Mast cell progenitor trafficking and maturation

Mast cell activation and neutrophil recruitment promotes early and robust inflammation in the meninges in EAE

The meninges are often considered inert tissues that house the CSF and provide protection for the brain and spinal cord. Yet emerging data demonstrates that they are also active sites of immune responses. Furthermore, the blood-CSF barrier surrounding meningeal blood vessels, together with the blood-brain barrier (BBB), is postulated to serve as a gateway for the pathological infiltration of immune cells into the CNS in multiple sclerosis (MS). Our previous studies using mast cell-deficient (Kit(W/Wv)) mice demonstrated that mast cells resident in the dura mater and pia mater exacerbate experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, by facilitating CNS inflammatory cell influx. Here we examined the underlying mechanisms that mediate these effects. We demonstrate that there are dramatic alterations in immune associated gene expression in the meninges in pre-clinical disease, including those associated with mast cell and neutrophil function. Meningeal mast cells are activated within 24 h of disease induction, but do not directly compromise CNS vascular integrity. Rather, through production of TNF, mast cells elicit an early influx of neutrophils, cells known to alter vascular permeability, into the meninges. These data add to the growing evidence that inflammation in the meninges precedes CNS immune cell infiltration and establish that mast cells are among the earliest participants in these disease-initiating events. We hypothesize that mast cell-dependent neutrophil recruitment and activation in the meninges promotes early breakdown of the local BBB and CSF-blood barrier allowing initial immune cell access to the CNS.

Temporal colonic gene expression profiling in the recurrent colitis model identifies early and chronic inflammatory processes

The recurrent TNBS-colitis model in BALB/c mice has been proposed as a model of Inflammatory Bowel Disease with a shifting pattern of local cytokines with the expression of Th1 cytokines during the early phase, Th17 cytokines during the intermediate phase and Th2 cytokines during late fibrotic stages. In this study, we evaluated the development of pathology in time–in conjunction with genome-wide gene expression in the colons–in response to three weekly intrarectal instillations of TNBS. During this time-frame mice develop colitis with extensive cellular infiltration of (sub)mucosa and mildly to moderately affected crypt architecture. These pathological processes were sensitive to local treatment with budesonide. Gene expression profiling confirmed an acute phase response after each intrarectal TNBS-challenge. In addition, a chronic inflammatory process developed over time particularly evident from a gradual increase in expression of mast cell related genes. The changes in pathological hallmarks were consistent with a temporal expression of mRNA encoding a selection of chemokines. In conclusion, the early stages of the recurrent TNBS-colitis model reflect several aspects of inflammatory bowel disease which are sensitive to immunomodulation.

Human cord blood derived immature basophils show dual characteristics, expressing both basophil and eosinophil associated proteins

Basophils are blood cells of low abundance associated with allergy, inflammation and parasite infections. To study the transcriptome of mature circulating basophils cells were purified from buffy coats by density gradient centrifugations and two-step magnetic cell sorting. However, after extensive analysis the cells were found to be transcriptionally inactive and almost completely lack functional mRNA. In order to obtain transcriptionally active immature basophils for analysis of their transcriptome, umbilical cord blood cells were therefore cultured in the presence of interleukin (IL)-3 for 9 days and basophils were enriched by removing non-basophils using magnetic cell sorting. The majority of purified cells demonstrated typical metachromatic staining with Alcian blue dye (95%) and expression of surface markers FcεRI and CD203c, indicating a pure population of cells with basophil-like phenotype. mRNA was extracted from these cells and used to construct a cDNA library with approximately 600 000 independent clones. This library served as tool to determine the mRNA frequencies for a number of hematopoietic marker proteins. It was shown that these cells express basophil/mast cell-specific transcripts, i.e. β-tryptase, serglycin and FcεRI α-chain, to a relatively low degree. In contrast, the library contained a high number of several eosinophil-associated transcripts such as: major basic protein (MBP), charcot leyden crystal (CLC), eosinophil cationic protein (ECP), eosinophil derived neurotoxin (EDN) and eosinophil peroxidase (EPO). Out of these transcripts, MBP and EPO were the most frequently observed, representing 8% and 3.2% of the total mRNA pool, respectively. Moreover, in a proteome analysis of cultured basophils we identified MBP and EPO as the two most prominent protein bands, suggesting a good correlation between protein and mRNA analyses of these cells. The mixed phenotype observed for these cells strengthens the conclusion that eosinophils and basophils are closely linked during human hematopoietic development. The dual phenotype also indicates that other cytokines than IL-3 or cell surface interactions are needed to obtain the full basophil specific phenotype in vivo.

Complement factor C5a as mast cell activator mediates vascular remodelling in vein graft disease

AIMS

Failure of vein graft conduits due to vein graft thickening, accelerated atherosclerosis, and subsequent plaque rupture is applicable to 50% of all vein grafts within 10 years. New potential therapeutic targets to treat vein graft disease may be found in components of the innate immune system, such as mast cells and complement factors, which are known to be involved in atherosclerosis and plaque destabilization. Interestingly, mast cells can be activated by complement factor C5a and, therefore, a direct role for C5a-mediated mast cell activation in vein graft disease is anticipated. We hypothesize that C5a-mediated mast cell activation is involved in the development and destabilization of vein graft lesions.

METHODS AND RESULTS

Mast cells accumulated in time in murine vein graft lesions, and C5a and C5a-receptor (CD88) expression was up-regulated during vein graft disease in apolipoprotein E-deficient mice. Mast cell activation with dinitrophenyl resulted in a profound increase in vein graft thickening and in the number of plaque disruptions. C5a application enhanced vein graft lesion formation, while treatment with a C5a-receptor antagonist resulted in decreased vein graft disease. C5a most likely exerts its function via mast cell activation since the mast cell inhibitor cromolyn totally blocked C5a-enhanced vein graft disease.

