Interleukin 3-dependent and -independent mast cells stimulated with IgE and antigen express multiple cytokines

Secretion of granulocyte-macrophage colony-stimulating factor by human blood monocytes is stimulated by engagement of Fc gamma receptors type I by solid-phase immunoglobulins requiring high-affinity Fc-Fc gamma receptor type I interactions

Despite reports on the secretion of granulocyte-macrophage-colony-stimulating factor (GM-CSF) by murine peritoneal macrophages in response to inflammatory stimuli, the ability of human monocytes to generate this growth factor has remained doubtful. Neither endotoxin, phorbol compounds, nor inflammatory cytokines have been shown to elicit GM-CSF by these cells. Our present studies indicate that exposure of monocytes to solid-phase murine IgG2a, but not to murine IgG1 and thus cross-linkage of the 72-kDa Fc gamma RI results in transcription of the GM-CSF gene, accumulation of stable GM-CSF mRNA and finally in release of biologically active GM-CSF protein. Cross-linking of Fc gamma RI by a murine anti-Fc gamma RI monoclonal antibody and goat anti-mouse antibody failed, however, to stimulate GM-CSF release. This suggests that high affinity Fc-Fc gamma RI interactions are required for induction of expression of GM-CSF by monocytes.

Inflammation and the allergic response

The atopic diseases--allergic rhinitis, asthma, and atopic dermatitis--are chronic inflammatory diseases characterized by an exacerbating and remitting course and can only rarely be associated causally with allergen exposure. The challenge to ascribe an allergic basis to these diseases is derived from the apparent inability to reconcile these chronic inflammatory features with a process thought to be initiated by the rapid release of mediators after the interaction of allergen with IgE-coated mast cells. The traditional understanding has been that mast cell activation results in the release of a series of preformed and rapidly synthesized substances that mediate the immediate onset of vasodilatation, vascular leakage, smooth muscle contraction, and irritant nerve receptor stimulation. These mediators, however, are rapidly degraded and are not thought to be associated with a significant inflammatory component. Recent studies, however, have established that the interaction of allergen with the immune system is, in fact, far more complex (Fig. 4). In addition to mast cell activation, allergen can interact with and activate T-lymphocytes and mononuclear phagocytic cells, leading to the secretion of cytokines and other inflammatory substances. Furthermore, the interaction of allergen with the mast cell may be far more complex, with the potential to stimulate the delayed release of newly synthesized cytokines. The interaction of allergen with the immune system also promotes the secondary release of inflammatory neuropeptides. Thus, the known spectrum of mediators released after allergen exposure has vastly been expanded. These include numerous still uncharacterized chemotactic and activating peptides; eicosanoids such as 5-HETE, 12-HETE, and leukotriene B4; platelet-activating factor; several proteases; neuropeptides and, most importantly, the cytokines. These mediators recruit and activate neutrophils, monocytes, basophils, and eosinophils, attract additional lymphocytes and mononuclear phagocytic cells, and induce mast cell proliferation with further mast cell degranulation. A vicious cycle subsequently develops, with further inflammation and tissue destruction. Thus, the interaction of allergen with the immune system has become a complex cascade capable of producing the chronic inflammatory changes characteristic of allergic diseases.

Differential expression of secretory granule proteases in mouse mast cells exposed to interleukin 3 and c-kit ligand

It is now established that the subclasses of mast cells (MC) that reside in mucosal and serosal environments can be distinguished from one another in terms of their expression of specific secretory granule- localized proteases and proteoglycans. Further, the hematopoietic- and connective tissue-derived cytokines that regulate expression of the genes that encode these constituents of the granule can now be identified using recently developed gene-specific probes and recombinant cytokines. When bone marrow-derived MC (BMMC) were developed with recombinant interleukin 3 (rIL-3) and maintained with this cytokine in the absence or presence of recombinant c-kit ligand (rKL), they remained safranin-, produced almost no 35S-labeled heparin proteoglycans, and contained greater levels of mouse MC protease (MMCP) -5 mRNA and mast cell carboxypeptidase A (MC-CPA) mRNA than MMCP-6 mRNA. They did not contain MMCP-4 or -2 mRNA, genes expressed late in the differentiation of progenitor cells into serosal and mucosal MCs, respectively. In contrast, BMMC developed with rKL alone or by sequential culture in medium containing rIL-3 followed by rKL expressed high levels of MMCP-4 and -6 mRNA, as well as the transcripts that encode MMCP-5 and MC-CPA. Although rKL-developed BMMC were safranin+ and produced substantial amounts of 35S-labeled heparin proteoglycans, they contained only minimal amounts of histamine and MC-CPA enzymatic activity relative to serosal MC. These are the first studies to characterize the transcriptional granule phenotype of a population of BMMC derived using any recombinant cytokine, to demonstrate a dissociation between histochemical staining and granule maturation, and to demonstrate antagonistic regulation of late expressed protease genes by a cytokine.

Serosal mast cells maintain their viability and promote the metabolism of cartilage proteoglycans when cocultured with chondrocytes

OBJECTIVE

To determine the consequences of mast cell (MC)-chondrocyte interactions.

METHODS

Cocultured cells were analyzed histochemically, morphologically, biochemically, and functionally.

