Yoshimichi Okayama

Development, migration, and survival of mast cells

Mast cells play a pivotal role in immediate hypersensitivity and chronic allergic reactions that can contribute to asthma, atopic dermatitis, and other allergic diseases. Because mast cell numbers are increased at sites of inflammation in allergic diseases, pharmacologic intervention into the proliferation, migration, and survival (or apoptosis) of mast cells could be a promising strategy for the management of allergic diseases. Mast cells differentiate from multipotent hematopoietic progenitors in the bone marrow. Stem cell factor (SCF) is a major chemotactic factor for mast cells and their progenitors. SCF also elicits cell-cell and cell-substratum adhesion, facilitates the proliferation, and sustains the survival, differentiation, and maturation, of mast cells. Therefore, many aspects of mast cell biology can be understood as interactions of mast cells and their precursors with SCF and factors that modulate their responses to SCF and its signaling pathways. Numerous factors known to have such a capacity include cytokines that are secreted from activated T cells and other immune cells including mast cells themselves. Recent studies also demonstrated that monomeric IgE binding to FcωRI can enhance mast-cell survival. In this review we discuss the factors that regulate mast cell development, migration, and survival.

IL-33 can promote survival, adhesion and cytokine production in human mast cells

IL-33 is a recently identified member of the IL-1 family of molecules, which also includes IL-1 and IL-18. IL-33 binds to the receptor, T1/ST2/IL-1R4, and can promote cytokine secretion by Th2 cells and NF-κB phosphorylation in mouse mast cells. However, the effects of these molecules, especially IL-33, in human mast cells are poorly understood. Expression of the receptors for IL-1 family molecules, specifically, IL-1R1, IL-18R and T1/ST2, was detectable intracellularly in human umbilical cord blood-derived mast cells (HUCBMCs) by flow cytometry, but was scarcely detectable on the cells’ surface. However, IL-1β, IL-18 or IL-33 induced phosphorylation of Erk, p38 and JNK in naïve HUCBMCs, and IL-33 or IL-1β, but not IL-18, enhanced the survival of naive HUCBMCs and promoted their adhesion to fibronectin. IL-33 or IL-1β also induced IL-8 and IL-13 production in naïve HUCBMCs, and enhanced production of these cytokines in IgE/anti-IgE-stimulated HUCBMCs, without enhancing secretion of either PGD2 or histamine. Moreover, IL-33-mediated IL-8 production by HUCBMCs was markedly reduced by the p38 MAPK inhibitor, SB203580. In contrast to findings with mouse mast cells, IL-18 neither induced nor enhanced secretion of the mediators PGD2 or histamine by HUCBMCs. Our findings identify previously unknown functions of IL-33 in human mast cells. One of these is that IL-33, like IL-1β, can induce cytokine production in human mast cells even in the absence of stimuli of FcɛRI aggregation. Our findings thus support the hypothesis that IL-33 may enhance mast cell function in allergic disorders and other settings, either in the presence or absence of co-stimulation of mast cells via IgE/antigen–FcɛRI signals.

IL-33 induces IL-13 production by mouse mast cells independently of IgE-FcεRI signals

The IL‐1‐related molecules, IL‐1 and IL‐18, can promote Th2 cytokine production by IgE/antigen‐FcεRI‐stimulated mouse mast cells. Another IL‐1‐related molecule, IL‐33, was identified recently as a ligand for T1/ST2. Although mouse mast cells constitutively express ST2, the effects of IL‐33 on mast cell function are poorly understood. We found that IL‐33, but not IL‐1β or IL‐18, induced IL‐13 and IL‐6 production by mouse bone marrow‐derived, cultured mast cells (BMCMCs) independently of IgE. In BMCMCs incubated with the potently cytokinergic SPE‐7 IgE without specific antigen, IL‐33, IL‐1β, and IL‐18 each promoted IL‐13 and IL‐6 production, but the effects of IL‐33 were more potent than those of IL‐1β or IL‐18. IL‐33 promoted cytokine production via a MyD88‐dependent but Toll/IL‐1R domain‐containing adaptor‐inducing IFN‐β‐independent pathway. By contrast, IL‐33 neither induced nor enhanced mast cell degranulation. At 200 ng/ml, IL‐33 prolonged mast cell survival in the absence of IgE and impaired survival in the presence of SPE‐7 IgE, whereas at 100 ng/ml, IL‐33 had no effect on mast cell survival in the absence of IgE and reduced mast cell survival in the presence of IgE. These observations suggest potential roles for IL‐33 in mast cell‐ and Th2 cytokine‐associated immune responses and disorders.

