Altered serum immunoglobulin response to model intestinal antigens during dietary exposure to vomitoxin (deoxynivalenol)

The intestinal barrier as an emerging target in the toxicological assessment of mycotoxins

Mycotoxins, the secondary metabolites of fungal species, are the most frequently occurring natural food contaminants in human and animal diets. Risk assessment of mycotoxins focused as yet on their mutagenic, genotoxic and potential carcinogenic effects. Recently, there is an increasing awareness of the adverse effects of various mycotoxins on vulnerable structures in the intestines. In particular, an impairment of the barrier function of the epithelial lining cells and the sealing tight junction proteins has been noted, as this could result in an increased translocation of luminal antigens and pathogens and an excessive activation of the immune system. The current review aims to provide a summary of the available evidence regarding direct effects of various mycotoxins on the intestinal epithelial barrier. Available data, based on different cellular and animal studies, show that food-associated exposure to certain mycotoxins, especially trichothecenes and patulin, affects the intestinal barrier integrity and can result in an increased translocation of harmful stressors. It is therefore hypothesized that human exposure to certain mycotoxins, particularly deoxynivalenol, as the major trichothecene, may play an important role in etiology of various chronic intestinal inflammatory diseases, such as inflammatory bowel disease, and in the prevalence of food allergies, particularly in children.

Deoxynivalenol-induced proinflammatory gene expression: mechanisms and pathological sequelae

The trichothecene mycotoxin deoxynivalenol (DON) is commonly encountered in human cereal foods throughout the world as a result of infestation of grains in the field and in storage by the fungus Fusarium. Significant questions remain regarding the risks posed to humans from acute and chronic DON ingestion, and how to manage these risks without imperiling access to nutritionally important food commodities. Modulation of the innate immune system appears particularly critical to DON's toxic effects. Specifically, DON induces activation of mitogen-activated protein kinases (MAPKs) in macrophages and monocytes, which mediate robust induction of proinflammatory gene expression-effects that can be recapitulated in intact animals. The initiating mechanisms for DON-induced ribotoxic stress response appear to involve the (1) activation of constitutive protein kinases on the damaged ribosome and (2) autophagy of the chaperone GRP78 with consequent activation of the ER stress response. Pathological sequelae resulting from chronic low dose exposure include anorexia, impaired weight gain, growth hormone dysregulation and aberrant IgA production whereas acute high dose exposure evokes gastroenteritis, emesis and a shock-like syndrome. Taken together, the capacity of DON to evoke ribotoxic stress in mononuclear phagocytes contributes significantly to its acute and chronic toxic effects in vivo. It is anticipated that these investigations will enable the identification of robust biomarkers of effect that will be applicable to epidemiological studies of the human health effects of this common mycotoxin.

n-3 polyunsaturated fatty acids and autoimmune-mediated glomerulonephritis

Consumption of n-3 polyunsaturated fatty acids (PUFAs) found in fish oil suppresses inflammatory processes making these fatty acids attractive candidates for both the prevention and amelioration of several organ-specific and systemic autoimmune diseases. Both pre-clinical and clinical studies have been conducted to determine whether fish oils containing the n-3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) can be used in the prevention and treatment of immunoglobulin A nephropathy (IgAN) and lupus nephritis. In a toxin-induced mouse model that mimics the early stages of IgAN, n-3 PUFA consumption suppresses aberrant interleukin (IL)-6-driven IgA production and mesangial IgA immune complex deposition by impairing phosphorylation of upstream kinases and activation of transcription factors essential for IL-6 gene transcription. n-3 PUFAs can also suppress production of anti-double-stranded DNA IgG antibodies and the resultant development of lupus nephritis in the NZBW F1 mouse and related models. These effects have been linked in part to impaired expression of proinflammatory cytokines and adhesion molecules as well as increases in antioxidant enzymes in kidney and immune organs. Several recent clinical trials have provided compelling evidence that n-3 PUFA supplementation could be useful in treatment of human IgAN and lupus nephritis, although some other studies suggest such supplementation might be without benefit. Future investigations employing genomics/proteomics and novel genetically altered mice should provide further insight into how n-3 PUFAs modulate these diseases as well help to identify clinically relevant biomarkers. The latter could be employed in future well-designed, long-term clinical studies that will resolve current controversies on n-3 PUFA efficacy in autoimmune-mediated glomerulonephritis.

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.

