Oral administration of collagen conjugated with cholera toxin induces tolerance to type II collagen and suppresses chondritis in an animal model of autoimmune ear disease

Immunomodulatory regulation by heat-labile enterotoxins and potential therapeutic applications

Introduction: Heat-labile enterotoxins (HLTs) and their cognate ganglioside receptors have been extensively studied because of their therapeutic potential. Gangliosides play arole in modulating effector cells of the immune system, and HLTs provide a novel means for stimulating ganglioside-mediated responses in immunocompetent cells.Areas covered: To evaluate the mechanisms of HLT adjuvanticity, a systemic literature review was performed using relevant keyword searches of the PubMed database, accessing literature published as recently as late 2020. Since HLTs bind to specific ganglioside receptors on immunocytes, they can act as regulators via stimulation or tapering of immune responses from associated signal transduction events. Binding of HLTs to gangliosides can increase proliferation of T-cells, increase cytokine release, augment mucosal/systemic antibody responses, and increase the effectiveness of antigen presenting cells. Subunit components also independently stimulate certain immune responses. Mutant forms of HLTs have potent immunomodulatory effects without the toxicity associated with holotoxins.Expert opinion: HLTs have been the subject of abundant research exploring their use as vaccine adjuvants, in the treatment of autoimmune conditions, in cancer therapy, and for weight loss, proving that these molecules are promising tools in the field of immunotherapy.

Adoptive Cellular Gene Therapy for the Treatment of Experimental Autoimmune Polychondritis Ear Disease

In the past, the clinical therapy for autoimmune diseases, such as autoimmune polychondritis ear disease, was mostly limited to nonspecific immunosuppressive agents, which could lead to variable responses. Currently, gene therapy aims at achieving higher specificity and less adverse effects. This concept utilizes the adoptive transfer of autologous T cells that have been retrovirally transduced ex vivo to express and deliver immunoregulatory gene products to sites of autoimmune inflammation. In the animal model of collagen-induced autoimmune polychondritis ear disease (CIAPED), the adoptive transfer of IL-12p40-expressing collagen type II (CII)-specific CD4+ T-cell hybridomas resulted in a significantly lower disease incidence and severity compared with untreated or vector-only-treated animals. In vivo cell detection using bioluminescent labels showed that transferred CII-reactive T-cell hybridomas accumulated in the inflamed earlobes of the mice with CIAPED. In vitro analysis demonstrated that IL-12p40-transduced T cells did not affect antigen-specific T-cell activation or systemic anti-CII Ab responses. However, IL-12p40-transduced T cells suppressed IFN-γ and augmented IL-4 production, indicating their potential to act therapeutically by interrupting Th1-mediated inflammatory responses via augmenting Th2 responses. These results indicate that the local delivery of IL-12p40 by T cells could inhibit CIAPED by suppressing autoimmune responses at the site of inflammation.

The Role of Dendritic Cell Maturation in the Induction of Insulin-Dependent Diabetes Mellitus

Dendritic cells (DCs) are the dominant class of antigen-presenting cells in humans and are largely responsible for the initiation and guidance of innate and adaptive immune responses involved in maintenance of immunological homeostasis. Immature dendritic cells (iDCs) phagocytize pathogens and toxic proteins and in endosomal vesicles degrade them into small fragments for presentation on major histocompatibility complex (MHC) II receptor molecules to naïve cognate T cells (Th0). In addition to their role in stimulation of immunity, DCs are involved in the induction and maintenance of immune tolerance toward self-antigens. During activation, the iDCs become mature. Maturation begins when the DCs cease taking up antigens and begin to migrate from their location in peripheral tissues to adjacent lymph nodes or the spleen where during their continued maturation the DCs present stored antigens on surface MHCII receptor molecules to naive Th0 cells. During antigen presentation, the DCs upregulate the biosynthesis of costimulatory receptor molecules CD86, CD80, CD83, and CD40 on their plasma membrane. These activated DC receptor molecules bind cognate CD28 receptors presented on the Th0 cell membrane, which triggers DC secretion of IL-12 or IL-10 cytokines resulting in T cell differentiation into pro- or anti-inflammatory T cell subsets. Although basic concepts involved in the process of iDC activation and guidance of Th0 cell differentiation have been previously documented, they are poorly defined. In this review, we detail what is known about the process of DC maturation and its role in the induction of insulin-dependent diabetes mellitus autoimmunity.