CONCLUSION

These data provide evidence that complement factor C5a-induced mast cell activation is highly involved in vein graft disease, which identifies new targets to prevent vein graft disease.

CD11c+ cells are required for antigen-induced increase of mast cells in the lung

Patients with allergic asthma have more lung mast cells, which likely worsens the symptoms. In experimental asthma, CD11c(+) cells have to be present during the challenge phase for several features of allergic inflammation to occur. Whether CD11c(+) cells play a role for Ag-induced increases of lung mast cells is unknown. In this study, we used diphtheria toxin treatment of sensitized CD11c-diphtheria toxin receptor transgenic mice to deplete CD11c(+) cells. We demonstrate that recruitment of mast cell progenitors to the lung is substantially reduced when CD11c(+) cells are depleted during the challenge phase. This correlated with an impaired induction of endothelial VCAM-1 and led to a significantly reduced number of mature mast cells 1 wk after challenge. Collectively, these data suggest that Ag challenge stimulates CD11c(+) cells to produce cytokines and/or chemokines required for VCAM-1 upregulation on the lung endothelium, which in turn is crucial for the Ag-induced mast cell progenitor recruitment and the increase in mast cell numbers.

Mast cell chemotaxis - chemoattractants and signaling pathways

Migration of mast cells is essential for their recruitment within target tissues where they play an important role in innate and adaptive immune responses. These processes rely on the ability of mast cells to recognize appropriate chemotactic stimuli and react to them by a chemotactic response. Another level of intercellular communication is attained by production of chemoattractants by activated mast cells, which results in accumulation of mast cells and other hematopoietic cells at the sites of inflammation. Mast cells express numerous surface receptors for various ligands with properties of potent chemoattractants. They include the stem cell factor (SCF) recognized by c-Kit, antigen, which binds to immunoglobulin E (IgE) anchored to the high affinity IgE receptor (FcεRI), highly cytokinergic (HC) IgE recognized by FcεRI, lipid mediator sphingosine-1-phosphate (S1P), which binds to G protein-coupled receptors (GPCRs). Other large groups of chemoattractants are eicosanoids [prostaglandin E₂ and D₂, leukotriene (LT) B₄, LTD₄, and LTC₄, and others] and chemokines (CC, CXC, C, and CX3C), which also bind to various GPCRs. Further noteworthy chemoattractants are isoforms of transforming growth factor (TGF) β1–3, which are sensitively recognized by TGF-β serine/threonine type I and II β receptors, adenosine, C1q, C3a, and C5a components of the complement, 5-hydroxytryptamine, neuroendocrine peptide catestatin, tumor necrosis factor-α, and others. Here we discuss the major types of chemoattractants recognized by mast cells, their target receptors, as well as signaling pathways they utilize. We also briefly deal with methods used for studies of mast cell chemotaxis and with ways of how these studies profited from the results obtained in other cellular systems.

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.

Activated MCTC mast cells infiltrate diseased lung areas in cystic fibrosis and idiopathic pulmonary fibrosis

Background

Although mast cells are regarded as important regulators of inflammation and tissue remodelling, their role in cystic fibrosis (CF) and idiopathic pulmonary fibrosis (IPF) has remained less studied. This study investigates the densities and phenotypes of mast cell populations in multiple lung compartments from patients with CF, IPF and never smoking controls.

Methods

Small airways, pulmonary vessels, and lung parenchyma were subjected to detailed immunohistochemical analyses using lungs from patients with CF (20 lung regions; 5 patients), IPF (21 regions; 7 patients) and controls (16 regions; 8 subjects). In each compartment the densities and distribution of MC_T and MC_TC mast cell populations were studied as well as the mast cell expression of IL-6 and TGF-β.

Results

In the alveolar parenchyma in lungs from patients with CF, MC_TC numbers increased in areas showing cellular inflammation or fibrosis compared to controls. Apart from an altered balance between MC_TC and MC_T cells, mast cell in CF lungs showed elevated expression of IL-6. In CF, a decrease in total mast cell numbers was observed in small airways and pulmonary vessels. In patients with IPF, a significantly elevated MC_TC density was present in fibrotic areas of the alveolar parenchyma with increased mast cell expression of TGF-β. The total mast cell density was unchanged in small airways and decreased in pulmonary vessels in IPF. Both the density, as well as the percentage, of MC_TC correlated positively with the degree of fibrosis. The increased density of MC_TC, as well as MC_TC expression of TGF-β, correlated negatively with patient lung function.

Conclusions

The present study reveals that altered mast cell populations, with increased numbers of MC_TC in diseased alveolar parenchyma, represents a significant component of the histopathology in CF and IPF. The mast cell alterations correlated to the degree of tissue remodelling and to lung function parameters. Further investigations of mast cells in these diseases may open for new therapeutic strategies.

Mast cell biology: introduction and overview

In recent years, the field of mast cell biology has expanded well beyond the boundaries of atopic disorders and anaphy laxis, on which it has been historically focused. The biochemical and signaling events responsible for the development and regulation of mast cells has been increasingly studied, aided in large part by novel breakthroughs in laboratory techniques used to study these cells. The result of these studies has been a more comprehensive definition of mast cells that includes added insights to their overall biology as well as the various disease states that can now be traced to defects in mast cells. This introductory chapter outlines and highlights the various topics of mast cell biology that will be discussed in further detail in subsequent chapters.