Expression of a Functional High-Affinity IgG Receptor, FcγRI, on Human Mast Cells: Up-Regulation by IFN-γ

Biologically relevant activation of human mast cells through Fc receptors is believed to occur primarily through the high-affinity IgE receptor FcεRI. However, the demonstration in animal models that allergic reactions do not necessarily require Ag-specific IgE, nor the presence of a functional IgE receptor, and the clinical occurrence of some allergic reactions in situations where Ag-specific IgE appears to be lacking, led us to examine the hypothesis that human mast cells might express the high-affinity IgG receptor FcγRI and in turn be activated through aggregation of this receptor. We thus first determined by RT-PCR that resting human mast cells exhibit minimal message for FcγRI. We next found that IFN-γ up-regulated the expression of FcγRI. This was confirmed by flow cytometry, where FcγRI expression on human mast cells was increased from ∼2 to 44% by IFN-γ exposure. FcεRI, FcγRII, and FcγRIII expression was not affected. Scatchard plots were consisted with these data where the average binding sites for monomeric IgG1 (Ka = 4–5 × 108 M−1) increased from ∼2,400 to 12,100–17,300 per cell. Aggregation of FcγRI on human mast cells, and only after IFN-γ exposure, led to significant degranulation as evidenced by histamine release (24.5 ± 4.4%): and up-regulation of mRNA expression for specific cytokines including TNF-α, GM-CSF, IL-3 and IL-13. These findings thus suggest another mechanism by which human mast cells may be recruited into the inflammatory processes associated with some immunologic and infectious diseases.

Oxidative stress in allergic and inflammatory skin diseases.

The skin is exposed to endogenous and environmental pro-oxidant agents, leading to the harmful generation of reactive oxygen species (ROS). The resulting oxidative stress damages proteins, lipids, and DNA. An imbalance between ROS and antioxidants can lead to an elevated oxidative stress level. Some evidence indicates that allergic and inflammatory skin diseases like atopic dermatitis, urticaria and psoriasis are mediated by oxidative stress. For example, monocytes from patients with atopic dermatitis are primed to generate ROS in response to zymosan, a Toll-like receptor 2 (TLR2) ligand, suggesting that Staphylococcus aureus may damage lesional skin of the disease by production of ROS. Mast cells generate mainly intracellular ROS following the aggregation of FceRI; these ROS may act as secondary messengers in the induction of several biological responses. The present review summarizes the involvement of ROS in the pathogenesis of allergic and inflammatory skin diseases.

T cell proliferation by direct cross-talk between OX40 ligand on human mast cells and OX40 on human T cells: Comparison of gene expression profiles between human tonsillar and lung-cultured mast cells

Mast cells (MCs) are the primary effector cells in allergic reactions and have also been found to activate T cells and to reside in close physical proximity to T cells. However, the molecular mechanisms involved in the MC-T cell interaction remain unclear. We hypothesized that human tonsillar MCs, which locate in the interfollicular areas, might interact with T cells. Thus, we first established a culture system of human tonsillar MCs and then compared gene expression profiles of tonsillar MCs with that of lung MCs before and after aggregation of FcεRI by using high-density oligonucleotide probe arrays. Here we show that resting tonsillar MCs, when compared with lung MCs, revealed significantly higher expression levels for CC chemokines (CCL3 and 4), which recruit T cells, and for TNFR superfamilies (OX40 ligand and 4-1BB ligand), which induce proliferation of T cells. After aggregation of FcεRI, not only tonsillar MCs but also lung MCs up-regulated the expression of these molecules. We confirmed that T cell proliferation is induced in direct cross-talk by the MC surface molecule OX40 ligand. These results suggest that human MCs may play important roles in adaptive immunity through the T cell responses.

NF-κB and TNF-α: A Positive Autocrine Loop in Human Lung Mast Cells?

The generation of cytokines, particularly TNF-α, by mast cells is crucial for the initiation of the allergic response. A key transcription factor involved in the synthesis of TNF-α is NF-κB. Using a mAb specific for the activated form of NF-κB, immunocytochemistry, confocal microscopy, and gel shift assays have been used in conjunction to localize this transcription factor to human lung mast cells and to study its activation. Activation of mast cells with stem cell factor (10 ng/ml) and anti-IgE (1 μg/ml) induced maximal activation of NF-κB at 4 and 2 h, respectively. In contrast, with TNF-α (5 ng/ml) maximal activation occurred within 15 min. Parallel falls in IκB were demonstrated. Confocal microscopy demonstrated the localization of the activated form of NF-κB to the nuclei of activated mast cells. NF-κB activation was verified using a gel shift assay. A supershift assay showed mast cell NF-κB to be composed primarily of p50 with smaller amounts of p65. No interaction with Abs for Rel-A, c-Rel, Rel-B, and p52 was seen. Immunocytochemistry and ELISAs showed TNF-α to be stored within mast cells and released into the extracellular environment following activation. The possible participation of TNF-α generated by mast cells in NF-κB activation by anti-IgE was investigated using a blocking Ab for TNF-α. The blocking Ab reduced NF-κB activation by anti-IgE by >50%, suggesting that the release of preformed mast cell-associated TNF-α acts as a positive autocrine feedback signal to augment NF-κB activation and production of further cytokine, including GM-CSF and IL-8.

