Impairment of thymus-dependent immune functions by exposure of the developing immune system to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Immune function of young adult mice following in utero exposure to cyclophosphamide

Long-lasting organic damage has been reported following in utero exposure to certain environmental or therapeutic agents. The sensitivity of the developing immune system to chemical insult during organogenesis or histogenesis was evaluated in mice employing the known immunosuppressive agent cyclophosphamide (CY). Experiments were conducted employing one of the following treatment regimens: (1) 1 microgram/g X d intravenously on d 9-12 or 14-17 of gestation; (2) 5 micrograms/g intravenously on 12 of gestation; (3) 1, 2.5, or 5 micrograms/g X d intraperitoneally on d 12 of gestation; or (4) 5, 10, or 20 micrograms/g intraperitoneally on d 17 of gestation. There were no surviving pups born to mothers administered CY by schedule 2; otherwise, numbers of surviving offspring were not affected by drug treatment, and no gross terata were observed. Employing this variety of exposure protocols, consistent enhancement or suppression of cell-mediated or humoral immune function was not observed in offspring of treated dams. Reduced body weight in 5- and 8-wk-old progeny was noted after exposure to 20 micrograms/g on gestational d 17. Increased in vitro B-lymphocyte blastogenic response to lipopolysaccharide occurred in 5-wk-old animals, and production of antibody to sheep erythrocytes was increased in 8-wk-old offspring exposed to CY at 20 micrograms/g on d 17 of gestation. The T-lymphocyte parameters were relatively unaffected by in utero exposure to CY, suggesting either that cell-mediated immune function was not affected by treatment or that homeostasis was restored prior to immunologic evaluation of offspring.

Differential immunotoxic effects of the environmental chemical benzo[a]pyrene in young and aged mice

Young (3-6 months), middle-aged (16-18 months) and aged (23-26 months) mice were exposed in vitro and in vivo to the immunotoxic environmental chemical benzo[a]pyrene. The generation of antibody producing cells to the T-dependent antigens of sheep erythrocytes was observed to be suppressed in all age groups. Significantly, aged mice were shown to exhibit a greater percent suppression of antibody responses than young or middle-aged mice both in vitro and in vivo. The results presented provide the first evidence that the degree of immunological toxicity of environmental chemicals may be partially dependent upon the chronological and immunological age of the animal.

Immunological consequences of dioctyltin dichloride (DOTC)-induced thymic injury

Inbred rats fed diets containing 75 ppm dioctyltin dichloride (DOTC) for 8 or 12 weeks demonstrated marked reduction in thymic weight. This reduction was accompanied by a decrease in the number of W3/25 positive phenotypic circulating lymphocytes and an impaired ability to respond to suboptimal mitogenic stimulation. Responsiveness to alloantigenic stimulation, as measured by mixed leucocyte reactions, was depressed in DOTC-fed animals whereas no effect on natural cytotoxicity in nonimmunized treated or control rats was evident. No difference was found in the ability of treated compared to untreated animals to mount specific antibody responses against sheep red blood cells, and no evidence was found to indicate toxicity to lymphocytes in vivo. The investigation showed that DOTC administration resulted in a selective immunodeficiency.

Effect of thyroidectomy and thyroxine on 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced immunotoxicity

Radiothyroidectomy protected against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced immunotoxicity in rats as assessed by the spleen anti-SRBC plaque-forming cell assay. Thyroxine (T4) replacement therapy partially reversed the effects of thyroidectomy on T4 and triiodothyronine (T3) serum levels, body weight and immune function as well as restored TCDD-induced immunotoxicity. Thus, hypothyroidism induced by TCDD exposure can be viewed as a protective response of the organism to reduce the insult caused by TCDD.