Ingestion of deoxynivalenol (DON) contaminated feed alters the pig vaccinal immune responses

Deoxynivalenol (DON), a mycotoxin produced by some Fusarium species, is a frequent contaminant of cereals. This toxin is known to modulate the immune function but only few studies have investigated the effect of DON on the vaccinal immune response. In the present experiment, 24 pigs received for 9 weeks either control feed or feed naturally contaminated with 2.2-2.5 mgDON/kg feed. At days 4 and 15 of the experiment, the animals were subcutaneously immunized with ovalbumin. Consumption of DON-contaminated diet does not have a major effect on the hematological and biochemical blood parameters. By contrast, ingestion of DON significantly affects the global and the specific immune response of the pigs. In the serum, DON increases the concentration of total IgA and, in vaccinated animals, DON also increases the concentration of ovalbumin-specific IgA and IgG. DON does not modulate lymphocytes proliferation after mitogenic stimulation but the toxin had a biphasic effect on lymphocyte proliferation after antigenic stimulation (up-regulation at day 21 and down-regulation at day 35-49). Because cytokines play a key role in immunity, the expression levels of TGF-beta, IFN-gamma, IL-4 and IL-6 were measured, by RT-PCR in the spleen, the ileum and the mesenteric lymph node of the animals at the end of the experiment. In the mesenteric lymph node, a significantly lower expression of both TGF-beta and IFN-gamma mRNA expression levels is observed in animals feed with DON when compared with control piglets. Taken together, our data indicate that DON alters the vaccinal immune response. These results may have implications for humans and animals consuming DON-contaminated food or feed as breakdown in vaccinal immunity may lead to the occurrence of disease even in properly vaccinated populations.

Modulation of Murine Host Response to Enteric Reovirus Infection by the Trichothecene Deoxynivalenol

Based on the known capacity of deoxynivalenol (DON) to target gut lymphoid tissue and IgA production, it was hypothesized that this mycotoxin interferes with the immune response to enteric reovirus infection. When mice were orally gavaged, first with 25 mg/kg bw DON, and then with reovirus serotype 1, strain Lang (T1/L) 2 or 12 h later, viral titers in the GI tract were 10-fold higher than control mice after 5 days. Virus was almost completely cleared in both treatment and control groups from intestinal tissue after 10 days. Real-time PCR indicated that, in infected control mice, reovirus lambda2 core spike (L2 gene) RNA per g feces in infected mice that were pretreated with DON was significantly higher at 1, 3, and 5 days than in infected mice only. In reovirus-infected mice, DON at doses of 10 and 25 mg/kg bw but not 2 and 5 mg/kg bw increased fecal L2 RNA, whereas DON doses as low as 2 mg/kg potentiated L2 RNA levels in Peyer's patches (PP). Reovirus-specific IgA levels in feces of mice treated with DON were significantly elevated, as were specific IgA responses in lamina propria and PP fragment cultures. Similar effects were observed for serum IgA and IgG. DON suppressed IFN-gamma responses in PP to reovirus at 3 and 5 days as compared to infected controls, while IL-2 mRNA concentrations were unaffected. Although reovirus alone did not induce Th2 cytokine mRNAs in PP, DON exposure significantly elevated IL-4, IL-6, and IL-10 mRNA expression at various times during the infection. ELISPOT revealed that mRNA expression data corresponded to suppression of IFN-gamma- and enhancement of IL-4-producing cell responses in PP cultures from DON-treated mice. Taken together, these data suggest that DON transiently increased both severity of the reovirus infection and shedding in feces as well as elevated reovirus IgA responses. These effects corresponded to suppressed Th1 and enhanced Th2 cytokine expression.

Docosahexaenoic acid attenuates mycotoxin-induced immunoglobulin a nephropathy, interleukin-6 transcription, and mitogen-activated protein kinase phosphorylation in mice

The purpose of this investigation was to evaluate the dose-dependent effects of docosahexaenoic acid (DHA) on deoxynivalenol (DON)-induced IgA nephropathy in mice and their relation to proinflammatory gene expression and mitogen-activated protein kinase (MAPK) activation. Consumption of a modified AIN-93G diet containing 1, 5, and 30 g/kg DHA resulted in dose-dependent increases of DHA in liver phospholipids with concomitant decreases in arachidonic acid compared with control diets. DHA dose dependently inhibited increases in serum IgA and IgA immune complexes (IC) as well as IgA deposition in the kidney in DON-fed mice; the 30 g/kg DHA diet had the earliest detectable effects and maximal efficacy. Both splenic interleukin-6 (IL-6) mRNA and heterogeneous nuclear RNA (hnRNA), an indicator of IL-6 transcription, were significantly reduced in DON-fed mice that consumed 5 and 30 g/kg DHA; a similar reduction was observed for cyclooxygenase (COX-2) mRNA. In a subsequent study, acute DON exposure (25 mg/kg body weight) induced splenic IL-6 mRNA and hnRNA as well as COX-2 mRNA in mice fed the control diet, whereas induction of both RNA species was significantly inhibited in mice fed 30 g/kg DHA. These latter inhibitory effects corresponded to a reduction in DON-induced phosphorylation of p38, extracellular-signal related kinase 1/2, and c-Jun N-terminal kinase 1/2 MAPKs in the spleen. Taken together, the results indicate that DHA dose-dependently inhibited DON-induced IgA dysregulation and nephropathy, and that impairment of MAPK activation and expression of COX-2 and IL-6 are potential critical upstream mechanisms.