RESULTS

Cocultured MC adhered to the chondrocytes and remained viable. Chondrocytes cocultured with nonactivated MC produced more proteoglycans than did chondrocytes cultured alone, and these proteoglycans possessed an intact hyaluronic acid-binding region. In contrast, most of the proteoglycans produced by chondrocytes cocultured with activated MC were degraded.

CONCLUSION

These studies indicate that a complex interaction occurs in which the nonactivated MC stimulates biosynthesis and the activated MC degrades cartilage proteoglycans.

The rat c-kit ligand, stem cell factor, induces c-kit receptor-dependent mouse mast cell activation in vivo. Evidence that signaling through the c-kit receptor can induce expression of cellular function

Interactions between products of the mouse W locus, which encodes the c- kit tyrosine kinase receptor, and the Sl locus, which encodes a ligand for c-kit receptor, which we have designated stem cell factor (SCF), have a critical role in the development of mast cells. Mice homozygous for mutations at either locus exhibit several phenotypic abnormalities including a virtual absence of mast cells. Moreover, the c-kit ligand SCF can induce the proliferation and maturation of normal mast cells in vitro or in vivo, and also can result in repair of the mast cell deficiency of Sl/Sld mice in vivo. We now report that administration of SCF intradermally in vivo results in dermal mast cell activation and a mast cell-dependent acute inflammatory response. This effect is c-kit receptor dependent, in that it is not observed when SCF is administered to mice containing dermal mast cells expressing functionally inactive c- kit receptors, is observed with both glycosylated and nonglycosylated forms of SCF, and occurs at doses of SCF at least 10-fold lower on a molar basis than the minimally effective dose of the classical dermal mast cell-activating agent substance P. These findings represent the first demonstration in vivo that a c-kit ligand can result in the functional activation of any cellular lineage expressing the c-kit receptor, and suggest that interactions between the c-kit receptor and its ligand may influence mast cell biology through complex effects on proliferation, maturation, and function.

Multichain immune recognition receptors: similarities in structure and signaling pathways

Cells involved in immune recognition bear characteristic and complex multichain receptors. Here, Achsah Keegan and William Paul propose, based on familial relationships in both extracellular and intracellular domains, that they be grouped in a set, designated the multichain immune recognition receptors.

The development of functionally responsive T cells

The work reviewed in this article separates T cell development into four phases. First is an expansion phase prior to TCR rearrangement, which appears to be correlated with programming of at least some response genes for inducibility. This phase can occur to some extent outside of the thymus. However, the profound T cell deficit of nude mice indicates that the thymus is by far the most potent site for inducing the expansion per se, even if other sites can induce some response acquisition. Second is a controlled phase of TCR gene rearrangement. The details of the regulatory mechanism that selects particular loci for rearrangement are still not known. It seems that the rearrangement of the TCR gamma loci in the gamma delta lineage may not always take place at a developmental stage strictly equivalent to the rearrangement of TCR beta in the alpha beta lineage, and it is not clear just how early the two lineages diverge. In the TCR alpha beta lineage, however, the final gene rearrangement events are accompanied by rapid proliferation and an interruption in cellular response gene inducibility. The loss of conventional responsiveness is probably caused by alterations at the level of signaling, and may be a manifestation of the physiological state that is a precondition for selection. Third is the complex process of selection. Whereas peripheral T cells can undergo forms of positive selection (by antigen-driven clonal expansion) and negative selection (by abortive stimulation leading to anergy or death), neither is exactly the same phenomenon that occurs in the thymic cortex. Negative selection in the cortex appears to be a suicidal inversion of antigen responsiveness: instead of turning on IL-2 expression, the activated cell destroys its own chromatin. The genes that need to be induced for this response are not yet identified, but it is unquestionably a form of activation. It is interesting that in humans and rats, cortical thymocytes undergoing negative selection can still induce IL-2R alpha expression and even be rescued in vitro, if exogenous IL-2 is provided. Perhaps murine thymocytes are denied this form of rescue because they shut off IL-2R beta chain expression at an earlier stage or because they may be uncommonly Bcl-2 deficient (cf. Sentman et al., 1991; Strasser et al., 1991). Even so, medullary thymocytes remain at least partially susceptible to negative selection even as they continue to mature.(ABSTRACT TRUNCATED AT 400 WORDS)

