Chronic helminth infection induces alternatively activated macrophages expressing high levels of CCR5 with low interleukin-12 production and Th2-biasing ability

Helminth infections induce Th2-type biased immune responses. Although the mechanisms involved in this phenomenon are not yet clearly defined, antigen-presenting cells (APC) could play an important role in this process. Here, we have used peritoneal macrophages (F4/80+) recruited at different times after challenge with Taenia crassiceps as APC and tested their ability to regulate Th1/Th2 differentiation. Macrophages from acute infections produced high levels of interleukin-12 (IL-12) and nitric oxide (NO), paralleled with low levels of IL-6 and prostaglandin E(2) (PGE(2)) and with the ability to induce strong antigen-specific CD4+ T-cell proliferation in response to nonrelated antigens. In contrast, macrophages from chronic infections produced higher levels of IL-6 and PGE(2) and had suppressed production of IL-12 and NO, associated with a poor ability to induce antigen-specific proliferation in CD4+ T cells. Failure to induce proliferation was not due to a deficient expression of accessory molecules, since major histocompatibility complex class II, CD40, and B7-2 were up-regulated, together with CD23 and CCR5 as infection progressed. These macrophages from chronic infections were able to bias CD4+ T cells to produce IL-4 but not gamma interferon (IFN-gamma), contrary to macrophages from acute infections. Blockade of B7-2 and IL-6 and inhibition of PGE(2) failed to restore the proliferative response in CD4+ T cells. Furthermore, studies using STAT6(-/-) mice revealed that STAT6-mediated signaling was essential for the expansion of these alternatively activated macrophages. These data demonstrate that helminth infections can induce different macrophage populations that have Th2-biasing properties.     

Induction of Th2 cell tolerance to a soluble antigen by blockade of the LFA-1-dependent pathway prevents allergic inflammation

In this article, we show that induction of Th2 cell tolerance prevents antigen-induced eosinophil recruitment into the tissue and IgE antibody production, and that ICAM-1/LFA-1 interaction is involved as a costimulatory signal in inducing T cell tolerance to a soluble antigen. In vivo pretreatment with anti-ICAM-1 monoclonal antibody (mAb), anti-LFA-1 mAb, and a soluble antigen inhibited antigen-induced eosinophil recruitment into the airways and IgE antibody production in mice in an antigen-specific manner. In vitro antigen-induced IL-2, IL-4 and IL-5 production were decreased in spleen cells of the mice pretreated with the two mAbs and the antigen, indicating the induction of both Th1 and Th2 cell tolerance in vivo. These results suggest that the induction of antigen-specific Th2 cell tolerance by allergen immunotherapy with blockade of the ICAM-/LFA-1 interaction would be a rational therapeutic approach to allergic inflammation such as asthma.     

High-dose oral tolerance prevents antigen-induced eosinophil recruitment into the mouse airways

We have previously shown that antigen-induced eosinophil recruitment into the tissue of sensitized mice is mediated by CD4+ T cells and IL- 5. To determine whether the induction of oral tolerance down-regulates antigen-induced eosinophil recruitment into the tissue, we studied the effect of oral administration of a protein antigen on antigen-induced eosinophil infiltration in the trachea of sensitized mice, on antigen- induced CD4+ T cell infiltration and IL-5 production in the airways, and on the in vitro production of IL-2, IL-4, IL-5 and IFN-gamma in spleen cells of the mice. Oral administration of a protein antigen in high doses inhibited antigen-induced eosinophil infiltration in the trachea and IgE antibody production in mice in an antigen-specific manner. The oral administration of antigen also suppressed both CD4+ T cell recruitment into the trachea and IL-5 levels in the bronchoalveolar lavage fluids of the mice after antigen inhalation. In vitro antigen-induced production of IL-2, IFN-gamma, IL-4 and IL-5 was decreased in spleen cells of antigen-fed mice, indicating the induction of both Th1 and Th2 cell tolerance in vivo. On the other hand, pretreatment with anti-transforming growth factor-beta antibody at the time of immunization with antigen had no significant effect on the inhibition of antigen-induced eosinophil recruitment and IgE antibody production in antigen-fed mice. Finally, antigen-specific CD4+ T cells were not deleted in TCR transgenic mice after antigen feeding by FACS analysis. Taken together, these results indicate that high-dose oral tolerance induces not only Th1 but also Th2 cell tolerance in vivo and thereby inhibits antigen-induced eosinophil recruitment into the tissue.      

