Effects of cholera toxin on macrophage production of co-stimulatory cytokines

dmLT Adjuvant Enhances Cytokine Responses to T Cell Stimuli, Whole Cell Vaccine Antigens and Lipopolysaccharide in Both Adults and Infants

Enhancement of mucosal immune responses in children and infants using novel adjuvants such as double mutant heat labile toxin (dmLT) is an important goal in the enteric vaccine field. dmLT has been shown to enhance mucosal IgA responses to the oral inactivated enterotoxigenic Escherichia coli (ETEC) vaccine ETVAX. dmLT can enhance IL-17A production from adult T cells, which may increase the production and secretion of mucosal IgA antibodies. However, the adjuvant mechanism remains to be fully elucidated and might differ between infants and adults due to age-related differences in the development of the immune system. The main objective of this study was to determine how dmLT influences antigen presenting cells and T cells from infants compared to adults, and the role of IL-1β for mediating the adjuvant activity. Peripheral blood mononuclear cells (PBMCs) from Bangladeshi infants (6-11 months) and adults (18-40 years) were stimulated with the mitogen phytohaemagglutinin (PHA), the superantigen Staphylococcal enterotoxin B (SEB), ETVAX whole cell component (WCC) or E. coli lipopolysaccharide (LPS) ± dmLT, and cytokine production was measured using ELISA and electrochemiluminescence assays. The adjuvant dmLT significantly enhanced SEB- and PHA-induced IL-17A, but not IFN-γ responses, in PBMCs from both infants and adults. Blocking experiments using an IL-1 receptor antagonist demonstrated the importance of IL-1 signaling for the adjuvant effect. dmLT, ETVAX WCC and LPS induced dose-dependent IL-1β responses of comparable magnitudes in infant and adult cells. Depletion experiments suggested that IL-1β was mainly produced by monocytes. dmLT enhanced IL-1β responses to low doses of WCC and LPS, and the adjuvant effect appeared over a wider dose-range of WCC in infants. dmLT and WCC also induced IL-6, IL-23 and IL-12p70 production in both age groups and dmLT tended to particularly enhance IL-23 responses to WCC. Our results show that dmLT can induce IL-1β as well as other cytokines, which in turn may enhance IL-17A and potentially modulate other immunological responses in both infants and adults. Thus, dmLT may have an important function in promoting immune responses to the ETVAX vaccine, as well as other whole cell- or LPS-based vaccines in infants in low- and middle-income countries.

Consuming cholera toxin counteracts age-associated obesity

During the past forty years there has been an inexplicable increase in chronic inflammatory disorders, including obesity. One theory, the ‘hygiene hypothesis’, involves dysregulated immunity arising after too few beneficial early life microbe exposures. Indeed, earlier studies have shown that gut microbe-immune interactions contribute to smoldering inflammation, adiposity, and weight gain. Here we tested a safe and well-established microbe-based immune adjuvant to restore immune homeostasis and counteract inflammation-associated obesity in animal models. We found that consuming Vibrio cholerae exotoxin subunit B (ctB) was sufficient to inhibit age-associated obesogenic outcomes in wild type mice, including reduced crown-like structures (CLS) and granulomatous necrosis histopathology in fat depots. Administration of cholera toxin reduced weight gain irrespective of age during administration; however, exposure during youth imparted greater slenderizing effects when compared with animals receiving ctB for the first time during adulthood. Beneficial effects were transplantable to other obesity-prone animals using immune cells alone, demonstrating an immune-mediated mechanism. Taken together, we concluded that oral vaccination with cholera toxin B helps stimulate health-protective immune responses that counteract age-associated obesity.

Requirement for Cyclic AMP/Protein Kinase A-Dependent Canonical NFκB Signaling in the Adjuvant Action of Cholera Toxin and Its Non-toxic Derivative mmCT

Cholera toxin (CT) is widely used as an effective adjuvant in experimental immunology for inducing mucosal immune responses; yet its mechanisms of adjuvant action remain incompletely defined. Here, we demonstrate that mice lacking NFκB, compared to wild-type (WT) mice, had a 90% reduction in their systemic and mucosal immune responses to oral immunization with a model protein antigen [Ovalbumin (OVA)] given together with CT. Further, NFκB^−/− mouse dendritic cells (DCs) stimulated in vitro with CT showed reduced expression of MHCII and co-stimulatory molecules, such as CD80 and CD86, as well as of IL-1β, and other pro-inflammatory cytokines compared to WT DCs. Using a human monocyte cell line THP1 with an NFκB activation reporter system, we show that CT induced NFκB signaling in human monocytes, and that inhibition of the cyclic AMP—protein kinase A (cAMP-PKA) pathway abrogated the activation and nuclear translocation of NFκB. In a human monocyte-CD4⁺ T cell co-culture system we further show that the strong Th17 response induced by CT treatment of monocytes was abolished by blocking the classical but not the alternative NFκB signaling pathway of monocytes. Our results indicate that activation of classical (canonical) NFκB pathway signaling in antigen-presenting cells (APCs) by CT is important for CT's adjuvant enhancement of Th17 responses. Similar findings were obtained using the almost completely detoxified mmCT mutant protein as adjuvant. Altogether, our results demonstrate that activation of the classical NFκB signal transduction pathway in APCs is important for the adjuvant action of both CT and mmCT.

ADP-ribosylating enterotoxins as vaccine adjuvants

Most infections are caused by pathogens that access the body at mucosal sites. Hence, development of mucosal vaccines to prevent local infection or invasion of pathogens appears highly warranted, especially since only mucosal immunization will stimulate strong local IgA responses and tissue resident memory CD4 and CD8 T cells. The most significant obstacle to developing such vaccines is the lack of approved adjuvants that can effectively and safely enhance relevant mucosal and systemic immune responses. The most potent mucosal adjuvants known today are the adenosine diphosphate (ADP)-ribosylating bacterial enterotoxins cholera toxin (CT) and Escherichia coli heat-labile toxins (LTs). Unfortunately, these molecules are also very toxic, which precludes their clinical use. However, much effort has been devoted to developing derivatives of these enterotoxins with low or no toxicity and retained adjuvant activity. Although it is fair to say that we know more about how these toxins affect the immune system than ever before, we still lack a detailed understanding of how and why these toxins are effective adjuvants. In the present review, we provide a state-of-the-art overview of the mechanism of action of the holotoxins and the strategies used for improving the toxin-based adjuvants.