The pathobiology of bronchial asthma

Early studies of patients dying from status asthmaticus revealed marked inflammation of the bronchial tree. Subsequent histological studies of the airways and examination of bronchoalveolar lavage fluid of subjects with mild asthma have confirmed the presence of airway inflammation in life. There is epithelial edema and desquamation, subepithelial deposition of collagen and fibronectin, and an inflammatory cell infiltrate in the mucosa. There are increased numbers of activated eosinophils, CD25-positive T lymphocytes, and immature macrophages with the phenotypic characteristics of blood monocytes. An increased expression of HLA class II is present on epithelium, macrophages, and other infiltrating cells. The severity of clinical asthma correlates with several measurements of the severity of the inflammatory response, suggesting a crucial role for airway inflammation in the pathophysiology of the disease. There is considerable interest and research into the mechanisms underlying the pathogenesis and maintenance of the inflammatory response in asthma. The development and maintenance of the inflammatory response in asthma is likely to be a consequence of a complicated interaction between various cells and the mediators they generate. The characterization of an ever-increasing number of cytokines is of particular interest. Interleukin-3, interleukin-5, and granulocyte-macrophage colony-stimulating factor are hematopoietic growth factors that increase the survival of eosinophils in culture and enhance certain eosinophil functions, such as mediator generation and toxicity. Alveolar macrophages derived from asthmatic subjects produce twofold to threefold more GM-CSF than do those from normal control subjects. Using in situ hybridization, the presence of IL-5 mRNA has been demonstrated in bronchial biopsies from asthmatic subjects. Thus IL-3, IL-5, and GM-CSF influence eosinophil function and survival, and may be generated by T lymphocytes and/or alveolar macrophages within the airways in asthma. In addition to these three cytokines, IL-4 and interferon-gamma may be crucial to the regulation of IgE biosynthesis. TNF-alpha and IL-1 are potentially important in the up-regulation of endothelial adhesion molecules. An important step in the recruitment of leukocytes to an inflammatory focus is margination to the vascular endothelium. Our understanding of the molecular events involved in migration of leukocytes to an inflammatory focus has been advanced by the discovery and characterization of a variety of cell adhesion molecules. The potential role of ELAM-1 and ICAM-1 in allergic inflammation is suggested by their up-regulation on vascular endothelium in association with late cutaneous responses to allergen and by their role in certain primate models of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokine production by mast cells and basophils

Mast cells and/or basophils have been implicated in the expression of a wide variety of biological responses, including immediate hypersensitivity reactions, host responses to parasites and neoplasms, angiogenesis, tissue remodeling, and immunologically non-specific inflammatory and fibrotic conditions. Recent findings suggest that an important mechanism by which mast cells influence such biological responses is through the production of a broad panel of multifunctional cytokines. In contrast, the extent to which basophils can produce cytokines is uncertain.

Fc epsilon receptors

Advances in our understanding of the molecular structure of Fc receptors have been made at a rapid pace. Details of how Fc receptors are involved in cell triggering, e.g. allergic mediator release from mast cells, and IgE synthesis are also continuing to be elucidated, although much work is still required. Recent highlights of investigations of mast-cell and lymphocyte IgE Fc receptors will be outlined.

Immediate and late airway response of allergic rhinitis patients to segmental antigen challenge. Characterization of eosinophil and mast cell mediators

Segmental antigen bronchoprovocation was used to define the nature of the inflammatory process in allergic airway disease. Bronchoalveolar lavage fluid obtained from allergic rhinitis patients 12 min after segmental antigen instillation (immediate response) revealed a significant increase in histamine and tryptase, but no cellular response. Repeat segmental lavage 48 h later (late response) showed marked and significant increases in both low and normal density eosinophils as well as striking elevations of eosinophil granular protein levels (major basic protein, eosinophil-derived neurotoxin, eosinophil cationic protein, and eosinophil peroxidase). Leukotriene C4, but not tryptase, concentrations were also consistently elevated in late lavage samples. Further, the late lavage samples showed a significant increase in interleukin-5 concentrations that correlated with the presence of eosinophils and eosinophil granular proteins. Neither eosinophils nor soluble mediators of eosinophils increased when normal subjects were similarly challenged with antigen. These data suggest that eosinophils are attracted to the airway during the late-phase allergic reaction and that IL-5 may produce changes in airway eosinophil density and promote the release of granular proteins to cause airway injury.

Histamine-releasing factors and inhibitors: historical perspectives and possible implications in human illness

The initiation of allergic reactions with the bridging of surface-bound IgE antibodies on mast cells and basophils by allergens is well recognized. However, it is clear that other factors most likely play a role in regulating these cells. A number of cytokines have been identified that modulate the secretory response of mast cells and basophils. Among the well-characterized cytokines, interleukin-3 and connective tissue-activating peptide III (or its degradation product, neutrophil-activating peptide 2) can increase the secretory response, whereas interleukin-8 specifically inhibits the response to cytokines. Additional factors are currently under investigation. Preliminary studies suggest an important role for these histamine-releasing factors in atopic disorders, as well as in other conditions in which an IgE-dependent mechanism is not demonstrable. Furthermore, these cytokines may modulate the response of basophils and mast cells in physiologic conditions, such as tissue repair and host defense.