The role of receptors in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity

There is good evidence that the Ah-(TCDD-) receptor plays a role in the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its congeners. TCDD and other chlorinated aromatic hydrocarbons with chlorine atoms in lateral positions (2,3,7,8-tetrachlorodibenzofuran, 3,3',4,4'-tetrachloroazoxybenzene, 3,3',4,4'(5,5')-tetra(hexa)chlorobiphenyl), all bind to the receptor and show a similar pattern of toxicity, although there is a wide range in potency. The Ah-receptor is viewed as the major product of the regulatory gene of the Ah-locus in the mouse. Several of the toxicities of TCDD and congeners (teratogenesis, thymic involution and hepatic porphyria) have been shown to segregate with the Ah-locus. In vitro studies using keratinizing cells or fetal thymus organ culture have shown a good correlation between activity as ligands of the receptor and toxicity for the compounds discussed. The great differences in toxic potency of these compounds in vivo may therefore be a result of variation in rate of metabolism and excretion rather than differences in affinity for the Ah-receptor. The physiological role of the Ah-receptor is discussed, whether it has developed as a response to exposure to toxic substances in the environment, as a means of induction of P-450-dependent polysubstrate mono-oxygenase activities in order to make those substances more liable for excretion--or is there a physiological ligand? TCDD has a long half-life in the body, and a sustained competition for binding to the receptor between TCDD and a ligand of importance for normal cell functions may result in toxicities such as the wasting syndrome. This tentative ligand could be of varying importance in different species, which might explain the great variation in sensitivity between species, the hamster being about 5000 times less sensitive than the guinea pig.

Immunosuppression in weanling and adult Sprague-Dawley rats induced by acute exposure to 3,3',4,4'-tetrachloroazoxybenzene

The acute immunomodulatory effects of the environmental and occupational contaminant, 3,3',4,4'-tetrachloroazoxybenzene (TCAOB), were investigated on selected immune parameters in weanling and adult Sprague-Dawley rats. Significant immunotoxic effects were found 17 days after 4 doses of 25 mg/kg TCAOB, administered i.p. The main non-immune toxic effects were decreased body, kidney, heart and testis weights, and a simultaneous increase in liver weight. The immune parameters showing significant suppression were: thymic weight, splenic plaque forming cell populations and function, pertioneal macrophage chemiluminescence, and bone marrow cellularity. Weanling animals were affected by TCAOB to a greater extent than adults on both the multiple and single dose regimens. The immunotoxic effects were found to be qualitatively similar to those of its isosteric analog, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The results demonstrate that TCAOB is a very potent immunotoxic compound and may have long-term effects after a single exposure. This study is the first investigation into the effect of TCAOB on immune functions.

A sensitive delayed-type hypersensitivity model in the rat for assessing in vivo cell-mediated immunity

Many drugs and other chemicals can alter cell-mediated immunity (CMI), a response that often correlates with delayed-type hypersensitivity (DTH). Several DTH assays were evaluated to determine a method best suited for assessing chemically induced modulation of CMI in rats. The effects of various antigens, adjuvants, doses, routes, and immunosuppressants were investigated. The DTH method which produced optimum results in rats uses a footpad swelling reaction elicited by specific preparations of bovine serum albumin (BSA) and Freund's complete adjuvant (FCA). The rats were sensitized with 100 micrograms BSA in FCA injected subcutaneously at the base of the tail, and were challenged 7 days later with 75 microliter of 2% heat-aggregated BSA suspension injected into the left rear footpad. Footpad swelling was measured with pressure calipers 24 h later and compared to the contralateral footpad which was sham-injected with 75 microliters of physiological saline. Antigen-injected footpads were nearly double the thickness (7-8 mm) of the control footpads (3-4 mm), and variation between animals was small (CV = 5%). Dexamethasone and cyclophosphamide significantly suppressed the DTH reaction. Histopathological examination of the DTH reaction sites revealed a mononuclear cell infiltrate which is characteristic of type IV hypersensitivity. In addition to being highly quantitative and sensitive, this method provides a simple and reproducible assessment of CMI responses in the rat.

Sensitivity to suppression of cytotoxic T cell generation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is dependent on the Ah genotype of the murine host

Susceptibility of mice to a variety of toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is genetically determined by the Ah locus. To determine if immunotoxicity following TCDD exposure was also regulated by the Ah locus, we tested the ability of low dose TCDD (4 ng/kg) to suppress the generation of allospecific cytotoxic T cells (CTL) by lymphocytes from "susceptible" C57B1/6, and "resistant" DBA/2, and from C57B1/6XDBA/2J F1 hybrid mice in vitro. To determine if TCDD acted directly on the "susceptible" lymphoid cells, the immune response of C57B1/6 leads to DBA/2 and DBA leads to C57B1/6 bone marrow chimeras was also measured. C57B1/6 and F1 mice proved susceptible to suppression consistent with the dominant effect of Ah. Susceptibility to suppression in chimeric mice, however, was determined by the Ah genotype of the host and not by the genotype of the grafted lymphomyeloid cells. Mixing experiments demonstrated that suppression of CTL generation by TCDD was due to suppressor T cells. The frequency of CTL precursors was not affected by TCDD. These results are consistent with the idea that TCDD acts by an Ah locus-dependent mechanism to indirectly promote development of suppressor T cells that block the generation of CTL from their precursors.

