The effects of dietary T-2 toxin on the immunological function and herpes simplex reactivation in Swiss mice

Immunopathological effects of experimental T-2 mycotoxicosis in Wistar rats

It is well known that T-2 toxin has cytotoxic radiomimetic like effects on the immune system. Because of scant research data demonstrating the chronic effects of low doses of the T-2 toxin on humoral and cellular responses in rats, the present experiment was undertaken. The animals were divided into four groups, namely, group I (0.5 ppm), group II (0.75 ppm) and group III (1.0 ppm) and group IV (control) were given toxin-free diet for 12 weeks and eight animals each were sacrificed at 2, 4, 6, 8, 10, and 12-week of the experimental period. The humoral immune response was evaluated based on hemagglutination test (HA), and levels of serum immunoglobulins (IgA, IgG, IgM) while the cell-mediated immune response was evaluated by delayed-type hypersensitivity (DTH) response to ovalbumin, lymphocyte stimulation index, analyses of CD4⁺ and CD8⁺ T lymphocytes and mRNA expression levels of selected cytokines like IL-2, IFN-γ, IL-4 and IL-10 by quantitative Real-time PCR in experimental groups. T-2 treatment caused suppression in both humoral and cell-mediated immune responses as evidenced by a decrease in all these parameters in toxin fed animals compared to the control in the dose and duration-dependent manner. This dose-dependent effect on the immune system has been further reflected largely by the depletion of lymphocytes from lymphoid organs as observed histopathologically in the spleen, thymus, and Peyer's patches in the present study.

Immunotoxicity of repeated low level exposure to T-2 toxin, a trichothecene mycotoxin, in CD-1 mice

Male CD-1 mice were gavaged with T-2 toxin (0.0-5.0 mg/kg body weight) every third day. Body weight gain was depressed by exposure to 2.5 mg/kg, or greater, T-2 toxin; this was not associated with decreased food intake. The weights of the liver, kidney, spleen, and thymus were affected by two weeks exposure to T-2 toxin. However, a persistent effect after four weeks was observed only for the thymus. Peripheral leucocyte counts were elevated in the highest dose groups after two and four weeks. Thymidine uptake by cells not simultaneously exposed to mitogen was increased in splenic cell cultures of mice exposed to 2.5 mg/kg T-2 toxin for two or four weeks. Phytohemagglutinin stimulation of splenic lymphocytes following two weeks of exposure was depressed in the 2.5 mg/kg dose group; this phenomenon was not observed after four weeks exposure. Response to pokeweed mitogen increased after four weeks of exposure to 2.5 mg/kg T-2 toxin. A delayed-type hypersensitivity response decreased following two weeks exposure to levels greater than 0.02 mg/kg. Production of I g M class antibodies by splenic lymphocytes, evaluated by a hemolytic plaque response to sheep erythrocytes, was depressed in the 2.5 mg/kg dose group after two weeks exposure to T-2 toxin. The sensitivity and specificity of T-2 toxin immunotoxicity was indicated by the various parameters evaluated.

Mechanisms of deoxynivalenol-induced gene expression and apoptosis

Fusarium infection of agricultural staples such as wheat, barley and corn with concurrent production of deoxynivalenol (DON) and other trichothecene mycotoxins is an increasingly common problem worldwide. In addition to its emetic effects, chronic dietary exposure to DON causes impaired weight gain, anorexia, decreased nutritional efficiency and immune dysregulation in experimental animals. Trichothecenes are both immunostimulatory or immunosuppressive depending on dose, frequency and duration of exposure as well as type of immune function assay. Monocytes, macrophages, as well as T- and B-lymphocytes of the immune system can be cellular targets of DON and other trichothecenes. In vitro exposure to low trichothecene concentrations upregulates expression both transcriptionally and post-transcriptionally of cytokines, chemokines and inflammatory genes with concurrent immune stimulation, whereas exposure to high concentrations promotes leukocyte apoptosis with concomitant immune suppression. DON and other trichothecenes, via a mechanism known as the 'ribotoxic stress response', bind to ribosomes and rapidly activate mitogen-activated protein kinases (MAPKs). The latter are important transducers of downstream signalling events related to immune response and apoptosis. Using cloned macrophages, two critical upstream transducers of DON-induced MAPK activation have been identified. One transducer is double-stranded RNA (dsRNA)-activated protein kinase (PKR), a widely expressed serine/threonine protein kinase that can be activated by dsRNA, interferon and other agents. The other transducer is haematopoetic cell kinase (Hck), a non-receptor associated Src oncogene family kinase. Pharmacological inhibitors and gene suppression studies have revealed that Hck and PKR contribute to DON-induced gene expression and apoptosis. PKR, Hck and other kinases bind to the ribosome and are activated following DON interaction. Future studies will focus on the sequence of molecular events at the ribosome level that drive selective activation of these upstream kinases.