The inhibitory effect of nebulized albuterol on the early and late asthmatic reactions and increase in airway responsiveness provoked by inhaled allergen in asthma

It is widely held that inhaled beta 2-adrenoceptor agonists inhibit the early asthmatic response (EAR) but not the late response (LAR) or attendant increase in bronchial responsiveness. In this study of 10 atopic asthmatic subjects, we have investigated the effects of a high dose of nebulized albuterol (2.5 mg) on the allergen-provoked EAR, LAR, and increase in histamine responsiveness. In a randomized blinded fashion, study subjects inhaled the following combinations: albuterol followed 10 min later by allergen, placebo followed by allergen, albuterol followed by saline (albuterol, placebo, and control study periods, respectively). Airway caliber was measured as FEV1 and followed at regular intervals for 7.5 h postallergen. Bronchial responsiveness to histamine was measured and recorded as the PC20 value before and at 1.5, 3.5, 5.5, and 7.5 h after allergen or control challenge. During the placebo study period, allergen challenge caused mean 29.6 +/- 6.4 and 24.4 +/- 6.4% falls in FEV1 at 20 min and 7.5 h, respectively (both p less than 0.05), and a progressive decrease in PC20 amounting to a geometric mean of 1.9 doubling dilutions at 7.5 h (p less than 0.05). Albuterol followed by allergen resulted in a 13.1 +/- 2.2% increase in FEV1 prior to allergen followed by abolition of the EAR and inhibition of the LAR with only a 9.2 +/- 3.5% fall in FEV1 at 7.5 h, significantly different from that of placebo at 7.5 h (p = 0.048). Similarly, PC20 histamine fell by only 0.64 doubling dilutions at 7.5 h, not significantly different from baseline values but different from placebo values (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-gamma inhibits serotonin release from mouse peritoneal mast cells

Conditioned medium (CM) from concanavalin A-activated mouse spleen cells inhibits antigen-induced 5-hydroxytryptamine (5-HT) release from mouse peritoneal mast cells when added for 24 or 48 h to cell cultures containing monoclonal IgE sensitizing antibody. We present the following evidence that the spleen cell-derived inhibitory factor is interferon-gamma (IFN-gamma): (a) CM from Con A-activated spleen cells and from Chinese hamster ovary (CHO) cells transfected with the murine (Mu)IFN-gamma gene both produced a graded inhibition of 5-HT release when added to peritoneal cell cultures containing IgE and subsequently challenged with antigen; (b) the relative inhibitory potency of the two preparations corresponded to their relative IFN content as determined by antiviral bioassay; (c) the inhibitory activity of spleen cell CM and of CM from IFN-gamma gene-transfected CHO cells was abolished by treatment with a rat monoclonal MuIFN-gamma-neutralizing antibody, i.e. 5-HT release returned to control levels, and (d) a highly immunopurified preparation of recombinant MuIFN-gamma retained the inhibitory activity, and was active at concentrations as low as 2 U/ml. The inhibitory activity of IFN-gamma appeared to be a direct effect of the cytokine on mast cells, since CM generated for different time periods from unfractionated peritoneal cells treated with purified recombinant MuIFN-gamma contained no inhibitory activity other than IFN-gamma itself, as demonstrated by neutralization of the cytokine with monoclonal antibody. Furthermore, purified recombinant MuIFN-gamma was equally active on mast cells enriched by density centrifugation up to 95% purity as on unfractionated peritoneal cells (1%-2% mast cells). Purified recombinant MuIFN-gamma inhibited 5-HT release induced by a range of different cell activators, namely antigen, anti-IgE, compound 48/80 and calcium ionophore A23187. Hence inhibition is not specific to IgE-dependent activation of mast cells, but seems to be directed more generally at the secretory process of these cells.

Human bone marrow non-B, non-T cells produce interleukin 4 in response to cross-linkage of Fc epsilon and Fc gamma receptors

Human bone marrow (BM) cells lacking T- and B-cell markers expressed RNA encoding interleukin (IL) 4 and secreted detectable amounts of IL-4 in supernatants in response to Fc epsilon or Fc gamma receptor (Fc epsilon R or Fc gamma R) cross-linking. In some experiments, IL-5 RNA expression in response to Fc epsilon R cross-linkage could also be detected. In contrast, RNA transcripts for, and secretion of, IL-2, IL-6, and interferon gamma were never observed. The presence of IL-3 in the cultures was essential for IL-4 production by non-B, non-T BM cells in response to Fc gamma R cross-linking and enhanced IL-4 RNA expression in response to Fc epsilon R cross-linking. Under the same experimental conditions, BM T and B lymphocytes, as well as peripheral blood T, B, and non-B, non-T cells, did not express IL-4 RNA. Prolonged incubation of non-B, non-T cells in IgE-free medium followed by extensive washing did not inhibit IL-4 production induced by anti-IgE antibodies, suggesting that the Fc epsilon R involved in the response has the characteristics of a high-affinity receptor. The Fc epsilon R+ cells were separated from the Fc epsilon R- cells by sorting non-B, non-T BM cell suspensions with fluorescein isothiocyanate-conjugated IgE and then assessed for both IL-4 RNA expression and alcian blue staining. Both IL-4-producing and alcian blue-positive cells segregated with the Fc epsilon R+ fraction. These data suggest that human BM cells, probably belonging to the mast cell and/or basophil lineage, are capable of producing IL-4 in response to Fc epsilon R or Fc gamma R cross-linkage.

