The role of ICOS in directing T cell responses: ICOS-dependent induction of T cell anergy by tolerogenic dendritic cells.

Tolerogenic dendritic cells (DC) play an important role in maintaining peripheral T cell tolerance in steady-state conditions through induction of anergic, IL-10-producing T cells with suppressive properties. ICOS, an activation-induced member of the CD28 family on T cells, is involved in the induction of IL-10, which itself could contribute to induction of anergy and development of suppressive T cells. Therefore, we analyzed the functional role of ICOS in the differentiation process of human CD4(+) T cells upon their interaction with tolerogenic DC.

Interleukin-2 immediate type hypersensitivity?

Two patients with metastatic malignant melanoma developed immediate type hypersensitivity-like symptoms while being treated with recombinant interleukin-(IL-)2 immunotherapy. Both patients showed positive skin prick tests to IL-2, enhanced basophil degranulation in vitro and responded to anti-histamines, but laboratory investigations suggested an IgE-independent, pseudoallergic mast cell degranulation against IL-2.

Different regulation of T helper 1- and T helper 2-promoting cytokine signalling factors in human dendritic cells after exposure to protein versus contact allergens.

Cytokine-dependent T helper 1 (Th1) differentiation versus T helper 2 (Th2) differentiation is controlled by distinct transcription factors. Previously, we have demonstrated that immature human dendritic cells (DC) from blood donors with allergies show rapid phosphorylation of the Th2-associated signal transducer and activator of transcription 6 (STAT6) upon contact with protein allergens. In the present study we investigated whether this process is regulated by the downstream molecules suppressor of cytokine signalling (SOCS) and/or by the factors T-bet and GATA3.

Human dendritic cells transfected with allergen-DNA stimulate specific immunoglobulin G4 but not specific immunoglobulin E production of autologous B cells from atopic individuals in vitro.

Atopic/allergic diseases are characterized by T helper 2 (Th2)-dominated immune responses resulting in immunoglobulin E (IgE) production. DNA-based immunotherapies have been shown to shift the immune response towards Th1 in animal models. In further studies we showed that human dendritic cells (DC) transfected with allergen-DNA are able to stimulate autologous CD4(+) T cells from atopic individuals to produce Th1 instead of Th2 cytokines and to activate interferon-gamma (IFN-gamma)-producing CD8(+) T cells.

Formalin-fixed Staphylococcus aureus particles prevent allergic sensitization in a murine model of type I allergy.

Background: Bacterial infections are supposed to act counterregulatory to the development of allergen-specific Th2 immune responses. We analyzed whether administration of extracellular Staphylococcus aureus inhibited experimental sensitization against allergens.

Methods: BALB/c mice were immunized with alum-adsorbed ovalbumin (OVA) together with formalin-fixed Staphylococcus particles.

Human CD4+CD25+ regulatory T cells: proteome analysis identifies galectin-10 as a novel marker essential for their anergy and suppressive function.

CD4(+)CD25(+)Foxp3(+) regulatory T cells (CD25(+) Treg cells) direct the maintenance of immunological self-tolerance by active suppression of autoaggressive T-cell populations. However, the molecules mediating the anergic state and regulatory function of CD25(+) Treg cells are still elusive. Using differential proteomics, we identified galectin-10, a member of the lectin family, as constitutively expressed in human CD25(+) Treg cells, while they are nearly absent in resting and activated CD4(+) T cells.

CD4-mediated functional activation of human CD4+CD25+ regulatory T cells.

Naturally occurring CD4(+)CD25(+)FoxP3(+) regulatory T cells (CD25(+) Tregs) constitute a specialized population of T cells that is essential for the maintenance of peripheral self-tolerance. The immune regulatory function of CD25(+) Tregs depends upon their activation. We found that anti-CD4 antibodies activate the suppressive function of human CD25(+) Tregs in a dose-dependent manner.

Dendritic cell-based immunotherapy of malignant melanoma: success and limitations.

Dendritic cells (DC) are professional antigen-presenting cells in the immune system which are able to induce primary T-cell responses. Because of their central role in the initiation of immune responses, DC are an important tool for tumor-antigen-specific immunotherapy of cancer. DC vaccination using tumor-antigen-loaded DC has led to tumor regression in individual advanced-stage cancer patients.

Oxymetazoline modulates proinflammatory cytokines and the T-cell stimulatory capacity of dendritic cells.