Oral delivery of ACE2/Ang-(1-7) bioencapsulated in plant cells protects against experimental uveitis and autoimmune uveoretinitis

Hyperactivity of the renin-angiotensin system (RAS) resulting in elevated Angiotensin II (Ang II) contributes to all stages of inflammatory responses including ocular inflammation. The discovery of angiotensin-converting enzyme 2 (ACE2) has established a protective axis of RAS involving ACE2/Ang-(1-7)/Mas that counteracts the proinflammatory and hypertrophic effects of the deleterious ACE/AngII/AT1R axis. Here we investigated the hypothesis that enhancing the systemic and local activity of the protective axis of the RAS by oral delivery of ACE2 and Ang-(1-7) bioencapsulated in plant cells would confer protection against ocular inflammation. Both ACE2 and Ang-(1-7), fused with the non-toxic cholera toxin subunit B (CTB) were expressed in plant chloroplasts. Increased levels of ACE2 and Ang-(1-7) were observed in circulation and retina after oral administration of CTB-ACE2 and Ang-(1-7) expressing plant cells. Oral feeding of mice with bioencapsulated ACE2/Ang-(1-7) significantly reduced endotoxin-induced uveitis (EIU) in mice. Treatment with bioencapsulated ACE2/Ang-(1-7) also dramatically decreased cellular infiltration, retinal vasculitis, damage and folding in experimental autoimmune uveoretinitis (EAU). Thus, enhancing the protective axis of RAS by oral delivery of ACE2/Ang-(1-7) bioencapsulated in plant cells provide an innovative, highly efficient and cost-effective therapeutic strategy for ocular inflammatory diseases.

Persistent suppression of type 1 diabetes by a multicomponent vaccine containing a cholera toxin B subunit-autoantigen fusion protein and complete Freund's adjuvant

Data presented here demonstrate multifunctional vaccination strategies that harness vaccinia virus mediated delivery of a gene encoding an immunoenhanced diabetes autoantigen in combination with complete Freund's adjuvant (CFA) that can maintain safe and durable immunologic homeostasis in NOD mice. Systemic coinoculation of prediabetic mice with recombinant vaccinia virus rVV-CTB::GAD and undiluted or 10-fold diluted CFA demonstrated a significant decrease in hyperglycemia and pancreatic islet inflammation in comparison with control animals during 17–61 and 17–105 weeks of age, respectively. Synergy in these beneficial effects was observed during 43–61 and 61–105 wks of age, respectively. Inflammatory cytokine and chemokine levels in GAD-stimulated splenocytes isolated from vaccinated mice were generally lower than those detected in unvaccinated mice. The overall health and humoral immune responses of the vaccinated animals remained normal throughout the duration of the experiments.

Suppression of dendritic cell activation by diabetes autoantigens linked to the cholera toxin B subunit