Augmentation of reverse arthus reaction by mast cells in mice

Immune complex-induced injury is an important pathogenic factor in antibody-mediated nephritis, systemic lupus erythematosus, rheumatoid arthritis, and other diseases. In this study we investigated the role mast cells in immune complex-mediated injury in mouse skin. Reverse Arthus reaction was induced in mast cell-deficient WBB6F1-W/Wv mice and their congenic controls (WBB6F1(-)+/+). Serial skin sections were evaluated for neutrophil infiltration, edema, and hemorrhage. In WBB6F1-W/Wv mice the neutrophil influx was only 40% and edema 60% of that in congenic controls. Hemorrhage was also significantly reduced in the mast cell-deficient mice. After mast cell reconstitution, the magnitude of the reaction in WBB6F1-W/Wv was equivalent to that in WBB6F1(-)+/+ mice. Mast cell release in reverse Arthus reaction was evaluated by measuring fluorescence intensity after avidin-FITC staining of mast cell granules. There was a 70% decrease in fluorescence intensity. The 5-lipoxygenase inhibitor A-63162 significantly decreased neutrophil accumulation (40%), edema (60%), and hemorrhage in WBB6F1(-)+/+, but not in mast cell-deficient mice. Mast cell reconstitution of WBB6F1-W/Wv mice restored the effect of A-63162. The results indicate that mast cells and their mediators, including leukotrienes, make an important contribution to reverse Arthus reaction.

Immunophilin ligands demonstrate common features of signal transduction leading to exocytosis or transcription

Investigations of the actions and interactions of the immunophilin ligands FK506, cyclosporin A (CsA), rapamycin, and 506BD suggest that complexes of FK506 with an FK506-binding protein or of CsA with a cyclophilin (CsA-binding protein) inhibit the T-cell receptor-mediated signal transduction that results in the transcription of interleukin 2. Now we report an identical spectrum of activities of FK506, CsA, rapamycin, and 506BD on IgE receptor-mediated signal transduction that results in exocytosis of secretory granules from the rat basophilic leukemia cell line RBL-2H3, a mast cell model. Both FK506 and CsA inhibit receptor-mediated exocytosis (CsA IC50 = 200 nM; FK506 IC50 = 2 nM) without affecting early receptor-associated events (hydrolysis of phosphatidylinositol, synthesis and release of eicosanoids, uptake of Ca2+). In contrast, rapamycin and 506BD, which share common structural elements with FK506, by themselves have no effect on IgE receptor-mediated exocytosis. Both compounds, however, prevent inhibition by FK506 but not by CsA. Affinity chromatography with FK506, CsA, and rapamycin matrices indicates that the same set of immunophilins present in RBL-2H3 cells have been found in Jurkat T cells and calf thymus; however, the relative amounts of these proteins differ in the two cell types. These results suggest the existence of a common step in cytoplasmic signaling in T cells and mast cells that may be part of a general signaling mechanism.

Induction of mast cell proliferation, maturation, and heparin synthesis by the rat c-kit ligand, stem cell factor

We investigated the effects of a newly recognized multifunctional growth factor, the c-kit ligand stem cell factor (SCF), on mouse mast cell proliferation and phenotype. Recombinant rat SCF164 (rrSCF164) induced the development of large numbers of dermal mast cells in normal mice in vivo. Many of these mast cells had features of "connective tissue-type mast cells" (CTMC), in that they were reactive both with the heparin-binding fluorescent dye berberine sulfate and with safranin. In vitro, rrSCF164 induced the proliferation of cloned interleukin 3 (IL-3)-dependent mouse mast cells and primary populations of IL-3-dependent, bone marrow-derived cultured mast cells (BMCMC), which represent immature mast cells, and purified peritoneal mast cells, which represent a type of mature CTMC. BMCMC maintained in rrSCF164 not only proliferated but also matured. Prior to exposure to rrSCF164, the BMCMC were alcian blue positive, safranin negative, and berberine sulfate negative; had a histamine content of 0.08 +/- 0.02 pg per cell; and incorporated [35S]sulfate into chondroitin sulfates. After 4 wk in rrSCF164, the BMCMC were predominantly safranin positive and berberine sulfate positive, had a histamine content of 2.23 +/- 0.39 pg per cell, and synthesized 35S-labeled proteoglycans that included substantial amounts (41-70%) of [35S]heparin. These findings identify SCF as a single cytokine that can induce immature, IL-3-dependent mast cells to mature and to acquire multiple characteristics of CTMC. These findings also directly demonstrate that SCF can regulate the development of a cellular lineage expressing c-kit through effects on both proliferation and maturation.

Mast cells and their role in urticaria

Mast cells are the primary effector cell type in urticaria and angioedema. Recognition of different types of mast cells has increased the understanding of their cell biology and may help refine the therapy of human allergic diseases. Mast cells containing chymase and tryptase (MCTC) and tryptase alone (MCT) are two distinct types distinguished on the basis of the neutral protease composition of their granules. MCT cells are distributed primarily in the lung and gastrointestinal mucosa, whereas MCTC cells lie primarily in skin and gastrointestinal submucosa. The appearance of MCT cells in intestinal tissue is T-lymphocyte dependent, whereas MCTC cells is not. The granules in unstimulated mature MCT cells typically contain complete scrolls, whereas those of MCTC cells often contain grating or lattice substructures. Major categories for the mediators of mast cells include performed mediators present in the secretory granule, newly generated lipid-derived mediators, and cytokines.