"Cystic fibrotics could survive cholera, choleraics could survive cystic fibrosis"; hypothesis that explores new horizons in treatment of cystic fibrosis

Cystic fibrosis, the most common inherited disease of white population, is a disease of CFTR channels, in which mucosal function of many organs especially respiratory tract is impaired. Decreased mucociliary clearance and accumulation of mucus in airways facilitates colonization of infectious microorganisms, followed by infection. Following chronic infection, persistent inflammation ensues, which results in airway remodeling and deterioration of mucociliary clearance and result in a vicious cycle. Here, it is hypothesized that cholera toxin (CT) could ameliorate symptoms of cystic fibrosis as CT could dilute the thickened mucus, improve mucociliary clearance and alleviate airway obstruction. CT strengthens immunity of airway mucosa and it could attenuates bacterial growth and reduce persistency of infection. CT also modulates cellular immune response and it could decrease airway inflammation, hinder airway remodeling and prevent respiratory deterioration. Thereby it is hypothesized that CT could target and ameliorate many of pathophysiologic steps of the disease and it explores new horizons in treatment of CF.

Neutrophils negatively regulate induction of mucosal IgA responses after sublingual immunization

Induction of mucosal immunoglobulin-A (IgA) capable of providing a first line of defense against bacterial and viral pathogens remains a major goal of needle-free vaccines given via mucosal routes. Innate immune cells are known to play a central role in induction of IgA responses by mucosal vaccines, but the relative contribution of myeloid cell subsets to these responses has not firmly been established. Using an in vivo model of sublingual vaccination with Bacillus anthracis edema toxin (EdTx) as adjuvant, we examined the role of myeloid cell subsets for mucosal secretory IgA responses. Sublingual immunization of wild-type mice resulted in a transient increase of neutrophils in sublingual tissues and cervical lymph nodes. These mice later developed Ag-specific serum IgG responses, but not serum or mucosal IgA. Interestingly, EdTx failed to increase neutrophils in sublingual tissues and cervical lymph nodes of IKKβ(ΔMye) mice, and these mice developed IgA responses. Partial depletion of neutrophils before immunization of wild-type mice allowed the development of both mucosal and serum IgA responses. Finally, co-culture of B cells with neutrophils from either wild-type or IKKβ(ΔMye) mice suppressed secretion of IgA, but not IgM or IgG. These results identify a new role for neutrophils as negative regulators of IgA responses.

Gut T cell receptor-γδ(+) intraepithelial lymphocytes are activated selectively by cholera toxin to break oral tolerance in mice

The gut immune system is usually tolerant to harmless foreign antigens such as food proteins. However, tolerance breakdown may occur and lead to food allergy. To study mechanisms underlying food allergy, animal models have been developed in mice by using cholera toxin (CT) to break tolerance. In this study, we identify T cell receptor (TCR)-γδ(+)  intraepithelial lymphocytes (IELs) as major targets of CT to break tolerance to food allergens. TCR-γδ(+)  IEL-enriched cell populations isolated from mice fed with CT and transferred to naive mice hamper tolerization to the food allergen β-lactoglobulin (BLG) in recipient mice which produce anti-BLG immunoglobulin (Ig)G1 antibodies. Furthermore, adoptive transfer of TCR-γδ(+)  cells from CT-fed mice triggers the production of anti-CT IgG1 antibodies in recipient mice that were never exposed to CT, suggesting antigen-presenting cell (APC)-like functions of TCR-γδ(+)  IELs. In contrast to TCR-αβ(+)  cells, TCR-γδ(+)  IELs bind and internalize CT both in vitro and in vivo. CT-activated TCR-γδ(+)  IELs express major histocompatibility complex (MHC) class II molecules, CD80 and CD86 demonstrating an APC phenotype. CT-activated TCR-γδ(+)  IELs migrate to the lamina propria, where they produce interleukin (IL)-10 and IL-17. These results provide in-vivo evidence for a major role of TCR-γδ(+)  IELs in the modulation of oral tolerance in the pathogenesis of food allergy.

Cholera-toxin suppresses carcinogenesis in a mouse model of inflammation-driven sporadic colon cancer

Human studies and clues from animal models have provided important links between gastrointestinal (GI) tract bacteria and colon cancer. Gut microbiota antigenic stimuli play an important role in shaping the intestinal immune responses. Therefore, especially in the case of inflammation-associated colon cancer, gut bacteria antigens may affect tumorigenesis. The present study aimed to investigate the effects of the oral administration of a bacterial product with known immunomodulatory properties on inflammation-driven colorectal neoplasmatogenesis. For that, we used cholera-toxin and a well-established mouse model of colon cancer in which neoplasia is initiated by a single dose of the genotoxic agent azoxymethane (AOM) and subsequently promoted by inflammation caused by the colitogenic substance dextran sodium sulfate (DSS). We found that a single, low, non-pathogenic dose of CT, given orally at the beginning of each DSS treatment cycle downregulated neutrophils and upregulated regulatory T-cells and IL-10 in the colonic mucosa. The CT-induced disruption of the tumor-promoting character of DSS-induced inflammation led to the reduction of the AOM-initiated colonic polypoidogenesis. This result adds value to the emerging notion that certain GI tract bacteria or their products affect the immune system and render the microenvironment of preneoplastic lesions less favorable for promoting their evolution to cancer.

IL12Rβ1: the cytokine receptor that we used to know

Human IL12RB1 encodes IL12Rβ1, a type I transmembrane receptor that is an essential component of the IL12- and IL23-signaling complex. IL12RB1 is well-established as being a promoter of delayed type hypersensitivity (DTH), the immunological reaction that limits tuberculosis. However, recent data demonstrate that in addition to promoting DTH, IL12RB1 also promotes autoimmunity. The contradictory roles of IL12RB1 in human health raises the question, what are the factors governing IL12RB1 function in a given individual, and how is inter-individual variability in IL12RB1 function introduced? Here we review recent data that demonstrate individual variability in IL12RB1 function is introduced at the epigenetic, genomic polymorphism, and mRNA splicing levels. Where and how these differences contribute to disease susceptibility and outcome are also reviewed. Collectively, recent data support a model wherein IL12RB1 sequence variability - whether introduced at the genomic or post-transcriptional level - contributes to disease, and that human IL12RB1 is not as simple a gene as we once believed.