Toll-Like Receptor 2-Dependent Extracellular Signal-Regulated Kinase Signaling in Mycobacterium tuberculosis-Infected Macrophages Drives Anti-Inflammatory Responses and Inhibits Th1 Polarization of Responding T Cells

Mycobacterium tuberculosis survives within macrophages and employs immune evasion mechanisms to persist in the host. Protective T helper type 1 (Th1) responses are induced, and the immune response in most individuals is sufficient to restrict M. tuberculosis to latent infection, but most infections are not completely resolved. As T cells and macrophages respond, a balance is established between protective Th1-associated and other proinflammatory cytokines, such as interleukin-12 (IL-12), interferon gamma (IFN-γ), and tumor necrosis factor alpha, and anti-inflammatory cytokines, such as IL-10. The mechanisms by which M. tuberculosis modulates host responses to promote its survival remain unclear. In these studies, we demonstrate that M. tuberculosis induction of IL-10, suppression of IL-12, and inhibition of class II major histocompatibility complex (MHC-II) molecules in infected macrophages are all driven by Toll-like receptor 2 (TLR2)-dependent activation of the extracellular signal-regulated kinases (ERK). Elimination of ERK signaling downstream of TLR2 by pharmacologic inhibition with U0126 or genetic deletion of Tpl2 blocks IL-10 secretion and enhances IL-12 p70 secretion. We demonstrate that M. tuberculosis regulation of these pathways in macrophages affects T cell responses to infected macrophages. Thus, genetic blockade of the ERK pathway in Tpl2^−/− macrophages enhances Th1 polarization and IFN-γ production by antigen-specific CD4⁺ T cells responding to M. tuberculosis infection. These data indicate that M. tuberculosis and its potent TLR2 ligands activate ERK signaling in macrophages to promote anti-inflammatory macrophage responses and blunt Th1 responses against the pathogen.     

Interferon-beta induces selective enhancement of antigen-specific T cell responses.

Interferon-beta (IFN-beta) inhibits mitogen-induced T cell responses, in part through downregulation of interleukin-12 (IL-12) or upregulation of IL-10. We have reexamined these findings using ragweed (RW) stimulated or tetanus toxoid (TT)-stimulated human peripheral blood mononuclear cells (PBMC) and nontransformed, antigen-specific, human Th0, Th1, and Th2 clones. IFN-beta induced concentration-dependent inhibition of phytohemagglutinin (PHA)-stimulated PBMC proliferation and enhancement of RW-stimulated or TTstimulated PBMC proliferation. Monocyte depletion of PBMC isolates resulted in concentration-dependent inhibition of RW-driven or TT-driven proliferation by IFN-beta. This response was unaltered by the addition of either exogenous recombinant human IL-12 (rHuIL-12) or saturating concentrations of anti-IL-10. Moreover, addition of exogenous rHuIL-10 to nondepleted RW-driven or TT-driven PBMC cultures did not alter the concentration-dependent enhancement of antigen-driven proliferation induced by IFN-beta. Th0, Th1, and Th2 clones stimulated in the presence of antigen and autologous, irradiated PBMC displayed concentration-dependent inhibition of proliferation in the presence of IFN-beta that was unaltered by the addition of either exogenous rHuIL-12 or a saturating concentration of anti-IL-10. Finally, whereas IFN-beta inhibited antigen-driven generation of IL-5, IL-12, IL-13, and IFN-gamma, IFN-beta enhanced generation of both IL-4 and IL-10. Thus, IFN-beta, induces a selective, IL-10-independent and IL-12-independent upregulation of antigen-specific T cell responses, supporting the role of IFN-beta as an immunomodulatory rather than an antiproliferative/immunosuppressive cytokine.     