Immunopathological effect of the mycotoxins cyclopiazonic acid and T-2 toxin on broiler chicken

Forty, newly hatched, unsexed broiler chicks were fed diets containing 10 ppm cyclopiazonic acid (CPA) and 1 ppm T-2 toxin (T2) either individually or in combination for 28 days to study the immunopathological effects. Lymphoid organs revealed lymphocytolysis and lymphoid depletion in all toxin fed birds. Thymic and splenic CD+4 and CD+8 lymphocytes decreased significantly (p<0.01) in toxin fed birds when compared to the control. Thymic CD+8 lymphocytes of T2 and CPA-T2 showed significant (p<0.01) decrease from that of CPA and control groups. Splenic CD+4 and CD+8 lymphocytes showed significant (p<0.01) decrease in CPA and CPA-T2 fed groups when compared to the control. The T2 group did not differ significantly from that of control. The stimulation index (SI) of splenocytes to concavalin A revealed significant (p<0.01) decrease in all toxin fed birds. Significant (p<0.01) decrease were observed for the haemagglutination inhibition (HI) titres to Newcastle disease virus vaccine F strain (NDV) of birds fed CPA, T2 and in combination. Significant (p<0.01) interaction was found for lymphocyte subsets, SI and HI titres to NDV. The study indicated the immunosuppressive effect of these toxins either alone or in combination in broiler chicks.

Effect of T-2 toxin on in vivo lipid peroxidation and vitamin E status in mice

The effects of an acute administration of T-2 toxin on vitamin E status and the corresponding degree of lipid peroxidation, as determined by the plasma and organ content of malondialdehyde (MDA), was studied in mice. The effects of T-2 toxin administration on the body weight and weights of liver, spleen and thymus were also assessed. T-2 toxin was administered in doses ranging from 1 to 6.25 mg/kg body weight, depending on the experiment, while the dietary content of vitamin E ranged from near 0 to 5000 IU/kg. There was a significant decrease in vitamin E content of plasma after the administration of the toxin with the concentrations remaining low for periods as long as 48-72 h. MDA content of liver increased significantly after 24-48 h of toxin administration in contrast to the controls. However, MDA levels returned to the control range after 72 h. The concentrations of MDA in liver were inversely related to the vitamin E content of the diet, and were always higher for the toxin-treated animals (significant linear regression between MDA content of liver and the log10 of vitamin E content of the diet). Weights of spleen and thymus decreased after T-2 toxin administration; however, the weight of liver either increased or did not change in the different experiments. In conclusion, T-2 toxin treatment of mice increased lipid peroxidation in the liver as measured by MDA production. This process was maximal after 48 h of T-2 challenge, and decreased thereafter. Plasma alpha-tocopherol levels decreased as soon as 6 h after the toxin challenge, while MDA did not increase until there was a severe depletion of vitamin E. These changes were accompanied by decrease in weight of spleen and thymus.

In vitro exposure of human lymphocytes to trichothecenes: individual variation in sensitivity and effects of combined exposure on lymphocyte function

The trichothecenes are mycotoxins produced by fungi of the genus Fusarium, which are commonly present in foods and feed of cereal origin. Owing to the lack of sufficient toxicological data for most of the trichothecenes, in vitro studies may contribute to risk assessments of these toxins. In the present report, human lymphocyte cultures were used to study the individual variation in sensitivity among humans and the effects on in vitro Ig production. Furthermore, proliferative responses of cells exposed to combinations of two of the toxins were studied. Four toxins, T-2 toxin, diacetoxyscirpenol (DAS), nivalenol (NIV) and deoxynivalenol (DON) were included in the study. All four of the tested trichothecenes effectively inhibited mitogen-induced lymphocyte proliferation. There were no statistically significant differences in sensitivity to the toxins between lymphocytes from female and male blood donors. The individual variation in sensitivity, evaluated as the range of IC50 values, was rather limited (within a factor of 3 to 4). Immunoglobulin production by pokeweed-stimulated human lymphocytes was also effectively inhibited with IC50 values similar to the IC50 values in the proliferation tests for DON and NIV. However, IC50 values for Ig synthesis in cultures exposed to T2 were approximately two to three times higher than the corresponding IC50 values found in the proliferation tests. At low levels of exposure, elevated Ig production was observed in lymphocyte cultures from four out of the five blood donors tested. This effect was most pronounced on IgA synthesis. Combinations of NIV with T2, DAS or DON resulted in additive toxicity in the lymphocyte proliferation test, while combinations of DON with T2 or DAS resulted in an inhibition that was slightly lower than what could have been expected from the inhibition produced by the individual toxins. In conclusion, the tested trichothecenes inhibited both proliferation and Ig production in human lymphocytes in a dose-dependent manner with limited variation in sensitivity between individuals. Enhanced Ig production was observed in cell cultures exposed to the lower doses of the toxins. Combined exposure to two of the toxins resulted mainly in additive or antagonistic effects, although synergistic effects cannot be excluded and should be further investigated. These findings indicate that the total intake of type A and B trichothecenes should be taken into account in risk assessments.