Cnr2 deficiency confers resistance to inflammation-induced preterm birth in mice

Infection-induced inflammation, frequently associated with increased production of proinflammatory cytokines, is considered a significant contributor to preterm birth. A G protein-coupled cannabinoid receptor 2 (CB2), encoded by Cnr2, is expressed in various immune cells and was shown to modulate immune responses. We show here that Cnr2, but not Cnr1, deficient mice are resistant to lipopolysaccharide (LPS)-driven preterm birth and suppression of serum progesterone levels. After LPS challenge, Cnr2(-/-) mice exhibited increased serum levels of IL-10 with decreased IL-6 levels. These changes were associated with reduced LPS-induced Ptgs2 expression at the maternal-conceptus interface on day 16 of pregnancy. LPS stimulation of Cnr2(-/-) dendritic cells in vitro resulted in increased IL-10 with reduced IL-6 production and correlated with increased cAMP accumulation. Collectively, our results suggest that increased IL-10 production occurring via augmented cAMP accumulation represents a potential mechanism for the resistance of Cnr2(-/-) mice to LPS-induced preterm birth. These results may have clinical relevance, because currently, there are limited options to prevent preterm birth.

The route less taken: pulmonary models of enteric Gram-negative infection

Many pathogens are capable of causing a fulminant infection in pulmonary tissues of mammals. Animal models have provided an extensive understanding of the genetic and molecular mechanisms of bacterial pathogenesis as well as host immune response in the lungs. Many clinically relevant Gram-negative bacteria are host-restricted. Thus, the powerful, informative tools of mouse models are not available for study with these organisms. However, over the past 30 years, enterprising work has demonstrated the utility of pulmonary infection with enteric pathogens. Such infection models have increased our understanding host-pathogen interactions in these organisms. Here, we provide a review and comparison of lung models of infection with enteric, Gram-negative bacteria relative to naturally occurring lung pathogens.

Promotion of colonization and virulence by cholera toxin is dependent on neutrophils

The innate immune response to Vibrio cholerae infection is poorly understood, but this knowledge is critical for the design of safe, effective vaccines. Using an adult mouse intestinal infection model, this study examines the contribution of neutrophils to host immunity, as well as the effect of cholera toxin and other secreted factors on this response. Depletion of neutrophils from mice with anti-Ly6G IA8 monoclonal antibody led to similar survival rates of mice infected with low or moderate doses of toxigenic V. cholerae El Tor O1. At a high dose, neutropenic mice showed increased rates of survival compared to neutrophil-replete animals. Expression of cholera toxin was found to be protective to the neutropenic host, and this phenotype can be replicated by the administration of purified toxin. Neutrophils do not effectively clear colonizing bacteria from the small intestine, nor do they alter induction of early immune-modulating signals. In both neutropenic and neutrophil-replete animals, the local response to infection is characterized by expression of interleukin 6 (IL-6), IL-10, and macrophage inflammatory protein 2 alpha (MIP-2). Overall, these data indicate that the innate immune response to toxigenic V. cholerae infection differs dramatically from the host response to nontoxigenic infection or vaccination, where neutrophils are protective to the host. In the absence of neutrophils, cholera toxin induces immunomodulatory effects that increase host survival. In cholera toxin-producing strains, similar to nontoxigenic infection, accessory toxins are critical to virulence, indicating that cholera toxin and the other secreted toxins modulate the host response by different mechanisms, with both contributing to bacterial persistence and virulence.

Phosphodiesterase 4 inhibition in the treatment of psoriasis, psoriatic arthritis and other chronic inflammatory diseases

Agents which increase intracellular cyclic adenosine monophosphate (cAMP) may have an antagonistic effect on pro-inflammatory molecule production so that inhibitors of the cAMP degrading phosphodiesterases have been identified as promising drugs in chronic inflammatory disorders. Although many such inhibitors have been developed, their introduction in the clinic has been hampered by their narrow therapeutic window with side effects such as nausea and emesis occurring at sub-therapeutic levels. The latest generation of inhibitors selective for phosphodiesterase 4 (PDE4), such as apremilast and roflumilast, seems to have an improved therapeutic index. While roflumilast has been approved for the treatment of exacerbated chronic obstructive pulmonary disease (COPD), apremilast shows promising activity in dermatological and rheumatological conditions. Studies in psoriasis and psoriatic arthritis have demonstrated clinical activity of apremilast. Efficacy in psoriasis is probably equivalent to methotrexate but less than that of monoclonal antibody inhibitors of tumour necrosis factor (TNFi). Similarly, in psoriatic arthritis efficacy is less than that of TNF inhibitors. PDE4 inhibitors hold the promise to broaden the portfolio of anti-inflammatory therapeutic approaches in a range of chronic inflammatory diseases which may include granulomatous skin diseases, some subtypes of chronic eczema and probably cutaneous lupus erythematosus. In this review, the authors highlight the mode of action of PDE4 inhibitors on skin and joint inflammatory responses and discuss their future role in clinical practice. Current developments in the field including the development of topical applications and the development of PDE4 inhibitors which specifically target the subform PDE4B will be discussed.

Neutrophils are essential for containment of Vibrio cholerae to the intestine during the proinflammatory phase of infection

Cholera is classically considered a noninflammatory diarrheal disease, in comparison to invasive enteric organisms, although there is a low-level proinflammatory response during early infection with Vibrio cholerae and a strong proinflammatory reaction to live attenuated vaccine strains. Using an adult mouse intestinal infection model, this study examines the contribution of neutrophils to host defense to infection. Nontoxigenic El Tor O1 V. cholerae infection is characterized by the upregulation of interleukin-6 (IL-6), IL-10, and macrophage inflammatory protein 2 alpha in the intestine, indicating an acute innate immune response. Depletion of neutrophils from mice with anti-Ly6G IA8 monoclonal antibody led to decreased survival of mice. The role of neutrophils in protection of the host is to limit the infection to the intestine and control bacterial spread to extraintestinal organs. In the absence of neutrophils, the infection spread to the spleen and led to increased systemic levels of IL-1β and tumor necrosis factor alpha, suggesting the decreased survival in neutropenic mice is due to systemic shock. Neutrophils were found not to contribute to either clearance of colonizing bacteria or to alter the local immune response. However, when genes for secreted accessory toxins were deleted, the colonizing bacteria were cleared from the intestine, and this clearance is dependent upon neutrophils. Thus, the requirement for accessory toxins in virulence is negated in neutropenic mice, which is consistent with a role of accessory toxins in the evasion of innate immune cells in the intestine. Overall, these data support that neutrophils impact disease progression and suggest that neutrophil effectiveness can be manipulated through the deletion of accessory toxins.