Interleukin 12 and innate molecules for enhanced mucosal immunity

Recent strategies for understanding the mechanisms underlying mucosal immune responses and subsequent development of mucosal vaccines for induction of targeted immunity now include cytokines and molecules of innate immunity. These studies have shown that cytokines influencing the development of T helper (Th) cells differentially affect the outcome of mucosal vs systemic immune responses to mucosal vaccines. Serum antigen-specific antibody (Ab) responses were enhanced when either IL-6 or IL-12 was mucosally administered with a protein antigen, while only IL-12 induced antigen-specific mucosal IgA Ab responses. Mucosal IL-6 and IL-12 also affected the type of Th cell responses induced by CD4⁺ T cells from mice that received IL-12 secreted larger amounts of IFN-γ and IL-6 when compared with mice nasally treated with IL-6. Discrepancies in the ability to enhance mucosal or systemic immune responses were also observed when human neutrophil peptide (HNP) defensins or lymphotactin were nasally coadministered with protein antigens. Only lymphotactin promoted mucosal secretory IgA (S-IgA) Ab responses while both lymphotactin and defensins enhanced systemic immunity to mucosally co-administered protein antigens. Mixed antigen-specific Th1-and Th2-type CD4⁺ T cell responses were induced in the systemic compartment by both lymphotactin and the mixture of HNP-1, HNP-2, and HNP-3 defensins. However, HNPs failed to significantly enhance cytokine secretion by mucosally derived, antigen-specific CD4⁺ T cells relative to those isolated from the systemic compartment. In summary, these studies clearly show that IL-12 and lymphotactin are able to trigger S-IgA Ab responses and provide new avenues for the design of safe and targeted mucosal vaccines.     

Th1 cells induce and Th2 inhibit antigen-dependent IL-12 secretion by dendritic cells

Dendritic cells are the most relevant antigen-presenting cells (APC) for presentation of antigens administered in adjuvant to CD4⁺ T cells. Upon interaction with antigen-specific T cells, dendritic cells (DC) expressing appropriate peptide-MHC class II complexes secrete IL-12, a cytokine that drives Th1 cell development. To analyze the T cell-mediated regulation of IL-12 secretion by DC, we have examined their capacity to secrete IL-12 in response to stimulation by antigen-specific Th1 and Th2 DO11.10 TCR-transgenic cells. These cells do not differ either in TCR clonotype or CD40 ligand (CD40L) expression. Interaction with antigen-specific Th1, but not Th2 cells, induces IL-12 p40 and p75 secretion by DC. The induction of IL-12 production by Th1 cells does not depend on their IFN-γ secretion, but requires direct cell-cell contact mediated by peptide/MHC class II-TCR and CD40-CD40L interactions. Th2 cells not only fail to induce IL-12 secretion, but they inhibit its induction by Th1 cells. Unlike stimulation by Th1, inhibition of IL-12 production by Th2 cells is mediated by soluble molecules, as demonstrated by transwell cultures. Among Th2-derived cytokines, IL-10, but not IL-4 inhibit Th1-driven IL-12 secretion. IL-10 produced by Th2 cells appears to be solely responsible for the inhibition of Th1-induced IL-12 secretion, but it does not account for the failure of Th2 cells to induce IL-12 production by DC. Collectively, these results demonstrate that Th1 cells up-regulate IL-12 production by DC via IFN-γ-independent cognate interaction, whereas this is inhibited by Th2-derived IL-10. The inhibition of Th1-induced IL-12 production by Th2 cells with the same antigen specificity represents a novel mechanism driving the polarization of CD4⁺ T cell responses.     

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.     

CD40/CD40 ligand interactions are required for T cell-dependent production of interleukin-12 by mouse macrophages

We have previously shown that T cell receptor-activated mouse T helper (Th)1 clones induce the production of interleukin (IL)-12 by splenic antigen-presenting cells (APC). Here, we show that the expression of CD40L by activated T cells is critical for T cell-dependent IL-12 production by mouse macrophages. IL-12 was produced in cultures containing alloreactive Th1 clones stimulated with allogeneic peritoneal macrophages, or in cultures of splenocytes stimulated with anti-CD3. Anti-CD40L monoclonal antibodies (mAb) inhibited the production of IL-12, but not IL-2, in these cultures by ?90% and had dramatic inhibitory effects on antigen-dependent proliferation of Th1 clones. In addition, both activated T cells and a Th1 clone derived from CD40L knockout mice failed to induce IL-12 production from splenic APC or peritoneal macrophages. Finally, macrophages cultured in the absence of T cells produced IL-12 upon stimulation with soluble recombinant CD40L in combination with either supernatants from activated Th1 clones or with interferon-γ and granulocyte/macrophage colony-stimulating factor. Thus, both CD40L-dependent and cytokine-mediated signals from activated T cells are required to induce the production of IL-12 by macrophages. A blockade at the level of IL-12 production may explain, at least in part, the dramatic ability of anti-CD40L mAb to inhibit disease in animal models that are dependent upon the generation of a cell-mediated immune response. Moreover, a defect in T cell-dependent induction of IL-12 may contribute to the immune status of humans that lack functional CD40L.     