The role of eosinophils in the pathophysiology of asthma

From current information, a number of conclusions can be drawn. Antigen activation of the allergic reaction in the airways is associated with an immediate rise in mast cell derived mediators, including histamine and tryptase. Associated with antigen activation of the allergic reaction is recruitment of eosinophils to the airways. This can best be seen in the airway lavage 48 hours after challenge with antigen. An increased presence of eosinophils suggests that they are an important contributor to the late allergic reaction and may be one of the major constituents in the development of bronchial inflammation. Although many factors participate in the late allergic inflammatory response, eosinophil-derived proteins are known to cause airway injury. Regulation of eosinophils in this process is not clearly established; however, our findings of increased IL-5 in relationship to the presence of eosinophils and their granular proteins suggests that this cytokine may be an important modulator of eosinophil function and activation following allergen challenge. However, much remains unknown in understanding bronchial inflammation and the eosinophil's role in the process. In conclusion, the eosinophil is a major cellular participant in late phase allergic airway disease. Its presence and known functions suggest that the eosinophil is a significant cellular factor in the development of allergic airways disease in asthma. Further advances in this area will follow continued studies, particularly those which involve biopsy and correlation with airway physiology.

Release of both preformed and newly synthesized tumor necrosis factor alpha (TNF-alpha)/cachectin by mouse mast cells stimulated via the Fc epsilon RI. A mechanism for the sustained action of mast cell-derived TNF-alpha during IgE-dependent biological responses

Mast cell-associated mediators are generally classified into two groups: the preformed mediators, which are stored in the cells' cytoplasmic granules and are released upon exocytosis, and the newly synthesized mediators, which are not stored but are produced and secreted only after appropriate stimulation of the cell. We now report that tumor necrosis factor alpha (TNF-alpha)/cachectin represents a new type of mast cell-associated mediator, in that IgE-dependent mast cell activation results in the rapid release of preformed stores of the cytokine followed by the synthesis and sustained release of large quantities of newly formed TNF-alpha. We also demonstrate that challenge with specific antigen induces higher levels of TNF-alpha mRNA at skin sites sensitized with IgE in normal mice or mast cell-reconstituted genetically mast cell-deficient WBB6F1-W/W1' mice than at identically treated sites in WBB6F1-W/W1' mice that are devoid of mast cells. These findings identify mast cells as a biologically significant source of TNF-alpha/cachectin during IgE-dependent responses and define a mechanism whereby stimulation of mast cells via the FC epsilon RI can account for both the rapid and sustained release of this cytokine.

Expression of endothelial-leukocyte adhesion molecule-1 in elicited late phase allergic reactions

To better understand the events involved in the local migration of inflammatory cells into sites of allergic reactions, we studied expression of the cytokine inducible endothelial cell (EC) neutrophil adhesion molecule, endothelial-leukocyte adhesion molecule (ELAM-1), in sequential skin biopsies from patients with respiratory allergy during the late phase reaction (LPR) between 20 min and until 24 h after intradermal allergen (ragweed or dust mites) injection. In 7 of 7 atopic patients but in only 1 of 4 apparently normal controls, allergen induced appearance of ELAM-1 on EC. ELAM-1 expression occurred concurrently with the development of inflammatory cell infiltrates by 3-4 h after intradermal injection. Saline injected sites in all subjects were negative. Skin organ cultures demonstrated that allergen could produce the same EC changes in vitro whether allergen was injected in vivo 20 min before culture or added during skin culture. These EC changes in organ culture were inhibited by the presence of combined anti-sera to both TNF-alpha and IL-1, but not by antisera to either cytokine alone. We conclude that EC activation occurs in elicited LPR and suggest that cytokine-induced EC activation may play a role in the migration of inflammatory cells into allergic skin reactions. Furthermore, resident cells in the skin rather than infiltrating leukocytes appear to be the source of the cytokines that mediate endothelial activation.

Mouse splenic and bone marrow cell populations that express high-affinity Fc epsilon receptors and produce interleukin 4 are highly enriched in basophils

Splenic and bone marrow cells from normal mice, and from mice that have been polyclonally activated by injection of anti-IgD antibody, contain cells that produce interleukin 4 (IL-4) in response to crosslinkage of Fc epsilon receptors (Fc epsilon R) or Fc gamma R or to ionomycin. Isolated Fc epsilon R+ cells have recently been shown to contain all of the IL-4-producing capacity of the nonlymphoid compartment of spleen and bone marrow. Here, purified Fc epsilon R+ cells are shown to be enriched in cells that contain histamine and express alcian blue-positive cytoplasmic granules. By electron microscopy, the vast majority of cytoplasmic granule-containing cells are basophils; they constitute approximately 25% and approximately 50%, respectively, of Fc epsilon R+ spleen and bone marrow cells from anti-IgD-injected mice. The Fc epsilon R- populations contain cells that form colonies typical of mast cells. The Fc epsilon R+ populations also contain cells that, upon culture with IL-3, form colonies of alcian blue-positive cells, but (in contrast to colonies derived from Fc epsilon R- populations) the colonies are small, and all the cells die within 2-3 weeks. The Fc epsilon R+ cells synthesize histamine during a 60-hr culture with IL-3, while the Fc epsilon R- cells do not. These results indicate that IL-4-producing Fc epsilon R+ cells are highly enriched in basophils.