The nasal decongestant oxymetazoline (OMZ) is frequently used in the topical treatment of rhinitis/sinusitis. As proinflammatory cytokines play a critical role in the development and maintenance of local inflammation, the aim of this study was to investigate the influence of OMZ on immune cells in order to diminish the mucosal infiltration of the nose. Peripheral blood mononuclear cells (PBMC) from buffy coats of healthy volunteers were isolated and stimulated in the presence or absence of OMZ.

A newly established murine immature dendritic cell line can be differentiated into a mature state, but exerts tolerogenic function upon maturation in the presence of glucocorticoid.

The phenotype and function of murine dendritic cells (DCs) are primarily studied using bone-marrow-derived DCs (BM-DCs), but may be hampered by the heterogeneous phenotype of BM-DCs due to their differential state of maturation. Here we characterize a newly established murine DC line (SP37A3) of myeloid origin. During maintainance in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and M-CSF, SP37A3 cells resemble immature DCs characterized by low expression of major histocompatibility complex (MHC) II and costimulatory molecules and low T-cell stimulatory capacity.

Skin mast cells control T cell-dependent host defense in Leishmania major infections.

Mast cells (MCs) initiate protective immunity against bacteria. Here we demonstrate that MCs also contribute to the control of parasitic skin infections by Leishmania major. L.

Interleukin-10-treated dendritic cells do not inhibit Th2 immune responses in ovalbumin/alum-sensitized mice.

Background: It is well known that the immunoregulatory cytokine interleukin (IL)-10 inhibits the accessory function of human dendritic cells (DC) in vitro. Recently, we have shown that these IL-10 DC inhibit the production of T helper cell 1 (Th1) and T helper cell 2 (Th2) cytokines by T cells from atopic individuals in vitro. The current study was set out to analyze whether IL-10 DC also exert inhibitory effects in vivo in a murine model of allergy to ovalbumin adsorbed to the adjuvant aluminium hydroxide (OVA/alum).

Low zone tolerance induced by systemic application of allergens inhibits Tc1-mediated skin inflammation.

Background: The induction of tolerance may be a promising target of strategies aimed at preventing harmful allergic diseases. Low zone tolerance (LZT), induced by epicutaneous application of low doses of contact allergens, inhibits the development of T(C)1-mediated contact hypersensitivity (CHS).

Objective: We evaluated the effect of systemic (oral, intravenous) administration of low amounts of haptens on specific immune reactions and tolerance induction.

Distinct roles for IL-1 receptor type I signaling in early versus established Leishmania major infections.

IL-1alpha/beta released by infected dendritic cells (DC) plays a critical role in the development of protective immunity against Leishmania major. Previous studies demonstrated that treatment of susceptible BALB/c mice with IL-1alpha during T-cell priming (days 1-3 post-infection) induced T helper (Th)1-mediated protection. In contrast, we now demonstrate that prolonged treatment with IL-1alpha (for 3 weeks) worsened disease outcome.

Induction of regulatory T cells by leflunomide in a murine model of contact allergen sensitivity.

Allergic contact dermatitis and contact hypersensitivity (CHS) are characterized by allergen-specific activation of CD8+ and CD4+ T cells and the production of cytokines resulting in an inflammatory response and tissue damage. We show here that the immunosuppressive compound leflunomide (N-[4-trifluoro-methylphenyl]-5-methylisoxazol-4 carboxamide, HWA 486) (LF) inhibited the contact allergic response induced in mice by epicutaneous application of the haptens dinitrofluorobenzene (DNFB) and oxazolone. The extent of ear swelling remained significantly reduced following repeated challenge with DNFB for up to 18 weeks.

Induction of strong and persistent MelanA/MART-1-specific immune responses by adjuvant dendritic cell-based vaccination of stage II melanoma patients.

A significant percentage of stage II melanoma patients (tumor thickness>1 mm) remain at risk of tumor recurrence after primary tumor excision. In this study, we used tumor antigen-pulsed dendritic cells as an adjuvant for immunization of these "high-risk" melanoma patients after resection of the primary tumor. A total of 13 patients were included and vaccinated 6 times every 14 days with autologous dendritic cells pulsed with a MelanA/MART-1 peptide in combination with a recall antigen.

Regulatory activity of human CD4 CD25 T cells depends on allergen concentration, type of allergen and atopy status of the donor.

Regulatory CD4+ CD25+ FoxP3-positive T cells (Treg) are functional in most atopic patients with allergic rhinitis and are able to inhibit T helper type 1 (Th1) and Th2 cytokine production of CD4+ CD25- T cells. This study was designed to analyse the following additional aspects: influence of allergen concentration, influence of the type of allergen, and influence of the atopy status of the donor on the strength of the regulatory activity. CD4+ CD25- T cells from healthy non-atopic controls or from grass-pollen-allergic or wasp-venom-allergic donors were stimulated alone or in the presence of Treg with autologous mature monocyte-derived dendritic cells which were pulsed with different concentrations of the respective allergens.