T-2 toxin induces thymic apoptosis in vivo in mice

A single intraperitoneal injection of T-2 toxin (0.35, 1.75, or 3.5 mg/kg body wt) induced time- and dose-dependent thymic atrophy in young female BALB/c mice. T-2 toxin (1.75 mg/kg) induced maximal atrophy by day 3 with complete recovery by day 7. Flow cytometric analysis showed that the CD4(+)CD8(+) double positive thymocyte population decreased markedly. Histopathological examination of the thymus indicated that the pattern of cell death in the thymocytes had a characteristic apoptotic morphology with cell shrinkage and nuclear condensation. The in vivo effects of T-2 toxin included the induction of DNA fragmentation of approximately 200 base pairs in ladder form and cell death in thymocytes. Furthermore, flow cytometric analysis of PI-stained thymocytes from animals dosed with T-2 toxin revealed the formation of apoptotic cells. Of nine kinds of trichothecene mycotoxins tested, T-2 toxin appeared to be the most potent agent to induce apoptosis in the thymus. We sought insight into the mechanism of T-2 toxin-induced apoptosis in vivo. Administration of the protein synthesis inhibitor, CHX (15 mg/kg ip), 5 min after T-2 toxin (1.75 mg/kg ip) inhibited the induction of apoptosis in thymocytes, suggesting that the de novo protein synthesis was necessary. By using adrenalectomized mice and anti-TNF-alpha antibody-injected mice, it was shown that neither endogenous glucocorticoid nor TNF-alpha appeared to be involved in the apoptotic process. Taken together, these findings suggest that T-2 toxin-induced thymic atrophy is associated with cell death through a mechanism of apoptosis.

Novel detoxification of the trichothecene mycotoxin deoxynivalenol by a soil bacterium isolated by enrichment culture

A mixed microbial culture capable of metabolizing deoxynivalenol was obtained from soil samples by an enrichment culture procedure. A bacterium (strain E3-39) isolated from the enrichment culture completely removed exogenously supplied deoxynivalenol from culture medium after incubation for 1 day. On the basis of morphological, physiological, and phylogenetic studies, strain E3-39 was classified as a bacterium belonging to the Agrobacterium-Rhizobium group. Thin-layer chromatographic analysis indicated the presence of one major and two minor metabolites of deoxynivalenol in ethyl acetate extracts of the E3-39 culture filtrates. The main metabolite was identified as 3-keto-4-deoxynivalenol by mass spectroscopy and 1H and 13C nuclear magnetic resonance analysis. The immunosuppressive toxicity of 3-keto-4-deoxynivalenol was evaluated by means of a bioassay based on the mitogen-induced and mitogen-free proliferations of mouse spleen lymphocytes. This compound exhibited a remarkably decreased (to less than one tenth) immunosuppressive toxicity relative to deoxynivalenol, indicating that the 3-OH group in deoxynivalenol is likely to be involved in exerting its immunosuppressive toxicity. Strain E3-39 was also capable of transforming 3-acetyldeoxynivalenol but not nivalenol and fusarenon-X.

T-2 tetraol is cytotoxic to a chicken macrophage cell line

Cytotoxic effects of T-2 tetraol, a T-2 toxin derivative, on the MQ-NCSU chicken macrophage cell line were quantified by direct in vitro exposure. Macrophage cultures were exposed to 1, 10, 20, 40, 80, 160, and 320 micrograms/mL of T-2 tetraol for 1 h. Macrophage viability after exposure to T-2 tetraol. Macrophage viability was reduced by increasing concentrations of T-2 tetraol (linear effect, P < or = 0.001; quadratic effect, P < or = 0.025). The ability of macrophages to adhere to glass surfaces was impaired by increasing concentrations of T-2 tetraol (linear effect, P < or = 0.003). This experiment demonstrates that T-2 tetraol is cytotoxic to chicken macrophages in vitro.