Antigen presenting cells, specifically dendritic cells (DCs) are a focal point in the delicate balance between T cell tolerance and immune responses contributing to the onset of type I diabetes (T1D). Weak adjuvant proteins like the cholera toxin B subunit when linked to autoantigens may sufficiently alter the balance of this initial immune response to suppress the development of autoimmunity. To assess adjuvant enhancement of autoantigen mediated immune suppression of Type 1 diabetes, we examined the cholera toxin B subunit (CTB)-proinsulin fusion protein (CTB-INS) activation of immature dendritic cells (iDC) at the earliest detectable stage of the human immune response. In this study, Incubation of human umbilical cord blood monocyte-derived immature DCs with CTB-INS autoantigen fusion protein increased the surface membrane expression of DC Toll-like receptor (TLR-2) while no significant upregulation in TLR-4 expression was detected. Inoculation of iDCs with CTB stimulated the biosynthesis of both CD86 and CD83 co-stimulatory factors demonstrating an immunostimulatory role for CTB in both DC activation and maturation. In contrast, incubation of iDCs with proinsulin partially suppressed CD86 co-stimulatory factor mediated DC activation, while incubation of iDCs with CTB-INS fusion protein completely suppressed iDC biosynthesis of both CD86 and CD83 costimulatory factors. The incubation of iDCs with increasing amounts of insulin did not increase the level of immune suppression but rather activated DC maturation by stimulating increased biosynthesis of both CD86 and CD83 costimulatory factors. Inoculation of iDCs with CTB-INS fusion protein dramatically increased secretion of the immunosuppressive cytokine IL-10 and suppressed synthesis of the pro-inflammatory cytokine IL12/23 p40 subunit protein suggesting that linkage of CTB to insulin (INS) may play an important role in mediating DC guidance of cognate naïve Th0 cell development into immunosuppressive T lymphocytes. Taken together, the experimental data suggests Toll like receptor 2 (TLR-2) plays a dominant role in CTB mediated INS inhibition of DC induced type 1 diabetes onset in human Type 1 diabetes autoimmunity. Further, fusion of CTB to the autoantigen was found to be essential for enhancement of immune suppression as co-delivery of CTB and insulin did not significantly inhibit DC costimulatory factor biosynthesis. The experimental data presented supports the hypotheses that adjuvant enhancement of autoantigen mediated suppression of islet beta cell inflammation is dependent on CTB stimulation of dendritic cell TLR2 receptor activation and co-processing of both CTB and the autoantigen in the same dendritic cell.

Autoantigens plus interleukin-10 suppress diabetes autoimmunity

BACKGROUND

Recombinant vaccinia virus (rVV) strains expressing the immunomodulatory cholera toxin B subunit (CTB) fused to the autoantigen glutamic acid decarboxylase (GAD) or the immunosuppressive cytokine interleukin-10 (IL-10) were independently able to generate only low levels of immune suppression of type 1 diabetes mellitus (T1DM). Here we suggest that a vaccinia virus (VV)-mediated combination of CTB::GAD fusion and IL-10 proteins promises a effective and durable immunotherapeutic strategy for T1DM.

METHODS

To explore this hypothesis, a CTB::GAD fusion gene was co-delivered with a gene encoding IL-10 by rVV infection (rVV-CTB::GAD + rVV-IL10) into 5-7-week-old non-obese diabetic (NOD) mice. The mice were assessed for vaccine protection against development of hyperglycemia from 12 to 64 weeks of age by assessment of pancreatic inflammation (insulitis) and splenocyte-secreted interferon-gamma and IL-10 cytokine levels.

RESULTS

By 36 weeks of age, from 54% to 80% of the mice in the negative control animal groups (either mock-infected or inoculated with unrelated plasmid or VV) had developed hyperglycemia. Similarly, no statistically significant improvement in protection against diabetes onset was achieved by inoculation with VV expressing CTB::GAD or IL-10 independently. Surprisingly, only 20% of mice co-inoculated with rVV-CTB::GAD + rVV-IL10 developed hyperglycemia by 28 weeks of age. Other treatment groups developed hyperglycemia by 32-36 weeks. After 36 weeks, diabetes incidence no longer increased in any groups until the end of experiment at 64 weeks of age. Histological analysis of pancreatic tissues of hyperglycemic mice revealed high levels of intra-islet insulitis. Analysis of insulitis at termination of the experiment showed that euglycemic mice co-inoculated with VV expressing CTB::GAD and IL-10 had more effectively reduced inflammation in comparison with the other groups.

CONCLUSIONS

A combinatorial vaccination strategy based on VV co-delivery of genes encoding the immunoenhanced autoantigen CTB::GAD and the anti-inflammatory cytokine IL-10 can maintain effective and durable euglycemia and immunological homeostasis in NOD mice with prediabetes.