Subnormal expression of cell-mediated and humoral immune responses in progeny disposed toward a high incidence of tumors after in utero exposure to benzo[a]pyrene

Pregnant mice were exposed to 150 micrograms benzo[a]pyrene (BaP) per gram of body weight during fetogenesis (d 11-17 of gestation) and the progeny were assayed for humoral and cell mediated immune responses at different time intervals after birth. Immature offspring (1-4 wk) were severely suppressed in their ability to produce antibody-(plaque-) forming cells (PFC) against sheep red blood cells (SRBC) and in the ability of their lymphocytes to undergo a mixed lymphocyte response (MLR). Lymphocytes from these progeny showed a moderate to weak capacity to inhabit production of colony-forming units (CFU) in host spleens following transfer with semiallogeneic bone marrow (BM) cells into lethally X-irradiated recipients syngeneic to the BM (in vivo graft-versus-host response, GVHR). A severe and sustained suppression in the MLR and the PFC response occurred from the fifth month up to 18 mo. The in vivo GVHR, also subnormal later in life, was not as severely suppressed as the other two parameters. Tumor incidence in the BP-exposed progeny was 8- to 10-fold higher than in those encountering corn oil alone from 18 to 24 mo of age. These data show that in utero exposure to the chemical carcinogen BaP alters development of components needed for establishing competent humoral and cell-mediated functions of the immune apparatus and leads to severe and sustained postnatal suppression of the defense mechanism. The immunodeficiency exhibited, particularly in the T-cell compartment (MLR, GVHR), before and during the increase in tumor frequency, may provide a favorable environment for the growth of nascent neoplasms induced by BaP.

In vivo and in vitro effects of 1,1-dimethylhydrazine on selected immune functions

The in vivo phase of the experiments reported here include the evaluation of immune function after short-or long-term treatment of mice with 1,1-dimethylhydrazine (UDMH). Long-term exposure (3 injections/week for 14 weeks) resulted in increased numbers of Jerne plaque-forming cells, a trend toward decreased induction of suppressor cell activity by concanavalin A (Con A), and no effects on mitogen-induced lymphocyte blast transformation (LBT), compared to saline-treated control mice. These effects were greatest at doses of 10 or 50 mg/kg, while higher doses had less of an effect. In vitro experiments were performed by adding UDMH to normal murine splenocytes in the LBT assay and con A-induced suppressor cell assay. The UDMH induced a significant enhanced response to lipopolysaccharide (LPS) at 10 and 50 micrograms/ml, and a suppressed response to both Con A and LPS at higher concentrations. The UDMH also caused a decrease in suppressor cell activity at 25 micrograms/ml. Selective abrogation of suppressor activity or alteration of the suppressor cell-helper ratio were suggested as possible mechanisms for the enhancement effect associated with UDMH.

Modulatory effect on the pesticide captan on the immune response in rats and mice

The effect of short-term oral administration of captan, [N-(trimethylthio)-4-cyclohexene-1,2-carboximide] on the immune response was studied in rats and mice. Animals were fed a diet with or without 0.3% (w/w) of captan for 7, 14, 21 and 42 days. The SRBC-antibody formation was depressed by about 70% in both species after 14 days of treatment. A release of inhibition occurred in mice at day 42. In a parallel manner, the lymphoblastic stimulation of splenic cells by PHA and by LPS was studied in captan-treated mice and their controls. The stimulation by PHA of splenic cells that were mainly T cells was clearly inhibited (45%) by day 14 of captan ingestion. Thereafter, the inhibition was only partially released until day 42. B cells, stimulated by LPS, presented a decrease in stimulation in captan-treated mice, during the first week of diet (20%). Then an important increase in the stimulation of these cells occurred at day 21 (85%) followed by a return to the normal value at day 42. These results pointed out a clear depressive effect of captan-diet on the immune response of the animals. The inhibition of SRBC-antibody formation during the first stage of the treatment may be correlated to the inhibitory effect of captan on T cells, which were cooperative with B cells for the expression of SRBC-antibody synthesis. These effects were obtained at a level of captan which was considerably lower than the toxic dose.