Mycotoxin T-2 and aflatoxin B1 as immunosuppressors in mice chronically infected with Toxoplasma gondii

The aim of this study was to determine whether repeated ingestion of mycotoxin T-2 (T2) or aflatoxin B1 (AFL) at low doses could contribute to the activation of toxoplasmosis in experimentally infected mice. Mice were divided into two groups: Control (C) and Infected (I). The cyst-forming Beverley strain of Toxoplasma gondii was used to produce the infection one month before treatment with mycotoxins. Mycotoxins were given intragastrically for a 50-day period. The average weight gain was reduced in the groups treated with mycotoxins. Mice developed specific IgG to T. gondii. Histopathological studies showed severe encephalitis in all groups infected. The number of unruptured and ruptured cysts was established and the severity of the lesions was evaluated, the groups treated with mycotoxins being the most severely affected. Immunohistochemical studies of the brain showed free antigen in tissues surrounding ruptured cysts. It is suggested that low and repeated doses of mycotoxins, necessary to produce a subclinical intoxication, precipitate Toxoplasma cyst rupture and consequently the activation of chronic toxoplasmosis.

Taxonomy, biology, and clinical aspects of Fusarium species

There are several taxonomic systems available for identifying Fusarium species. The philosophy used in each taxonomic system is discussed as well as problems encountered in working with Fusarium species in culture. Fusarium species are toxigenic, and the mycotoxins produced by these organisms are often associated with animal and human diseases. The implications for the association of the carcinogens, fumonisins, produced by Fusarium moniliforme and other Fusarium species with human diseases are discussed. Foreign-body-associated fusarial infection such as keratitis in contact lens wearers, onychomycosis, skin infections, and disseminated multiorgan infections are discussed. Disseminated fusarial hyalohyphomycosis has emerged as a significant, usually fatal infection in the immunocompromised host. Successful outcome is determined by the degree of immunosuppression, the extent of the infection, and the presence of a removable focus such as an indwelling central venous catheter. These infections may be clinically suspected on the basis of a constellation of clinical and laboratory findings, which should lead to prompt therapy, probably with one of the newer antifungal agents. Perhaps the use of such agents or the use of colony-stimulating factors may improve the outcome of this devastating infection. However, until new approaches for treatment develop, effective preventive measures are urgently needed.

Effect of dietary T-2 toxin on biogenic monoamines in discrete areas of the rat brain

Acute T-2 toxin treatments alter biogenic monoamine concentrations in the brain; however, these perturbations have not been well documented or demonstrated in feeding trials. In this study, the effect of dietary T-2 toxin on regional brain concentrations of biogenic monoamines and their metabolites was investigated in male rats fed a semi-synthetic diet containing 0, 2.5 or 10 ppm T-2 toxin for either 7 or 14 days. Reduction in feed consumption, feed efficiency and weight gain was observed in rats fed either 2.5 or 10 ppm T-2 toxin. This effect was transient in animals fed the 10 ppm T-2 toxin diet, with feed consumption, feed efficiency and weight gain improving significantly during wk 2. T-2 toxin affected brain biogenic monoamine concentrations. In the nucleus raphe magnus, serotonin, 5-hydroxy-3-indoleacetic acid and norepinephrine increased in a dose-dependent manner, and dopamine increased transiently. In the substantia nigra of rats fed 10 ppm T-2, epinephrine increased after 7 days and norepinephrine decreased after 14 days, when compared with controls. Dihydroxyphenylacetic acid concentrations in the paraventricular nucleus and medial forebrain bundle were lower in T-2 toxin-treated rats than in control animals. The observed effects of T-2 toxin on brain monoamines and the resulting neurochemical imbalance may account for the physiological manifestation of trichothecene intoxication.