Cellular and molecular mechanisms for immune modulation by deoxynivalenol and other trichothecenes: unraveling a paradox

Macrophages, T cells, and B cells of the immune system are central targets of deoxynivalenol (DON) and other trichothecenes-mycotoxins that can be immunostimulatory or immunosuppressive depending on dose, exposure frequency and timing of functional immune assay. Notably, low dose trichothecene exposure transcriptionally and post-transcriptionally upregulates expression of cytokines, chemokines and inflammatory genes with concurrent immune stimulation, whereas high dose exposure 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 signaling events related to immune response and apoptosis. Using cloned macrophages, our laboratory has identified two critical upstream transducers of DON-induced MAPK activation. One transducer is double-stranded RNA-(dsRNA)-activated protein kinase (PKR), a widely-expressed serine/theonine protein kinase that can be activated by dsRNA, interferon, and other agents. The second transducer is hematopoetic cell kinase (Hck), a non-receptor associated Src family kinase. Inhibitors and gene silencing studies have revealed that Hck and PKR play roles in DON induced gene expression and apoptosis. Future studies should focus on the molecular linkages between these kinases and trichothecene toxicity.

Deoxynivalenol-induced IgA production and IgA nephropathy-aberrant mucosal immune response with systemic repercussions

Dietary exposure to the common foodborne mycotoxin deoxynivalenol (DON) selectively upregulates serum immunoglobulin A (IgA) in the mouse, most of which is polymeric, thus suggesting that the mucosal immune system is a primary target. When ingested, DON has no adjuvant or antigen properties but, rather, induces polyclonal IgA synthesis and serum elevation in an isotype-specific fashion. Resultant hyperelevated IgA is polyspecific, autoreactive and is likely to be involved in immune complex formation as well as kidney mesangial deposition. These latter effects mimic IgA nephropathy, the most common human glomerulonephritis. At the cellular level, DON upregulates production of T helper cytokines and enhances T cell help for IgA secretion. Analogous effects are observed in the macrophage with IL-6 being of particular importance based on ex vivo reconstitution and antibody ablation studies as well as experiments with IL-6 deficient mice. Upregulation of cytokines by DON involves both increased transcriptional activation and mRNA stability which are mediated by activation of mitogen-activated protein kinases. Interestingly, dietary omega-3 fatty acids can downregulate these processes and ameliorate DON-induced IgA nephropathy. From the perspective of gut mucosal immunotoxicology, these studies demonstrate that the capacity of a chemical to affect mucosal immune response can have systemic repercussions and, further, that these effects can be modulated by an appropriate nutritional intervention.

Effects of vomitoxin ingestion on murine models for systemic lupus erythematosus

Dietary exposure to the trichothecene vomitoxin (VT) results in reduced body weight gain, elevated serum IgA, terminal differentiation of Peyer's patch B cells to IgA secreting plasma cells haematuria, and increased kidney mesangial IgA accumulation in B6C3F1 mice and other inbred strains. These effects closely mimic a human autoimmune-like kidney disease known as IgA nephropathy. Using NZBW/F1, MRL/lpr, and BXSB mouse strains as models of systemic lupus erythematosus, we assessed whether consumption of diet containing 5 ppm or 10 ppm VT will similarly affect mice genetically prone to autoimmunity. Reduced weight gains were seen in NZBW/F1 and MRL/lpr mice fed both doses of VT within 2-3 weeks. In contrast, VT had little effect on weight gain by BXSB mice. Serum Ig levels in all three strains generally did not differ from control mice. Haematuria was significantly increased when all three strains were fed VT. In NZBW/F1 Peyer's patch cultures stimulated with lipopolysaccharide (LPS), prior VT exposure significantly increased the IgG and IgM secretion but had no effect on IgA. In MRL/lpr Peyer's patch cultures stimulated with LPS, VT exposure increased IgA secretion but not IgM or IgG. BXSB Peyer's patch cultures prepared from VT treatment groups produced significantly more IgA than controls when cultured with LPS or Concanavalin A. Whereas mesangial deposition of IgA and IgG was significantly lower in the treatment groups of NZBW/F1 and MRL/lpr mice compared with control, BXSB mice had significantly higher IgA, IgG, and complement (C3) deposition when fed VT. The results suggest that although dietary VT differentially affected mice with aberrant immune systems, these strains did not appear to be any more sensitive to the mycotoxin than were more immunologically robust inbred strains.