Interleukin-10 is expressed by bovine type 1 helper, type 2 helper, and unrestricted parasite-specific T-cell clones and inhibits proliferation of all three subsets in an accessory-cell-dependent manner.

Murine interleukin-10 (IL-10) is produced by type 2 helper (Th2) cells and selectively inhibits cytokine synthesis by type 1 helper (Th1) cells, whereas human IL-10 is produced by and inhibits proliferation and cytokine synthesis by both Th1 and Th2 subsets. This study reports that bovine IL-10 mRNA is expressed by Th0, Th1, and Th2 clones of bovine T cells specific for either Babesia bovis or Fasciola hepatica but not by two CD8+ T-cell clones. The antigen-induced proliferative responses of all three subsets of CD4+ cells were inhibited by human IL-10, and low levels (10 U/ml) of exogenous human IL-2 restored the suppressed response. However, proliferation of one Th1 clone was never inhibited but was enhanced by IL-10. Human IL-10 also inhibited the expression of gamma interferon and IL-4 mRNA in Th0 clones. In the absence of accessory cells (AC), the responses of Th clones to concanavalin A or IL-2 were not inhibited by IL-10, whereas antigen-specific responses of Th1 and Th2 cells were reduced when IL-10-pretreated macrophages were used as AC. Together, our results with bovine T cells support the concept that IL-10 primarily affects AC function and does not directly inhibit CD4+ T cells and demonstrate that the immunoregulatory effects of IL-10 are not selectively directed at Th1 populations, as they are in mice.     

Dietary nucleotides can up-regulate antigen-specific Th1 immune responses and suppress antigen-specific IgE responses in mice

BACKGROUND: It has been reported that dietary nucleotides enhance T helper cell activities. In this study, we have determined the effects of dietary nucleotides on antigen-specific Th1 and Th2 responses and IgE responses. METHODS: Ovalbumin (OVA)-specific T cell receptor (TCR) transgenic (OVA-TCR Tg) mice, 3 weeks old, were fed a nucleotide-free diet (NT(-) diet) or the NT(-) diet supplemented with dietary nucleotides (NT(+) diet) for 4 weeks. Cytokine production by spleen cells and macrophages obtained from these mice was measured in vitro. BALB/c mice, 3 weeks old, immunized intraperitoneally with OVA adsorbed onto alum, were fed the NT(-) diet or the NT(+) diet for 4 weeks. Serum levels of antigen-specific antibodies in the BALB/c mice were determined by ELISA. RESULTS: The level of production of antigen-specific interferon-gamma by spleen cells was significantly higher in the OVA-TCR Tg mice fed the NT(+) diet than in the control mice. The levels of secretion of bioactive IL-12 by spleen cells and peritoneal macrophages were also significantly increased in the NT(+) diet group. The serum OVA-specific IgE level was significantly decreased in BALB/c mice fed the NT(+) diet compared with those fed the NT(-) diet. CONCLUSION: These results show that dietary nucleotides up-regulate the antigen-specific Th1 immune response through the enhancement of IL-12 production and suppress the antigen-specific IgE response.     

Corticosteroids inhibit the production of inflammatory mediators in immature monocyte-derived DC and induce the development of tolerogenic DC3.