Inhibition profiles of sodium cromoglycate and nedocromil sodium on mediator release from mast cells of human skin, lung, tonsil, adenoid and intestine

We have studied an aspect of the functional heterogeneity of human mast cells, namely responsiveness to the inhibitory effects of sodium cromoglycate and nedocromil sodium. The effects of these drugs were examined on the release of histamine and PGD2 from mast cells of human skin, lung, tonsils, adenoids and intestine. A high concentration, 1000 μM, of sodium cromoglycate was required to significantly inhibit histamine release from lung and tonsillar mast cells. Nedocromil sodium, 1000 μM, was more effective than sodium cromoglycate against histamine release from lung, tonsillar and adenoidal cells. Both compounds showed tachyphylaxis in lung and tonsillar mast cells but not in adenoidal and intestinal mast cells. In contrast, in intestinal mast cells, the effect of nedocromil sodium was weaker and more variable than sodium cromoglycate. Skin mast cells differed from mast cells of the other anatomical sites in being unresponsive to sodium cromoglycate and nedocromil sodium. Our results confirm that high concentrations of sodium cromoglycate and nedocromil sodium are required to achieve even modest inhibition of mediator release from human mast cells under in vitro conditions. Notwithstanding this, the results also indicate that differences exist among skin, lung, tonsillar, adenoidal and intestinal mast cells with respect to their sensitivity to sodium cromoglycate and nedocromil sodium, thus extending our knowledge of functional heterogeneity within the human mast cell populations.

A Comparison of Mediators Released or Generated by IFN-γ-Treated Human Mast Cells Following Aggregation of FcγRI or FcεRI

The high affinity receptor for IgG (FcγRI, CD64) is expressed on human mast cells, where it is up-regulated by IFN-γ and, thus, may allow mast cells to be recruited through IgG-dependent mechanisms in IFN-γ-rich tissue inflammation. However, the mediators produced by human mast cells after aggregation of FcγRI are incompletely described, and it is unknown whether these mediators are distinct from those produced after activation of human mast cells via FcεRI. Thus, we investigated the release of histamine and arachidonic acid metabolites and examined the chemokine and cytokine mRNA profiles of IFN-γ-treated cultured human mast cells after FcγRI or FcεRI aggregation. Aggregation of FcγRI resulted in histamine release and PGD2 and LTC4 generation. These responses were qualitatively indistinguishable from responses stimulated via FcεRI. Aggregation of FcεRI or FcγRI led to an induction or accumulation of 22 cytokine and chemokine mRNAs. Among them, seven cytokines (TNF-α, IL-1β, IL-5, IL-6, IL-13, IL-1R antagonist, and GM-CSF) were significantly up-regulated via aggregation of FcγRI compared with FcεRI. TNF-α mRNA data were confirmed by quantitative RT-PCR and ELISA. Furthermore, we confirmed histamine and TNF-α data using IFN-γ-treated purified human lung mast cells. Thus, aggregation of FcγRI on mast cells led to up-regulation and/or release of three important classes of mediators: biogenic amines, lipid mediators, and cytokines. Some cytokines, such as TNF-α, were released and generated to a greater degree after FcγRI aggregation, suggesting that selected biologic responses of mast cells may be preferentially generated through FcγRI in an IFN-γ-rich environment.

Tissue remodeling induced by hypersecreted epidermal growth factor and amphiregulin in the airway after an acute asthma attack.

BACKGROUND Epidermal growth factor receptor ligands, such as epidermal growth factor (EGF) and amphiregulin, may play key roles in tissue remodeling in asthma. However, the kinetics of EGF and amphiregulin secretion in the airway after an acute asthma attack and the effect of prolonged airway exposure to these ligands on airway remodeling are unknown. OBJECTIVE To measure the EGF and amphiregulin concentrations in sputa obtained from patients with asthma under various conditions, and to examine the effects of EGF and amphiregulin on the proliferation or differentiation of airway structural cells. METHODS Epidermal growth factor and amphiregulin levels were measured by ELISA in sputum specimens collected from 14 hospitalized children with asthma during an acute asthma attack, 13 stable outpatients with asthma, 8 healthy control children, and 7 children with respiratory tract infections. The effects of EGF and amphiregulin on the proliferation and/or differentiation of normal human bronchial epithelial cells (NHBE), bronchial smooth muscle cells (BSMC), and normal human lung fibroblasts (NHLF) were examined. RESULTS The sputum levels of EGF were significantly higher for about a week after an acute asthma attack compared with the levels in stable subjects with asthma and control subjects. In contrast, upregulation of amphiregulin in the sputa of patients with asthma was observed only during the acute attack. EGF caused proliferation of NHBE, BSMC, and NHLF, whereas amphiregulin induced proliferation of only NHBE. Prolonged exposure of NHBE to EGF and amphiregulin induced mucous cell metaplasia in an IL-13-independent manner. CONCLUSION Acute asthma attacks are associated with hypersecretion of EGF and amphiregulin in the airway. Recurrent acute attacks may aggravate airway remodeling.