Mast cells lacking the high affinity immunoglobulin E receptor are deficient in Fc epsilon RI gamma messenger RNA

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Human eosinophils and mast cells: Birds of a feather flock together

While the origin of the phrase "birds of a feather flock together" is unclear, it has been in use for centuries and is typically employed to describe the phenomenon that people with similar tastes or interests tend to seek each other out and congregate together. In this review, we have co-opted this phrase to compare innate immune cells of related origin, the eosinophil and mast cell, because they very often accumulate together in tissue sites under both homeostatic and inflammatory conditions. To highlight overlapping yet distinct features, their hematopoietic development, cell surface phenotype, mediator release profiles and roles in diseases have been compared and contrasted. What emerges is a sense that these two cell types often interact with each other and their tissue environment to provide synergistic contributions to a variety of normal and pathologic immune responses.

Interleukin-18 has an Important Role in Differentiation and Maturation of Mucosal Mast Cells

A significant amount of correlational evidence has linked increased levels of IL-18 with allergic diseases in both human and animal models, and, as mast cells are major mediators of allergies, we hypothesized that IL-18 may have a role in mast cell biology. Rationale for our hypothesis is based on the evidence that IL-3 deficient mice are not devoid of mast cells, even though IL-3 is a major differentiation and growth factor for mast cells. Accordingly, we cultured IL-18 responsive bone marrow CD34+ cells in vitro under a variety of conditions and cytokine combinations to examine mast cell differentiation and maturation using flow cytometry, quantitative PCR,and immunostaining techniques. Additionally, in vivo mast cell transformation and maturation were also analysed using endogenous IL-18 gene-deficient or Fabpi-IL-18 overexpressed mice. Our data indicate that both IL-3 and IL-18 exposed CD34+ bone marrow precursors differentiate and mature into mast cells. Further, we observed that IL-18 differentiates mast cells independent of IL-3, as pharmacologic blockade of IL-3 does not prevent in vitro IL-18-driven mast cell differentiation. Further, we found that endogenous IL-18 deficiency restricts maturation of IL-3 generated mast cells and IL-18 derived mast cells require IL-3 for their survival. Additionally, we observed IL-18 intestinal overexpression promotes tissue mast cell proliferation and mucosal mast cell development. Taken together, we provide the evidence that IL-18 has an important contributory role in mast cell differentiation, maturation and in vivo development of mucosal mast cells. Therefore, IL-18 may represent a future pharmacologic target for treating mast cell-mediated allergic diseases.

The antigen presentation function of bone marrow-derived mast cells is spatiotemporally restricted to a subset expressing high levels of cell surface FcepsilonRI and MHC II

Background

At present, it is highly controversial whether pure mast cells can serve as antigen presenting cells, and it is not known whether the capacity of antigen presenting function is temporally restricted to a particular subset of differentiated mast cells. Evidence is presented for a novel surface FcεRI^hi , MHC II +, and c-kit + pure mast cell subset, temporally restricted as antigen-presenting cells in the immune axis of T-cell activation.

Results

Bone marrow-derived mast cells (BMMC) cultured in the presence of IL-3 for three weeks are pure mast cells based on surface expression of lineage-specific marker, c-kit and FcεRI. Herein we present the first demonstration that approximately 98.7% c-kit + and FcεRI expressing BMMC, further depleted of any contaminated professional antigen-presenting cells, are still fully capable of presenting antigens, i.e., OVA protein, OVA peptide, and IgE-TNP-OVA, to OVA peptide-specific T-cell hybridomas. Notably, IgE-dependent antigen presentation is more efficient compared to that resulting from direct antigen uptake. Importantly, we present the novel finding that only surface FcεRI^hi mast cells, also expressing surface MHC II exhibited antigen-presenting function. In contrast, surface FcεRI^lo mast cells without expressing surface MHC II were not capable of antigen presentation. Interestingly, the antigen-presenting function of BMMC was irrevocably lost during the third and fourth week in IL-3 or SCF containing cultures.