Corticosteroids (CS) are potent immunosuppressive agents that are known to affect T cell-mediated inflammation by the inhibition of proliferation and cytokine production, as well as the immunostimulatory function of monocytes and macrophages. Not much is known of the effect of corticosteroids on dendritic cells (DC), the professional T cell stimulatory antigen-presenting cells. We report that the endogenous CS hydrocortisone and the synthetic CS clobetasol-17-propionate strongly inhibited the production of the inflammatory mediators interleukin (IL)-12 p70, tumor necrosis factor alpha (TNF-alpha), and IL-6 by lipopolysaccharide (LPS)-stimulated monocyte-derived immature DC (iDC) in vitro. In contrast, the stimulatory capacity, antigen uptake, and the expression of costimulatory molecules were not affected. In accordance with the decreased production of IL-12 p70, CS-treated iDC induced less production of the inflammatory Th1 cytokine interferon-y and enhanced levels of the Th2 cytokines IL-10 and IL-5 in staphylococcal enterotoxin B-stimulated CD4+ Th cells. Furthermore, CS inhibited the maturation of iDC as assessed by the lack of expression of CD83 as well as by the prevention of the loss of antigen uptake capacities. These type 3 DC (DC3) matured in the presence of CS produce less IL-12 p70 and have a decreased T cell stimulatory capacity. Moreover, uncommitted T cells that encounter the CS-induced DC3 develop into Th2-biased cells, which may additionally decrease the Th1-mediated tissue damage but, on the other hand, Th2 cytokines may promote undesirable elevation of IgE and eosinophilia. These findings indicate that suppression of T cell-mediated inflammation by CS not only relies on direct effects on T cells, but also on various effects on DC, their professional antigen-presenting cells.     

Induction of a Th17 cell response by Helicobacter pylori Urease subunit B

Th17 cells represent a novel subset of CD4⁺ T cells, which is associated with Helicobacter pylori infection. In the present study, we investigated the potential role of Urease subunit B (UreB) in the induction of Th17 cell response. Co-cultured splenic lymphocytes from H. pylori-infected mice with the recombinant UreB (rUreB) elevated IL-17 secretion and caused an increase in the number of Th17 cells. The expression of IL-6 and IL-23 p19 was significantly increased in rUreB-stimulated macrophages. Whole cell protein (WCP) of UreB-deficient strain (UreB⁻ strain) induced less Th17 cell responses than that of wild-type strain. In addition, subcutaneous and intranasal immunization of rUreB elicited antigen-specific Th17 cell responses. Intranasal immunization of rUreB reduced H. pylori colonization in the stomach, which was closely related with the increased rUreB-specific Th17 cell responses. These results suggest that UreB is an important protein which is able to elicit Th17 cell responses against H. pylori both in vivo and in vitro.     

Interleukin 25 in allergic airway inflammation

T helper 2 (Th2) cells induce allergic inflammation through the production of cytokines such as interleukin (IL)-4, IL-5 and IL-13. Recently, it has been demonstrated that a novel IL-17 family cytokine IL-25 (IL-17E) is a product of activated Th2 cells and mast cells. Interestingly, when systemically administered to mice, IL-25 induces IL-4, IL-5 and IL-13 production from undefined non-T/non-B cells and then induces Th2-type immune responses such as blood eosinophilia and increased serum immunoglobulin E levels. In addition, we have recently shown that IL-25 mRNA is expressed in the lung after an inhaled antigen challenge in sensitized mice and that neutralization of the produced IL-25 by soluble IL-25 receptor decreases antigen-induced eosinophil and CD4+ T cell recruitment into the airways. Moreover, we have shown that the enforced expression of IL-25 in the lung significantly enhances antigen-induced Th2 cytokine production and eosinophil recruitment into the airways, and that the IL-25-mediated enhancement of antigen-induced eosinophil recruitment is inhibited by the depletion of CD4+ T cells. Thus, it is suggested that IL-25 plays an important role in enhancing allergic airway inflammation by a CD4+ T-cell-dependent mechanism.     

Do T helpers 1 and 2 recognize different class II MHC molecules? Humoral and cellular immune responses to soluble allergen from Aspergillus fumigatus Asp f2

Cellular signals leading to T helper (Th)1/Th2 shift are not well known. Here we demonstrate that Th1 possibly recognizes peptides presented by the IE molecule of MHC class II while Th2 is activated by the recognition of peptides presented by the IA molecule. BALB/c mice immunized with Asp f2 developed stable IA-restricted Th2 immune response to the 12th day after immunization, as analyzed by IL-2 production. On the contrary, early Th0 cells did not secrete IL-2 upon Asp f2 stimulation but did produce a high level of IL-2 if stimulated in the presence of anti-IA Abs. This effect of anti-IA Abs on early Th0 cells was both MHC IE and CD4(+) cell restricted. In vivo blocking of Asp f2 peptide presentation by the IA molecule led to the formation of antigen-specific cytotoxicity as demonstrated using immune splenocytes as effector cells and Asp f2 loaded P815 cells as targets.     

