Susumu Nakae

Mast cells in the development of adaptive immune responses.

Mast cells are so widely recognized as critical effector cells in allergic disorders and other immunoglobulin E–associated acquired immune responses that it can be difficult to think of them in any other context. However, mast cells also can be important as initiators and effectors of innate immunity. In addition, mast cells that are activated during innate immune responses to pathogens, or in other contexts, can secrete products and have cellular functions with the potential to facilitate the development, amplify the magnitude or regulate the kinetics of adaptive immune responses. Thus, mast cells may influence the development, intensity and duration of adaptive immune responses that contribute to host defense, allergy and autoimmunity, rather than simply functioning as effector cells in these settings.

Mast cell–derived interleukin 10 limits skin pathology in contact dermatitis and chronic irradiation with ultraviolet B

Allergic contact dermatitis, such as in response to poison ivy or poison oak, and chronic low-dose ultraviolet B irradiation can damage the skin. Mast cells produce proinflammatory mediators that are thought to exacerbate these prevalent acquired immune or innate responses. Here we found that, unexpectedly, mast cells substantially limited the pathology associated with these responses, including infiltrates of leukocytes, epidermal hyperplasia and epidermal necrosis. Production of interleukin 10 by mast cells contributed to the anti-inflammatory or immunosuppressive effects of mast cells in these conditions. Our findings identify a previously unrecognized function for mast cells and mast cell–derived interleukin 10 in limiting leukocyte infiltration, inflammation and tissue damage associated with immunological or innate responses that can injure the skin.

IL-33 can promote survival, adhesion and cytokine production in human mast cells

IL-33 is a recently identified member of the IL-1 family of molecules, which also includes IL-1 and IL-18. IL-33 binds to the receptor, T1/ST2/IL-1R4, and can promote cytokine secretion by Th2 cells and NF-κB phosphorylation in mouse mast cells. However, the effects of these molecules, especially IL-33, in human mast cells are poorly understood. Expression of the receptors for IL-1 family molecules, specifically, IL-1R1, IL-18R and T1/ST2, was detectable intracellularly in human umbilical cord blood-derived mast cells (HUCBMCs) by flow cytometry, but was scarcely detectable on the cells’ surface. However, IL-1β, IL-18 or IL-33 induced phosphorylation of Erk, p38 and JNK in naïve HUCBMCs, and IL-33 or IL-1β, but not IL-18, enhanced the survival of naive HUCBMCs and promoted their adhesion to fibronectin. IL-33 or IL-1β also induced IL-8 and IL-13 production in naïve HUCBMCs, and enhanced production of these cytokines in IgE/anti-IgE-stimulated HUCBMCs, without enhancing secretion of either PGD2 or histamine. Moreover, IL-33-mediated IL-8 production by HUCBMCs was markedly reduced by the p38 MAPK inhibitor, SB203580. In contrast to findings with mouse mast cells, IL-18 neither induced nor enhanced secretion of the mediators PGD2 or histamine by HUCBMCs. Our findings identify previously unknown functions of IL-33 in human mast cells. One of these is that IL-33, like IL-1β, can induce cytokine production in human mast cells even in the absence of stimuli of FcɛRI aggregation. Our findings thus support the hypothesis that IL-33 may enhance mast cell function in allergic disorders and other settings, either in the presence or absence of co-stimulation of mast cells via IgE/antigen–FcɛRI signals.

Mast Cells Enhance T Cell Activation: Importance of Mast Cell Costimulatory Molecules and Secreted TNF

We recently reported that mast cells stimulated via FcεRI aggregation can enhance T cell activation by a TNF-dependent mechanism. However, the molecular mechanisms responsible for such IgE-, Ag- (Ag-), and mast cell-dependent enhancement of T cell activation remain unknown. In this study we showed that mouse bone marrow-derived cultured mast cells express various costimulatory molecules, including members of the B7 family (ICOS ligand (ICOSL), PD-L1, and PD-L2) and the TNF/TNFR families (OX40 ligand (OX40L), CD153, Fas, 4-1BB, and glucocorticoid-induced TNFR). ICOSL, PD-L1, PD-L2, and OX40L also are expressed on APCs such as dendritic cells and can modulate T cell function. We found that IgE- and Ag-dependent mast cell enhancement of T cell activation required secreted TNF; that TNF can increase the surface expression of OX40, ICOS, PD-1, and other costimulatory molecules on CD3+ T cells; and that a neutralizing Ab to OX40L, but not neutralizing Abs to ICOSL or PD-L1, significantly reduced IgE/Ag-dependent mast cell-mediated enhancement of T cell activation. These results indicate that the secretion of soluble TNF and direct cell-cell interactions between mast cell OX40L and T cell OX40 contribute to the ability of IgE- and Ag-stimulated mouse mast cells to enhance T cell activation.