Conclusions

This is the first observation to attribute a spatiotemporally restricted antigen-presenting function to a subset of three-week old pure BMMC expressing both high levels of surface FcεRI and surface MHC II. We propose that mast cells play an important role in immune deviating and/or sustaining the activation of infiltrating CD4 T-cells, and modulating T-cell mediated allergic inflammation via its flexibility to present antigens and antigen-IgE complexes.

New developments in FcepsilonRI regulation, function and inhibition

The high-affinity Fc receptor for IgE (FcepsilonRI), a multimeric immune receptor, is a crucial structure for IgE-mediated allergic reactions. In recent years, advances have been made in several important areas of the study of FcepsilonRI. The first area relates to FcepsilonRI-mediated biological responses that are antigen independent. The second area encompasses the biological relevance of the distinct signalling pathways that are activated by FcepsilonRI; and the third area relates to the accumulated evidence for the tight control of FcepsilonRI signalling through a broad array of inhibitory mechanisms, which are being developed into promising therapeutic approaches.

Functional expression of high-affinity receptor for immunoglobulin E on mast cells precedes that of tryptase during differentiation from human bone marrow-derived CD34 progenitors cultured in the presence of stem cell factor and interleukin-6

BACKGROUND

CD34(+) progenitor cells develop into tryptase(+), CD117(+) mast cells when cultured in the presence of recombinant human stem cell factor (rhSCF). However, spontaneous IgE receptor (FcepsilonRI) expression during human mast cell development is not well examined.

OBJECTIVE

Here, the expression and function of FcepsilonRI in and on human bone marrow-derived mast cells (HBMMCs) during development were investigated.

METHODS AND RESULTS

At 4 weeks of culture, predominant cells expressed high-affinity IgE receptor alpha chain (FcepsilonRIalpha) on the cell surface determined by flow cytometry, but CD117 was less expressed. Immunocytochemistry with antitryptase mAb and anti-FcepsilonRIalpha mAb revealed intracellular and surface expression of FcepsilonRIalpha at 2 weeks of culture, but tryptase was less expressed. FcepsilonRIalpha mRNA transcript preceded that of tryptase mRNA at 2 weeks of culture determined by real-time RT-PCR, and FcepsilonRIalpha, FcepsilonRIbeta, FcepsilonRIgamma, and tryptase mRNA increased along with differentiation. FcepsilonRIalpha cross-link on HBMMC and 4-week-old mast cells/mast cell precursors induced the release of IL-5 and granulocyte macrophage-colony stimulating factor, which was enhanced by rhSCF.

CONCLUSION

These data indicated that HBMMC constitutively and spontaneously expressed functional FcepsilonRI subunits at the early stage of differentiation, probably because of the differences in the ability and functional property of progenitors.

IL-10 Inhibits FcεRI Expression in Mouse Mast Cells

FcepsilonRI expression and function is a central aspect of allergic disease. Using bone marrow-derived mouse mast cell populations, we have previously shown that the Th2 cytokine IL-4 inhibits FcepsilonRI expression and function. In the current study we show that the Th2 cytokine IL-10 has similar regulatory properties, and that it augments the inhibitory effects of IL-4. FcepsilonRI down-regulation was functionally significant, as it diminished inflammatory cytokine production and IgE-mediated FcepsilonRI up-regulation. IL-10 and IL-4 reduced FcepsilonRI beta protein expression without altering the alpha or gamma subunits. The ability of IL-4 and IL-10 to alter FcepsilonRI expression by targeting the beta-chain, a critical receptor subunit known to modulate receptor expression and signaling, suggests the presence of a Th2 cytokine-mediated homeostatic network that could serve to both initiate and limit mast cell effector function.

