Interleukin-4-triggered, STAT6-dependent production of a factor that induces mouse mast cell apoptosis

Role of Mast Cells in Regulation of T Cell Responses in Experimental and Clinical Settings

Mast cells secrete a wide spectrum of stored or newly synthesized pro-inflammatory, anti-inflammatory, and/or immunosuppressive mediators and express several costimulatory and inhibitory surface molecules. Mast cells finely tune activities of T cells, B cells, and regulatory cells and effectively contribute to the development of different T cell-associated responses by influencing their recruitment, activation, proliferation, and differentiation. The interaction between mast cells and T cells, with regard to cellular functionality and immune responses, can be assessed in both activating and inhibitory regulations. While Th2 cytokines, including IL-5 and IL-9, stimulate stem cell factor (SCF)-dependent proliferation of mast cells, Th1 cytokine IFN-γ suppresses SCF-mediated differentiation of mast cell progenitors. Mast cell mediators such as CCL5 have a role in the recruitment of CD8+ T cells to viral infection sites where their ability in clearance of viral reservoirs is needed. The capacity of mast cells in presenting antigens by classes I and II MHC molecules to CD4+ and CD8+ T cells respectively is considered one of the main antigen-dependent interactions of mast cells with T cells. Interestingly, Tregs recruit mast cells to different sites through secretion of IL-9, while the OX40L (expressed on mast cell)-OX40(expressed on T cell) interaction inhibits the extent of the mast cell degranulation. Recently, the capability of exosomes to carry regulatory receptors of the mast cell surface and their role in T cell activation has been investigated. Functional interplay between mast cells and T cell subsets has been suggested primarily by investigating their co-localization in inflamed tissues and involvement of mast cells in autoimmune diseases. In this review, the interactions of mast cells with T cells are reviewed in cell-to-cell, cytokine, and exosome categories.

STAT6 deficiency ameliorates Graves' disease severity by suppressing thyroid epithelial cell hyperplasia

Signal transducer and activator of transcription 6 (STAT6) is involved in epithelial cell growth. However, little is known regarding the STAT6 phosphorylation status in Graves' disease (GD) and its role in thyroid epithelial cells (TECs). In this study, we found that STAT6 phosphorylation (p-STAT6) was significantly increased in TECs from both GD patients and experimental autoimmune Graves' disease mice and that STAT6 deficiency ameliorated GD symptoms. Autocrine IL-4 signalling in TECs activated the phosphorylation of STAT6 via IL-4 R engagement, and the downstream targets of STAT6 were Bcl-xL and cyclin D1. Thus, the IL-4-STAT6-Bcl-xL/cyclin D1 pathway is crucial for TEC hyperplasia, which aggravates GD. More importantly, in vitro and in vivo experiments demonstrated that STAT6 phosphorylation inhibited by AS1517499 decreased TEC hyperplasia, thereby reducing serum T3 and T4 and ameliorating GD. Thus, our study reveals that in addition to the traditional pathogenesis of GD, in which autoantibody TRAb stimulates thyroid-stimulating hormone receptors and consequently produces T3, T4, TRAb could also trigger TECs producing IL-4, and IL-4 then acts in an autocrine manner to activate p-STAT6 signalling and stimulate unrestricted cell growth, thus aggravating GD. These findings suggest that STAT6 inhibitors could be potent therapeutics for treating GD.

The potential anti-proliferative effect of β-sitosterol on human mast cell line-1 cells

Thymic stromal lymphopoietin (TSLP) was reported to induce mast cell proliferation and aggravate allergic reactions through activation of mouse double minute 2 (MDM2). We aimed to ascertain that β-sitosterol (SI), which is one of the several phytosterols found mostly in foods, would regulate TSLP-induced mast cell proliferation. The results showed that SI significantly decreased the proliferation of human mast cell line (HMC-1) cells promoted by TSLP. SI significantly decreased the mRNA expression of Ki-67 in the TSLP-treated HMC-1 cells. SI significantly suppressed the production and mRNA expression of interleukin-13 in the TSLP-treated HMC-1 cells. Furthermore, SI downregulated the expression of MDM2 and phosphorylation of STAT6, whereas it upregulated the expression of p53, activation of caspase-3, and cleavage of poly ADP-ribose polymerase in the TSLP-treated HMC-1 cells. Results of this study suggest that SI may be a potential therapeutic agent for mast cell-mediated allergic diseases.