Phenotypic differences between Th1 and Th17 cells and negative regulation of Th1 cell differentiation by IL‐17

Recent evidence fromseveral groups indicates that IL‐17‐producing Th17 cells, rather than, as once was thought, IFN‐γ‐producing Th1 cells, can represent the key effector cells in the induction/development of several autoimmune and allergic disorders. Although Th17 cells exhibit certain phenotypic and developmental differences from Th1 cells, the extent of the differences between these two T cell subsets is still not fully understood. We found that the expression profile of cell surface molecules on Th17 cells has more similarities to that of Th1 cells than Th2 cells. However, although certain Th1‐lineage markers [i.e., IL‐18 receptor α, CXCR3, and T cell Ig domain, mucin‐like domain‐3 (TIM‐3)], but not Th2‐lineage markers (i.e., T1/ST2, TIM‐1, and TIM‐2), were expressed on Th17 cells, the intensity of expression was different between Th17 and Th1 cells. Moreover, the expression of CTLA‐1, ICOS, programmed death ligand 1, CD153, Fas, and TNF‐related activation‐induced cytokine was greater on Th17 cells than on Th1 cells. We found that IL‐23 or IL‐17 can suppress Th1 cell differentiation in the presence of exogenous IL‐12 in vitro. We also confirmed that IL‐12 or IFN‐γ can negatively regulate Th17 cell differentiation. However, these cytokines could not modulate such effects on T cell differentiation in the absence of APC.

Mast cells in the promotion and limitation of chronic inflammation

Summary:u2002 Observations of increased numbers of mast cells at sites of chronic inflammation have been reported for over a hundred years. Light and electron microscopic evidence of mast cell activation at such sites, taken together with the known functions of the diverse mediators, cytokines, and growth factors that can be secreted by appropriately activated mast cells, have suggested a wide range of possible functions for mast cells in promoting (or suppressing) many features of chronic inflammation. Similarly, these and other lines of evidence have implicated mast cells in a variety of adaptive or pathological responses that are associated with persistent inflammation at the affected sites. Definitively characterizing the importance of mast cells in chronic inflammation in humans is difficult. However, mice that genetically lack mast cells, especially those which can undergo engraftment with wildtype or genetically altered mast cells, provide a means to investigate the importance of mast cells and specific mast cell functions or products in diverse models of chronic inflammation. Such work has confirmed that mast cells can significantly influence multiple features of chronic inflammatory responses, through diverse effects that can either promote or, perhaps more surprisingly, suppress aspects of these responses.

IL-33 induces IL-13 production by mouse mast cells independently of IgE-FcεRI signals

The IL‐1‐related molecules, IL‐1 and IL‐18, can promote Th2 cytokine production by IgE/antigen‐FcεRI‐stimulated mouse mast cells. Another IL‐1‐related molecule, IL‐33, was identified recently as a ligand for T1/ST2. Although mouse mast cells constitutively express ST2, the effects of IL‐33 on mast cell function are poorly understood. We found that IL‐33, but not IL‐1β or IL‐18, induced IL‐13 and IL‐6 production by mouse bone marrow‐derived, cultured mast cells (BMCMCs) independently of IgE. In BMCMCs incubated with the potently cytokinergic SPE‐7 IgE without specific antigen, IL‐33, IL‐1β, and IL‐18 each promoted IL‐13 and IL‐6 production, but the effects of IL‐33 were more potent than those of IL‐1β or IL‐18. IL‐33 promoted cytokine production via a MyD88‐dependent but Toll/IL‐1R domain‐containing adaptor‐inducing IFN‐β‐independent pathway. By contrast, IL‐33 neither induced nor enhanced mast cell degranulation. At 200 ng/ml, IL‐33 prolonged mast cell survival in the absence of IgE and impaired survival in the presence of SPE‐7 IgE, whereas at 100 ng/ml, IL‐33 had no effect on mast cell survival in the absence of IgE and reduced mast cell survival in the presence of IgE. These observations suggest potential roles for IL‐33 in mast cell‐ and Th2 cytokine‐associated immune responses and disorders.