Mucosal adjuvants and long-term memory development with special focus on CTA1-DD and other ADP-ribosylating toxins

The ultimate goal for vaccination is to stimulate protective immunological memory. Protection against infectious diseases not only relies on the magnitude of the humoral immune response, but more importantly on the quality and longevity of it. Adjuvants are critical components of most non-living vaccines. Although little attention has been given to qualitative aspects of the choice of vaccine adjuvant, emerging data demonstrate that this function may be central to vaccine efficacy. In this review we describe efforts to understand more about how adjuvants influence qualitative aspects of memory development. We describe recent advances in understanding how vaccines induce long-lived plasma and memory B cells, and focus our presentation on the germinal center reaction. As mucosal vaccination requires powerful adjuvants, we have devoted much attention to the adenosine diphosphate (ADP)-ribosylating cholera toxin and the CTA1-DD adjuvants as examples of how mucosal adjuvants can influence induction of long-term memory.

Gene expression profiling identifies STAT3 as a novel pathway for immunomodulation by cholera toxin adjuvant

Earlier studies have reported on both proinflammatory and anti-inflammatory activities of cholera toxin (CT). As CT is a powerful adjuvant, we were interested in identifying genes with a possible involvement in these functions. A global gene expression analysis in mouse B cells showed that CT regulated <100 annotated genes, which encoded transcription factors, G proteins, cell-cycle regulators, and immunoregulating molecules. Interestingly, CT regulated the expression of the signal transducer and activator of transcription (STAT)3 gene and influenced the level and activation of both isoforms STAT3 alpha and STAT3 beta, in vitro in a B-cell line and in Peyer's patch (PP) B cells and in vivo in freshly isolated splenic B cells from CT-treated mice. This effect was cAMP dependent and was not seen with CTB. B cells pre-exposed to CT were significantly more susceptible to the activation of STAT3 by interleukin (IL)-6 and IL-10. This exerted a stronger inhibitory effect of IL-10 on lipopolysaccharide (LPS)-stimulated B-cell proliferation and cytokine production (IL-6). Moreover, IgG1 and IgA production induced by LPS and IL-10 were enhanced by the addition of CT to cultures of PP or splenic B cells. This is the first study to provide a molecular mechanism that can reconcile previous findings of proinflammatory and anti-inflammatory effects by CT adjuvant.

Decreased potency of the Vibrio cholerae sheathed flagellum to trigger host innate immunity

Vibrio cholerae is a monoflagellated gram-negative bacterium that causes the severe diarrheal disease cholera. In contrast to Salmonella enterica serovar Typhimurium infection, which is accompanied by both acute diarrhea and high-level inflammation, V. cholerae infection is largely noninflammatory in human hosts. Bacterial flagella are composed of flagellin, a highly conserved protein that is also a target of the innate immune response. Because the V. cholerae flagellum is covered by a sheath, we hypothesized that it might be less prone to activation of the innate immune response than nonsheathed flagella, such as those produced by Salmonella serovar Typhimurium. Indeed, compared with Salmonella serovar Typhimurium flagella, V. cholerae flagella demonstrated significantly reduced NF-kappaB activation in A549 human pulmonary epithelial cells. However, V. cholerae flagellin monomers, FlaD and FlaC, were almost equally potent with purified FliC, a monomer derived from Salmonella serovar Typhimurium flagella, in NF-kappaB activation. Heat- and acid-induced dissociation assays showed that Salmonella serovar Typhimurium flagella disassembled far more readily into monomeric flagellins than V. cholerae flagella, suggesting that the differential levels of NF-kappaB activation by V. cholerae and Salmonella serovar Typhimurium flagella are likely attributable to the difference in their flagellin shedding. Our results suggest that monomer dissociation of V. cholerae flagella is suppressed likely due to the presence of the sheath and that this unique structural feature of V. cholerae flagella may have evolved as a strategy to evade flagellin-triggered host innate immune responses in various host species.

Induction of cell signaling events by the cholera toxin B subunit in antigen-presenting cells

Cholera toxin (CT) is one of the most effective and widely studied mucosal adjuvants. Although the ADP-ribosylating A subunit has been implicated in augmenting immune responses, the receptor-binding B subunit (CT-B) has greater immunogenicity and may be a repository of adjuvant activity without potential toxicity. In order to elucidate mechanisms of immune modulation by CT-B alone, primary B cells and macrophages were assessed for responses to CT-B in vitro, as measured by the expression of cell surface markers, cellular signaling events, and cytokine secretion. Increased phosphorylation of multiple signaling molecules, including Erk1/2 and p38, was detected. CT-B also induced transactivation of the transcription elements cyclic AMP-responsive element and NF-kappaB, the latter of which was inhibited by phosphotyrosine inhibition. While specific inhibition of MEK1/2 did not reduce CT-B induction of cell surface marker expression, it did attenuate CT-B-mediated interleukin-6 secretion. These data show that CT-B induces a set of signaling events related to cellular activation, surface molecule expression, and cytokine production that has potential implications for elucidating CT-B adjuvant activity in the absence of enzymatically active holotoxin.