Induction of interleukin-12 production in mouse macrophages by berberine,a benzodioxoloquinolizine alkaloid,deviates CD4+ T cells from a Th2 to a Th1 response

In this study we investigated whether berberine-mediated induction of interleukin-12 (IL-12) production in antigen-presenting cells could regulate a cytokine profile of antigen-primed CD4+ T helper (Th) cells. Pretreatment with berberine induced IL-12 production in both macrophages and dendritic cells, and significantly increased the levels of IL-12 production in lipopolysaccharide-stimulated macrophages and in CD40 ligand-stimulated dendritic cells. Importantly, berberine pretreatment of macrophages increased their ability to induce interferon-gamma (IFN-gamma) and reduced their ability to induce IL-4 in antigen-primed CD4+ T cells. Berberine did not influence the macrophage cell surface expression of the class II major histocompatibility complex molecule, the co-stimulatory molecules CD80 and CD86, and intracellular adhesion molecule-1. Addition of neutralizing anti-IL-12p40 monoclonal antibody to cultures of berberine-pretreated macrophages and CD4+ T cells restored IL-4 production in antigen-primed CD4+ T cells. The in vivo administration of berberine resulted in the enhanced induction of IL-12 production by macrophages when stimulated in vitro with lipopolysaccharide or heat-killed Listeria monocytogenes, leading to the inhibition of the Th type 2 cytokine profile (decreased IL-4 and increased IFN-gamma production) in antigen-primed CD4+ T cells. These findings may point to a possible therapeutic use of berberine or medicinal plants containing berberine in the Th type 2 cell-mediated immune diseases such as allergic diseases.     

The effect of TGF-beta1 on immune responses of naïve versus memory CD4+ Th1/Th2 T cells

The role of TGF-beta1 in the regulation of T cell responses has been perplexing, possibly because it is dependent on the type of T cell being regulated and its cytokine microenvironment. In the present study, we demonstrate that TGF-beta1 has a profound inhibitory effect on naive CD4+ T cell undergoing differentiation under defined neutral, Th1 and Th2 priming conditions. In addition, we show that if CD4+ T cells are primed in the presence of TGF-beta1, they exhibit reduced secondary anti-CD3/anti-CD28-induced and antigen-specific immune responses (even when TGF-beta is absent during the secondary response), which is not due to reduced expression of co-stimulatory molecules or to inadequate IL-2 production. Finally, with respect to the effect of TGF-beta on fully differentiated antigen-specific memory CD4+ T cells, we demonstrate that while antigen-specific activation and cytokine secretion by memory Th1 T cells is inhibited by TGF-beta1, such inhibition is associated with partial down-regulation of IL-12 receptor beta2 chain expression. In contrast, memory Th2 T cells are not subject to TGF-beta1 -mediated suppression. In summary, these studies reveal that TGF-beta1 is a powerful negative regulator of the primary immune response of CD4+ T cells, but only Th1 T cells are subject to such regulation after the memory stage of T cell differentiation has been reached. Thus, these studies define the potential regulatory role of TGF-beta1 in Th1 and Th2 T cell-mediated autoimmunity.     

