Barbara Frossi

Mast Cells Boost Myeloid-Derived Suppressor Cell Activity and Contribute to the Development of Tumor-Favoring Microenvironment

Danelli and colleagues demonstrate interactions between mast cells and myeloid-derived suppressor cells in the mucosa of colon carcinoma patients and in the colon and spleen of tumor-bearing mice and establish the role of CD40/CD40L in the activity of these cells in colon cancer. Inflammation plays crucial roles at different stages of tumor development and may lead to the failure of immune surveillance and immunotherapy. Myeloid-derived suppressor cells (MDSC) are one of the major components of the immune-suppressive network that favors tumor growth, and their interaction with mast cells is emerging as critical for the outcome of the tumor-associated immune response. Herein, we showed the occurrence of cell-to-cell interactions between MDSCs and mast cells in the mucosa of patients with colon carcinoma and in the colon and spleen of tumor-bearing mice. Furthermore, we demonstrated that the CT-26 colon cancer cells induced the accumulation of CD11b+Gr1+ immature MDSCs and the recruitment of protumoral mast cells at the tumor site. Using ex vivo analyses, we showed that mast cells have the ability to increase the suppressive properties of spleen-derived monocytic MDSCs, through a mechanism involving IFNγ and nitric oxide production. In addition, we demonstrated that the CD40:CD40L cross-talk between the two cell populations is responsible for the instauration of a proinflammatory microenvironment and for the increase in the production of mediators that can further support MDSC mobilization and tumor growth. In light of these results, interfering with the MDSC:mast cell axis could be a promising approach to abrogate MDSC-related immune suppression and to improve the antitumor immune response. Cancer Immunol Res; 3(1); 85–95. ©2014 AACR.

CD4+CD25+ regulatory T cells suppress mast cell degranulation and allergic responses through OX40-OX40L interaction

T regulatory (Treg) cells play a role in the suppression of immune responses, thus serving to induce tolerance and control autoimmunity. Here, we explored whether Treg cells influence the immediate hypersensitivity response of mast cells (MCs). Treg cells directly inhibited the FcvarepsilonRI-dependent MC degranulation through cell-cell contact involving OX40-OX40L interactions between Treg cells and MCs, respectively. When activated in the presence of Treg cells, MCs showed increased cyclic adenosine monophosphate (cAMP) concentrations and reduced Ca(2+) influx, independently of phospholipase C (PLC)-gamma2 or Ca(2+) release from intracellular stores. Antagonism of cAMP in MCs reversed the inhibitory effects of Treg cells, restoring normal Ca(2+) responses and degranulation. Importantly, the in vivo depletion or inactivation of Treg cells caused enhancement of the anaphylactic response. The demonstrated crosstalk between Treg cells and MCs defines a previously unrecognized mechanism controlling MC degranulation. Loss of this interaction may contribute to the severity of allergic responses.

Mast cells counteract regulatory T-cell suppression through interleukin-6 and OX40/OX40L axis toward Th17-cell differentiation

The development of inflammatory diseases implies inactivation of regulatory T (Treg) cells through mechanisms that still are largely unknown. Here we showed that mast cells (MCs), an early source of inflammatory mediators, are able to counteract Treg inhibition over effector T cells. To gain insight into the molecules involved in their interplay, we set up an in vitro system in which all 3 cellular components were put in contact. Reversal of Treg suppression required T cell-derived interleukin-6 (IL-6) and the OX40/OX40L axis. In the presence of activated MCs, concomitant abundance of IL-6 and paucity of Th1/Th2 cytokines skewed Tregs and effector T cells into IL-17-producing T cells (Th17). In vivo analysis of lymph nodes hosting T-cell priming in experimental autoimmune encephalomyelitis revealed activated MCs, Tregs, and Th17 cells displaying tight spatial interactions, further supporting the occurrence of an MC-mediated inhibition of Treg suppression in the establishment of Th17-mediated inflammatory responses.