Prostaglandin I2 analogs inhibit proinflammatory cytokine production and T cell stimulatory function of dendritic cells

Signaling through the PGI(2) receptor (IP) has been shown to inhibit inflammatory responses in mouse models of respiratory syncytial viral infection and OVA-induced allergic responses. However, little is known about the cell types that mediate the anti-inflammatory function of PGI(2.) In this study, we determined that PGI(2) analogs modulate dendritic cell (DC) cytokine production, maturation, and function. We report that PGI(2) analogs (iloprost, cicaprost, treprostinil) differentially modulate the response of murine bone marrow-derived DC (BMDC) to LPS in an IP-dependent manner. The PGI(2) analogs decreased BMDC production of proinflammatory cytokines (IL-12, TNF-alpha, IL-1alpha, IL-6) and chemokines (MIP-1alpha, MCP-1) and increased the production of the anti-inflammatory cytokine IL-10 by BMDCs. The modulatory effect was associated with IP-dependent up-regulation of intracellular cAMP and down-regulation of NF-kappaB activity. Iloprost and cicaprost also suppressed LPS-induced expression of CD86, CD40, and MHC class II molecules by BMDCs and inhibited the ability of BMDCs to stimulate Ag-specific CD4 T cell proliferation and production of IL-5 and IL-13. These findings suggest that PGI(2) signaling through the IP may exert anti-inflammatory effects by acting on DC.

Adjuvants modulating mucosal immune responses or directing systemic responses towards the mucosa

In developing veterinary mucosal vaccines and vaccination strategies, mucosal adjuvants are one of the key players for inducing protective immune responses. Most of the mucosal adjuvants seem to exert their effect via binding to a receptor/or target cells and these properties were used to classify the mucosal adjuvants reviewed in the present paper: (1) ganglioside receptor-binding toxins (cholera toxin, LT enterotoxin, their B subunits and mutants); (2) surface immunoglobulin binding complex CTA1-DD; (3) TLR4 binding lipopolysaccharide; (4) TLR2-binding muramyl dipeptide; (5) Mannose receptor-binding mannan; (6) Dectin-1-binding ss 1,3/1,6 glucans; (7) TLR9-binding CpG-oligodeoxynucleotides; (8) Cytokines and chemokines; (9) Antigen-presenting cell targeting ISCOMATRIX and ISCOM. In addition, attention is given to two adjuvants able to prime the mucosal immune system following a systemic immunization, namely 1alpha, 25(OH)2D3 and cholera toxin.

Induction of immunomodulator transcriptional responses by cholera toxin

Cholera toxin (CT) is the causative agent of cholera, binds to GM1 glycosphingolipids, induces the production of cellular cAMP and is also a very powerful mucosal adjuvant. Although the mechanism of the CT induction of cAMP production is well understood, molecular mechanisms of the adjuvanticity of cholera toxin are yet to be delineated. Here, we examined the interaction of CT with human lymphocytes and monocytes by analyzing the host transcriptional profiles using cDNA arrays. The time courses of the transcriptional activations and repressions of affected genes in lymphocytes and monocytes in response to cholera toxin were determined. CT induced the expression of IL-8 and MIP-1 early in the CT exposure. VEGF, TIMP1, HIF-1alpha, MMP11, hek 8, MCP1, IL-6, GCP 2, urokinase plasminogen activator, and TNF-alpha receptor were upregulated after 4h CT treatment. These genes showed increased expression for 48 h. MRP-14, MRP-8A increased expression after 16 h CT treatment. RT-PCR and real-time PCR using cDNA specific primers confirmed the CT induction and repression of selected genes. The results suggest that immunomodulatory genes were among the genes that were affected the most by CT, and induction of these genes may contribute to the CT adjuvanticity.

A mutant of Escherichia coli enterotoxin inducing a specific Thl-type of T cells to varicella-zoster vaccine enhances the production of IL-12 by IFNgamma-stimulated macrophages

A mutant of Escherichia coli enterotoxin induces specific Thl-type T cells to varicella-zoster vaccine. The mutant increased IL-12p40, TNFalpha and nitric oxide production by IFNgamma-stimulated bone marrow macrophages but cholera toxin did not. Anti-TNFalpha antibodies blocked its stimulation of IL-12p40 production but iNOS inhibitor did not. IL-12p40 and IL-12p35 production was stimulated at the level of mRNA formation by the mutant. Cholera toxin suppressed IL-12beta1 expression by spleen T cells stimulated with anti-CD3 antibodies but the mutant did not. These findings indicate that the mutant may induce Thl-type response to the vaccine through its IL-12 and TNFalpha induction by macrophages.

Mucosal adjuvants

Induction of immune responses following oral immunization is frequently dependent upon the co-administration of appropriate adjuvants that can initiate and support the transition from innate to adaptive immunity. The three bacterial products with the greatest potential to function as mucosal adjuvants are the ADP-ribosylating enterotoxins (cholera toxin and the heat-labile enterotoxin of Escherichia coli), synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN), and monophosphoryl lipid A (MPL). The mechanism of adjuvanticity of the ADP-ribosylating enterotoxins is the subject of considerable debate. Our own view is that adjuvanticity is an outcome and not an event. It is likely that these molecules exert their adjuvant function by interacting with a variety of cell types, including epithelial cells, dendritic cells, macrophages, and possibly B- and T-lymphocytes. The adjuvant activities of CpG and MPL are due to several different effects they have on innate and adaptive immune responses and both MPL and CpG act through MyD88-dependent and -independent pathways. This presentation will summarize the probable mechanisms of action of these diverse mucosal adjuvants and discuss potential synergy between these molecules for use in conjunction with plant-derived vaccines.

Cholera toxin induced gene expression alterations

The cholera toxin (CT) is a well-known inducer of cAMP and cAMP regulates gene expression of many genes. However, little is known as to the alterations in gene expression in response to CT. Here the alterations of the expression of 800 selected genes in response to CT were examined using cDNA microarrays. Gene expression alterations in human lymphocytes and monocytes were found after exposure to CT at varying concentrations for different time periods. Over 200 genes showed varying degrees of alterations of expression in CT-treated cells. The CT-induced changes in gene expression were compared by cDNA microarrays under the same conditions to those in response to forskolin, a specific activator of adenylate cyclase, and MDL-12, an irreversible inhibitor of adenylate cyclase. Thirty-five CT-responsive genes were found responded similarly to forskolin but differently to MDL-12. Fourteen CT-responsive genes were affected similarly by MDL-12 but differently by forskolin. Many of these CT responsive genes were involved in immunity, inflammation and oxidative stress. The CT induced responses correlated with those induced by CT subunits. The down regulation of Th1 markers and upregulation of Th2 markers by CT are consistent with the CT induction of Th2 cells.