Modulation of resistance to mastitis pathogens by pretreatment of mice with T-2 toxin

T-2 toxin, a secondary metabolite of Fusarium species, is a mycotoxin with immunomodulatory activity. In the present investigation the effects of T-2 toxin on host resistance was studied. The virulence of Escherichia coli and Staphylococcus aureus in the mammary glands of mice treated with T-2 toxin was compared with their virulence in control mice. Virulence was estimated from the ability to induce various types of lesions and bacterial growth in the mammary gland. Pretreatment of mice with a single dose (3 mg/kg body weight) of T-2 toxin by gavage reduced the virulence of both E. coli (P less than 0.05) and S. aureus (P less than 0.01). Microscopic lesions in the infected glands varied in character, from consistently non-reactive necrosis of the entire mammary gland to limited inflammatory reactions. The former were more abundant in control mice than in mice treated with T-2 toxin. Although treatment by gavage with T-2 toxin (0.75 mg/kg body weight/day) for 14 days prior to inoculation had no significant effect on the course of the mastitis infection, virulence was slightly lower in the T-2 toxin treated mice. Both single-dose and successive treatment with T-2 toxin enhanced the respiratory burst activity of macrophages. Pre-inoculation treatment with T-2 toxin also caused a significant increase in the number of peritoneal cells, T-2 toxin did not show bacterial effects on the E. coli or S. aureus strains used for the inoculations. The data indicate that T-2 toxin has modulatory effects on the cell-mediated immune system, and that enhancement of resistance to common mastitis pathogens in mice pretreated with a single dose of T-2 toxin is associated with migration and activation of macrophages.

Species-specific hemolysis of erythrocytes by T-2 toxin

The tricothecene mycotoxin, T-2 toxin interacts differently with mammalian erythrocytes. Pig, man, rabbit, guinea pig, horse, dog, rat, and mouse erythrocytes are all lysed to a varying degree by T-2 toxin. But cow, sheep, goat, buffalo, and deer erythrocytes are all resistant to hemolysis by T-2 toxin. Since erythrocytes from ruminant animals contain little or no phosphatidylcholine, perhaps the presence of phosphatidylcholine in the membrane is required for the hemolytic action of T-2 toxin. Sheep erythrocytes were used to encapsulate T-2 toxin further confirming the resistance of erythrocytes from animals with ruminant physiology to T-2 toxin lysis.

Impaired murine resistance to Salmonella typhimurium following oral exposure to the trichothecene T-2 toxin

On orally exposing Salmonella-resistant C3H/HeN mice to the trichothecene T-2 toxin (1 mg/kg body weight), challenging with Salmonella typhimurium, and continuing to dose with T-2 toxin on alternate days for 3 wk, the LD50 for the organism decreased by five orders of magnitude, in comparison with control mice not treated with T-2 toxin. In the absence of S. typhimurium, T-2 toxin did not cause lethal effects when administered at this level. Increased mortality in response to S. typhimurium challenge was dependent on T-2 toxin dose in the range 0 to 1 mg/kg for this regimen. The toxin did not significantly affect intestinal infection but did increase splenic counts in mice challenged with a range of S. typhimurium doses and also accelerated body-weight loss in infected animals. Mice challenged with the organism exhibited similar mortality when T-2 toxin treatment was begun 1 day prior to infection or at 5 or 9 days after infection. A time-related decrease in mortality, relative to that found for the standardized co-challenge described above, was observed when T-2 toxin administration was begun at 9, 13 or 23 days after infection. The results indicated that, depending on the challenge dose of the organism, both early and late phase acquired immune response to S. typhimurium could be impaired by T-2 toxin. Markedly enhanced susceptibility to gram-negative bacterial infection is another manifestation of trichothecene toxicity and may be an important aetiological factor in animal health problems that are associated with these mycotoxins.

Antibody producing ability of mouse spleen cells after subacute dietary exposure to T-2 toxin

The effects of T-2 toxin on the antibody producing ability of CD-1 mice after dietary exposure to 0, 2.5, 5 and 15 ppm of T-2 toxin for 29 days was studied. The antibody response against sheep red blood cells, a T-lymphocyte and macrophage-dependent response was suppressed at 2.5, 5 and 15 ppm of T-2 toxin exposure. In contrast, the antibody responses against dinitrophenyl-aminoethylcarbamylmethyl - Ficoll (DNP - Ficoll), a T-lymphocyte independent macrophage-dependent response, and Escherichia coli 0127 (LPS), a T-lymphocyte and macrophage-independent response, were not affected. These results suggest that the inhibitory effects of T-2 toxin on antibody-producing ability after subacute dietary exposure appear to be a direct affect on T-lymphocyte function, possibly involving the T-helper lymphocytes.