Up-regulation of IL-33 expression in various types of murine cells by IL-3 and IL-4

The crucial roles of the novel cytokine IL-33 in allergic, inflammatory, infectious and autoimmune diseases are becoming characterized. However, the cytokines which regulate IL-33 expression and secretion are still largely unknown. In this study, IL-3 and IL-4 were found to up-regulate IL-33 mRNA expression in mouse peritoneal exudate cells by a two-color DNA microarray and further confirmed by real time PCR and ELISA. IL-3 and IL-4 synergistically promote IL-33 mRNA expression and IL-33 intracrine in the heterogeneous cell populations as peritoneal exudates cells, bone marrow cells and splenic cells. IL-3 and IL-4 also induced IL-33 introcrine in the peritoneal exudate cells from the macrophage-deficient op/op mice, suggesting that macrophage is not the only target of IL-3 and IL-4 in the heterogeneous peritoneal exudate cells. Furthermore, IL-3 and IL-4 were verified to promote the IL-33 intracrine in the homogeneous cell population as fibroblasts and mast cells. These results indicate that up-regulation of IL-33 expression by IL-3 and IL-4 is not a feature particular to a specific type of cells. Up to 100 cytokines were screened, but none of them stimulated the secretion or release of IL-33 in the culture system. In summary, we confirm for the first time that IL-3 and IL-4 are critical for IL-33 intracrine in murine cells of various types, indicating that IL-3 and IL-4 may play an important role in the constitutive expression of IL-33 in vivo.

Mast cell homeostasis and the JAK-STAT pathway

The Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway mediates important responses in immune cells. Activation of any of the four JAK family members leads to phosphorylation of one or more of seven STAT family members. Phosphorylation of STAT family members leads to their dimerization and translocation into the nucleus, in which they bind specific DNA sequences to activate gene transcription. Regulation of JAKs and STATs therefore has a significant effect on signal transduction and subsequent cellular responses. Mast cells are important mediators of allergic disease and asthma. These cells have the ability to cause profound inflammation and vasodilation upon the release of preformed mediators, as well as subsequent synthesis of new inflammatory mediators. The regulation of mast cells is therefore of intense interest for the treatment of allergic disease. An important regulator of mast cells, STAT5, is activated downstream of the receptors for immunoglobulin E, interleukin-3 and stem cell factor. STAT5 contributes to mast cell homeostasis, by mediating proliferation, survival, and mediator release. Regulators of the JAK-STAT pathway, such as the suppressors of cytokine signaling (SOCS) and protein inhibitor of activated STAT (PIAS) proteins, are required to fine tune the immune response and maintain homeostasis. A better understanding of the role and regulation of JAKs and STATs in mast cells is vital for the development of new therapeutics.

Subcutaneous interleukin-4 (IL-4) for relapsed and resistant non-Hodgkin lymphoma: A phase II trial in the North Central Cancer Treatment Group, NCCTG 91-78-51

Interleukin-4 (IL-4), a pleiotropic cytokine, has in vitro activity against non-Hodgkin lymphoma (NHL). This phase II study was conducted to learn the efficacy and toxicity of IL-4 in patients with NHL. Patients with relapsed or refractory indolent or aggressive NHL were eligible to receive 2.5 or 5.0 mcg/kg of subcutaneous IL-4 for 28 days of a 42-day cycle. Patients with response and acceptable toxicity after two cycles were eligible to continue treatment for six cycles. The target overall response rate (ORR) was 20%. Forty-one patients were enrolled and assessable for toxicity; two were ineligible after histology review. The ORR was 13% (5/39) with one complete and four partial responses. All responders were treated with 5.0 mcg/kg; the median time to progression was 84 days, the median duration of response for responders was 8.3 months. The most common toxicities of any grade in all patients were edema (66%), malaise (56%), and elevated liver function tests (56%). Grade 3 and 4 toxicities were more common at 5.0 mcg/kg, leading to a reduction in the starting dose. Although the study observed anti-tumor activity with IL-4, the ORR goal of the study was not achieved. Agents that target the IL-4 receptor can potentially benefit patients with NHL; however, alternative schedules using IL-4 in shorter duration and in combination with other agents would be required to overcome toxicities observed in this study.

