects were only observed in the highest-dose group (90 mg/kg), but compared to the general toxicity, some parameters indicating immunotoxic effects were also affected at lower doses (10 and 30 mg/kg). In conclusion, immunotoxicity of B[a]p can be detected using parameters of the immune system such as described in the recently updated OECD 407 guideline. In the present study thymus weight changed and spleen B-cell populations were affected at a dose of 10 mg/kg, a level where no overt general toxicity was noted.

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

The ultimate goal of any animal model in immunotoxicity testing is that it be a sensitive predictor of xenobiotic-induced immune dysfunction in humans. Such models should be capable of identifying the target(s) within the immune system affected by the xenobiotic. In particular the tier testing models have been successfully used to identify and characterize a variety of different immunotoxicants in animals as it pertains to immunosuppression and reduced resistance to infectious diseases. These tier models in mice and rats have been validated in interlaboratory studies. Although these protocols were designed for studies of rats and mice, some have been applied successfully for studying immunotoxicity in other animal species, including non-human primates. A great amount of data has been generated by the application of these models, which demonstrate that xenobiotics alter the immune system of animals. In man, the database on chemical-induced immunosuppression is limited, as the use of markers of immunotoxicity has received little attention in clinical and epidemiological studies. Such studies have not been performed frequently, and their interpretation often does not permit unequivocal conclusions to be drawn, due for instance to the presence of confounding factors and the uncontrolled nature of exposure. Also, testing possibilities in humans are limited and immune function changes by chemical exposure are often subtle. In humans, a number of agents have been shown to have immunosuppressive properties (including PCBs, PCDDs, PCDFs, oxidant gases, and ultraviolet radiation), but the strongest evidence stems from the clinical use of immunosuppressant drugs in transplant patients. These human data do in general terms confirm the data gained with experimental animals. Immunotoxicity assessment in rodents therefore adequately forms the basis for human risk assessment. Knowledge on the predictability of these animal models and immune assays can be further improved by comparison of the human and animal data obtained in the development of drugs.

Histopathology of the immune system as a tool to assess immunotoxicity.

Immunotoxicology studies the undesired effects of interactions between xenobiotics and the immune system, mainly in toxicity experiments in rodents. The histopathology of the lymphoid organs is a cornerstone in such studies. In this review we describe practical aspects of sampling lymphoid organs and subsequent tissue processing and application of conventional and advanced histologic techniques. Thereafter, some aspects of proper reading and interpretation of histopathology is discussed, in relation to modifying factors such as age, sex, strain of animals, housing conditions, and nutritional status. These factors can substantially confound the outcome and interpretation of experiments, due to the highly dynamic characteristics of the immune system. Immunotoxicity tests are normally performed in a tiered approach. We describe the screening tier in the rat species that has been developed in the National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands, and illustrate the value of histopathology by an example of immunotoxicity testing of pesticides. Subsequently, the tiered approach in the mouse species followed by the National Toxicology Program in the USA, is described. In the evaluation of chemicals with suspected immunotoxic potential using this approach, histopathology proved to be less sensitive in 'flagging' immunotoxicity. This may be related to the lower doses that are applied in this toxicity design, because at higher doses histopathology is a sensitive indicator of toxicity. A global description of pathologic alterations after toxic insult is given, followed by representative examples taken from immunosuppressive drugs--the cytostatic agent 5-fluorouracil, and drugs interfering with cytokine expression, namely, Cyclosporin A, FK-506, and Rapamycin.

Acnegenic activity of 3-methylcholanthrene and benzo[a]pyrene, and a comparative study with 2,3,7,8-tetrachlorodibenzo-p-dioxin in the rabbit and hairless mouse.

The non-halogenated hydrocarbons 3-methylcholanthrene (MC) and benzo[a]pyrene (BP) were tested for acnegenic activity using the rabbit ear test. Both compounds induced characteristics follicular hyperkeratosis, although their acnegenic potency was approximately 4 orders of magnitude lower when compared to the potent acnegen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). These results are discussed in view of the hypothesis that the acnegenic activity of TCDD and its congeners is mediated through stereospecific binding to a cytosolic receptor protein. In an experiment with hairless (hrhr) mice, which mutant has been described as an animal model for testing acnegenic potency, reduction in sebaceous gland tissue but no follicular hyperkeratosis was observed after application of a total dose of 0.4 microgram TCDD on the back skin. At a 10 times lower dose, no effects were seen. The hairless mouse strain used was responsive to TCDD as judged from the dose-related increase in the activity of aryl hydrocarbon hydroxylase (AHH) in liver microsomes, the increased liver weight and the histopathological changes in the liver. In comparison, a total dose of 0.12 microgram TCDD produced a strong follicular hyperkeratosis in the rabbit ear. From these results and from literature data, the adequacy of the hairless mouse for the testing of compounds for acnegenic potency is questioned.

Alterations of dendritic cells in the rat thymus without epithelial cell loss during cyclosporine treatment and recovery.

After cyclosporine treatment, dendritic cells disappear from the rat thymic medulla. The present study was undertaken to examine the ultrastructural alterations in the dendritic cell population during 14-day cyclosporine treatment and subsequent 6-week recovery. Four dendritic cell subtypes were defined ultrastructurally by a newly developed classification system. In addition, the potential effect of cyclosporine on six medullary epithelial cell subtypes was studied. During cyclosporine treatment, a prominent reduction of dendritic cells was seen at the ultrastructural level, whereas the total number of medullary epithelial cells remained largely unchanged. These findings were confirmed by immunohistochemistry. The number of mature dendritic cells declined later than the number of immature ones. A decrease in the antigen-processing capacity of remaining dendritic cells was suggested by the disappearance of Birbeck granules and the reduced number of tubulovesicular complexes. These findings support a disturbance of clonal deletion during cyclosporine treatment. The dendritic cell alterations appeared reversible 4 weeks after the restoration of the original architecture. During recovery, dendritic cells displaying lysosomal elements outnumbered those found in the normal uninvoluted thymus. This phenomenon probably reflects an enhanced turnover of cell organelles. No treatment-related effect on epithelial cell subtypes was seen.