Pertussis toxin potentiates Th1 and Th2 responses to co-injected antigen: adjuvant action is associated with enhanced regulatory cytokine production and expression of the co-stimulatory molecules B7- 1, B7-2 and CD28

Pertussis toxin (PT) is a major virulence factor of Bordetella pertussis which exerts a range of effects on the immune system, including the enhancement of IgE, IgA and IgG production, delayed-type hypersensitivity reactions, and the induction of experimental autoimmune diseases. However, the mechanism by which PT mediates adjuvanticity remains to be defined. In this investigation we have shown that PT can potentiate antigen-specific T cell proliferation and the secretion of IFN-gamma, IL-2, IL-4 and IL-5 when injected with foreign antigens. A chemically detoxified PT and a genetic mutant with substitutions/deletions in the S-1 and B oligomer components that abrogate enzymatic and binding activity displayed no adjuvant properties. In contrast, a non-toxic S-1 mutant devoid of enzymatic activity but still capable of receptor binding retained its adjuvanticity, augmenting the activation of both Th1 and Th2 subpopulations of T cells. In an attempt to address the mechanism of T cell activation, we found that PT stimulated the production of IFN- gamma and IL-2 by naive T cells and IL-1 by macrophages. Therefore potentiation of distinct T cell subpopulations may have resulted in part from the positive influence of IFN-gamma on the development of Th1 cells and the co-stimulatory role of IL-1 for Th2 cells. Furthermore, PT augmented expression of the co-stimulatory molecules B7-1 and B7-2 on macrophages and B cells, and CD28 on T cells, suggesting that the adjuvant effect may also be associated with facilitation of the second signal required for maximal T cell activation. This study demonstrates that the immunopotentiating properties of PT are largely independent of ADP-ribosyltransferase activity, but are dependent on receptor binding activity and appear to involve enhanced activation of T cells.      

Role and regulation of IL-12 in the in vivo response to staphylococcal enterotoxin B.

Injection of a staphylococcal superantigen (SAg) such as staphylococcal enterotoxin B (SEB) in adult mice results in cytokine production and cell proliferation which can lead to septic shock. The aim of the present work was to identify the cytokines and co-stimulatory molecules regulating the in vivo systemic release of IFN-gamma, a cytokine known to play an important role in the pathophysiology associated with bacterial infections. We demonstrate in this study that (i) in contrast to lipopolysaccharide (LPS), SEB administration induces high levels of the p70, bioactive form, of IL-12; (ii) IL-12 production in response to SEB requires both CD40-dependent signals and IFN-gamma secretion; (iii) the early systemic release of IFN-gamma (3 h post-treatment) in response to SEB is IL-12 independent, while the sustained, late response (6-9 h post-treatment) requires endogenous IL-12 production; (iv) IL-12 produced during the primary SEB response (day 0) is responsible for priming cells in vivo to high IFN-gamma production upon secondary challenge (day 2); (v) the priming effect of IL-12 is TCR unrelated, as SEB-primed animals secrete high levels of IFN-gamma in response to both staphylococcal enterotoxin A and LPS administered 48 h later. The ability of bacterial SAg to induce septic shock and to modulate the immune response to unrelated antigens may therefore be related to their unique capacity to induce systemic IL-12 production in vivo. These observations also help to explain why SEB-primed animals, known to express an anergic phenotype 48 h post-treatment (as judged by defective IL-2 production and proliferation), nevertheless display an increased capacity to secrete the inflammatory cytokine IFN-gamma.     

An immunomodulatory arabinomannan extracted from Mycobacterium tuberculosis, Z-100, restores the balance of Th1/Th2 cell responses in tumor bearing mice

The regulatory effect of Z-100 on the balance of Th1/Th2 cell responses in BALB/c mice bearing Meth-A fibrosarcoma was investigated. In tumor bearing mice, Th1 cytokine production (IL-2, IFN-gamma) are suppressed and Th2 cytokine production (IL-4, IL-10) are increased, as compared with those of normal mice. The administration of Z-100 (10 mg/kg) to tumor bearing mice restored the balance of Th1/Th2 cell responses from Th2 dominant state to the normal state. This regulatory effect of Z-100 was eliminated by depletion of adherent cells from splenocytes derived from tumor bearing mice, and by the treatment with 2-ClAdo (a macrophage inhibitor). Similarly, this regulatory effect was diminished by the treatment with anti-IL-12 mAb and anti-IFN-gamma mAb. In addition, the IL-12 p40 mRNA expression in splenic adherent cells and IFN-gamma mRNA expression in CD4+ T cells were increased by the administration of Z-100 to tumor bearing mice. These results suggested that Z-100 restored the balance of Th1/Th2 cell responses to the normal one in tumor bearing mice through the activation of macrophages and up-regulation of IL-12 production from macrophages and IFN-gamma production from CD4+ T cells.