Thymic atrophy induced by acute exposure of 3,3',4,4'-tetrachloroazobenzene and 3,3',4,4'-tetrachloroazoxybenzene in rats

The effects of 3,3',4,4'-tetrachloroazobenzene (TCAB) and 3,3',4,4'-tetrachloroazoxybenzene (TCAOB) on lymphoid organs in male Sprague-Dawley rats were investigated in various acute exposure studies. Significant thymic atrophy was observed in rats 10 days after the i.p. administration of either compound (on days 1 and 5) at a dose of 25 mg/kg. When 8-week-old animals were studied, the relative thymus weight was reduced to 69% and 49% of the control value by the respective treatment of TCAB and TCAOB. In 2 groups of weanling rats the same dosage of TCAOB was able to reduce the relative thymus weight to 31% and 38% of the comparable control animals. In addition, TCAOB causes a decrease in the body weight gain and a decrease in the weights of major organs in the weanling animals. This toxic response cannot be explained solely on the basis of decreased food intake since qualitatively the same results were observed in a pair-feeding experiment. The involvement of glucocorticoid hormones was rejected as the underlying mechanism since adrenalectomy was found to provide no protection towards the degenerative effect seen upon the lymphoid tissues. This investigation constitutes the first study concerning the effects of these 2 environmental and occupational toxicants on lymphoid organs.

Examination of bone marrow, immunologic parameters and host susceptibility following pre- and postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The effects of pre/postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on various immunological, bone marrow and host susceptibility assays were examined in B6C3F1 hybrid mice. Exposure was accomplished by maternal dosing on Day 14 of gestation and again on Days 1, 7, and 14 following birth, employing dosages of 0, 1.0, 5.0 or 15.0 micrograms/kg body weight. The 15.0 micrograms/kg dosage was lethal to 70% of the offspring with the remainder of that dosage group revealing overt toxicity. Bone marrow toxicity occurred in both the 15.0 and 5.0 micrograms/kg dosage groups as evidenced by bone marrow hypocellularity and depressed colony formation of macrophage-granulocyte progenitor cells and pleuripotent stem cells. Evidence was presented that depression of lymphoproliferative responses following mitogen stimulation in TCDD-immunosuppressed mice was due to a functional defect of lymphocyte activation rather than suppressor cell activity. Administration of either Listeria monocytogenes or syngeneic PYB6 tumor cells in mice exposed to relatively low levels of TCDD during pre- and postnatal development increased their susceptibility to either bacterial or tumor challenge.

Immunotoxicity assessment: screening and function studies

As a screening procedure to detect immunotoxic effects, different parameters are discussed. These criteria include growth, weight and histology of lymphoid and endocrine organs, haematology, as well s serum immunoglobulin concentrations which can be quantified using the enzyme-linked immunosorbent assay (ELISA). Secondly, different function tests are discussed to assess in the rat the cell-mediated immunity, the humoral immunity and the phagocytosis by macrophages. These tests should be performed when in a screening study an indication of immunotoxicity is found at a relevant dose level. The aim of functional assessment is to determine the functional significance of an effect on the immune response and to gain more insight into the mode of action of the chemical. Finally, examples are given of compounds that suppress or stimulate immune responses; and advantages are discussed of performing function tests during the development phase of the immune system.

The effects of methylnitrosourea on the immune system and hematopoietic system of adult specific pathogen free cats

The effects of a single non-carcinogenic dose of 15 mg/kg methylnitrosourea (MNU) on the immune and hematopoietic systems of adult specific-pathogen-free (SPF) cats were determined. The cell-mediated-immune (CMI) system was markedly suppressed, as evidenced by: (i) Prolonged cutaneous allograft retention time (41-84 days); (ii) Decreased lymphocyte blast transformation response to mitogens (2% of pretreatment response to pokeweed mitogen or concanavalin A) and antigen (12% of untreated control cat response to keyhole limpet hemocyanin); (iii) Reduced number of absolute erythrocyte-rosetting T-cells in the peripheral blood. This immunosuppression lasted at least 3 months, the duration of the experiment. Suppression of the hematopoietic system was also noted as evidenced by: (i) Peripheral lymphopenia lasting 3 months and neutropenia lasting 3 weeks; (ii) Bone marrow hypocellularity lasting 3 weeks; (iii) Hypoplasia of neutrophilic precursors lasting 3 weeks and erythroid precursors lasting 4 days. It was concluded that a single non-carcinogenic dose of MNU induces a prolonged suppression of the CMI system and a brief suppression of hematopoiesis in adult SPF cats. The immunosuppression may in part be responsible for the previously observed increased susceptibility to feline leukemia virus infection and disease of adult SPF cats treated with MNU.