Endogenous suppression of mast cell development and survival by IL-4 and IL-10

Mast cell development is an important component of atopic and chronic inflammatory diseases such as asthma, multiple sclerosis, rheumatoid arthritis, and atherosclerosis. In this study, we found that IL-4 and IL-10 were produced constitutively in cultures of developing mast cells, correlating with mast cell purity. Deletion of either gene increased mast cell numbers and Fc epsilon RI expression during culture in IL-3 + stem cell factor (SCF). By adding exogenous IL-4 and IL-10 to bone marrow (BM) cultures containing IL-3 + SCF, we found that IL-4 + IL-10 suppressed mast cell development through mechanisms not used by either cytokine alone. IL-4 + IL-10 elicited a rapid cell death coincidental with reduced Kit receptor expression and signaling and enhanced mitochondrial damage and caspase activation. IL-4 or IL-10 costimulation, unlike either cytokine alone, altered mast cell ontogeny to yield predominantly macrophages in cultures that typically produce mast cells. This effect was observed consistently with unseparated BM cells, purified mouse BM stem cells, and erythrocyte-depleted human umbilical cord blood cells. These experiments demonstrated a major role for Stat6 and Stat3, but not the Stat3-induced transcriptional repressor Ets variant gene 3. Genetic background was also a critical factor, as BALB/c-derived BM cells were completely resistant to IL-10-mediated killing and expressed lower levels of IL-10R. Collectively, these results support the theory that IL-4 and IL-10 function as endogenous regulators of mast cell progenitor development, consistent with a role in immune homeostasis. Loss of this homeostasis, perhaps via genetic polymorphism, could contribute to the etiology of mast cell-associated disease.

Mast cells and cancer--no longer just basic science

The incorporation of new anti-cancer kinase inhibitors within cancer management is rapidly increasing. Mast cells are sensitive to several of these new anti-cancer agents most notably to c-Kit inhibitors. As a result, studies investigating the role of mast cells in tumors may have direct clinical relevance and consequently, important clinical implications. Here we review some of the basic attributes of mast cells, especially those related to the new "targeted" drugs. Mast cell roles such as modulators of regulatory T-cells, inducers of angiogenesis and promoters of clot formation are discussed. We also review recent mouse tumor models and human pathological data which implicate mast cells as having both pro- and anti-tumor growth properties. These studies expose a complex, emerging picture of mast cell involvement in tumor biology. It seems that mast cell modulator drugs may improve the efficacy of anti-tumor therapy under certain circumstances, whilst under others, may negatively affect drug efficacy.

Mast cell production of IL-4 and TNF may be required for protective and pathological responses in gastrointestinal helminth infection

Expulsion of the gastrointestinal nematode Trichinella spiralis is associated with Th2 responses and intestinal inflammation, which correlate with a marked mast cell (MC) response. To address the role of MC-derived cytokines in the induction of protective responses, WBB6F1-KitW/KitW-v (W/W(v)) mice were reconstituted with wild-type, tumor necrosis factor (TNF)-alpha(-/-), or interleukin (IL)-4(-/-) bone marrow (BM) prior to infection with T. spiralis. W/W(v) mice reconstituted with TNF-alpha(-/-) or IL-4(-/-) BM expelled the parasite less efficiently and showed diminished enteropathy, whereas protective responses were normal in W/W(v) mice reconstituted with wild-type BM and were accompanied by intestinal pathology. MC responses were reduced in W/W(v) mice reconstituted with IL-4(-/-) BM and to a lesser extent when reconstituted with TNF-alpha(-/-). These results suggest that MC-derived IL-4 and TNF may regulate the induction of protective Th2 responses and intestinal inflammation associated with the expulsion of T. spiralis. Significantly, these studies suggest a role for MC-derived cytokines as autocrine growth factors.

G6b-B cell surface inhibitory receptor expression is highly restricted to CD4+ T-cells and induced by interleukin-4–activated STAT6 pathway

The G6b-B gene encodes a novel cell surface receptor of the immunoglobulin superfamily that activates inhibitory signaling pathways by triggering SHP-1/SHP-2 via immunoreceptor tyrosine-based inhibitory motifs (ITIM) in its cytoplasmic domain. We previously identified decreased G6b-B expression in peripheral blood mononuclear cells (PBMC) during acute cellular cardiac allograft rejection. We studied the expression of G6b-B in different human mononuclear cell populations and its regulation. Real-time polymerase chain reaction (PCR) revealed that G6b-B mRNA is higher in CD4+ T cells or monocytes, but is not different between CD25+ CD4+ T cells and CD25- CD4+ T cells. G6b-B mRNA was increased in CD4+ T cells in presence of interleukin-4 in dose- and time-dependent manners. To understand the regulatory mechanism, we analyzed a 1.9-kb 5'-flanking region of the G6b-B translation start site and found a putative cis-acting element for Signal Transducer and Activator of Transcription (STAT)-6. Luciferase-reporter-gene-assay and electrophoretic mobility shift assays identified the STAT6 site as necessary for the induction of G6b-B by IL-4. Our study demonstrates that G6b-B expression is highly restricted to peripheral CD4+ T cells and up-regulated by the IL-4-induced STAT6 pathway, strongly suggesting that G6b-B is involved in regulation of the immune response by CD4+ T cell-mediated and IL-4 induced regulatory mechanisms.