Cytotoxic effect of T-2 mycotoxin on cells in culture as determined by a rapid colorimetric bioassay

We developed a colorimetric assay for determining metabolic activity (viability) of cells exposed to toxic agents. This system is based on the ability of mitochondrial enzymes in viable cells to modify a tetrazolium salt into a blue formazan product that can be detected spectrophotometrically at 570 nm. The assay works equally well for mammalian and insect cell lines and at 48 hr color formation is linear over a cell input range of 1.56-50 X 10(4) cells/ml. The inhibitory effects of T-2 mycotoxin on tetrazolium cleavage in L929 cells is comparable to that observed for protein and DNA synthesis (50% inhibition = 6-8 ng/ml). Using this system to analyze the lethal effect of T-2 toxin on cells from various animal species, it was found that bovine cells were the most sensitive (50% inhibition at 2.2 ng/ml) while hamster cells were the most resistant (50% inhibition at 26.2 ng/ml). Murine cells exhibited intermediate sensitivity (50% inhibition at 10.9 ng/ml). Variable toxin susceptibility was also observed among different cell types. Lymphocytes were 3-fold more sensitive to the T-2 inhibitory effects than comparable tissue culture cell lines. These data indicate that the colorimetric assay system could have broad applications in toxicological studies. Further, the observed differences in species sensitivity may provide insight into the primary mechanism of the T-2 toxin-cell interaction that ultimately leads to cell death.

Maternal toxicity, embryolethality and abnormal fetal development in CD-1 mice following one oral dose of T-2 toxin

An experiment was undertaken to determine the teratogenic effect of oral administration of T-2 toxin, a trichothecene mycotoxin. Firstly, a dose response study using 0, 0.5, 1.0, 2.0, 3.0, 3.5 and 4.0 mg/kg T-2 toxin in propylene glycol, on day 9 of pregnancy, was undertaken. Maternal deaths and toxicity was noted in the 4.0 and 3.5 mg/kg groups post-toxin administration. These groups gained less weight throughout gestation than the rest of the groups, because no fetuses were found in the 4.0 mg/kg group and the 3.5 mg/kg group had significantly fewer fetuses than the remaining groups. The total fetal weight was similar among all groups with fetuses, and normal sex ratio of offspring was seen. More major and minor defects were seen in the 3.0 mg/kg T-2 toxin treated group than any other group. Secondly, a day response trial using a single dose of 3.0 mg/kg T-2 toxin given on either days 6, 7, 8, 10, 11 or 12 of gestation was undertaken. Maternal mortality, with placental hemorrhage, was observed. Fetal loss was greater in the T-2 toxin treated groups than in the starved controls. The greatest number of dead term fetuses was seen in mice treated on day 9 of gestation. Normal sex ratios were present in the offspring. Major skeletal defects were more numerous in mice treated on day 7 of gestation, whereas minor defects, retardations and variants were more common in mice treated on day 8. It was concluded that a single oral dose of T-2 toxin in propylene glycol is primarily maternotoxic and embryolethal, and that defective development was possibly secondary to maternal toxicity.

Modulation of cell-mediated resistance to listeriosis in mice given T-2 toxin

The modulating effect of preinoculation and postinoculation treatment with a single oral 4.0 mg/kg dosage of T-2 toxin on cell-mediated resistance was studied in mice inoculated with Listeria monocytogenes. Toxin treatment caused significant decreases in thymus and spleen weights, bone marrow cellularity, and in the total number of circulating leukocytes, lymphocytes, and neutrophils. Enhancement or suppression of resistance to listeriosis was dependent on the time of toxin administration relative to the time of Listeria challenge. Preinoculation treatment on Day 2 or 4 prior to Listeria challenge significantly enhanced resistance and decreased mortality due to listeriosis by as much as 50%. In contrast, resistance was suppressed and mortality was increased by 50% in mice that were treated with toxin after Listeria challenge. Enhanced resistance to listeriosis was accompanied by a significant increase in the influx of macrophages into Listeria-elicited peritoneal exudates. In addition, in vivo phagocytosis of sheep red blood cells by peritoneal macrophages was significantly increased in toxin-treated mice that were sensitized with sheep erythrocytes. The data indicate that T-2 toxin has a modulating effect on cell-mediated resistance and that enhancement of resistance to listeriosis in mice pretreated with T-2 toxin is associated with increased migration/activation of macrophage effector cells.