Ingestion of yogurt containing Lactobacillus acidophilus and Bifidobacterium to potentiate immunoglobulin A responses to cholera toxin in mice

Lactic acid bacteria have been reported to have benefits for the prevention and treatment of some forms of diarrhea and related conditions. To determine whether these effects might involve direct stimulation of the gastrointestinal immune response, we administered yogurt to try to enhance mucosal and systemic antibodies against an orally presented immunogen, cholera toxin. Yogurts were manufactured with starter cultures containing different species and strains of lactic acid bacteria. Mice were fed these yogurts for 3 wk, during which they were also orally immunized twice with 10 micrograms of cholera toxin. Blood was collected on d 0 and 21, and fecal pellets were collected weekly. Mice that were immunized orally with cholera toxin responded by producing specific intestinal and serum immunoglobulin (Ig)A anti-cholera toxin. Antibody responses of the IgA isotype were significantly increased in mice fed yogurts made with starters containing the conventional yogurt bacteria Lactobacillus bulgaricus and Streptococcus thermophilus supplemented with Lactobacillus acidophilus, Bifidobacterium bifidum, and Bifidobacterium infantis. Yogurt that was manufactured with starters containing only conventional yogurt bacteria produced less IgA anti-cholera toxin than did the control group fed nonfat dry milk. Although strong responses were also observed for IgG anti-cholera toxin in serum, the responses did not differ among groups. Thus, administration of yogurt supplemented with L. acidophilus and Bifidobacterium spp. enhanced mucosal and systemic IgA responses to the cholera toxin immunogen.

Effects of intermittent vomitoxin exposure on body weight, immunoglobulin levels and haematuria in the B6C3F1 mouse

Continuous dietary exposure of female B6C3F1 mice to the trichothecene vomitoxin (VT) results in reduced body weight gain, elevated production of serum immunoglobulin A (IgA), kidney mesangial IgA deposition and glomerulonephritis. To assess whether intermittent consumption of dietary VT, as might occur during natural animal and human exposures, has similar effects to those for continuous consumption, a comparison was made between two schedules of dietary exposure. Female B6C3F1 mice were fed for 13 weeks with either a semipurified AIN-76A diet containing 20 ppm VT continuously or with 20 ppm VT intermittently (every other week). The effect these diets had on body weight gain, serum immunoglobulin (Ig) profile, mesangial Ig deposition and haematuria were assessed and compared with each other as well as with mice fed a control diet. Reduced body weight gains in the treatment groups were seen as early as 2 weeks. After week 4, the mean body weight of the intermittent group appeared higher than the continuous group during the weeks when it was fed a control diet, but dropped to continuous group levels during the weeks they were fed VT. Serum IgA levels in the intermittent group remained at control levels and were significantly lower than the continuous group during the course of the study. In contrast, serum IgG and serum immunoglobulin M (IgM) levels for the intermittent and continuous groups were significantly decreased compared with control. Mesangial IgA deposition was significantly lower in the intermittent group compared with the continuous group, and had levels comparable to mice on the control diet. Haematuria was significantly greater in both treatment groups compared with control at weeks 5 and 13 when the intermittent group was fed VT containing diet, but haematuria in the intermittent group dissipated at week 10 when it was fed control diet. The results presented here suggest that the type of dietary exposure regimen is critical in determining the extent of toxic effects induced by VT. Thus, when animal models are used for assessing the toxic effects of mycotoxins, it may be useful to consider the effects of intermittent and sporadic exposure.