Laboratory studies on the immune effects of halogenated aromatics

The effects of TCDD exposure on the developing immune system were investigated in Wistar/Fischer hybrid or Fischer rats. Fetal and neonatal rats were exposed to TCDD through maternal dosing (5 muk/kg) on day 18 of gestation and on days 0, 7, and 14 of postnatal life (group 1). Another group of neonatal rats was exposed to TCDD through maternal dosing on days 0, 7, and 14 of postnatal life only (group 2). Variable but significant effects on body weights and thymus/body weight ratios were found up to 133 days of age. Cell mediated immune functions were depressed up to 133 days of age in both groups but less severely in animals exposed only postnatally. Furthermore, TCDD suppressed cell-mediated immune functions without affecting humoral immune function. Adoptive cell transfer studies indicated suppression of T-cell functions was selective in that "helper" cell function was not suppressed. In other studies, the effects on lymphocyte function following brief exposure of spleens from B6C3F1 mice to TCDD in dimethylsulfoxide (DMSO) were investigated. DNA, RNA and protein synthesis were inhibited at concentrations less than 2 X 10(-7) M TCDD in DMSO. This concentration accounted for approximately 0.2 ng TCDD uptake per spleen. The structurally related chemicals 3,4,3',4'-tetrachlorobiphenyl and 1-amino, 3,7,8-trichlorodibenzop-p-dioxin did not show significant lymphocyte effects even at two-fold higher concentrations. The ability of lymphocyte mitogens to bind to their cell surface receptors was not affected by TCDD treatment. TCDD was slightly cytolytic to lymphocytes after 48 hours of culture. DMSO treatment alone was also slightly toxic to lymphoid cells as indicated by a 10--20% loss of cell viability, although this occurred within 4 hours after DMSO exposure. Studies were performed to investigate the effects of 2,3,7,8-tetrachlorodibenzofuran (TCDF) on immune function in adult Hartley guinea pigs. Animals received 6 weekly doses of either 0, 0.05, 0.17, 0.5 or 1.0 microgram TCDF/kg body weight. TCDF slightly depressed cell-mediated immune functions, particularly at the higher dose levels as indicated by decreased lymphocyte blastogenesis, delayed hypersensitivity reactions, and production of macrophage inhibitor factor. Additionally, thymus-to-body-weight ratios were slightly reduced in the 0.5 and 1.0 microgram dosage groups. Serum IgG levels and antibody titer to BGG did not differ from controls. These results indicate that TCDF-induced immunosuppression is similar to that of TCDD.

Investigations on the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on parameters of various immune functions

The effects of TCDD exposure on parameters of immune function during the developmental period were investigated. Exposures were performed in Fischer/Wistar rats. Fetal and neonatal rats were exposed to TCDD through maternal dosing (5 micrograms/Kg) on day 18 of gestation and on days 0, 7, and 14 of postnatal life (group 1). Another group of neonatal rats were exposed to TCDD through maternal dosing on days 0, 7, and 14 of postnatal life only (group 2). Body weights and relative thymus weights were found to be suppressed up to 135 days of age in group 1 but only up to 35 days of age in group 2. Parameters of cell-mediated and humoral immune function were investigated. TCDD suppressed cell-mediated immune function without affecting humoral immune function. TCDD-exposed animals had recovered normal cell-mediated immune function by 270 days of age. A group of inbred Fischer rats was exposed to TCDD as described for group 1 above. At 45 days of age these animals were utilized in lymphocyte homing studies. It was found that TCDD exposure alters homing patterns of lymphocytes from exposed animals when adoptively transferred to untreated animals. In addition, lymphocytes from nonexposed animals did not home normally when injected into TCDD-exposed recipients.