H2O2 induces translocation of APE/Ref-1 to mitochondria in the Raji B-cell line

Reactive oxygen species (ROS) are generated as by‐products of respiration and are used as signal transducing intermediates in out–in signaling pathways. ROS are also generated during inflammatory responses and it has been shown that hydrogen peroxide may trigger activation of B‐lymphocytes, similar to cross‐linking of surface immunoglobulins. On the other hand, both exogenous and endogenous generated ROS are a major source of nuclear and mitochondrial DNA (mtDNA) damage. The base excision repair (BER) enzyme APE/Ref‐1 normally repairs small nuclear DNA lesion such as oxidized or alkylated bases. It is not clear though whether DNA repair mechanisms able to abolish oxidative damage from nuclear DNA are present into mitochondria too. Here we show by confocal microscopy and Western blot analysis that in the B‐lymphocyte Raji cell line a fraction of APE/Ref‐1 rapidly re‐localizes into mitochondria following H2O2 activation. Targeting of APE/Ref‐1 to mitochondria is not associated with cytochrome‐c loss or apoptosis induction. These findings indicate that the APE/Ref‐1 translocates to mitochondria in response to oxidative stress and thereby it might exert a protective function.

Mast cells enhance proliferation of B lymphocytes and drive their differentiation toward IgA-secreting plasma cells

The evidence of a tight spatial interaction between mast cells (MCs) and B lymphocytes in secondary lymphoid organs, along with the data regarding the abundance of MCs in several B-cell lymphoproliferative disorders prompted us to investigate whether MCs could affect the proliferation and differentiation of B cells. To this aim, we performed coculture assays using mouse splenic B cells and bone marrow-derived MCs. Both nonsensitized and activated MCs proved able to induce a significant inhibition of cell death and an increase in proliferation of naive B cells. Such proliferation was further enhanced in activated B cells. This effect relied on cell-cell contact and MC-derived interleukin-6 (IL-6). Activated MCs could regulate CD40 surface expression on unstimulated B cells and the interaction between CD40 with CD40 ligand (CD40L) on MCs, together with MC-derived cytokines, was involved in the differentiation of B cells into CD138(+) plasma cells and in selective immunoglobulin A (IgA) secretion. These data were corroborated by in vivo evidence of infiltrating MCs in close contact with IgA-expressing plasma cells within inflamed tissues. In conclusion, we reported here a novel role for MCs in sustaining B-cell expansion and driving the development of IgA-oriented humoral immune responses.

Selective Activation of Fyn/PI3K and p38 MAPK Regulates IL-4 Production in BMMC under Nontoxic Stress Condition

Mast cells have the ability to react to multiple stimuli, implicating these cells in many immune responses. Specific signals from the microenvironment in which mast cells reside can activate different molecular events that govern distinct mast cells responses. We previously demonstrated that hydrogen peroxide (H2O2) promotes IL-4 and IL-6 mRNA production and potentates FcεRI-induced cytokine release in rat basophilic leukemia RBL-2H3 cells. To further evaluate the effect of an oxidative microenvironment (which is physiologically present in an inflammatory site) on mast cell function and the molecular events responsible for mast cell cytokine production in this environment, we analyzed the effect of H2O2 treatment on IL-4 production in bone marrow-derived, cultured mast cells. Our findings show that nanomolar concentrations of H2O2 induce cytokine secretion and enhance IL-4 production upon FcεRI triggering. Oxidative stimulation activates a distinct signal transduction pathway that induces Fyn/PI3K/Akt activation and the selective phosphorylation of p38 MAP kinase. Moreover, H2O2 induces AP-1 and NFAT complexes that recognize the IL-4 promoter. The absence of Fyn and PI3K or the inhibition of p38 MAPK activity demonstrated that they are essential for H2O2-driven IL-4 production. These findings show that mast cells can respond to an oxidative microenvironment by initiating specific signals capable of eliciting a selective response. The findings also demonstrate the dominance of the Fyn/p38 MAPK pathway in driving IL-4 production.

Oxidative stress stimulates IL-4 and IL-6 production in mast cells by an APE/Ref-1-dependent pathway

Mast cells are exposed to an oxidative environment in the course of allergic and inflammatory reactions. We have examined the effects of H2O2 stimulation in a primary rat basophilic leukemia cell line (RBL‐2H3) and compared with IgE‐dependent stimulation. Like IgE stimulation, H2O2 up‐regulates IL‐4 and IL‐6 gene expression and cytokine secretion, shows a little effect on IL‐5 but does not induce IL‐10 gene expression. Simultaneous H2O2 treatment and FcϵRI triggering of mast cells has additive effects on IL‐4 expression. In addition, we show that both stimuli induce the nuclear translocation of APE/Ref‐1, a bifunctional enzyme that stimulates the DNA‐binding activity of several transcription factors through the reduction of highly reactive cysteines. Conditional inactivation of APE/Ref‐1 expression abolishes H2O2‐induced IL‐4 and IL‐6 gene expression but does not affect that induced by FcϵRI stimulation. Our findings indicate that oxidative stress activates the gene expression of a specific cytokine pattern in mast cells through an APE/Ref‐1‐dependent pathway, which is distinct from theone that is activated by FcϵRI stimulation. Nonetheless, H2O2 and FcϵRI signalings are additive in augmenting IL‐4 production. Most importantly, oxidative stress can induce a pro‐type 2 inflammatory response from mast cells that is independent of FcϵRI stimulation.

