Polyps wrap mast cells and Treg within tumorigenic tentacles

The role of regulatory T cells and genes involved in their differentiation in pathogenesis of selected inflammatory and neoplastic skin diseases. Part II: The Treg role in skin diseases pathogenesis

Regulatory FOXP3+ T cells (Tregs) constitute 5% to 10% of T cells in the normal human skin. They play an important role in the induction and maintenance of immunological tolerance. The suppressive effects of these cells are exerted by various mechanisms including the direct cytotoxic effect, anti-inflammatory cytokines, metabolic disruption, and modulation of the dendritic cells function. The deficiency of Treg cells number or function are one of the basic elements of the pathogenesis of many skin diseases, such as psoriasis, atopic dermatitis, bacterial and viral infections. They also play a role in the pathogenesis of T cell lymphomas of the skin (cutaneous T cell lymphomas - CTCL), skin tumors and mastocytosis. Here, in the second part of the cycle, we describe dysfunctions of Tregs in selected skin diseases.

Mast cells: potential positive and negative roles in tumor biology

Mast cells are immune cells that reside in virtually all vascularized tissues. Upon activation by diverse mechanisms, mast cells can secrete a broad array of biologically active products that either are stored in the cytoplasmic granules of the cells (e.g., histamine, heparin, various proteases) or are produced de novo upon cell stimulation (e.g., prostaglandins, leukotrienes, cytokines, chemokines, and growth factors). Mast cells are best known for their effector functions during anaphylaxis and acute IgE-associated allergic reactions, but they also have been implicated in a wide variety of processes that maintain health or contribute to disease. There has been particular interest in the possible roles of mast cells in tumor biology. In vitro studies have shown that mast cells have the potential to influence many aspects of tumor biology, including tumor development, tumor-induced angiogenesis, and tissue remodeling, and the shaping of adaptive immune responses to tumors. Yet, the actual contributions of mast cells to tumor biology in vivo remain controversial. Here, we review some basic features of mast cell biology with a special emphasis on those relevant to their potential roles in tumors. We discuss how using in vivo tumor models in combination with models in which mast cell function can be modulated has implicated mast cells in the regulation of host responses to tumors. Finally, we summarize data from studies of human tumors that suggest either beneficial or detrimental roles for mast cells in tumors.

The Role of Mast Cells in Molding the Tumor Microenvironment

Mast cells (MCs) are granulocytic immune cells that reside in tissues exposed to the external environment. MCs are best known for their activity in allergic reactions, but they have been involved in different physiological and pathological conditions. In particular, MC infiltration has been shown in several types of human tumors and in animal cancer models. Nevertheless, the role of MCs in the tumor microenvironment is still debated because they have been associated either to good or poor prognosis depending on tumor type and tissue localization. This dichotomous role relies on MC capacity to secrete a broad spectrum of molecules with modulatory functions, which may condition the final tumor outcome also promoting angiogenesis and tissue remodeling. In this review, we analyze the multifaceted role of mast cell in tumor progression and inhibition considering their ability to interact with: i) immune cells, ii) tumor cells and iii) the extracellular matrix. Eventually, the current MC targeting strategies to treat cancer patients are discussed. Deciphering the actual role of MCs in tumor onset and progression is crucial to identify MC-targeted treatments aimed at killing cancer cells or at making the tumor vulnerable to selected anti-cancer drugs.

β-Catenin promotes colitis and colon cancer through imprinting of proinflammatory properties in T cells

The density and type of lymphocytes that infiltrate colon tumors are predictive of the clinical outcome of colon cancer. High densities of T helper 17 (T(H)17) cells and inflammation predict poor outcome, whereas infiltration by T regulatory cells (Tregs) that naturally suppress inflammation is associated with longer patient survival. However, the role of Tregs in cancer remains controversial. We recently reported that Tregs in colon cancer patients can become proinflammatory and tumor-promoting. These properties were directly linked with their expression of RORγt (retinoic acid-related orphan receptor-γt), the signature transcription factor of T(H)17 cells. We report that Wnt/β-catenin signaling in T cells promotes expression of RORγt. Expression of β-catenin was elevated in T cells, including Tregs, of patients with colon cancer. Genetically engineered activation of β-catenin in mouse T cells resulted in enhanced chromatin accessibility in the proximity of T cell factor-1 (Tcf-1) binding sites genome-wide, induced expression of T(H)17 signature genes including RORγt, and promoted T(H)17-mediated inflammation. Strikingly, the mice had inflammation of small intestine and colon and developed lesions indistinguishable from colitis-induced cancer. Activation of β-catenin only in Tregs was sufficient to produce inflammation and initiate cancer. On the basis of these findings, we conclude that activation of Wnt/β-catenin signaling in effector T cells and/or Tregs is causatively linked with the imprinting of proinflammatory properties and the promotion of colon cancer.