Effects of 2,3,7,8-tetrachlorodibenzofuran (TCDF) on the immune system in guinea pigs

The effects of TCDF exposure on the immune system were investigated in Hartley guinea pigs. TCDF was administered by gavage at doses of 0.05, 0.17, 0.5 or 1.0 microgram/kg body weight once weekly for six weeks. Thymus/body weight ratios were suppressed in the higher dosage groups. Parameters of cell-mediated and humoral immune function were investigated. TCDF modestly suppressed cell-mediated immune function and had slight effects on humoral-mediated functions. TCDF immunosuppression appears similar to that induced following exposure to TCDD.

Assessment of immunobiological effects induced by chemicals, drugs or food additives. I. Tier testing and screening approach

The indications of immunologic dysfunction following low level exposure of rodents or even man to certain chemicals and drugs have raised concern regarding methodology and approaches for routine assessment of immunobiological effects. The immunogiological effect observed may either indicate impaired immunopotentiation or hypersensitization. The assays selected for testing should be relevant to the human experience and adaptable to certain practical considerations such as cost, reproducibility of data, ease of performance and application to routine toxicology studies. Using these considerations, a tier approach was proposed consisting of assays for screening for immunologic effects (Tier I) and assays to help define the mechanisms responsible for the immunobiological effects observed (Tier II). A tier of assays was also proposed for measuring the sensitization potential of certain compounds. Certain assays from the screening tier were assembled into a hypothetical and practical test battery to screen for immunological effects of a chemical with potential immunosuppressive properties. Information provided by this test battery should provide a reasonable and sensitive data base from which a standard of evaluation could be made regarding the safety of the test (1) compound.

Physiological mechanisms of diethylstilbestrol organotropic carcinogenesis

Treatment of pregnant women with diethylstilbestrol (DES) during pregnancy has been demonstrated to be associated with an increased risk in the female offspring for development of an otherwise very rare type of malignancy: clear-cell adenocarcinoma of the vagina and cervix. The present knowledge about this association is reviewed. In experimental animals, many different types of malignancy can be induced by DES administered in large doses and during long periods. For the human situation there are as yet no indications that exposure to DES during fetal life has resulted in any generally increased incidence of malignant tumors. By injecting neonatal mice with DES for the first five days after birth, histologically malignant changes develope in the uterine cervix of the animals when more than one year old. A comparison is made between this animal model and development of tumors in the human female offspring of DES treated mothers. In the female mice, neonatal DES treatment results in a disturbed epithelial differentiation process in the upper part of the vagina and the uterine cervix, a disturbed development of the hypothalamic-pituitary gland control system as well as a disturbance in the normal development of the lymphoid system. The abnormal epithelial differentiation process results in development of adenosis and within these areas the malignant changes later appear. We do no know whether adenosis is a pre-cancerous condition or not, in the meaning that it contains dormant malignant cells. Other factors could act upon adenosis to result in cancer. The reasons for DES being called a "carcinogen" are reviewed. The possibility for factors in the environment acting as potential transplacental carcinogens in the human fetus should not be excluded.

The effect of perinatal exposure to tetrachlorodibenzo-p-dioxin on the immune response of young mice

The immunocompetence of 5 week old offspring from mice fed control chow or chow containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was evaluated. The 5 ppb maternal feeding level was the only level that produced symptoms of intoxication in the offspring (i.e., facial alopecia and periorbital edema). Mice from mothers fed either 2.5 or 5 ppb of TCDD demonstrated thymus cortex atrophy and a significantly reduced spleen anti-SRBC plaque forming cell (PFC) response, but had normal serum anti-SRBC antibody levels following primary and secondary immunization. Contact sensitivity response to DNFB was significantly reduced only in offspring from mothers fed 5 ppb of TCDD. The blastogenic response of splenic T- and B-lymphocytes to concanavalin-A and E. coli lipopolysaccharide was unaffected by perinatal TCDD exposure. This correlated with the normal appearance of the T- and B-cell dependent areas of the spleens from these animals. There was no significant difference in the differential white blood cell counts between control and TCDD-exposed offspring. Offspring from mothers fed up to 5 ppb of TCDD withstood a live Listeria challenge as well as controls. However, maternal feeding levels as low as 1 ppb of TCDD rendered offspring more sensitive to an endotoxin challenge.