T cell receptor-independent CD2 signal transduction in FcR+ cells

CD2 subserves both adhesion and signal transduction functions in T cells, thymocytes, and natural killer (NK) cells. In mature T lymphocytes, CD2-mediated signaling function apparently requires surface expression of T cell receptors (TCRs). In contrast, in CD2+ CD3- NK cells and thymocytes, signal transduction through CD2 is TCR independent. To resolve this paradox and characterize TCR-independent triggering mechanisms, we transfected a human CD2 cDNA into a murine mast cell line, C1.MC/57 (Fc epsilon RI+, Fc gamma RII+, Fc gamma RIII+), which is known to produce interleukin 6 (IL-6) as well as release histamine in response to crosslinking of Fc epsilon RI. In the CD2 transfectant, a combination of anti-T11(2) + anti-T11(3) monoclonal antibodies (mAbs) induced a rise in intracellular free calcium [( Ca2+]i), IL-6 production, and histamine release. As expected, no activation was mediated by the same mAbs in C1.MC/57. F(ab)'s fragments of the activatory combination of anti-T11(2) + anti-T11(3) mAbs induced IL-6 in the CD2-transfected mast cells, demonstrating an Fc gamma receptor ectodomain-independent triggering mechanism. In addition, either intact anti-T11(2) or anti-T11(3) IgG alone, which failed to induce [Ca2+]i mobilization in the transfectant, was able to induce IL-6 production. A mAb directed against both Fc gamma RII (previously denoted as Fc gamma RIIb) and Fc gamma RIII (previously denoted as Fc gamma RIIa) inhibits this induction. These results indicate that: (a) Ca2+ mobilization is not essential for IL-6 production; and (b) crosslinking of CD2 and Fc gamma receptors via intact anti-CD2 IgG stimulates IL-6 production. Thus, CD2-mediated IL-6 production occurs by both Fc receptor ectodomain-independent as well as Fc receptor ectodomain-dependent mechanisms in these nonlymphoid cells. Northern blot analysis demonstrates that although the mast cells do not express CD3 zeta or CD3 eta mRNA, they express Fc epsilon RI gamma mRNA. The latter is a known component of Fc gamma RIII as well as Fc epsilon RI, has significant homology to CD3 zeta/eta, and is thought to have a signal transduction function. In these mast cells, CD2 signaling machinery does not require CD3 zeta/eta and may be linked to the Fc epsilon RI gamma subunit. We predict that this subunit or a related structure may confer a TCR-independent signal transduction pathway upon CD2 in CD3- NK cells, thymocytes, and certain B lymphocytes.

Systemic Mastocytosis: Retrospective Review of a Decade's Clinical Experience at the Brigham and Women's Hospital

The clinical experience with a group of 21 patients with systemic mastocytosis followed at our institution is summarized. Cutaneous and gastrointestinal symptoms and findings were the most prominent chronic manifestations; episodic vascular collapse was the most dramatic acute event. All patients had indolent mastocytosis. There was no mortality.

Regulation and biological function of helminth-induced cytokine responses

The immunological hallmarks of infection with parasitic helminths, namely eosinophilia, mastocytosis and increased IgE synthesis, all appear to be induced by cytokines from the TH2 subset of CD4+ T cells: IgE production is stimulated by interleukin 4 (IL-4), eosinophilia by IL-5 and mastocytosis by IL-3 and IL-4. Here, Fred Finkelman and colleagues argue that the functional significance of the eosinophilia-mastocytosis-IgE axis in helminth infection is unclear and suggest that in some worm infections TH2-cell cytokines may contribute to host protection, while in others they may promote parasite survival.

Differential induction of cytokine-specific mRNA in human PBL after in vitro culture with either IL2 or IL4

The present study was designed to investigate whether human equivalents of murine T helper cell subsets can be demonstrated by propagation of peripheral blood lymphocytes (PBL) with either recombinant human (rh) interleukin (IL) 2 or rhIL4 in the presence of neutralising antibodies. Cells of both cultures, termed T-IL2 or T-IL4, respectively, were challenged on day 8 using a combination of phorbol-12-myristate-13-acetate (PMA) and the Ca2(+)-ionophore A23187 (Io). Total cellular RNA was isolated at different time points after PMA/Io-stimulation and the expression of 7 distinct cytokine genes was assessed by Northern analysis. Whereas maximal accumulation of mRNA species for IL2, GM-CSF, TNF alpha and TNF beta did not reveal major differences between cells of T-IL2 and T-IL4 cultures, substantial differences emerged for the induction of IFN gamma and IL3 messages. Accumulation of IFN gamma-mRNA consistently was 2- to 13-fold higher in T-IL2 than in T-IL4 cells, depending on the time point of RNA harvest. In contrast, IL3-specific mRNA levels induced in T-IL4 cells were 2-5 times greater than those in T-IL2. If PBL cultured with IL2 for 7-8 days were subsequently shifted to IL4 and further propagated until day 14, the mRNA induction pattern seen for IFN gamma and IL3 was similar to that obtained if cells had continuously been propagated with IL2. Collectively, these results indicate a selective outgrowth of distinct responder phenotypes by IL2 or IL4 rather than a direct modulation of cytokine expression by these factors.