Experimental murine IgA nephropathy following passive administration of vomitoxin-induced IgA monoclonal antibodies

Oral exposure of mice to vomitoxin (VT) induces elevated levels of serum IgA, circulating IgA immune complexes (IgA-IC), mesangial IgA deposition and haematuria, which all mimic the clinical signs of human IgA nephropathy (IgAN). To further assess the effects of VT-induced IgA in the murine model, B6C3F1 and BALB/C mice were injected intraperitoneally with affinity-purified monoclonal IgA derived from Peyer's patch hybridomas of VT-exposed mice. In B6C3F1 mice, serum IgA, IgM and IgA-IC levels were increased two- to fivefold in treatment groups after 4 and 6 wk compared with controls, whereas increases in serum IgG as high as 18-fold were observed. Urinary erythrocyte counts were also significantly elevated in treatment groups after 2, 4 and 6 wk compared with controls. Concurrent increases in IgA and IgG complexes containing casein, the dietary protein source, occurred in treatment mice. Mesangial IgA, IgG, IgM and C3 deposition were significantly increased in all treatment mice after 6 wk. Electron-dense deposits occurred in the glomeruli of IgA-injected mice after 6 wk. All the above parameters were similarly affected in BALB/C mice. Injection of IgA-secreting hybridoma cells into BALB/C mice increased serum IgA, IgA-IC and IgG levels as well as elevated mesangial IgA, IgG and C3 deposition and haematuria after 2-3 weeks compared with controls. In total, these data indicate that passive administration of VT-induced IgAs can induce the hallmarks of IgA nephropathy. Casein, an antigen found in the diet used for these mice, appeared to form IC with IgA or IgG and these IC may participate in the pathogenesis of this nephropathy.

Effects of diets with graded levels of naturally deoxynivalenol-contaminated oats on immune response in growing pigs

A trial was conducted to evaluate the effect of including different levels of deoxynivalenol (DON)-contaminated oats in the complete diets of growing pigs on immune response and performance. The diets contained 0.6, 1.8 and 4.7 mg DON/kg, and both restricted and ad libitum feeding were used. Performance was recorded as weight gain, feed intake, efficiency of feed utilization and carcass quality. Immune response parameters recorded included primary and secondary antibody titres after injections of five different antigens: Human serum albumin (HSA), sheep red blood cells (SRBC), paratuberculosis vaccine (MPT), tetanus toxoid (TT) and diphteria toxoid (DT). A johnin test was also performed. Lymphocyte stimulation response was measured with three different mitogens (PWM, ConA and PHA). A significant, DON dose-dependent reduction in secondary antibody response to tetanus toxoid was observed. A slightly higher mitogen response after PHA stimulation in lymphocytes from the medium and high DON groups compared to the low DON group after 9 weeks was considered inconclusive. No other indication of dose-dependent immune response inhibition or stimulation was found. Significantly reduced feed intake with increased levels of DON was observed in groups fed restricted rations according to weight, but not in animals fed ad libitum.

Vomitoxin (deoxynivalenol)-induced IgA nephropathy in the B6C3F1 mouse: dose response and male predilection

Oral exposure to the trichothecene vomitoxin (VT or deoxynivalenol) in mice induces marked elevation of total and autoreactive IgA, IgA immune complexes, and mesangial IgA deposition in a manner that is highly analogous to human IgA nephropathy. In this study, immunopathologic markers indicative of IgA nephropathy were compared in male and female B6C3F1 mice fed semipurified AIN-76A diet containing 0, 2, 10 or 25 ppm VT for 12 weeks. Males fed 10 and 25 ppm VT and females fed 25 ppm VT had increased serum IgA at 4 weeks. At week 8, male mice fed the minimal dose of 2 ppm VT and female mice fed 10 ppm also exhibited elevated serum IgA. IgA levels were consistently higher in treatment males than females with significant differences being observed in the 10-ppm dose group at 4 and 12 weeks. IgA coproantibodies were marginally increased (maximum of 2-fold) in mice of both genders fed 10 and 25 VT. At 8 and 12 weeks, serum IgM was depressed in male and female mice eating 10 and 25 ppm VT, whereas consistent effects on serum IgG or IgE were not observed. In similar fashion, male mice in the 2, 10 and 25 ppm VT groups exhibited microscopic hematuria as early as 4 weeks, whereas this occurred in females fed 10 and 25 ppm VT only at week 10 with urinary erythrocyte counts being lower than male counterparts. Mesangial deposition of IgA and C3 was significantly increased in males exposed to 2, 10 and 25 ppm VT and in females exposed to 10 and 25 ppm VT, with males exhibiting a greater deposition than corresponding females. Based on these immunological parameters, males appeared more susceptible than female mice to VT-induced IgA dysregulation and IgA nephropathy in terms of latency, threshold dose, and severity.