AB toxins: a paradigm switch from deadly to desirable

To ensure their survival, a number of bacterial and plant species have evolved a common strategy to capture energy from other biological systems. Being imperfect pathogens, organisms synthesizing multi-subunit AB toxins are responsible for the mortality of millions of people and animals annually. Vaccination against these organisms and their toxins has proved rather ineffective in providing long-term protection from disease. In response to the debilitating effects of AB toxins on epithelial cells of the digestive mucosa, mechanisms underlying toxin immunomodulation of immune responses have become the focus of increasing experimentation. The results of these studies reveal that AB toxins may have a beneficial application as adjuvants for the enhancement of immune protection against infection and autoimmunity. Here, we examine similarities and differences in the structure and function of bacterial and plant AB toxins that underlie their toxicity and their exceptional properties as immunomodulators for stimulating immune responses against infectious disease and for immune suppression of organ-specific autoimmunity.

CD167 acts as a novel costimulatory receptor in T-cell activation

Optimal T-cell activation requires both an antigen-specific and a costimulatory signal. CD167 is a tyrosine kinase receptor for native type I collagen, its physiologic functions include matrix homeostasis and cell growth, adhesion, branching, and migration, but the specific role of CD167 in T cells has not yet been characterized. In this study, we found that CD167 expression on T cells was up-regulated after activation. Cooperation of CD167 engagement with suboptimal TCR/CD3 signals induced T-cell proliferation, enhanced expression of activation markers such as CD25 and CD69, elevated intracellular calcium mobilization and tyrosine phosphorylation, and introduced a bias toward a TH1/Tc1 immune response. Cooperation of CD167 engagement also enhanced mixed lymphocyte responses to alloantigens. Moreover, CD167 rapidly localized to the aggregated lipid rafts upon T-cell activation, this provided a molecular base for the signaling machinery of CD167. Together these findings, we demonstrate for the first time that CD167 could serve as a novel costimulatory receptor for T-cell activation.

Mucosally induced immunological tolerance, regulatory T cells and the adjuvant effect by cholera toxin B subunit

Induction of peripheral immunological tolerance by mucosal administration of selected antigens (Ags) ('oral tolerance') is an attractive, yet medically little developed, approach to prevent or treat selected autoimmune or allergic disorders. A highly effective way to maximize oral tolerance induction for immunotherapeutic purposes is to administer the relevant Ag together with, and preferably linked to the non-toxic B subunit protein of cholera toxin (CTB). Oral, nasal or sublingual administration of such Ag/CTB conjugates or gene fusion proteins have been found to induce tolerance with superior efficiency compared with administration of Ag alone, including the suppression of various autoimmune disorders and allergies in animal models. In a proof-of-concept clinical trial in patients with Behcet's disease, this was extended with highly promising results to prevent relapse of autoimmune uveitis. Tolerization by mucosal Ag/CTB administration results in a strong increase in Ag-specific regulatory CD4(+) T cells, apparently via two separate pathways: one using B cells as APCs and leading to a strong expansion of Foxp3(+) Treg cells which can both suppress and mediate apoptotic depletion of effector T cells, and one being B cell-independent and associated with development of Foxp3(-) regulatory T cells that express membrane latency-associated peptide and transforming growth factor (TGF-beta) and/or IL-10. The ability of CTB to dramatically increase mucosal Ag uptake and presentation by different APCs through binding to GM1 ganglioside (which makes most B cells effective APCs irrespective of their Ag specificity), together with CTB-mediated stimulation of TGF-beta and IL-10 production and inhibition of IL-6 formation may explain the dramatic potentiation of oral tolerance by mucosal Ags presented with CTB.