FcεRIγ-ITAM Is Differentially Required for Mast Cell Function In Vivo

The cross-linking of IgE-bound FcepsilonRI by Ags triggers mast cell activation leading to allergic reactions. The in vivo contribution of FcepsilonRIgamma signaling to IgE/FcepsilonRI-mediated mast cell responses has not yet been elucidated. In this study FcepsilonRIgamma(-/-) mast cells were reconstituted with either wild-type or mutant FcepsilonRIgamma in transgenic mice and transfected mast cells in vitro. We demonstrate that FcepsilonRIgamma-immunoreceptor tyrosine-based activation motif is essential for degranulation, cytokine production, and PG synthesis as well as for passive systemic anaphylaxis. Recent reports have suggested that cell surface FcepsilonRI expression and mast cell survival are regulated by IgE in the absence of Ag, although the molecular mechanism is largely unknown. We also found that the promotion of mast cell survival by IgE without Ags is mediated by signals through the FcepsilonRIgamma-immunoreceptor tyrosine-based activation motif. In contrast, the IgE-mediated up-regulation of FcepsilonRI is independent of FcepsilonRIgamma signaling. These results indicate that FcepsilonRIgamma-mediated signals differentially regulate the receptor expression, activation, and survival of mast cells and systemic anaphylaxis.

Evidence for a differential expression of the FcepsilonRIgamma chain in dendritic cells of atopic and nonatopic donors

While mast cells and basophils constitutively express the high-affinity IgE receptor (Fc epsilon RI), it is absent or weakly expressed on APCs from normal donors. Fc epsilon RI is strongly upregulated on APCs from atopic donors and involved in the pathophysiology of atopic diseases. Despite its clinical relevance, data about Fc epsilon RI regulation on APCs are scarce. We show that in all donors intracellular alpha chain of the Fc epsilon RI (Fc epsilon RI alpha) accumulates during DC differentiation from monocytes. However, expression of gamma chains of the Fc epsilon RI (Fc epsilon RI gamma), mandatory for surface expression, is downregulated. It is low or negative in DCs from normal donors lacking surface Fc epsilon RI (Fc epsilon RI(neg) DCs). In contrast, DCs from atopics express surface Fc epsilon RI (Fc epsilon RI(pos) DCs) and show significant Fc epsilon RI gamma expression, which can be coprecipitated with Fc epsilon RI alpha. In Fc epsilon RI(neg) DCs lacking Fc epsilon RI gamma, immature and core glycosylated Fc epsilon RI alpha accumulates in the endoplasmic reticulum. In Fc epsilon RI(pos) DCs expressing Fc epsilon RI gamma, an additional mature form of Fc epsilon RI alpha exhibiting complex glycosylation colocalizes with Fc epsilon RI gamma in the Golgi compartment. IgE binding sustains surface-expressed Fc epsilon RI on DCs from atopic donors dependent on baseline protein synthesis and transport and enhances their IgE-dependent APC function. We propose that enhanced Fc epsilon RI on DCs from atopic donors is driven by enhanced expression of otherwise limiting amounts of Fc epsilon RI gamma and is preserved by increased IgE levels.

Catecholamines in murine bone marrow derived mast cells

Cultured murine bone marrow derived mast cells (BMMC) were found to store high levels of dopamine (3753+/-844 pg/10(7) cells) and occasionally produce norepinephrine and epinephrine. The catecholamine synthesis inhibitor, alpha-methyl-para-tyrosine, decreased intracellular catecholamine concentrations, and activation with ionomycin stimulated dopamine release. Neither dopaminergic receptor antagonists nor exogenous dopamine < or =10 microM affected IL-3-induced cell proliferation. High exogenous dopamine (20-100 microM) decreased proliferation and increased apoptosis, and the anti-oxidant ascorbic acid prevented these effects. Increased expression of the anti-apoptotic factor Bcl-2 or loss of pro-apoptotic Bax expression attenuated dopamine-induced apoptosis, suggesting the apoptosis proceeds through a mitochondrial pathway.

Regulation of mast cell number and function

Mast cells are complex, multifunctional cells that have unique phenotypes and growth requirements. Regulation in vitro of human mast cell growth and function differs from regulation of rodent mast cells. Human cell yields in vitro vary depending on tissue of origin, use of mononuclear or CD34+ progenitor cells, presence of cytokines, and serum-free versus serum-containing mediums. This article presents a summary of recent advances in the understanding of cytokine regulation of mast cell numbers and function in rodents and humans.