Immunological responsiveness of mouse spleen cells after in vivo or in vitro exposure to 3-acetyldeoxynivalenol

The effects of 3-acetyldeoxynivalenol (3-AcDON) on mitogen-induced lymphocyte proliferation and antibody production were studied in male CD-1 mice exposed to 0, 2.5, 5 or 10 ppm 3-AcDON in the diet for 35 days. Mitogen-induced lymphocyte proliferation and T-cell-independent antibody responses to dinitrophenyl-ficoll or Escherichia coli were not altered by dietary exposure to 3-AcDON. The T-cell-dependent antibody response to sheep red blood cells was increased in the group fed 10 ppm 3-AcDON. In vitro, 3-AcDON inhibited lymphocyte proliferation in a dose-dependent manner. Inhibition was observed when the toxin was present during the first 8 hr in phytohaemagglutinin-stimulated cultures and during the first 24 hr in lipopolysaccharide-stimulated cultures. This suggests that 3-AcDON blocks an early step in lymphocyte activation. This inhibition was not restored by thiol reducing agents (dithiothreitol, L-cysteine or 2-mercaptoethanol). Similarly, the addition of lymphokines, including interleukin-1 or interleukin-2, did not alter the inhibitory effects of 3-AcDON. These results suggest that the in vitro effects of 3-AcDON may not reflect its in vivo immunotoxicity. However, 3-AcDON may serve as a chemical probe for examining the activation process of lymphocyte proliferation.

Experimental T-2 toxicosis in swine following inhalation exposure: effects on pulmonary and systemic immunity, and morphologic changes

Thirty-four, 9- to 11-week-old, male castrated, crossbred, specific pathogen-free derived pigs were exposed to a T-2 toxin aerosol at a nebulized dose of 0 or 9 mg/kg in pairs, each pair consisting of 1 control and 1 T-2 treated pig which were exposed on the same day. Twenty to 30% of the toxin (1.8 to 2.7 mg/kg) was retained by the pigs. Five pairs were killed on each of 1, 3 and 7 days after dosing. Two pairs of pigs were designated as a 0.33-day group when one T-2 treated pig died and the other was killed in a moribund state at 8 to 10 hours after dosing. The pulmonary and systemic immunity and morphologic changes of the lungs and other organs were examined. Bronchoalveolar lavage was performed to obtain alveolar macrophages (AM) and pulmonary lymphocytes (PL). The phagocytic ability of AM and mitogen-induced blastogenic responses of enriched PL and peripheral blood lymphocytes were evaluated. Clinically, all of the T-2 treated pigs vomited and were cyanotic, anorexic, lethargic and laterally recumbent. In the 0.33-, 1-, and 3-day T-2 treated pigs, there was a marked reduction in AM phagocytosis and mitogen-induced blastogenic responses of PL but not of peripheral blood lymphocytes. Mild to moderate, multifocal interstitial pneumonia was seen in the majority of the T-2 treated pigs. In pigs dying following inhalation of T-2 toxin, there was a more severe pneumonia, as well as marked necrosis of lymphoid tissues, severe necrohemorrhagic gastroenteritis and edema of the gall bladder wall, and multifocal necrosis of the heart and pancreas. Thus, inhalation exposure to T-2 toxin can result in clinical signs and morphologic changes resembling those reported previously in pigs given T-2 toxin intravascularly (iv) at a dose of 1.2 mg/kg (approximate LD50) or greater, as well as death. Mild pulmonary injury as well as transient impairment of pulmonary immunity was present in pigs surviving inhalation exposure.

Suppression of immune response in the B6C3F1 mouse after dietary exposure to the Fusarium mycotoxins deoxynivalenol (vomitoxin) and zearalenone

The effect that dietary exposure to the naturally-occurring Fusarium graminearum toxins deoxynivalenol (DON) and zearalenone (ZEA) may have on immune function was assessed in the B6C3F1 mouse. Dietary DON depressed the plaque-forming response to sheep red blood cells, the delayed hypersensitivity response to keyhole limpet haemocyanin and the ability to resist Listeria monocytogenes. Listerial resistance was similarly decreased in control mice fed restricted diets comparable to the dietary restriction caused by DON-induced feed refusal, whereas equivalent food restriction did not decrease the plaque or delayed hypersensitivity responses. ZEA ingestion decreased resistance to L. monocytogenes but did not affect splenic plaque-forming or delayed hypersensitivity responses. Resistance to Listeria was reduced to a greater extent by co-administration of DON and ZEA than by DON alone, whereas the ability of DON to inhibit the delayed hypersensitivity response was significantly lessened in the presence of ZEA. While effects on resistance to Listeria and delayed hypersensitivity were detectable in mice ingesting the mycotoxins for 2-3 wk, these effects disappeared upon extension of the feeding period to 8 wk. In contrast, some effect on the plaque-forming response was detectable with both the 2- and the 8-wk period of mycotoxin ingestion. Immunosuppression can thus result from ingestion of F. graminearum-infected agricultural staples, the suppression being attributable to interactions between direct immunotoxic effects of DON and ZEA and nutritional effects associated with DON-induced food refusal.