Type II collagen oral tolerance; mechanism and role in collagen-induced arthritis and rheumatoid arthritis

Oral tolerance means a diminished immune response to previously fed antigens. Repeated oral administrations of type II collagen (CII) induce oral tolerance and inhibit the development of collagen-induced arthritis (CIA). Dendritic cells (DCs) in the gut-associated lymphoid tissue (GALT) take up the CII and then present it to T cells to generate regulatory T cells (Tregs), which induce systemic immune tolerance to CII. Inhibitory cytokines, such as transforming growth factor (TGF)-beta and interleukin (IL)-10, and several immune regulatory molecules, including indoleamine 2,3-dioxygenase (IDO) and retinoic acid, play an important role in Treg generation. Each DC subset may play different roles, and CD11c+CD11b+DCs and IDO+DCs are important in the generation of antigen-inducible Tregs in CII oral tolerance. Upon stimulation with the antigen involved in its generation, Treg is activated and regulates the immune response through inhibitory cytokine production, cell-to-cell contact-dependent mechanisms, DC modification, and bystander suppression. The DCs and Tregs are deeply involved in oral tolerance through reciprocal interactions. Several clinical trials have been conducted in RA patients to examine the efficacy of CII oral tolerance. An understanding the mechanism of oral tolerance to CII would give clinicians new insights into the development of natural immune tolerance and new therapeutic approaches for the treatment of autoimmune diseases.

Induction of tolerance by oral administration of beta-tubulin in an animal model of autoimmune inner ear disease

Induction of peripheral tolerance by oral administration of low-dose beta-tubulin antigen may be an effective, antigen-specific method to suppress experimental autoimmune hearing loss. Five groups of mice were fed with phosphate-buffered saline (PBS), ovalbumin (OVA), 20, 30 or 200 microg of beta-tubulin, respectively. All mice were then immunized by beta-tubulin. Hearing thresholds were measured before and after immunization. Inner ear histology and cytokine profile were examined. Mice fed with 20 or 30 microg of beta-tubulin showed less hearing loss and less inner ear damage compared to the groups treated with PBS, OVA or 200 microg of beta-tubulin. Interferon-gamma (IFN-gamma) was decreased while interleukin-4 (IL-4), IL-5, IL-13 and TGF-beta were increased in both sera and in cell culture supernatants of the mice fed with 20 or 30 microg of beta-tubulin. However, no cytokine profile change was found in the group treated with 200 microg of tubulin. These results suggest that a low dose of beta-tubulin is active orally in an antigen-specific fashion and capable of inhibiting the autoimmune reactions in the inner ear by suppressing Th1 (IFN-gamma) and increasing Th2 and Th3 (IL-4, IL-5, IL-13 and TGF-beta) cytokines. Oral antigen tolerance may be used to treat autoimmune inner ear disease.

Cholera toxin B subunit promotes the induction of regulatory T cells by preventing human dendritic cell maturation

Cholera toxin B subunit (CTB) is an efficient mucosal carrier molecule for the generation of immune responses to linked antigens. There is also good evidence that CTB acts as an immunosuppressant, as it is able to down-modulate human monocyte/macrophage cell line activation and to suppress Th1-type responses. In the present study, we examined the possibility that recombinant CTB (rCTB) may affect human dendritic cell (DC) functions in response to LPS stimulation and may induce the generation of DC with the capacity to generate CD4(+) regulatory T cells (Tregs). Our findings show that rCTB partially prevents the LPS-induced maturation process of monocyte-derived DC (MDDC) and decreases their IL-12 production with no relevant effect on IL-10 production. LPS-stimulated MDDC pretreated with rCTB are able to promote the induction of low proliferating T cells, which show an enhanced IL-10 production associated with a reduced IFN-gamma production and the same high levels of TGF-beta as the control. These T cells suppress proliferation of activated autologous T cells. Transwell experiments and blockade of IL-10R and TGF-beta showed that the immunomodulatory effect is mediated by soluble factors. Thus, T cells induced by rCTB-conditioned MDDC acquire a regulatory phenotype and activity similar to those described for type 1 Tregs.