Signaling by IL-12 and IL-23 and the immunoregulatory roles of STAT4

Produced in response to a variety of pathogenic organisms, interleukin (IL)-12 and IL-23 are key immunoregulatory cytokines that coordinate innate and adaptive immune responses. These dimeric cytokines share a subunit, designated p40, and bind to a common receptor chain, IL-12R beta 1. The receptor for IL-12 is composed of IL-12R beta 1 and IL-12R beta 2, whereas IL-23 binds to a receptor composed of IL-12R beta 1 and IL-23R. Both cytokines activate the Janus kinases Tyk2 and Jak2, the transcription factor signal transducer and activator of transcription 4 (STAT4), as well as other STATs. A major action of IL-12 is to promote the differentiation of naive CD4+ T cells into T-helper (Th) 1 cells, which produce interferon (IFN)-gamma, and deficiency of IL-12, IL-12R subunits or STAT4 is similar in many respects. In contrast, IL-23 promotes end-stage inflammation. Targeting IL-12, IL-23, and their downstream signaling elements would therefore be logical strategies for the treatment of immune-mediated diseases.

The B subunit of Escherichia coli heat-labile enterotoxin induces both caspase-dependent and -independent cell death pathways in CD8+ T cells

The nontoxic B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a potent immunomodulatory molecule that acts both as an adjuvant and to stimulate immune deviation processes, resulting in the suppression of Th1-associated inflammatory responses. The ability of EtxB to alter immune reactivity is dependent on its ability to modulate immune cell function through binding to cell surface molecules, the principal receptor of which is the ubiquitous GM1-ganglioside. EtxB activates B cells and antigen-presenting cells and induces the selective apoptosis of murine CD8+ T cells. We postulated that these effects are mediated by the induction of intracellular signaling pathways following EtxB-receptor interaction. We have previously shown that CD8+ T-cell apoptosis induced by EtxB results from the activation of the transcription factor NF-kappaB and caspases. Here we report that while caspase activity is required for apoptosis, additional features of cell death are caspase independent. EtxB induces a rapid loss of mitochondrial membrane potential and cell viability that are unaffected by caspase inhibitors. In addition, our data suggest that these processes are independent of the activity of Bax and Bcl-2 but are mediated by nitric oxide synthase.

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.

Association of adherence and motility in interleukin 8 induction in human intestinal epithelial cells by Vibrio cholerae

Interleukin 8 (IL-8) mRNA expression in Vibrio cholerae-infected human intestinal epithelial cells Int407 was determined by quantitative real-time RT-PCR and secretion measured by ELISA. Incubation of Int407 with V. cholerae O395 resulted in increased IL-8 mRNA expression as early as within 2 h of infection. Kinetics of IL-8 secretion reached a peak at about 8 h (780 pg/ml) and decreased thereafter. Induction of IL-8 was significantly high among various toxin-producing strains of V. cholerae belonging to serovar O1, O139 and non-O1 compared to non-toxinogenic strains. Induction of IL-8 was maximum in V. cholerae O395, required live cells and was dependent on de novo protein synthesis. The bacterial culture supernatant and crude cell envelope showed IL-8 stimulating activity. Infection of the monolayer with V. cholerae O395 cheY4 null mutant (O395YN), defective in adherence and motility, resulted in highly reduced levels of IL-8 expression, while hyperadherent and hypermotile mutant (O395Y) with the cheY4 gene duplicated also showed very high IL-8 expression. Another hyperadherent icmF insertion mutant (O395F) with reduced motility showed almost half the amount of IL-8 expression compared to O395Y. These results clearly indicate that both motility and adherence to intestinal epithelial cells are possible triggering factors contributing to IL-8 mRNA expression by V. cholerae.

Exploiting immune surveillance mechanisms in mucosal vaccine development

Historically, immune responsiveness was regarded by many as an ability to discriminate self from non-self, but this definition has recently been revised to be a distinction between threatening infectious organisms versus innocuous molecules from autologous tissues. Such distinctions can be made in the context of adjuvant effects from triggering of 'pattern recognition receptors' by pathogen-associated molecules. Mucosal sites such as airway and intestinal passages present a particularly interesting challenge to this system, as distinctions must be effectively made between innocuous non-self molecules associated with food and commensal bacteria versus pathogenic viruses and bacteria. Given the simultaneous presence of all these molecular types at mucosal lymphoid sites, immunological discrimination mechanisms must be especially precise, as immune responses must be directed only at pathogen-associated targets. Ongoing research is identifying genes that may be critical to triggering mucosal immunity; an understanding of their role in discrimination may lead to the development of new vaccines.

Role of B7 costimulatory molecules in immune responses and T-helper cell differentiation in response to recombinant HagB from Porphyromonas gingivalis

In addition to antigen-specific signals mediated through the T-cell receptor, T cells also require antigen nonspecific costimulation for activation. The B7 family of molecules on antigen-presenting cells, which include B7-1 (CD80) and B7-2 (CD86), play important roles in providing costimulatory signals required for development of antigen-specific immune responses. Hemagglutinin B (HagB) is a nonfimbrial adhesin of the periodontopathic microorganism Porphyromonas gingivalis and is thought to be involved in the attachment of the bacterium to host tissues. However, the immune mechanisms involved in responses to HagB and their roles in pathogenesis have yet to be elucidated. Therefore, the purpose of this study was to determine the role of B7 costimulatory molecules on T-helper-cell differentiation for the induction of immune responses to HagB. Mice deficient in either or both of the costimulatory molecules B7-1 and B7-2 were used to explore their role in immune responses to HagB after subcutaneous immunization. B7-1(-/-) mice had levels of immunoglobulin G (IgG) anti-HagB antibody activity in serum similar to those of wild-type mice, whereas lower serum IgG anti-HagB antibody responses were seen in B7-2(-/-) mice. Moreover, significantly lower numbers of IgG antibody-secreting cells and lower levels of CD4(+)-T-cell proliferation were observed in B7-2(-/-) mice compared to wild-type mice. No serum IgG response to HagB was detected in B7-1/B7-2(-/-) mice. Analysis of the subclass of the serum IgG responses and the cytokines induced in response to HagB revealed that B7-2(-/-) mice had significantly lower IgG1 and higher IgG2a anti-HagB antibody responses compared to wild-type mice. The B7-2(-/-) mice also had significantly reduced levels of interleukin-4 (IL-4) and IL-5 and enhanced level of gamma interferon. Furthermore, assessment of B7-1 and B7-2 expression on B cells and macrophages derived from wild-type BALB/c mice after in vitro stimulation with HagB revealed a predominant upregulation in the expression of the B7-2 costimulatory molecule on B cells and macrophages. Essentially no change was seen in the expression of B7-1. Taken together, these results suggest a critical role for B7, especially B7-2, for the preferential induction of a Th2-like response to HagB.