Novel pathogenic mechanism and therapeutic approaches to angioedema associated with C1 inhibitor deficiency.

BACKGROUND Activation of bradykinin-mediated B2 receptor has been shown to play an important role in the onset of angioedema associated with C1 inhibitor deficiency. This finding has led to the development of novel therapeutic drugs such as the B2 receptor antagonist icatibant. However, it is unclear whether other receptors expressed on endothelial cells contribute to the release of kinins and vascular leakage in these patients. The recognition of their role may have obvious therapeutic implications. OBJECTIVE Our aim was to investigate the involvement of B1 and gC1q receptors in in vitro and in vivo models of vascular leakage induced by plasma samples obtained from patients with C1 inhibitor deficiency. METHODS The vascular leakage was evaluated in vitro on endothelial cells by a transwell model system and in vivo on rat mesentery microvessels by intravital microscopy. RESULTS We observed that the attack phase plasma from C1 inhibitor-deficient patients caused a delayed fluorescein-labeled albumin leakage as opposed to the rapid effect of bradykinin, whereas remission plasma elicited a modest effect compared with control plasma. The plasma permeabilizing effect was prevented by blocking the gC1q receptor-high-molecular-weight kininogen interaction, was partially inhibited by B2 receptor or B1 receptor antagonists, and was totally prevented by the mixture of the 2 antagonists. Involvement of B1 receptor was supported by the finding that albumin leakage caused by attack phase plasma was enhanced by IL-1beta and was markedly reduced by brefeldin A. CONCLUSION Our data suggest that both B1 receptor and gC1q receptor are involved in the vascular leakage induced by hereditary and acquired angioedema plasma.

The mast cell: an antenna of the microenvironment that directs the immune response

Mast cells (MCs) have long been considered as critical effector cells during immunoglobulin (Ig)E‐mediated allergic disease and immune response to parasites. Recent studies, however, suggest that this understanding of MC function is incomplete and does not consider the complex roles that MCs play in adaptive and innate immunity. The added function gives an innovative vision of regulation of immune responses and the development of autoimmune diseases. It had been assumed that the aggregation of Fc ɛ receptor I with IgE and specific antigen is the main stimulus able to induce the MC activation, degranulation, release, and generation of mediators of the allergic reaction. However, MCs exhibit an array of molecules involved in cell–cell and cell–extracellular matrix adhesion, mediating delivery of costimulatory signals that empower those cells with an ability to react to multiple nonspecific and specific stimuli. Their tissue distribution and their capability to release many cytokines after stimulation indicate MCs as potential regulatory linkers between innate and acquired immunity. In this review, we will summarize some findings on the roles of MCs in innate and acquired immunity, on the molecular mechanism and signaling pathways, and on selective signals that induce discrete MC response and its ability to polarize adaptive‐immune response.

Mast Cell: An Emerging Partner in Immune Interaction

Mast cells (MCs) are currently recognized as effector cells in many settings of the immune response, including host defense, immune regulation, allergy, chronic inflammation, and autoimmune diseases. MC pleiotropic functions reflect their ability to secrete a wide spectrum of preformed or newly synthesized biologically active products with pro-inflammatory, anti-inflammatory and/or immunosuppressive properties, in response to multiple signals. Moreover, the modulation of MC effector phenotypes relies on the interaction of a wide variety of membrane molecules involved in cell–cell or cell-extracellular-matrix interaction. The delivery of co-stimulatory signals allows MC to specifically communicate with immune cells belonging to both innate and acquired immunity, as well as with non-immune tissue-specific cell types. This article reviews and discusses the evidence that MC membrane-expressed molecules play a central role in regulating MC priming and activation and in the modulation of innate and adaptive immune response not only against host injury, but also in peripheral tolerance and tumor-surveillance or -escape. The complex expression of MC surface molecules may be regarded as a measure of connectivity, with altered patterns of cell–cell interaction representing functionally distinct MC states. We will focalize our attention on roles and functions of recently discovered molecules involved in the cross-talk of MCs with other immune partners.