Immune-mediated inner ear disease

The incidence of autoimmune inner ear disease (AIED) is difficult to determine: probably it is a rare disease, accounting for <1% of all cases of hearing impairment or dizziness. Nevertheless, the diagnosis of AIED might be overlooked because of the lack of a specific diagnostic test. The hallmark of this clinically diagnosed condition is the presence of a rapidly progressive, often fluctuating, bilateral sensorineural hearing loss (SNHL) over a period of weeks to months. The progression of hearing loss is too rapid to be diagnostic for presbycusis and too slow to conclude a diagnosis of sudden SNHL. Vestibular symptoms, such as generalized imbalance, ataxia, positional vertigo and episodic vertigo may be present in almost 50% of patients. Occasionally only one ear is affected initially, but bilateral hearing loss occurs in most patients, with symmetric or asymmetric audiometric thresholds. Almost 25-50% of patients also have tinnitus and aural fullness, which can fluctuate. Systemic autoimmune diseases coexist in 15-30% of patients.

The immunobiology of Th1 polarization in high-pathology schistosomiasis

Schistosomiasis is a serious global helminthic disease, in which the main immunopathology consists of a granulomatous and fibrosing reaction against tissue-trapped parasite eggs. The severity of this inflammatory process, the product of a CD4(+) T-cell-mediated immune response against parasite egg antigens, is, however, markedly uneven, both in human patients and among mouse strains in an experimental model. Severe schistosomiasis is associated with persistently elevated pro-inflammatory T-helper-1 (Th1)-type cytokines, whereas milder pathology is present when Th2 cytokines dominate. This scenario is supported by the pronounced pathology resulting from the obliteration of pathways that facilitate Th2 differentiation and by the development of more intense lesions in mouse strains that fail to downregulate the Th1 response. Genetically prone high-pathology mice have a higher proportion of CD4(+) T cells in lymph nodes and granulomas, in which the Th1 phenotype is driven by interleukin-12; they also develop a dominant repertoire against peptide 234-246 of the major Sm-p40 egg antigen, utilizing a strikingly restricted T-cell receptor structure that involves Valpha11.3beta8. In turn, low-pathology mice exhibit enhanced CD4(+) T-cell apoptosis, which contributes to limit pathology. The definition of distinctive immune profiles associated with polar forms of schistosomiasis opens opportunities for targeted immuno-intervention in individuals suffering from or at risk of severe disease.

Cholera Toxin Prevents Th1-Mediated Autoimmune Disease by Inducing Immune Deviation

Cholera toxin (CT), a major enterotoxin produced by Vibrio cholerae, is known for its properties as a mucosal adjuvant that promotes Th2 or mixed Th1 + Th2 responses. In this study, we explore the ability of CT to act as a systemic adjuvant to counteract the Th1 response leading to experimental autoimmune uveitis. We report that susceptible B10.RIII mice immunized with a uveitogenic regimen of the retinal Ag interphotoreceptor retinoid-binding protein could be protected from disease by a single systemic injection of as little as 2 micro g of CT at the time of immunization. The protected mice were not immunosuppressed, but rather displayed evidence of immune deviation. Subsequent adaptive responses to interphotoreceptor retinoid-binding protein showed evidence of Th2 enhancement, as indicated by reduced delayed-type hypersensitivity in the context of enhanced Ag-specific lymphocyte proliferation and IL-4 production. Ag-specific production of several other cytokines, including IFN-gamma, was not appreciably altered. The inhibitory effect of CT was dependent on the enzymatic A subunit of CT, because the cell-binding B subunit alone could not block disease development. Mice given CT displayed detectable IL-4 levels in their serum within hours of CT administration. This innate IL-4 production was critical for protection, as infusion of neutralizing Ab against IL-4 to mice, given a uveitogenic immunization and treated with CT, counteracted immune deviation and abrogated protection. Our data indicate that systemic administration of CT inhibits experimental autoimmune uveitis by skewing the response to the uveitogenic autoantigen to a nonpathogenic phenotype.