The high-affinity IgE receptor (Fc epsilon RI): from physiology to pathology

The high affinity receptor for immunoglobulin E (designated Fc epsilon RI) is the member of the antigen (Ag) receptor superfamily responsible for linking pathogen-or allergen-specific IgEs with cellular immunologic effector functions. This review provides background information on Fc epsilon RI function combined with more detailed summaries of recent progress in understanding specific aspects of Fc epsilon RI biology and biochemistry. Topics covered include the coordination and function of the large multiprotein signaling complexes that are assembled when Fc epsilon RI and other Ag receptors are engaged, new information on human receptor structures and tissue distribution, and the role of the FcR beta chain in signaling and its potential contribution to atopic phenotypes.

Stem cell factor and interleukin-4 induce murine bone marrow cells to develop into mast cells with connective tissue type characteristics in vitro

In this study, we have developed a method to obtain mast cells with connective tissue type mast cell (CTMC) characteristics directly from mouse bone marrow (BM) cells. BM cells were grown for 3 weeks in presence of interleukin-4 (IL-4) plus stem cell factor (SCF). SCF alone poorly supported growth and development of mast cells. IL-4 dose-dependently enhanced the expression of c-kit and high-affinity receptor for IgE (Fc(epsilon)RI) on the cell surface of SCF-cultured BM cells. Furthermore, cytoplasmic granulation and histamine synthesis of BM-derived mast cells were increased in presence of IL-4 and SCF. Histochemical staining demonstrated that granules were safranin positive. BM-derived mast cells could be activated for granule exocytosis (beta-hexosaminidase release) and lipid mediator generation (LTC4 production) via Fc(epsilon)RI after sensitization with IgE and subsequent crosslinking with multivalent antigen. In addition, mast cells derived from BM cells cultured with SCF plus IL-4 could be activated by substance P, a nonimmunologic stimulus, to release beta-hexosaminidase. The results presented indicate that IL-4 and SCF both have a prominent role in the development of mast cells from murine BM cells in vitro. Mast cells can directly be derived from BM cells in presence of SCF and IL-4 and the cultured cells show typical hallmarks of CTMC, indicating that precursor cells for CTMC may be present in BM. The described culture procedure may be useful to investigate the molecular aspects of the development of committed mast cell lineages.

Regulation of the High Affinity Receptor for IgE on Human Epidermal Langerhans Cells

Human epidermal Langerhans cells (LC) express variable amounts of the high affinity receptor for IgE (FcεRI); the strongest expression is characteristic of atopic dermatitis. The receptor is suggested to take part in the pathophysiology of this disease by acting as a link between aeroallergens and Ag-specific T cells in an IgE-mediated, delayed-type hypersensitivity reaction. In the present study we show that even in the absence of surface expression, normal LC maintain an intracellular pool of the α-chain of FcεRI (FcεRIα) of the same m.w. as the surface-bound FcεRIα that is able to bind significant amounts of IgE. The lack of surface expression is linked to the absence or very low expression of the γ-chain (FcεRIγ). Moreover, the amount of FcεRIα expressed at the cell surface significantly correlates with the amount of FcεRIγ. LC differentiation toward lymphoid dendritic cells is accompanied by the disappearance of transcripts for FcεRIα, but not for FcεRIγ. This leads to a rapid decrease in the intracellular and surface levels of FcεRIα, which cannot be influenced by IL-4, IgE, or other agents. Overall, our findings suggest that these mechanisms enable LC to be highly versatile APCs by rapidly adapting the surface level of FcεRI to distinct inflammatory environments.

Identification of Fc epsilon RIneg mast cells in mouse bone marrow cell cultures. Use of a monoclonal anti-p161 antibody

A monoclonal hamster antibody (K-1) specific for a 161-kD mast cell surface glycoprotein was derived. p161 is expressed on normal and cultured mast cells and on some macrophages, but not on basophils or other hematopoietic cells. A population of Fc epsilon Rneg cells expressing p161 was found in short term cultures of bone marrow cells grown in interleukin (IL)-3. These cells were purified and propagated for extended periods in IL-3. They express c-kit and Fc gamma RII/III, contain alcian blue-positive granules and histamine, and secrete IL-3 in response to ionomycin treatment. Their morphology is consistent with that of mast cells. We propose that they represent Fc epsilon RIneg mast cells that can be detected and purified because of their p161 expression.