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.

Activation and suppression of the proinflammatory immune response by Vibrio cholerae toxins

Vibrio cholerae induces either non-inflammatory diarrhea or inflammatory gastroenteritis, depending on the presence of cholera toxin, a fluid secretion inducer and a modulator of host immunity. In the absence of cholera toxin, other toxins induce inflammation, resulting in gastroenteritis. Thus, multiple toxins likely affect the safety of live attenuated vaccines.

Role of mast cells and pro-inflammatory mediators on the intestinal secretion induced by cholera toxin

Recent data suggest that diarrhea caused by Vibrio cholerae involves a pro-inflammatory mediators release, such as cytokines, prostaglandin and nitric oxide. The aim of this study was to investigate the role of mast cells and their mediators in the intestinal secretion induced by cholera toxin. We examined the dose responses, time course and role of mast cells and pro-inflammatory mediators in cholera toxin intestinal secretory response, in vivo. Cholera toxin caused a dose-dependent secretion, in ligated small intestine loops, at 18 h. Rats treated with 48/80 compound or ketotifen had a significant decrease in the intestinal secretory response. Cholera toxin secretion was significantly reduced by an unspecific histamine/serotonin receptor antagonist, histamine receptor antagonist, phospholipase A2 and cyclooxygenase inhibitors, platelet-activating factor (PAF) receptor antagonists and TNF-alpha synthesis blockers. On the other hand, pretreatment with a specific serotonin receptor antagonist and lipoxygenase inhibitors failed to block this effect. Analysis of the intestinal fluid from rats injected with cholera toxin, revealed that cholera toxin induces the release of IL-1beta and TNF-alpha into fluid. The data suggest that, at least in part, mast cells are involved in cholera toxin-induced secretion, as well as point to the importance of histamine, prostaglandins, PAF, IL-1beta and TNF-alpha in this process.

Human keratinocytes express fractalkine/CX3CL1

BACKGROUND

fractalkine/CX3CL1 is a unique chemokine that has properties of both chemoattractants and adhesion molecules. The major source of this chemokine in the skin is still controversial.

OBJECTIVE

studies were undertaken to determine the expression of fractalkine in human skin.

METHODS

RT-PCR, Western blotting, and immunostaining were performed with normal human epidermal keratinocytes (NHEK) and HaCaT cells, human keratinocyte cell line, for the presence of fractalkine. Biopsy specimens of normal and diseased skin were also investigated.

RESULTS

we identified that NHEK and HaCaT cells expressed fractalkine mRNA and protein. The combination of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma upregulated their expression by NHEK. Immunohistochemistry demonstrated fractalkine expression in keratinocytes in lichen planus and psoriasis vulgaris. RT-PCR also showed that lesional skin of psoriatic patients expressed higher levels of fractalkine mRNA than non-lesional skin from the same patients.

CONCLUSION

these results suggests that keratinocytes strongly express fractalkine in lichen planus and psoriasis vulgaris and that the fractalkine-CXC3CR1 system in the diseased skin can be a target for the treatment.

Induction of cellular immunity to varicella-zoster virus glycoproteins tested with pernasal coadministration of Escherichia coli enterotoxin in mice

A mutant of Escherichia coli enterotoxin promotes the induction of cellular immunity to a live varicella vaccine (the Oka strain) as a mucosal adjuvant in mice. An investigation was carried out to determine which of the purified glycoproteins of the virus among three induced cellular immunity with a single nasal administration. Spleen cells from mice immunized nasally with the vaccine and toxin produced interleukin-2 (IL-2) at the same level on restimulation in vitro with glycoprotein H: glycoprotein L (gH:gL), gB, and gE:gI, but not IL-4. The spleen cells from mice immunized with gH:gL, gB, or gE:gI and toxin produced IL-2 on restimulation with gH:gL, gB, or gE:gI, respectively, and the vaccine, but not IL-4. Immunization with gH:gL and the toxin showed increased thymidine uptake and production of IL-2 and interferon-gamma (IFN-gamma) of the spleen cells, but not IL-4, depending on the dose of gH:gL used for immunization and restimulation in vitro. Purified gE:gI and gB have been reported to be the strongest stimulators of cellular immunity to varicella upon subcutaneous injection and are useful as a subunit vaccine. All the glycoproteins tested are excellent stimulators of cellular immunity to the virus and itself on nasal co-immunization with the toxin.

Effects of recombinant cholera toxin B subunit on IL-1beta production by macrophages in vitro

Recombinant cholera toxin B subunit (rCTB) is a safe and potent mucosal adjuvant. As a clue to the mechanism of the adjuvant effect of rCTB, the profile of cytokines secreted in vitro by the mouse peritoneal macrophage (Mphi) treated with rCTB was examined. IL-1beta secretion, intracellular production, and expression of its mRNA of LPS-stimulated Mphi was greatly enhanced by treatment with rCTB. IL-1beta production in response to other microbial stimulators, such as Pansorbin, Sansorbin, insoluble peptidoglycan, and Taxol, was also potentiated by rCTB. Mphi pretreated with rCTB before 24 hr could maintain the ability to produce a high level of IL-1beta, suggesting that this ability may be involved in the adjuvant activity of rCTB on Mphi stimulation. The possibility of close association between rCTB and signal transduction of a Toll-like receptor family in Mphi is discussed.