Mast Cell-Associated TNF Promotes Dendritic Cell Migration

Mast cells represent a potential source of TNF, a mediator which can enhance dendritic cell (DC) migration. Although the importance of mast cell-associated TNF in regulating DC migration in vivo is not clear, mast cells and mast cell-derived TNF can contribute to the expression of certain models of contact hypersensitivity (CHS). We found that CHS to FITC was significantly impaired in mast cell-deficient KitW-sh/W-sh or TNF−/− mice. The reduced expression of CHS in KitW-sh/W-sh mice was fully repaired by local transfer of wild-type bone marrow-derived cultured mast cells (BMCMCs), but was only partially repaired by transfer of TNF−/− BMCMCs. Thus, mast cells, and mast cell-derived TNF, were required for optimal expression of CHS to FITC. We found that the migration of FITC-bearing skin DCs into draining lymph nodes (LNs) 24 h after epicutaneous administration of FITC in naive mice was significantly reduced in mast cell-deficient or TNF−/− mice, but levels of DC migration in these mutant mice increased to greater than wild-type levels by 48 h after FITC sensitization. Mast cell-deficient or TNF−/− mice also exhibited significantly reduced migration of airway DCs to local LNs at 24 h after intranasal challenge with FITC-OVA. Migration of FITC-bearing DCs to LNs draining the skin or airways 24 h after sensitization was repaired in KitW-sh/W-sh mice which had been engrafted with wild-type but not TNF−/− BMCMCs. Our findings indicate that mast cell-associated TNF can contribute significantly to the initial stages of FITC-induced migration of cutaneous or airway DCs.

Nonredundant Function of Phosphodiesterases 4D and 4B in Neutrophil Recruitment to the Site of Inflammation

Neutrophils have been implicated in the pathogenesis of many inflammatory lung diseases, including chronic obstructive pulmonary disease and asthma. With this study, we investigated how disruption of cAMP signaling impacts the function of neutrophil recruitment to the lung. Four genes code for type 4 phosphodiesterases (PDE4s), enzymes critical for regulation of cAMP levels and cell signaling. Ablation of two of these genes, PDE4B and PDE4D, but not PDE4A, has profound effects on neutrophil function. In a paradigm of mouse lung injury induced by endotoxin inhalation, the number of neutrophils recovered in the bronchoalveolar lavage was markedly decreased in PDE4D−/− and PDE4B−/− mice 4 and 24 h after exposure to LPS. Acute PDE4 inhibition with rolipram had additional inhibitory effects on neutrophil migration in PDE4B−/− and, to a lesser extent, PDE4D−/− mice. This decreased neutrophil recruitment occurred without major changes in chemokine accumulation in bronchoalveolar lavage, suggesting a dysfunction intrinsic to neutrophils. This hypothesis was confirmed by investigating the expression of adhesion molecules on the surface of neutrophils and chemotaxis in vitro. CD18 expression was decreased after ablation of both PDE4B and PDE4D, whereas CD11 expression was not significantly affected. Chemotaxis in response to KC and macrophage inflammatory protein-2 was markedly reduced in PDE4B−/− and PDE4D−/− neutrophils. The effect of PDE4 ablation on chemotaxis was comparable, but not additive, to the effects of acute PDE4 inhibition with rolipram. These data demonstrate that PDE4B and PDE4D play complementary, but not redundant, roles in the control of neutrophil function.

RabGEF1 is a negative regulator of mast cell activation and skin inflammation

Mast cell activation induced by aggregation of FcεRI receptors with immunoglobulin E and antigen is mediated through the activation of multiple protein kinase cascades. Here we report that the regulatory protein RabGEF1 bound to Ras and negatively regulated Ras activation and its downstream effector pathways in FcεRI-dependent mast cell activation. RabGEF1-deficient mast cells showed enhanced degranulation and release of lipid mediators and cytokines in response to FcεRI aggregation. RabGEF1-deficient mice developed severe skin inflammation and had increased numbers of mast cells. Thus, RabGEF1 is a negative regulator of FcεRI-dependent mast cell activation, and a lack of RabGEF1 results in the development of skin inflammation in vivo.