Interaction of T-2 toxin with bovine carrier erythrocytes: effects on cell lysis, permeability, and entrapment

Hemolysis, morphological changes, binding, and effect on encapsulation of exogenous substances were used as a basis to study the interaction of the trichothecene mycotoxin, T-2 toxin, with erythrocytes. T-2 toxin did not cause hemolysis of bovine erythrocytes but readily hemolyzed rat erythrocytes. T-2 toxin interaction with bovine erythrocytes was minimal because T-2 toxin did not bind appreciably to the erythrocytes. Entrapment of T-2 toxin in carrier erythrocytes was independent of toxin concentration, and interaction of T-2 toxin with erythrocytes did not affect the entrapment of the markers sucrose or inulin. T-2 toxin rapidly diffuses from carrier erythrocytes with less than 20% remaining after 4 hr of incubation. Cross-linking of the erythrocyte membrane with glutaraldehyde prevents T-2 toxin efflux from carrier erythrocytes.

Studies of immune function of CD-1 mice exposed to aflatoxin B1

The immunotoxic potential of aflatoxin B1 (AFB1), a secondary metabolite of Aspergillus flavus and a known animal hepatocarcinogen, was evaluated in CD-1 mice. Male mice received 0, 0.03, 0.145 or 0.70 mg/kg of AFB1 orally every other day for 2 weeks in a corn oil:ethanol vehicle. Splenic lymphocytes were cultured in the presence of lipopolysaccharide (LPS), phytohemagglutinin (PHA), or pokeweed mitogen (PWM). A dose-related inhibition of [3H]thymidine uptake in lymphocyte cultures, with or without the above mitogens, was observed after 2 weeks of AFB1 exposure. Synthesis of DNA was decreased in mixed lymphocyte cultures. Primary antibody production by splenic cells, from animals challenged with a T-dependent antigen (sheep red blood cells), was affected by AFB1. No effects were observed, however, when animals were challenged with a T-independent antigen (LPS). A dose-related suppression of a delayed-type hypersensitivity reaction to keyhole limpet hemocyanin was observed. The results suggested that AFB1 was immunotoxic in CD-1 mice.

Immunotoxic effects of T-2 mycotoxin on cell-mediated resistance to Listeria monocytogenes infection

The effect of T-2 toxin on cell-mediated resistance to bacterial infection was evaluated in mice exposed to Listeria monocytogenes. Mice were inoculated with 4.0 X 10(5) (LD50) or 4.0 X 10(4) (nonlethal) L. monocytogenes on day 0 and treated orally on days 0, 1, 2, and 3 with 2.0, 1.0, or 0 mg/kg T-2 toxin. Toxin induced suppression of resistance was indicated by the rapid growth of Listeria in the spleen and by significant (P less than 0.005) increases in mortality due to listeriosis. Necrosis and depletion of lymphoid tissue, lymphopenia, and a marked decrease in the influx of lymphocytes and macrophages into Listeria elicited peritoneal exudates and at sites of infection in the liver and spleen occurred in the toxin treated mice. The immunotoxic effect of T-2 toxin on cell-mediated resistance to listeriosis was dosage dependent and attributed to toxin induced lymphoid depletion and the failure of surviving lymphocytes and mononuclear cells to clear the host of infection.

Cutaneous injury by topical T-2 toxin: involvement of microvessels and mast cells

Topical applications of various doses of T-2 toxin to rats led to delayed skin reactions. Following a dose-dependent latent period of 12-24 hr, there appeared vascular dilation, stasis, edema and mononuclear cell infiltration, with many degranulating mast cells. These signs were earliest and strongest in the subcutis. Epidermal necrosis occurred 1-2 days later and was probably caused secondarily by ischemia, due to microcirculatory failure. Ultrastructurally, endothelial cells of small vessels were the earliest sites of change. While intercellular junctions remained closed and pinocytosis decreased, the cytoplasm contained many ribosomes, vacuoles, and abnormal mitochondria. Another early effect of topical T-2 toxin was an increase in number and degranulation of mast cells, especially in the subcutis. The resemblance of the skin injury to that produced by irradiation is noted.