Regulatory dendritic cells act as regulators of acute lethal systemic inflammatory response

Dendritic cell subsets in health and disease

The dendritic cell (DC) system of antigen-presenting cells controls immunity and tolerance. DCs initiate and regulate immune responses in a manner that depends on signals they receive from microbes and their cellular environment. They allow the immune system to make qualitatively distinct responses against different microbial infections. DCs are composed of subsets that express different microbial receptors and express different surface molecules and cytokines. Our studies lead us to propose that interstitial (dermal) DCs preferentially activate humoral immunity, whereas Langerhans cells preferentially induce cellular immunity. Alterations of the DC system result in diseases such as autoimmunity, allergy, and cancer. Conversely, DCs can be exploited for vaccination, and novel vaccines that directly target DCs in vivo are being designed.

Conventional dendritic cells regulate the outcome of colonic inflammation independently of T cells

We explored the physiological role of conventional dendritic cells (cDCs) in acute colitis induced by a single cycle of dextran sodium sulfate administration. Depending on their mode of activation and independently of T cells, cDCs can enhance or attenuate the severity of dextran sodium sulfate-induced colitis. The latter beneficial effect was achieved, in part, by IFN-1 induced by Toll-like receptor 9-activated cDCs. IFN-1 inhibits colonic inflammation by regulating neutrophil and monocyte trafficking to the inflamed colon and restraining the inflammatory products of tissue macrophages. These data highlight a novel role of cDCs in the regulation of other innate immune cells and position them as major players in acute colonic inflammation.

Regulatory dendritic cells protect against allergic airway inflammation in a murine asthmatic model

BACKGROUND

Dendritic cells (DCs) are crucial for the induction of immunity and tolerance. Despite an improved understanding of the DC-mediated control of T(H)1-biased immunity, little is known about how DCs regulate T(H)2-mediated immunity.

OBJECTIVE

The effects of immunostimulatory mature DCs (maDCs) and regulatory DCs (DCregs) on T(H)2-driven allergic immunity involving IgE production were examined.

METHODS

A murine model of airway hyperresponsiveness; the adoptive transfer of maDCs, DCregs, and T cells; and T-cell function were studied.

RESULTS

Antigen-pulsed maDCs inhibited antigen-specific IgE production but enhanced the production of antigen-specific IgG1 and IgG2a. Analysis of Ifng-/- mice and Il21r-/- mice revealed that the inhibitory effect of antigen-pulsed maDCs on antigen-specific IgE production involved IL-21-producing T follicular helper cells but not IFN-gamma-producing T(H)1 cells. In contrast, antigen-pulsed DCregs impaired the production of antigen-specific IgE, IgG1, and IgG2a. In vivo blockade experiments showed that antigen-specific CD4+CD25+Foxp3+ regulatory T cells mainly mediated the suppressive effect of antigen-pulsed DCregs on the production of antigen-specific IgE. Antigen-pulsed maDCs promoted airway inflammation, whereas antigen-pulsed DCregs markedly suppressed the pathogenesis.

CONCLUSION

DCregs abolish T(H)2-mediated IgE production and allergic inflammation based on antigen-specific dominant tolerance, whereas maDCs exacerbate the pathogenesis despite inhibiting the IgE response through the activation of diverse types of T(H) cell responses.

Role of interleukin-1beta in activating the CD11c(high) CD45RB- dendritic cell subset and priming Leishmania amazonensis-specific CD4+ T cells in vitro and in vivo

Cutaneous leishmaniasis associated with Leishmania amazonensis infection is characterized by uncontrolled parasite replication and profound immunosuppression; however, the underlying mechanisms remain largely unclear. One possibility is that the L. amazonensis parasite modulates antigen-presenting cells, favoring the generation of pathogenic Th cells that are capable of recruiting leukocytes but insufficient to fully activate their microbicidal activities. To test this possibility, we infected bone marrow-derived dendritic cells (DCs) of C57BL/6 mice with L. amazonensis or Leishmania major promastigotes and assessed the activation of DC subsets and their capacity in priming CD4(+) T cells in vitro. In comparison to L. major controls, L. amazonensis-infected DCs secreted lower levels of interleukin-1alpha (IL-1alpha) and IL-1beta, were less potent in activating the IL-12p40-producing CD11c(high) CD45RB(-) CD83(+) CD40(+) DC subset, and preferentially activated CD4(+) T cells with a IFN-gamma(low) IL-10(high) IL-17(high) phenotype. Although the addition of IL-1beta at the time of infection markedly enhanced DC activation and T-cell priming, it did not skew the cytokine profile of DCs and pathogenic Th cells, as local injection of IL-1beta following L. amazonensis infection accelerated Th cell activation and disease progression. This study suggests that intrinsic defects at the level of DC activation are responsible for the susceptible phenotype in L. amazonensis-infected hosts and that this parasite may have evolved unique mechanisms to interfere with innate and adaptive immunity.

The yin and yang of intestinal epithelial cells in controlling dendritic cell function

Recent work suggests that dendritic cells (DCs) in mucosal tissues are "educated" by intestinal epithelial cells (IECs) to suppress inflammation and promote immunological tolerance. After attack by pathogenic microorganisms, however, "non-educated" DCs are recruited from nearby areas, such as the dome of Peyer's patches (PPs) and the blood, to initiate inflammation and the ensuing immune response to the invader. Differential epithelial cell (EC) responses to commensals and pathogens may control these two tolorogenic and immunogenic functions of DCs.

