Defective suppression of Th2 cytokines by CD4+CD25+ regulatory T cells in birch allergics during birch pollen season

Regulatory T cells as a target for induction of immune tolerance in allergy

PURPOSE OF REVIEW

Reduced activity of regulatory T cells has recently been described in several diseases, including allergy. This concept of an alteration in the balance between the suppression and activation of harmful T helper type 2 immunity in allergy has important potential implications for strategies to prevent and control disease.

RECENT FINDINGS

The past year has seen several important advances in analysing the determinants of this balance and models for inducing tolerance through regulatory T cells, including several different subtypes. These include the recognition that although T helper type 2 responses drive atopic sensitization, the expression of disease involves additional factors, and of a potential role for regulatory T cells in the development of neonatal tolerance. In addition to CD4CD25 regulatory T cells, experimental protocols for the induction of IL-10-producing, transforming growth factor beta and T helper type 1 regulatory T cells have been described in mouse models of airway disease. IL-6 and co-stimulation have been identified as potential determinants of the balance between the suppression and activation of allergic responses.

SUMMARY

Different strategies for inducing regulatory T cells in animal models of allergic inflammation and an improved understanding of the factors accentuating or reducing suppression have identified important questions for future translational research.

Immune mechanisms of allergen-specific sublingual immunotherapy

Sublingual immunotherapy has been shown in some clinical studies to modulate allergen-specific antibody responses [with a decrease in the immunoglobulin E/immunoglobulin G4 (IgE/IgG4) ratio] and to reduce the recruitment and activation of proinflammatory cells in target mucosa. Whereas a central paradigm for successful immunotherapy has been to reorient the pattern of allergen-specific T-cell responses in atopic patients from a T helper (Th)2 to Th1 profile, there is currently a growing interest in eliciting regulatory T cells, capable of downregulating both Th1 and Th2 responses through the production of interleukin (IL)-10 and/or transforming growth factor (TGF)-beta. We discuss herein immune mechanisms involved during allergen-specific sublingual immunotherapy (SLIT), in comparison with subcutaneous immunotherapy. During SLIT, the allergen is captured within the oral mucosa by Langerhans-like dendritic cells expressing high-affinity IgE receptors, producing IL-10 and TGF-beta, and upregulating indoleamine dioxygenase (IDO), suggesting that such cells are prone to induce tolerance. The oral mucosa contains limited number of proinflammatory cells, such as mast cells, thereby explaining the well-established safety profile of SLIT. In this context, second-generation vaccines based on recombinant allergens in a native conformation formulated with adjuvants are designed to target Langerhans-like cells in the sublingual mucosa, with the aim to induce allergen-specific regulatory T cells. Importantly, such recombinant vaccines should facilitate the identification of biological markers of SLIT efficacy in humans.

Staphylococcal enterotoxin B inhibits regulatory T cells by inducing glucocorticoid-induced TNF receptor-related protein ligand on monocytes

BACKGROUND

Superantigens inhibit naturally occurring CD4+CD25+ regulatory T-cell (nTreg) activity, yet the mechanism for this is unknown.

OBJECTIVE

We tested the hypothesis that staphylococcal enterotoxin B (SEB), a prototypic superantigen, inhibits the ability of nTregs to suppress T-effector cell (Teff) proliferation by an antigen-presenting cell-dependent cell contact mechanism and the induction of glucocorticoid-induced TNF receptor-related protein ligand (GITR-L) on monocytes.

METHODS

Cell proliferation assays were performed on immunomagnetic-bead separated CD4+CD25+, CD4+CD25- T cells and CD14+ monocytes using anti-CD3, SEB, or a neutralizing anti-GITR-L antibody for stimulation. A cytokine permeable membrane insert separating cells in culture was used to evaluate the role of cell contact. Proliferation was measured by [3H]-thymidine incorporation or a carboxyfluorescein diacetate succinimidyl ester assay. GITR-L expression was determined by RT-PCR and immunostaining.

RESULTS

Antigen-presenting cell contact was required for proliferation of nTregs and loss of their ability to suppress Teff proliferation as confirmed by carboxyfluorescein diacetate succinimidyl ester. At baseline, monocytes expressed no GITR-L, but after SEB stimulation, GITR-L gene and protein expression increased significantly over a period of 24 hours (P<.05). When GITR-L activity was neutralized with blocking antibody, as opposed to isotype control, nTregs suppressed Teff proliferation despite the presence of SEB (P<.05). Likewise, loss of GITR-L at 48 hours was associated with restoration of nTreg activity (P<or=.05).

CONCLUSION

Staphylococcal enterotoxin B upregulates GITR-L on monocytes and inhibits nTreg ability to suppress Teff proliferation via a cell contact interaction.

CLINICAL IMPLICATIONS

Prevention of GITR-L induction on monocytes by SEB may be a novel target for control of inflammation in superantigen-driven diseases such as atopic dermatitis.