Effects of cholera toxin on innate and adaptive immunity and its application as an immunomodulatory agent

Cholera toxin (CT) is a potent vaccine adjuvant when administered via parenteral, mucosal, or transcutaneous routes. It also inhibits innate inflammatory responses induced by pathogen-derived molecules, such as lipopolysaccharide (LPS). We demonstrated previously that CT promotes the induction of regulatory type 1 T cells (Tr1) as well as T helper type 2 cells (Th2). T cells from mice immunized with antigen in the presence of CT produced high levels of interleukin (IL)-10 and IL-5 and low levels of IL-4 and interferon-gamma (IFN-gamma). Here, we demonstrate that immunization with antigen in the presence of CT induced a population of antigen-specific CD4(+) T cells that produced IL-10 in the absence of IL-4, in addition to cells that coexpressed IL-4 and IL-10 or produced IL-4 only. CT-generated Tr1 cells inhibited antigen-specific proliferation as well as IFN-gamma production by Th1 cells, and this suppression was cell contact-independent. It is interesting that coincubation with Th1 cells significantly enhanced IL-10 production by the Tr1 cells. As IL-10 can promote the differentiation of Tr1 cells, we investigated cytokine production by dendritic cells (DC) following exposure to CT. Previous data showed that CT can modulate the expression of costimulatory molecules and inhibit the production of chemokines and cytokines, including IL-12 and tumor necrosis factor alpha and enhance IL-10 production. Here, we show that CT synergizes with LPS to induce IL-6 and IL-1beta in addition to IL-10 production by immature DC. Therefore, CT may promote the induction of Th2 and Tr1 cells in part via selective modulation of DC cytokine production and costimulatory molecule expression.

Diminished immunopathology in Schistosoma mansoni infection following intranasal administration of cholera toxin B-immunodominant peptide conjugate correlates with enhanced transforming growth factor-beta production by CD4 T cells

In Schistosoma mansoni infection, CD4 T cells specific for parasite egg antigens mediate perioval granuloma formation in the liver and intestines. Mice of the CBA strain develop a severe form of disease and a significant proportion of their CD4 T cell response is directed against the major egg antigen Sm-p40 and its immunodominant T cell epitope peptide 234-246. Here, we show that intranasal (i.n.) treatment of infected CBA mice with a fusion protein of the cholera toxin B subunit (CTB) with peptide 234-246 (CTB::pep) results in significant down-modulation of hepatic granulomatous inflammation and fibrosis. Moreover, egg antigen-stimulated dispersed hepatic granuloma cells, as well as mesenteric lymph node CD4 T cells from the CTB::pep-treated mice, produced significantly more transforming growth factor (TGF)-beta than that produced by treated or untreated controls. The data demonstrate that i.n. administration of a single immunodominant peptide conjugated to CTB can lead to down-regulation of the hepatic immunopathology associated with schistosomiasis, and that this down-regulation is, at least in part, mediated by TGF-beta.

Cholera toxin B pretreatment of macrophages and monocytes diminishes their proinflammatory responsiveness to lipopolysaccharide

The cholera toxin B chain (CTB) has been reported to suppress T cell-dependent autoimmune diseases and to potentiate tolerance of the adaptive immune system. We have analyzed the effects of CTB on macrophages in vitro and have found that preincubation with CTB (10 microg/ml) suppresses the proinflammatory reaction to LPS challenge, as demonstrated by suppressed production of TNF-alpha, IL-6, IL-12(p70), and NO (p < 0.01) in cells of macrophage lines. Pre-exposure to CTB also suppresses LPS-induced TNF-alpha and IL-12(p70) formation in human PBMC. Both native and recombinant CTB exhibited suppressive activity, which was shared by intact cholera toxin. In cells of the human monocyte line Mono Mac 6, exposure to CTB failed to suppress the production of IL-10 in response to LPS. Control experiments excluded a role of possible contamination of CTB by endotoxin or intact cholera toxin. The suppression of TNF-alpha production occurred at the level of mRNA formation. Tolerance induction by CTB was dose and time dependent. The suppression of TNF-alpha and IL-6 production could be counteracted by the addition of Abs to IL-10 and TGF-beta. IFN-gamma also antagonized the actions of CTB on macrophages. In contrast to desensitization by low doses of LPS, tolerance induction by CTB occurred silently, i.e., in the absence of a measurable proinflammatory response. These findings identify immune-deviating properties of CTB at the level of innate immune cells and may be relevant to the use of CTB in modulating immune-mediated diseases.