The cross-talk between dendritic and regulatory T cells: good or evil?

Dendritic cell and NK cell reciprocal cross talk promotes gamma interferon-dependent immunity to blood-stage Plasmodium chabaudi AS infection in mice

Dendritic cells (DCs) are important accessory cells for promoting NK cell gamma interferon (IFN-gamma) production in vitro in response to Plasmodium falciparum-infected red blood cells (iRBC). We investigated the requirements for reciprocal activation of DCs and NK cells leading to Th1-type innate and adaptive immunity to P. chabaudi AS infection. During the first week of infection, the uptake of iRBC by splenic CD11c(+) DCs in resistant wild-type (WT) C57BL/6 mice was similar to that in interleukin 15(-/-) (IL-15(-/-)) and IL-12p40(-/-) mice, which differ in the severity of P. chabaudi AS infection. DCs from infected IL-15(-/-) mice expressed costimulatory molecules, produced IL-12, and promoted IFN-gamma secretion by WT NK cells in vitro as efficiently as WT DCs. In contrast, DCs from infected IL-12p40(-/-) mice exhibited alterations in maturation and cytokine production and were unable to induce NK cell IFN-gamma production. Coculture of DCs and NK cells demonstrated that DC-mediated NK cell activation required IL-12 and, to a lesser extent, IL-2, as well as cell-cell contact. In turn, NK cells from infected WT mice enhanced DC maturation, IL-12 production, and priming of CD4(+) T-cell proliferation and IFN-gamma secretion. Infected WT mice depleted of NK cells, which exhibit increased parasitemia, had impaired DC maturation and DC-induced CD4(+) Th1 cell priming. These findings indicate that DC-NK cell reciprocal cross talk is critical for control and rapid resolution of P. chabaudi AS infection and provide in vivo evidence for the importance of this interaction in IFN-gamma-dependent immunity to malaria.

Critical immunological pathways are downregulated in APECED patient dendritic cells

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic autoimmune disease caused by mutations in the autoimmune regulator (AIRE) gene. AIRE functions as a transcriptional regulator, and it has a central role in the development of immunological tolerance. AIRE regulates the expression of ectopic antigens in epithelial cells of the thymic medulla and has been shown to participate in the development of peripheral tolerance. However, the mechanism of action of AIRE has remained elusive. To further investigate the role of AIRE in host immune functions, we studied the properties and transcript profiles in in vitro monocyte-differentiated dendritic cells (moDCs) obtained from APECED patients and healthy controls. AIRE-deficient monocytes showed typical DC morphology and expressed DC marker proteins cluster of differentiation 86 and human leukocyte antigen class II. APECED patient-derived moDCs were functionally impaired: the transcriptional response of cytokine genes to pathogens was drastically reduced. Interestingly, some changes were observable already at the immature DC stage. Pathway analyses of transcript profiles revealed that the expression of the components of the host cell signaling pathways involved in cell-cell signalling, innate immune responses, and cytokine activity were reduced in APECED moDCs. Our observations support a role for AIRE in peripheral tolerance and are the first ones to show that AIRE has a critical role in DC responses to microbial stimuli in humans.

Dendritic cells as immune regulators: the mouse model

Dendritic cells (DC) are central to the immune system because of their role in antigen presentation leading to either tolerance or immunity among cells of the adaptive immune response. It is becoming increasingly evident that DC show extensive plasticity in terms of their origin and function, giving rise to a number of subsets represented differentially in all lymphoid organs. This article considers the tolerogenic capacity of murine DC and draws a distinction between DC that induce tolerance in the immature state and immunity in an inflammatory context, and those that act as regulatory cells inducing immunosuppression in the presence of inflammation.

Finnish Allergy Programme 2008-2018--time to act and change the course

BACKGROUND

The prevalence of allergic diseases has grown in Finland, similarly to many other western countries. Although the origin of allergy remains unresolved, increasing body of evidence indicates that the modern man living in urban built environment is deprived from environmental protective factors (e.g. soil microorganisms) that are fundamental for normal tolerance development. The current dogma of allergen avoidance has not proved effective in halting the 'epidemic', and it is the Finnish consensus that restoring and strengthening tolerance should more be in focus.

AIM

The national 10-year programme is aimed to reduce burden of allergies. The main goals are to (i) prevent the development of allergic symptoms; (ii) increase tolerance against allergens; (iii) improve the diagnostics; (iv) decrease work-related allergies; (v) allocate resources to manage and prevent exacerbations of severe allergies and (vi) decrease costs caused by allergic diseases.

METHODS

For each goal, specific tasks, tools and evaluation methods are defined. Nationwide implementation acts through the network of local co-ordinators (primary care physicians, nurses, pharmacists). In addition, three nongovernmental organizations (NGOs) take care of the programme implementation. The 21 central hospital districts carry out a three step educational process: (i) healthcare personnel; (ii) representatives and educators of NGOs and (iii) patients and the general population. For outcome evaluation, repeated surveys are performed and healthcare registers employed at the beginning, at 5 years, and at the end of the programme. The process will be evaluated by an independent external body.