Murine mast cells synthesize basement membrane components. A potential role in early fibrosis

Mast cells are resident in tissues, particularly in association with endothelial and epithelial cell basement membranes, and increase at sites of inflammation, injury, and fibrosis. Although mast cells are known to both release and generate proinflammatory molecules in response to inflammatory stimuli, little is known about their normal biologic function. Here we demonstrate that IL-3-dependent mouse PT18 mast cells, mouse bone marrow-derived mast cells, and rat basophilic leukemia cells express large amounts of mRNA for collagen IV, laminin, and heparan sulfate proteoglycan. Western blot analysis confirmed that mast cells synthesize and secrete significant amounts collagen IV and laminin B1 and B2 chains. These data suggest that mast cells may contribute to normal tissue repair and/or the early overproduction of basement membrane components seen in a variety of fibrotic conditions.

Recruitment of neutrophils during IgE-dependent cutaneous late phase reactions in the mouse is mast cell-dependent. Partial inhibition of the reaction with antiserum against tumor necrosis factor-alpha

Much of the clinically important pathology associated with IgE-dependent disorders is thought to reflect the actions of the blood-borne leukocytes recruited during these responses. To evaluate the extent to which mast cells are responsible for the leukocyte infiltration associated with IgE-dependent cutaneous reactions, we attempted to elicit these responses in normal mice, genetically mast cell-deficient W/Wv mice, and in W/Wv mice selectively repaired of their mast cell deficiency by the intradermal injection of cultured mast cells derived from the congenic normal (+/+) mice. We found that the tissue swelling associated with IgE-dependent passive cutaneous anaphylaxis reactions developed rapidly and diminished markedly from 2 to 4 h after antigen challenge, but remained detectable for at least 24 h after elicitation of the responses. Infiltration of leukocytes (predominantly neutrophils) also occurred at these sites, but reached maximal levels 6-12 h after antigen challenge, persisted at high levels for 24 h, and largely waned by 48 h. Virtually all of the tissue swelling and leukocyte infiltration associated with IgE-dependent cutaneous reactions was mast cell dependent. Intradermal injection of 40 U of recombinant murine TNF-alpha (rmTNF-alpha) elicited neutrophil infiltration similar in magnitude and kinetics to that observed after IgE-dependent mast cell degranulation. A rabbit anti-rmTNF-alpha (R anti-rmTNF-alpha) antiserum, which was able to inhibit 84% of the neutrophil infiltration observed after i.d. injection of rmTNF-alpha, inhibited IgE-, and mast cell-dependent leukocyte infiltration by 47 +/- 7% in three separate experiments. These findings indicate that TNF-alpha contributes to mast cell-dependent recruitment of leukocytes during IgE-dependent cutaneous late phase reactions, but suggest that other mast cell-associated mediators probably also contribute to this response.

The growth and differentiation of mast cells

Mast cells (MCs) are local immune cells involved in host defense mechanisms and allergic response. They usually develop from MC committed progenitor cells which in turn are derived from uncommitted hemopoietic stem cells. MC precursors are supposed to develop in the bone marrow (bm) cavities as well as in extramedullary tissues. MC precursor cells also have the potential to circulate in the blood stream. After homing in the tissues they give rise to mature MCs. Recruitment and differentiation as well as terminal maturation of MCs is regulated by a complex network of factors. Two major arms of control have been delineated based on in vitro studies and experimental animal models. The first involves the response of the progenitor cells to growth inducing cytokines, such as IL-3. This type of control promotes the generation of MC precursor cells. The second arm of control involves the microenvironmental network interacting with the MC progenitors. It consists of both stroma cell- and immune cell-derived differentiation factors and the direct interaction of cells. It may be important for homing of MC progenitors during embryogenesis and probably throughout life. The stromal component also determines terminal differentiation towards a particular type of MCs and also supports in vitro development of MCs in long term cultures. Growth and function of the mature MCs in the various tissues may be triggered by additional factors including the interactions of MCs with other leukocytes and nerve cells. The coupling of MC activation processes with subsequent proliferation may be a triggering factor in allergic disease. This article attempts to provide a synthesis of current knowledge on MC development.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal IgGs from an autoimmune MRL/Mp-lpr/lpr mouse induce an interleukin-3-dependent myeloid cell line to produce tumor necrosis factor alpha and interleukin-6

We previously reported that two IgG mAbs, 1D11 and 1G10, derived from an autoimmune MRL/Mp-lpr/lpr(MRL/l) mouse, induced IL-3 synthesis in the IL-3-dependent myeloid cell line, FDC-P2/185-4. In this study, we found that these mAbs induced TNF-alpha and IL-6 production in FDC-P2/185-4 cells. Both TNF-alpha and IL-6 were secreted rapidly within 1 hr after the addition of mAb to the cells. Increases of TNF-alpha and IL-6 mRNA were also observed in FDC-P2/185-4 cells stimulated with MRL/l-derived mAb. The anti-Fc gamma RII mAb 2.4G2 suppressed TNF-alpha and IL-6 production induced by these mAbs. Our results suggest that some IgGs of MRL/l mice may have the capacity to induce cytokine synthesis in Fc gamma R-bearing cells.