B cells are not required for T cell priming in low zone tolerance to contact allergens and contact hypersensitivity.

Low zone tolerance (LZT) to contact allergens is induced by epicutaneous exposure to haptens in subsensitizing doses resulting in an inhibition of contact hypersensitivity (CHS), which, in contrast, occurs after sensitization with immunogenic doses of allergens. Performing the protocol of tolerance induction resulted in robust LZT to allergens in B cell-deficient mice in vivo, indicating that B cells are not required for the induction and effector phase of LZT. However, CHS reactions in vivo were restricted in B cell-deficient mice as compared to wild-type (WT) mice.

Neurotrophin-3 regulates mast cell functions in neonatal mouse skin.

Nerve growth factor (NGF) has long been recognized as an important mast cell (MC) growth factor. To explore whether other neurotrophins (NTs) of the NGF family, which are widely expressed in mouse skin, affect the numbers and/or functions of MCs we examined the effects of NT-3 on neonatal skin MCs. We demonstrate that TrkC, the high affinity NT-3 receptor, is expressed by virtually all neonatal skin MCs in C57BL/6 mice, which indicates that MCs can respond to NT-3.

Human CD25+ regulatory T cells: two subsets defined by the integrins alpha 4 beta 7 or alpha 4 beta 1 confer distinct suppressive properties upon CD4+ T helper cells.

Down-regulation of autoreactive T cell responses in vivo includes cell-contact-dependent as well as contact-independent mechanisms. Infectious tolerance is a contact-dependent mechanism used by naturally occurring CD25(+) T regulatory cells (Tregs) to confer suppressive activity upon conventional CD4(+) T cells thereby generating secondary T helper suppressor cells(Th(sup)), which inhibit T cell activation via soluble mediators. Here, we describe two distinct subsets of human Tregs, characterized by expression of either the alpha(4)beta(7) integrin or the alpha(4)beta(1) integrin.

Importance of the inducible costimulator molecule for the induction of allergic immune responses and its decreased expression on T helper cells after venom immunotherapy.

The inducible costimulator (ICOS), a newly identified member of the CD28 receptor family that is induced after T-cell activation, and its ligand (ICOSL), being expressed on activated monocytes and dendritic cells play a key role in T-cell-mediated immune responses. As ICOS costimulation also seems to regulate T helper 2 effector cells, the aim of this study was to analyse the function of this molecule in allergic immune responses and their specific therapy, mainly venom immunotherapy (VIT). CD4+ T cells from grass pollen-, or bee or wasp venom-allergic donors were stimulated in the presence of autologous mature dendritic cells, which were pulsed with different allergen doses.

Modification of the human allergic immune response by allergen-DNA-transfected dendritic cells in vitro.

Background: Atopic-allergic diseases are characterized by T(H)2-dominated immune responses, resulting in IgE production. DNA-based immunotherapies have been shown to shift the immune response toward a T(H)1-type response in animal models.

Objective: The aim of the study was to analyze whether dendritic cells (DCs) transfected with allergen-DNA conjugates are able to stimulate human autologous CD4(+) T cells, CD8(+) T cells, or both from atopic individuals to produce T(H)1 cytokines instead of T(H)2 cytokines.

Early adenoviral gene expression mediates immunosuppression by transduced dendritic cell (DC): implications for immunotherapy using genetically modified DC.

Long-lasting, high-level gene expression in the absence of a toxic or inflammatory response to viral Ags is necessary for the successful application of genetically modified dendritic cell (DC). We previously demonstrated that efficient transduction of mature DC using DeltaE1DeltaE3 adenoviruses suppressed their stimulatory capacity for T cells. The current study was designed to investigate in more detail the suppressive effect of Ad-DC.

Thiol antioxidants block the activation of antigen-presenting cells by contact sensitizers.

Strong contact sensitizers are able to induce signal transduction mechanisms such as tyrosine phosphorylation and activation of MAP kinases in antigen-presenting cells. We studied the capacity of different antioxidants (ascorbic acid, alpha-tocopherol, pyrrolidine dithiocarbamate, N-acetylcysteine, and glutathione) to block the increase in tyrosine phosphorylation in human monocytes seen after stimulation with strong contact sensitizers. Human peripheral blood mononuclear cells were stimulated with 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone in the presence or absence of these antioxidants.