The contribution of accessory toxins of Vibrio cholerae O1 El Tor to the proinflammatory response in a murine pulmonary cholera model

The contribution of accessory toxins to the acute inflammatory response to Vibrio cholerae was assessed in a murine pulmonary model. Intranasal administration of an El Tor O1 V. cholerae strain deleted of cholera toxin genes (ctxAB) caused diffuse pneumonia characterized by infiltration of PMNs, tissue damage, and hemorrhage. By contrast, the ctxAB mutant with an additional deletion in the actin-cross-linking repeats-in-toxin (RTX) toxin gene (rtxA) caused a less severe pathology and decreased serum levels of proinflammatory molecules interleukin (IL)-6 and murine macrophage inflammatory protein (MIP)-2. These data suggest that the RTX toxin contributes to the severity of acute inflammatory responses. Deletions within the genes for either hemagglutinin/protease (hapA) or hemolysin (hlyA) did not significantly affect virulence in this model. Compound deletion of ctxAB, hlyA, hapA, and rtxA created strain KFV101, which colonized the lung but induced pulmonary disease with limited inflammation and significantly reduced serum titers of IL-6 and MIP-2. 100% of mice inoculated with KFV101 survive, compared with 20% of mice inoculated with the ctxAB mutant. Thus, the reduced virulence of KFV101 makes it a prototype for multi-toxin deleted vaccine strains that could be used for protection against V. cholerae without the adverse effects of the accessory cholera toxins.

Contribution of the ADP-ribosylating and receptor-binding properties of cholera-like enterotoxins in modulating cytokine secretion by human intestinal epithelial cells

When epithelial cells first encounter cholera toxin (Ctx) produced by Vibrio cholerae they secrete not only chloride ions responsible for causing diarrhoea, but also a number of cytokines that may contribute to the toxin's potent immunomodulatory properties. Much less is known about the ability of the heat-labile enterotoxin of Escherichia coli (Etx), a close homologue of Ctx, to elicit cytokine secretion by epithelial cells. This study shows that treatment of human intestinal epithelial T84 cells with Etx induces expression of IL-6, IL-10, IL-1R antagonist, as well as IL-1alpha and IL-1beta and low levels of IL-8. Such induction was totally dependent on the intrinsic ADP-ribosylating activity of the toxin A-subunit, and could be mimicked by cAMP-elevating agents, such as forskolin and dibutyryl cAMP. By comparison, neither an enzymically inactive mutant of Etx nor EtxB was able to induce cytokine secretion. The behaviour of Ctx and CtxB was very similar to that of Etx and EtxB, respectively. The spectrum of cytokines released by Etx and Ctx indicates that the toxins may create a local microenvironment that strongly biases the immune response towards an anti-inflammatory and a polarized Th2 response.

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.

Effects of the adjuvant cholera toxin on dendritic cells: stimulatory and inhibitory signals that result in the amplification of immune responses

Cholera toxin (CT) is a potent mucosal adjuvant. When administered through the mucosal route CT amplifies B and T lymphocyte responses to co-administered antigens. Since the discovery of CT as a mucosal adjuvant, other bacterial enterotoxins have been found to have this property. These molecules or their detoxified derivatives are all important for the development of mucosal vaccines for human use, and it is thus necessary to understand their mechanism of action. CT has immunomodulatory effects on different cell types, however, the interaction of CT with dendritic cells (DCs), which have a primary role in the priming of immune responses, may be crucial for its adjuvant activity.

Modulation of human lymphocyte proliferative response with aging

Previously, we have demonstrated age-associated alterations in transmembrane signaling. One of the most reproducible alterations found in the immune response with aging is the decrease of lymphocyte proliferation on stimulation with various different mitogens. Here, we confirm that proliferative responses to stimulation with phytohaemagglutin (PHA), recombinant human IL-2, or anti-CD3 monoclonal antibody are all greater in the young (20-25 years) than old (60-87 years) population. We attempted to modulate the proliferative response using various agents acting at different levels of transmembrane signaling (pertussis toxin, cholera toxin, isoproterenol, PMA, Ca ionophore A23187), as well as at the level of the lymphocyte plasma membrane (methyl-beta-cyclodextrin, MBCD), or by using antioxidant vitamins (Vitamin E or C). None of these agents was able to restore effectively the proliferative response of lymphocytes from the aged to the level of young subjects. Even the combination of A23187 and PMA acting directly on calcium metabolism and protein kinase C activity was insufficient to restore the decreased mitogenic capacity of T cells from elderly subjects. Cyclodextrin, which decreases the cholesterol content of the membrane, increased the proliferative response of lymphocytes of elderly subjects, but not to the level of the young. Vitamin E had a very strong inhibitory effect on lymphocyte stimulation in both the age groups, except in combination with MBCD in T cells of the elderly, while Vitamin C had no significant modulatory effect. MAPK ERK and p38 activation was found to be decreased with aging in T cells after anti-CD3 mAb stimulation. Vitamin E but not Vitamin C strongly inhibited MAPK ERK or p38 activation. The direct activation of certain molecules or the modulation of the cholesterol content of the membrane seems to be effective immunomodulatory interventions with aging.

Inhibition of Th1- and Enhancement of Th2-Initiating Cytokines and Chemokines in Trichosanthin- Treated Macrophages

Trichosanthin (TCS), the major effective component from Chinese herb Trichosanthes Kirilowii Maxim, is also a potent allergen. Our previous work has shown that TCS can upregulate interleukin-4 (IL-4) and interleukin-13 (IL-13) while inhibit interferon-gamma (IFN-gamma) in mesenteric lymph node cells after TCS immunization. Thus, TCS can arouse a T helper 2 (Th2) response in the draining lymph node. However, little is known about the early effects of TCS on antigen-presenting cells, the initiator of T cell response. In the current study, the effects of TCS on macrophage cytokines and chemokine expression were investigated. Peritoneal macrophages were treated with or without TCS in the presence of lipopolysaccharide (LPS). We found that TCS increased macrophage interleukin-10 (IL-10) and monocyte chemoattractant protein-1 (MCP-1) expression, whereas it decreased interleukin-12 (IL-12) and tumor necrosis factor-alpha (TNF-alpha) expression. Our study clearly demonstrated that TCS, as an allergen, has differential effects on macrophage Th1/Th2 initiative factors, effects that are likely to facilitate its inducing of Th2 and immunoglobulin E (IgE) response.