Role of gender and strain in vomitoxin-induced dysregulation of IgA production and IgA nephropathy in the mouse

Prolonged dietary exposure of female B6C3F1 mice to the trichothecene vomitoxin results in hyperproduction of immunoglobulin A (IgA) with a concurrent immunopathology that mimics human IgA nephropathy. To assess the role of gender and strain in the mouse model, semipurified AIN-76A diet containing 25 ppm vomitoxin was fed to B6C3F1 male mice and to B6C3F1, BALB/c, C3H/HeN, C3H/HeJ, and C57BL/6 female mice for 8 wk, and immunopathologic indicators of IgA nephropathy were compared to mice fed clean diet. At the cessation of the experiment, all treatment groups weighed less than respective controls. Serum IgA was increased in male and female B6C3F1 mice as well as in C3H/HeJ, C57BL/6, and BALB/c female mice compared to corresponding controls. Serum IgA levels were two- to sixfold higher in B6C3F1 male treatment animals compared to female treatment groups from all strains. In contrast, at wk 8 serum IgG levels were unaffected or decreased, and serum IgM was decreased in all groups at wk 8. There was a trend toward increased IgA production by Peyer's patch (PP) lymphocytes isolated from treatment mice as compared to controls in all groups except the C3H/HeJ mice. Notably, IgA levels were 18-fold higher in B6C3F1 male treatment PP cultures than in B6C3F1 female treatment cultures. Hematuria was significantly greater in treatment mice than respective controls at both wk 4 and 8. Increased mesangial IgA deposition was also detectable in all treatment groups except the C57BL/6 mouse. The results suggested that the male B6C3F1 mouse and the five strains of female mice exhibited many of the immunopathologic effects found in IgA nephropathy and that IgA elevation was more marked in male B6C3F1 than female B6C3F1 mice.

Polyclonal autoreactive IgA increase and mesangial deposition during vomitoxin-induced IgA nephropathy in the BALB/c mouse

To establish the relationship between autoreactive antibodies and vomitoxin-induced immunoglobulin A (IgA) nephropathy, the effects of dietary vomitoxin exposure on the antigen specificity of serum IgA, IgA-producing cells and accumulated mesangial IgA in BALB/c mice were assessed. Exposure to dietary vomitoxin for 8 wk caused a significant increase in total serum IgA. There was a concurrent significant increase in serum IgA specific for trinitrophenol (TNP), phosphorylcholine, cardiolipin and sphingomyelin compared with controls, suggesting an elevation of autoreactive IgA. Casein, a protein found in the AIN-76A diet, could inhibit binding of serum IgA to sphingomyelin and cardiolipin, indicating that these antibodies may be polyspecific. When enzyme-linked immunospot assay was used to monitor autoreactive IgA production, trends were observed towards increased IgA-secreting cells specific for TNP, cardiolipin and sphingomyelin in Peyer's patches from vomitoxin-fed mice compared with control mice. IgA-producing cells reactive with TNP were increased in the spleen of vomitoxin-fed mice whereas effects on IgA-secreting cells for the other antigens were marginal. Marked deposition of mesangial IgA was also observed in vomitoxin-fed mice compared with controls. When IgA was eluted from the kidney sections of treated mice and tested by enzyme-linked immunosorbent assay, it exhibited a strong binding to the above antigen panel as well as inulin, DNA and casein. These data suggest that dietary vomitoxin induced the polyclonal activation of IgA-producing cells and that resultant autoreactive IgA was subsequently deposited in the kidney mesangium.

Polyspecific and autoreactive IgA secreted by hybridomas derived from Peyer's patches of vomitoxin-fed mice: characterization and possible pathogenic role in IgA nephropathy

A total of 122 immunoglobulin (Ig)A-producing hybridoma clones were isolated from the Peyer's patches of vomitoxin-fed BALB/c mice and the resultant antibodies were characterized for their antigenic specificity and pathogenic potential. When reactivity was tested against a panel consisting of DNA, sphingomyelin, thyroglobulin, collagen, casein, cardiolipin and bovine serum albumin conjugates of phosphorylcholine, inulin and trinitrophenol that were representative of self and non-self antigens, approximately 95% of the monoclonal IgAs bound to at least one of the panel antigens and 80% bound to more than one antigen. The polyspecificity of some of the monoclonal IgAs was further suggested by demonstrating the capacity of one antigen to inhibit binding of monoclonal IgA to another antigen. Protein staining and Western blotting of gradient native polyacrylamide gels, indicated that trimeric IgA predominated in the isolated monoclonal IgAs. Repeated injections of mice with representative monoclonal IgAs induced microhaematuria in three of four of the clones tested but not IgA deposition in the kidney glomerulus. In addition, three of the four monoclonal IgAs caused IgG and C3 deposition in the kidney mesangium. These and previous results suggest that dietary vomitoxin promotes the polyclonal activation and expansion of IgA-secreting B cells at the Peyer's patch level and that resultant polyspecific, autoreactive IgA may contribute to kidney pathogenesis.