Infections and allergy - helminths, hygiene and host immune regulation

There is increasing evidence that helminth infections can protect the host against Th2-mediated allergic pathologies, even though helminths themselves are strong Th2 inducers. In murine model systems, alleviation of allergy is not achieved through immune deviation to Th1, but is linked to expansion of regulatory T cell activity. Parasite infection does not prevent allergen sensitisation, but restricts the Th2 effector phase responsible for inflammation. Suppression of allergic inflammation can be transferred by Treg phenotype cells from an infected, allergen-naïve animal to an uninfected, sensitized recipient. Patent allergy in humans is also known to be modulated by helminth infections, suggesting that a similar regulatory network may be controlling immunopathologic disease in man.

CD4+ CD25+ FOXP3+ regulatory T cells from human thymus and cord blood suppress antigen-specific T cell responses

Activation of self-reactive T cells in healthy adults is prevented by the presence of autoantigen-specific CD4+CD25+ regulatory T cells (CD25+ Treg). To explore the functional development of autoantigen-reactive CD25+ Treg in humans we investigated if thymic CD25+ Treg from children aged 2 months to 11 years and cord blood CD25+ Treg are able to suppress proliferation and cytokine production induced by specific antigens. While CD4+CD25- thymocytes proliferated in response to myelin oligodendrocyte glycoprotein (MOG), tetanus toxoid and beta-lactoglobulin, suppression of proliferation was not detected after the addition of thymic CD25+ Treg. However, CD25+ Treg inhibited interferon (IFN)-gamma production induced by MOG, which indicates that MOG-reactive CD25+ Treg are present in the thymus. In contrast, cord blood CD25+ Treg suppressed both proliferation and cytokine production induced by MOG. Both cord blood and thymic CD25+ Treg expressed FOXP3 mRNA. However, FOXP3 expression was lower in cord blood than in thymic CD25+ T cells. Further characterization of cord blood CD25+ T cells revealed that FOXP3 was highly expressed by CD25+CD45RA+ cells while CD25+CD45RA- cells contained twofold less FOXP3, which may explain the lower expression level of FOXP3 in cord blood CD25+ T cells compared to thymic CD25+ T cells. In conclusion, our data demonstrate that low numbers of MOG-reactive functional CD25+ Treg are present in normal thymus, but that the suppressive ability of the cells is broader in cord blood. This suggests that the CD25+ Treg may be further matured in the periphery after being exported from the thymus.

CD4+CD25+-regulatory T cells from mouse to man

Immunological tolerance is one of the fundamental concepts of the immune system. During the past decade, CD4+CD25+-regulatory T cells have emerged as key players in the development of tolerance to autoantigens as well as to foreign antigens. Still many questions remain illusive regarding the basic properties of CD4+CD25+-regulatory T cells. This review aims to recapitulate some of the current understandings about the phenotype, function and clinical relevance of murine and human CD4+CD25+-regulatory T cells.

CD4CD25 regulatory T lymphocytes in allergy and asthma

Allergic asthma is characterized by airway hyper-responsiveness and chronic mucosal inflammation mediated by CD4(+) Th2 lymphocytes. Regulatory CD4(+)CD25(+) T cells are important components of the homeostasis of the immune system, as impaired CD4(+)CD25(+) T cell activity can cause autoimmune diseases and allergy. The mechanism of suppression by CD4(+)CD25(+) T cells remains controversial; different in vivo and in vitro studies raise possible roles for the immunosuppressive cytokines interleukin-10 and transforming growth factor-beta, forkhead transcription factor Foxp3, glucocorticoid-induced tumor necrosis factor receptor, cytotoxic lymphocyte associated antigen-4, 4-1BB costimulator receptor, a CD4-related molecule LAG-3, and neuropilin-1. Current data suggest that Th2 responses to allergens are normally suppressed by CD4(+)CD25(+) T cells. Suppression by CD4(+)CD25(+) T cells is decreased in allergic individuals. Furthermore, CD4(+)CD25(+) T cells play a key role in regulating airway eosinophilic inflammation. The immunomodulatory properties of CD4(+)CD25(+) T cells do extend to Th2 responses, most notably by limiting the development of a proinflammatory CD4(+) Th2 phenotype characterized by reduced cytokine production. An understanding of the roles of CD4(+)CD25(+) T cells in vivo could provide better insight into the design of novel approaches to modulate the chronic airway inflammatory reaction evident in bronchial asthma.

Potential role of interleukin-10-secreting regulatory T cells in allergy and asthma

Allergic diseases are caused by aberrant T-helper-2 immune responses in susceptible individuals. Both naturally occurring CD4(+)CD25(+) regulatory T cells and inducible populations of antigen-specific interleukin-10-secreting regulatory T cells inhibit these inappropriate immune responses in experimental models. This article discusses the evidence that regulatory T-cell function might be impaired in allergic and asthmatic disease and that certain therapeutic regimens might function, at least in part, to promote regulatory T-cell generation. Current research strategies seek to exploit these observations to improve the generation of allergen-specific regulatory T-cell populations with the potential to provide the safe and long-term alleviation of disease symptoms.