CONCLUSION

The Finnish initiative is a comprehensive plan to reduce burden of allergies. The aim is to increase immunological tolerance and change attitudes to support health instead of medicalizing common and mild allergy symptoms. It is time to act, when allergic individuals are becoming a majority of western populations and their numbers are in rapid increase worldwide. The Programme is associated with the Global Alliance of Chronic Respiratory Diseases (GARD), WHO.

Suppression by CD4+CD25+ regulatory T cells is dependent on expression of heme oxygenase-1 in antigen-presenting cells

Heme oxygenase-1 (HO-1) has been viewed as a cytoprotective protein, ameliorating the effects of inflammatory cellular damage, and as beneficial in allograft protection from acute and chronic rejection, suggesting important functions in both innate and adaptive immune responses. Mice deficient in HO-1 exhibit defective immune regulation characterized by a proinflammatory phenotype. We examined if impaired regulatory T cell (Treg) function contributes to the immunoregulatory defects observed in HO-1(-/-) mice. HO-1(-/-) mice exhibited a significantly higher proportion of Foxp3-expressing cells among total CD4(+) and CD4(+)CD25(+) cells in comparison to HO-1(+/+) mice, and HO-1(-/-) Treg cells were at least as effective as HO-1(+/+) Treg cells in suppressing proliferation of effector T cells in vitro from either HO-1(+/+) or HO-1(-/-) mice. However, the absence of HO-1 in antigen-presenting cells abolished the suppressive activity of Treg cells on effector T cells. These findings demonstrate that HO-1 activity in antigen-presenting cells is important for Treg-mediated suppression, providing an explanation for the apparent defect in immune regulation in HO-1(-/-) mice.

Suppression by CD4+CD25+ regulatory T cells is dependent on expression of heme oxygenase-1 in antigen-presenting cells

Heme oxygenase-1 (HO-1) has been viewed as a cytoprotective protein, ameliorating the effects of inflammatory cellular damage, and as beneficial in allograft protection from acute and chronic rejection, suggesting important functions in both innate and adaptive immune responses. Mice deficient in HO-1 exhibit defective immune regulation characterized by a proinflammatory phenotype. We examined if impaired regulatory T cell (Treg) function contributes to the immunoregulatory defects observed in HO-1(-/-) mice. HO-1(-/-) mice exhibited a significantly higher proportion of Foxp3-expressing cells among total CD4(+) and CD4(+)CD25(+) cells in comparison to HO-1(+/+) mice, and HO-1(-/-) Treg cells were at least as effective as HO-1(+/+) Treg cells in suppressing proliferation of effector T cells in vitro from either HO-1(+/+) or HO-1(-/-) mice. However, the absence of HO-1 in antigen-presenting cells abolished the suppressive activity of Treg cells on effector T cells. These findings demonstrate that HO-1 activity in antigen-presenting cells is important for Treg-mediated suppression, providing an explanation for the apparent defect in immune regulation in HO-1(-/-) mice.

Indoleamine 2,3-dioxygenase-expressing dendritic cells are involved in the generation of CD4+CD25+ regulatory T cells in Peyer's patches in an orally tolerized, collagen-induced arthritis mouse model

INTRODUCTION

The present study was devised to understand the role of systemic indoleamine 2,3-dioxygenase (IDO) in the tolerance induction for orally tolerized mice in collagen-induced arthritis (CIA). We examined whether IDO-expressing dendritic cells (DCs) are involved in the generation of CD4+CD25+ regulatory T cells during the induction of oral tolerance in a murine CIA model.

METHODS

Type II collagen was fed six times to DBA/1 mice beginning 2 weeks before immunization, and the effect on arthritis was assessed. To examine the IDO expression, the DCs of messenger RNA and protein were analyzed by RT-PCR and Flow cytometry. In addition, a proliferative response assay was also carried out to determine the suppressive effects of DCs through IDO. The ability of DCs expressing IDO to induce CD4+CD25+ T regulatory cells was examined.

RESULTS

CD11c+ DCs in Peyer's patches from orally tolerized mice expressed a higher level of IDO than DCs from nontolerized CIA mice. IDO-expressing CD11c+ DCs were involved in the suppression of type II collagen-specific T-cell proliferation and in the downregulation of proinflammatory T helper 1 cytokine production. The suppressive effect of IDO-expressing CD11c+ DCs was mediated by Foxp3+CD4+CD25+ regulatory T cells.

CONCLUSION

Our data suggest that tolerogenic CD11c+ DCs are closely linked with the induction of oral tolerance through an IDO-dependent mechanism and that this pathway may provide a new therapeutic modality to treat autoimmune arthritis.