Effects of low-level dietary deoxynivalenol on haematological and clinical parameters of the pig

The subacute toxic effects of dietary deoxynivalenol (DON) were examined in grower pigs during a 32 day feeding period. DON was incorporated into the feed at 0, 1, and 3 mg/kg, added as either the purified toxin (P) or as naturally contaminated corn (N). Growth performance and blood biochemical and haematological parameters were monitored throughout the study. At the higher toxin levels (diets 3P, 3N) significantly lower feed consumption and body weight gains were evident soon after the start of feeding, but while weight gains of pigs fed the pure DON diet (3P) recovered after several days, values for pigs fed the naturally contaminated diet (3N) remained depressed over the course of the study. It is possible that these observations reflected the presence of other unidentified toxic compounds in the naturally contaminated grain. Generally, blood chemistry parameters of pigs fed the contaminated diets were not different from controls, with the exception of alpha-globulin and possibly cortisol in animals receiving diets 3N or 3P. Data suggested that the effect of DON on the alpha-globulin fraction may have been independent of the feed refusal syndrome associated with this toxin. Alterations in several haematological measurements were noted to occur sporadically with the 3 ppm diets, including higher RBC count, haematocrit and platelet level, however these effects could not be separated from the influence of decreased feed intake and were of limited value in diagnosing the effects of low level dietary DON on swine.

Vomitoxin-induced dysregulation of serum IgA, IgM and IgG reactive with gut bacterial and self antigens

The effect of dietary vomitoxin exposure on immunoglobulins that react with naturally occurring gut bacterial and self antigens was assessed in the B6C3F1 mouse. Ingestion of 25 ppm vomitoxin for 4 and 8 wk resulted in significantly elevated total IgA but depressed total IgG and IgM in serum when compared with control mice fed semi-purified diet only. IgA specific for phosphorylcholine (PC) and inulin (haptens associated with intestinal bacteria) increased significantly in mice fed vomitoxin whereas IgM with the identical specificity decreased. When sera were assessed for autoantibodies recognizing DNA and bromelated mouse red blood cells (MRBC), vomitoxin-exposed mice exhibited elevated specific IgA as compared with controls. This occurred together with decreases in DNA-specific IgG and IgM, and decreases in MRBC-specific IgM. Additionally, vomitoxin exposure did not enhance the specific serum IgA response to orally administered trinitrophenylated sheep red blood cells (TNP-SRBC), but significantly depressed TNP-specific serum IgG. The results suggest that hyperelevation of total and specific serum IgA for oral and self antigens occurs during vomitoxin feeding and that may be coupled with down-regulation of total and specific IgM or IgG. These effects could be contributory to the capacity of vomitoxin to induce IgA immune complex glomerulonephritis.

Dietary exposure to the trichothecene vomitoxin (deoxynivalenol) stimulates terminal differentiation of Peyer's patch B cells to IgA secreting plasma cells

The effects of 8 weeks of dietary exposure to the fungal toxin vomitoxin (25 ppm) on the kinetics of in vitro immunoglobulin (Ig) production and appearance of IgA-secreting cells in lymphocyte culture were assessed in the B6C3F1 mouse. The feeding regimen resulted in an IgA:IgG serum ratio of 2.4 compared to 0.4 in controls indicating that there was dysregulation of IgA production in the systemic compartment. Prior toxin feeding had no effect on viability of Peyer's patch (PP) or splenic lymphocyte cultures. IgA production, as determined by enzyme-linked immunosorbent assay, was significantly greater in treatment PP and splenic lymphocytes cultured for 2-11 days than in corresponding controls. Similar trends were found for IgG production in PP cultures although levels were much lower. There were 1.7 and 2.0 times more IgA-producing cells, as measured by the ELISPOT assay, in freshly prepared PP and splenic lymphocytes from treatment mice compared to control mice, respectively. In contrast, after 2 days there were 10.9, 3.2, and 12.4 times more IgA-secreting cells in concanavalin A (Con A), LPS, and unstimulated treatment PP cultures, respectively, and 4.0, 2.0, and 3.5 times times more IgA-secreting cells in 2-day treatment spleen cultures, respectively. Both IgA and IgG secretion in Con A-stimulated cultures were significantly greater when treatment T cells and control B cells were combined than when control T cells and control B cells were combined. Increased Ig secretion attributable to T cell effects was not observed in LPS-stimulated or unstimulated PP reconstitution cultures or in spleen reconstituted cultures with and without mitogen. The results provide evidence that dietary vomitoxin enhances terminal differentiation of IgA secreting cells in PP. This and resultant migration of IgA secreting cells into the systemic compartment favor a shift from IgG to IgA as the primary serum isotype.