Oxidative stress and innate immunity status in chickens exposed to high dose of ascorbic acid

The effects of high dose ascorbic acid (10 000 mg·kg(-1) in the diet) and the transition metal on the presence of oxidative stress in the internal organs of growing chicks, as well as on the innate immune system status, were investigated. Supplementation with a high dose of ascorbic acid had pro-inflammatory effects on the intestinal mucosa, and lysozyme levels were decreased significantly in all organs studied. High-dose ascorbic acid caused an imbalance between prooxidative and antioxidative activities and was associated with the generation of semiquinone radicals. We observed that ascorbic acid increased iron and cadmium absorption. When a high dose of ascorbic acid was applied, elevated kidney and intestinal mucosa iron concentrations were observed. The amount of free malondialdehyde in the above organs has increased as well. These data have important implications for the mechanism of the oxidative stress development under the influence of high dose of ascorbic acid, indicating the importance of the side reactions of the mitochondrial electron transport chain with the formation of semiquinone radicals and the role of transition metals in this process.

Mast cells and inflammation-associated colorectal carcinogenesis

Close association between chronic inflammation and cancer has been recently highlighted. Indeed, inflammatory bowel disease (IBD) has been strongly linked with an increased risk of development of colorectal cancer (CRC). Inflammatory cell-produced inflammatory mediators, such as proinflammatory cytokines and inducible enzymes, contribute to this association. In an inflammatory microenvironment, infiltrating macrophages and mast cells mediate production of these inflammatory mediators to promote growth of tumors in target tissues. In contrast to macrophages, contribution of mast cells to CRC development in inflamed colon is not well understood. This study aimed to determine the role of mast cells in inflammation-associated colorectal carcinogenesis. CRC was induced by administration of the colonic carcinogen, azoxymethane (AOM), and the tumor promoter dextran sodium sulfate (DSS) in male mast cell-deficient WBBF(1)-kit (W/W-v) (W/W(v)) and mast cell-normal WBB6F(1)-+/+(WT) mice. At week 12, the W/W(v) mice had markedly lower inflammation scores in the colon when compared with WT mice. The mRNA levels of colonic proinflammatory cytokines and inducible enzymes were also decreased in W/W(V) mice at weeks 12 and 20, when compared with WT counterparts. Colorectal tumors, including CRC, were identified by histopathological analysis performed 20 weeks thereafter. Importantly, there were less neoplastic and preneoplastic colonic lesions in the W/W(v) mice compared with the WT mice. Thus, for the first time, our study shows that mice lacking mast cells are less susceptible to inflammation-associated colorectal carcinogenesis. Our findings also suggest that mast cells and their selected cytokines could play an important role in inflammation-mediated tumorigenesis through regulation of proinflammatory cytokines and inducible inflammatory enzymes.

Abating colon cancer polyposis by Lactobacillus acidophilus deficient in lipoteichoic acid

An imbalance of commensal bacteria and their gene products underlies mucosal and, in particular, gastrointestinal inflammation and a predisposition to cancer. Lactobacillus species have received considerable attention as examples of beneficial microbiota. We have reported previously that deletion of the phosphoglycerol transferase gene that is responsible for lipoteichoic acid (LTA) biosynthesis in Lactobacillus acidophilus (NCK2025) rendered this bacterium able to significantly protect mice against induced colitis when delivered orally. Here we report that oral treatment with LTA-deficient NCK2025 normalizes innate and adaptive pathogenic immune responses and causes regression of established colonic polyps. This study reveals the proinflammatory role of LTA and the ability of LTA-deficient L. acidophilus to regulate inflammation and protect against colonic polyposis in a unique mouse model.

The inflammatory network in the gastrointestinal tumor microenvironment: lessons from mouse models

Accumulating evidence has indicated that inflammatory responses are important for cancer development. Epidemiological studies have shown that regular use of non-steroidal anti-inflammatory drugs (NSAIDs) reduces the risk of colon cancer development. Subsequently, mouse genetic studies have shown that cyclooxygenase (COX)-2, one of the target molecules of NSAIDs, and its downstream product, prostaglandin E(2) (PGE(2)), play an important role in gastrointestinal tumorigenesis. Bacterial infection stimulates the Toll-like receptor (TLR)/MyD88 pathway in tumor tissues, which leads to the induction of COX-2 in stromal cells, including macrophages. Induction of the COX-2/PGE(2) pathway in tumor stroma is important for the development and maintenance of an inflammatory microenvironment in gastrointestinal tumors. In such a microenvironment, tumor-associated macrophages express proinflammatory cytokines, including tumor necrosis factor (TNF)-α and interleukin (IL)-6, and these cytokines, respectively, activate the nuclear factor (NF)-κB and Stat3 transcription factors in epithelial cells, as well as in stromal cells. Recent mouse studies have uncovered the role of such an inflammatory network in the promotion of gastrointestinal tumor development. Genetically engineered and chemically induced mouse tumor models which mimic sporadic or inflammation-associated tumorigenesis were used in these studies. In this review article, we focus on mouse genetic studies using these tumor models, which have contributed to the elucidation of the molecular mechanisms associated with the inflammatory network in gastrointestinal tumors, and we also discuss the role of each pathway in cancer development. The involvement of immune cells such as macrophages, mast cells, and regulatory T cells in tumor promotion is also discussed.