Changes in dendritic cell function in the immune response to sepsis. Cell- & tissue-based therapy

Sepsis represents a complex clinical syndrome of significant morbidity and mortality. This continues to be the case in intensive care units around the world, despite extensive use of antibiotics, aggressive surgical intervention and optimization of nutritional support. Furthermore, the failure of > 30 anti-inflammatory mediator therapeutic trials implies, beyond the issue of trial design, there remains the necessity to develop a better understanding of the evolving pathophysiology of this syndrome. Studies indicate that the development of marked immune suppression in sepsis is more often associated with morbid outcome. Dendritic cells, a critical immune cell type bridging the innate and adaptive immune response, not only are affected (killed) by the systemic inflammatory response but also contribute to (by impaired function) the development of immune suppression during sepsis. Here the authors attempt to review emerging data indicating the key role dendritic cells may play in sepsis-induced immune suppression. Undoubtedly, a better understanding of the dendritic cell's response during sepsis will be critical to developing novel strategies for fighting this deadly disease.

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

Immune responses against pathogens require fine regulation to avoid excessive inflammation, which could be harmful to the host. Moreover, the immune system must be tolerant to nonpathogenic antigens to prevent allergy, autoimmunity, and transplant rejection. There is accumulating evidence that interactions between dendritic cells (DC) and regulatory T (Treg) cells play a crucial role in the balance between immune response and tolerance. Communications between these cells are complex, bidirectional, and mediated by soluble or cell surface molecules. The maturation status of DC, which may be influenced by different microenvironmental factors, is considered as an important checkpoint for the induction of peripheral tolerance through modifications of the activation status of T cells. Moreover, several lines of experimental evidence suggest that different subsets or the functional status of DC are also involved in the promotion of Treg cell differentiation. A better knowledge of the regulatory mechanisms of the immune response induced or inhibited by DC via their interactions with Treg cells could be relevant for the development of new, immunotherapeutic approaches.

"Alternatively activated" dendritic cells preferentially secrete IL-10, expand Foxp3+CD4+ T cells, and induce long-term organ allograft survival in combination with CTLA4-Ig

In this study, we propagated myeloid dendritic cells (DC) from BALB/c (H2(d)) mouse bone marrow progenitors in IL-10 and TGF-beta, then stimulated the cells with LPS. These "alternatively activated" (AA) DC expressed lower TLR4 transcripts than LPS-stimulated control DC and were resistant to maturation. They expressed comparatively low levels of surface MHC class II, CD40, CD80, CD86, and programmed death-ligand 2 (B7-DC; CD273), whereas programmed death-ligand 1 (B7-H1; CD274) and inducible costimulatory ligand expression were unaffected. AADC secreted much higher levels of IL-10, but lower levels of IL-12p70 compared with activated control DC. Their poor allogeneic (C57BL/10; B10) T cell stimulatory activity and ability to induce alloantigen-specific, hyporesponsive T cell proliferation was not associated with enhanced T cell apoptosis. Increased IL-10 production was induced in the alloreactive T cell population, wherein CD4+Foxp3+ cells were expanded. The AADC-expanded allogeneic CD4+CD25+ T cells showed enhanced suppressive activity for T cell proliferative responses compared with freshly isolated T regulatory cells. In vivo migration of AADC to secondary lymphoid tissue was not impaired. A single infusion of BALB/c AADC to quiescent B10 recipients induced alloantigen-specific hyporesponsive T cell proliferation and prolonged subsequent heart graft survival. This effect was potentiated markedly by CTLA4-Ig, administered 1 day after the AADC. Transfer of CD4+ T cells from recipients of long-surviving grafts (>100 days) that were infiltrated with CD4+Foxp3+ cells, prolonged the survival of donor-strain hearts in naive recipients. These data enhance insight into the regulatory properties of AADC and demonstrate their therapeutic potential in vascularized organ transplantation.

Therapeutic treatment of experimental colitis with regulatory dendritic cells generated with vasoactive intestinal peptide

BACKGROUND & AIMS

Crohn's disease is a chronic debilitating disease characterized by severe T helper cell (Th)1-driven inflammation of the colon partially caused by a loss of immune tolerance against mucosal antigens. The use of regulatory dendritic cells (DCs) with the capacity to induce regulatory T cells has been proposed recently for the treatment of Crohn's disease in a strategy to restore immune tolerance. Vasoactive intestinal peptide is an immunomodulatory neuropeptide that induces regulatory DCs. The aim of this study was to investigate the therapeutic effect of vasoactive intestinal peptide-induced regulatory DCs (DC(VIP)) in a murine model of colitis.

METHODS

We examined the therapeutic action of DC(VIP) in the colitis induced by intracolonic administration of trinitrobenzene sulfonic acid, evaluating diverse clinical signs of the disease including weight loss, diarrhea, colitis, and histopathology. We also investigated the mechanisms involved in the potential therapeutic effect of DC(VIP), such as inflammatory cytokines and chemokines, Th1-type response, and the generation of regulatory T cells.

RESULTS

DC(VIP) injection significantly ameliorated the clinical and histopathologic severity of colitis, abrogating body weight loss, diarrhea, and inflammation, and increasing survival. The therapeutic effect was associated with down-regulation of both inflammatory and Th1-driven autoimmune response, by regulating a wide spectrum of inflammatory mediators directly through activated macrophages, and by generating interleukin-10-secreting regulatory T cells with suppressive capacity on autoreactive T cells.

CONCLUSIONS

The possibility to generate/expand ex vivo regulatory DC(VIP) opens new therapeutic perspectives for the treatment of Crohn's disease in human beings, and may minimize the dependence on nonspecific immunosuppressive drugs used currently for autoimmune disorders.