Effect of dietary administration of the trichothecene vomitoxin (deoxynivalenol) on IgA and IgG secretion by Peyer's patch and splenic lymphocytes

Prolonged dietary exposure of mice to the trichothecene vomitoxin induces abnormally high levels of serum IgA and kidney mesangial IgA accumulation in a manner that is highly analogous to the human glomerulonephritis IgA nephropathy. In this study, the capacity of Peyer's patch and splenic lymphocytes to produce IgA and IgG were compared in B6C3F1 mice that were fed diets with and without 25 ppm vomitoxin for up to 12 wk. Serum IgA increased 2-, 4- and 8-fold after 4, 8 and 12 wk, respectively, of vomitoxin exposure and it became the primary serum isotype, whereas serum IgG was unaffected. On termination of the experiment there were increased numbers of IgA-secreting cells in Peyer's patches after 8 wk of toxin exposure and in the spleen after 4, 8 and 12 wk of toxin exposure. There were also increased numbers of IgG-secreting cells in Peyer's patches on termination of the experiment at 4, 8 and 12 wk but no effects was observed in the spleen. Supernatant IgA and IgA-secreting cell numbers were also markedly elevated in lymphocyte cultures obtained from Peyer's patches and, to a lesser extent, from spleens of treated mice compared with controls. Based on output of treated mice relative to corresponding controls, IgA secretion was greatest in concanavalin-A-stimulated and unstimulated Peyer's patch cultures. Enhanced IgG secretion and IgG-secreting cells were also observed in mitogen-stimulated and unstimulated Peyer's patch lymphocyte cultures of treated relative to control mice, but differences in splenocyte cultures were negligible. Based on total Ig output, IgA production was 8- to 20-fold greater than IgG production in both control and treatment Peyer's patch cultures. In contrast, vomitoxin treatment caused a shift from primarily IgG production in lipopolysaccharide-stimulated spleen cultures to equivalent IgA production. These data provide in vitro evidence that ingestion of vomitoxin promotes terminal differentiation of IgA-secreting progenitors in the Peyer's patch and, to a lesser extent, in the spleen. These functional changes are consistent with the shift from IgG to IgA as the primary serum isotype.

Elevated membrane IgA+ and CD4+ (T helper) populations in murine Peyer's patch and splenic lymphocytes during dietary administration of the trichothecene vomitoxin (deoxynivalenol)

Recent investigations indicate that dietary exposure to the trichothecene vomitoxin increases total and antigen-specific serum immunoglobulin A (IgA) and glomerular IgA accumulation in mice. In this study, the effects of 25 ppm dietary vomitoxin on the histological and lymphocytic profile of component immune organs in the mucosal lymphocyte migratory pathway were evaluated in the B6C3F1 mouse. Vomitoxin administration resulted in marked stimulation of the size and frequency of germinal centres in Peyer's patches, mesenteric lymph nodes and the spleen. A slight increase in the percentage of B cells in the Peyer's patch was observed, although vomitoxin treatment had no effect on the percentage of B cells in the spleen. The percentage of IgA+ cells in Peyer's patches and spleen were approximately twice that of controls at 4, 8 and 12 wk of vomitoxin exposure whereas the percentage of IgG+ cells decreased in these two organs. Exposure to vomitoxin increased the percentage of T cells in Peyer's patches and the spleen. The percentage of CD4+ cells (T helper subset) increased slightly in Peyer's patches and more markedly (30-50%) in the spleen following vomitoxin treatment. Contrastingly, there was only a slight increase in the percentage of CD8+ cells (T cytotoxic/suppressor subset) in the spleens of vomitoxin-treated mice in comparison with controls, and no effect in Peyer's patches. The relative effects of vomitoxin on these two T cells populations was also reflected in increased CD4+: CD8+ ratios in Peyer's patches and spleen. These results are consistent with the hypothesis that dietary vomitoxin modulates normal regulation of the IgA response at the Peyer's patch level and that this is manifested in an altered lymphocyte distribution pattern in both the mucosal and systemic compartment. Notably increased levels of IgA+ and CD4+ cells are indicative of IgA-producing progenitors and T helper subsets, respectively, that in tandem could favour IgA hyperproduction and elevated IgA in serum.