The significant role of mast cells in cancer

Mast cells (MC) are a bone marrow-derived, long-lived, heterogeneous cellular population that function both as positive and negative regulators of immune responses. They are arguably the most productive chemical factory in the body and influence other cells through both soluble mediators and cell-to-cell interaction. MC are commonly seen in various tumors and have been attributed alternatively with tumor rejection or tumor promotion. Tumor-infiltrating MC are derived both from sentinel and recruited progenitor cells. MC can directly influence tumor cell proliferation and invasion but also help tumors indirectly by organizing its microenvironment and modulating immune responses to tumor cells. Best known for orchestrating inflammation and angiogenesis, the role of MC in shaping adaptive immune responses has become a focus of recent investigations. MC mobilize T cells and antigen-presenting dendritic cells. They function as intermediaries in regulatory T cells (Treg)-induced tolerance but can also modify or reverse Treg-suppressive properties. The central role of MC in the control of innate and adaptive immunity endows them with the ability to tune the nature of host responses to cancer and ultimately influence the outcome of disease and fate of the cancer patient.

Mast cells and Th17 cells contribute to the lymphoma-associated pro-inflammatory microenvironment of angioimmunoblastic T-cell lymphoma

Reports focusing on the immunological microenvironment of peripheral T-cell lymphomas (PTCL) are rare. Here we studied the reciprocal contribution of regulatory (Treg) and interleukin-17-producing (Th17) T-cells to the composition of the lymphoma-associated microenvironment of angioimmunoblastic T-cell lymphoma (AITL) and PTCL not otherwise specified on tissue microarrays from 30 PTCLs not otherwise specified and 37 AITLs. We found that Th17 but not Treg cells were differently represented in the two lymphomas and correlated with the amount of mast cells (MCs) and granulocytes, which preferentially occurred in the cellular milieu of AITL cases. We observed that MCs directly synthesized interleukin-6 and thus contribute to the establishment of a pro-inflammatory, Th17 permissive environment in AITL. We further hypothesized that the AITL clone itself could be responsible for the preferential accumulation of MCs at sites of infiltration through the synthesis of CXCL-13 and its interaction with the CXCR3 and CXCR5 receptors expressed on MCs. Consistent with this hypothesis, we observed MCs efficiently migrating in response to CXCL-13. On these bases, we conclude that MCs have a role in molding the immunological microenvironment of AITL toward the maintenance of pro-inflammatory conditions prone to Th17 generation and autoimmunity.

The tumor microenvironment in colorectal carcinogenesis

Colorectal cancer is the second leading cause of cancer-related mortality in the United States. Therapeutic developments in the past decade have extended life expectancy in patients with metastatic disease. However, metastatic colorectal cancers remain incurable. Numerous agents that were demonstrated to have significant antitumor activity in experimental models translated into disappointing results in extending patient survival. This has resulted in more attention being focused on the contribution of tumor microenvironment to the progression of a number of solid tumors including colorectal cancer. A more complete understanding of interactions between tumor epithelial cells and their stromal elements will enhance therapeutic options and improve clinical outcome. Here we will review the role of various stromal components in colorectal carcinogenesis and discuss the potential of targeting these components for the development of future therapeutic agents.

Exploring a regulatory role for mast cells: 'MCregs'?

Regulatory cells can mould the fate of the immune response by direct suppression of specific subsets of effector cells, or by redirecting effectors against invading pathogens and infected or neoplastic cells. These functions have been classically, although not exclusively, ascribed to different subsets of T cells. Recently, mast cells have been shown to regulate physiological and pathological immune responses, and thus to act at the interface between innate and adaptive immunity assuming different functions and behaviors at discrete stages of the immune response. Here, we focus on these poorly defined, and sometimes apparently conflicting, functions of mast cells.

Biology and clinical observations of regulatory T cells in cancer immunology

This review specifically examines the role of regulatory T cells (Tregs) in cancer in both mice and the clinic. Due to the rapid refinement of the definition of Tregs and their heterogeneity, emphasis is given to research findings over the past three years. For clarity, this review is broadly divided into three short sections that outline the basic biology of Tregs - (1) Treg lineage and development, (2) Treg subsets, and (3) mechanisms of Treg-mediated immune suppression; followed by two more comprehensive sections that cover; (4) clinical observations of Tregs and cancer, and (5) modifications of Treg biology as cancer immunotherapies. The latter two sections discuss the measurement of function and frequency of Treg in model systems and clinical trials and possible ways to interfere with Treg-mediated immune suppression with the focus on recent pre-clinical and clinical findings.