Allogeneic Hematopoietic Cell Transplantation in Advanced Systemic Mastocytosis: A retrospective analysis of the DRST and GREM registries

We identified 71 patients with AdvSM (aggressive SM [ASM], SM with an associated hematologic neoplasm [SM-AHN, e.g., acute myeloid leukemia, SM-AML], mast cell leukemia [MCL]) in two national registries (DRST/GREM) who received an allogeneic hematopoietic cell transplantation (alloHCT) performed in Germany from 1999-2021. Median overall survival (OS) of ASM/SM-AHN (n = 30, 45%), SM-AML (n = 28, 39%) and MCL ± AHN (n = 13, 19%) was 9.0, 3.3 and 0.9 years (P = 0.007). Improved median OS was associated with response of SM (17/41, 41%; HR 0.4 [0.2-0.9], P = 0.035) and/or of AHN (26/43, 60%, HR 0.3 [0.1-0.7], P = 0.004) prior to alloHCT. Adverse predictors for OS included absence of KIT D816V (10/61, 16%, HR 2.9 [1.2-6.5], P < 0.001) and a complex karyotype (9/60, 15%, HR 4.2 [1.8-10.0], P = 0.016). HLA-match, conditioning type or transplantation at centers reporting above-average alloHCTs (≥7) had no impact on OS. Taking into account competing events at years 1, 3 and 5, relapse-related mortality and non-relapse mortality rate were 15%/23%, 20%/30% and 23%/35%, respectively. Irrespective of subtype, subsequent treatment response was achieved in 13/30 (43%) patients and was highest on midostaurin/avapritinib (7/9, 78%). We conclude that outcome of alloHCT in AdvSM is more affected by disease phenotype and treatment response prior to transplant than by transplant characteristics.

Reappraisal of mast cell leukemia based on a single institution review of 16 cases: Mast cell morphology determines clinical outcome

Cytologic abnormalities of atypical mast cells in mastocytosis. The mature mast cells have oval-shaped nuclei, cytoplasmic hypogranulation and spindle-shaped cytology. or well-differentiated displaying a round nucleus with condensed chromatin, and abundant dense cytoplasmic granulations. Immature mast cells include promastocytes and metachromatic blast-like forms.

Granularity in disease classification impacts survival prediction in advanced systemic mastocytosis: A single institution study of 329 informative cases

The World Health Organization (WHO) classification system categorizes advanced systemic mastocytosis (SM-Adv) into aggressive SM (ASM), mast cell leukemia (MCL), and SM with associated hematological neoplasm (SM-AHN). By contrast, the International Consensus Classification (ICC) requires "immature" MC cytomorphology for the diagnosis of MCL and limits SM-AHN to myeloid neoplasms (SM-AMN). The current study includes 329 patients with SM-Adv (median age 65 years, range 18-88; males 58%): WHO subcategories SM-AHN (N = 212; 64%), ASM (N = 99; 30%), and MCL (N = 18; 6%); ICC subcategories SM-AMN (N = 190; 64%), ASM (N = 99; 33%), and MCL (N = 9; 3%); WHO-defined MCL with "mature" MC cytomorphology and SM-AHN associated with lymphoid neoplasms were operationally labeled as "MCL-mature" (N = 9) and SM-ALN (N = 22), respectively, and distinguished from ICC-defined MCL and SM-AMN. Multivariable analysis that included the Mayo alliance risk factors for survival in SM (age >60 years, anemia, thrombocytopenia, increased alkaline phosphatase) revealed more accurate survival prediction with the ICC versus WHO classification order: (i) survival was significantly worse with MCL-immature versus MCL-mature (hazard ratio [HR] 15; p < .01), (ii) prognostic distinction between MCL and SM-AHN/AMN was confirmed in the context of ICC (HR 9.3; p < .01) but not WHO classification order (p = .99), (iii) survival was similar between MCL-mature and SM-AMN (p = .18), and (iv) SM-AMN (HR 1.7; p < .01) but not SM-ALN (p = .37) was prognostically distinct from ASM. The current study provides evidence for the independent prognostic contribution of both the ICC system for SM-Adv and the Mayo alliance risk factors for survival in SM.

Recent advances in the understanding and therapeutic management of mastocytosis

Mastocytosis is a rare disease due to the abnormal accumulation of mast cells in various tissues. Its clinical presentation is heterogeneous depending on mast cell infiltration and mediators release. In some cases, it is associated with hematological malignancies. Prognosis varies from very good with a life expectancy similar to the general population in indolent forms of the disease to a survival time of just a few months in mast cell leukemia. Although in most cases a somatic KIT D816V mutation is found in tumor mast cells, the physiopathology of the disease is not yet fully understood. Additional germline and somatic mutations may explain this heterogeneity. Treatments aim at blocking effect of mast cell mediators, reducing mast cell activation and tumor burden. New drugs mainly directed against the tyrosine kinase activity of KIT have dramatically changed the quality of life and prognosis of mast cell diseases. Present and future therapeutic strategies are discussed in this review.

Effects of the Schisandra fructus water extract on cytokine release from a human mast cell line

Schisandra fructus has been used for treatment of cough and thirst in Korea. However, its therapeutic mechanisms remain largely unclear. To investigate the biological effect of Schisandra fructus water extract (SFWE), we examined the effect of SFWE on the phorbol 12-myristate 13-acetate (PMA) and calcium ionophore A23187-induced pro-inflammatory cytokine secretion in the human mast cell line HMC-1. HMC-1 cells were stimulated with PMA plus A23187 in the presence or absence of SFWE. Tumor necrosis factor (TNF)-alpha, interleukin 6 (IL-6), and granulocyte-macrophage colony-stimulating factor (GM-CSF) productions were measured by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction. Inhibitory IkappaB/nuclear factor-kappaB (NF-kappaB) expression was assessed by western blot. SFWE suppressed PMA plus A23187-induced TNF-alpha, IL-6, and GM-CSF production in dose-dependent manners. Furthermore, SFWE inhibited IkappaB degradation and NF-kappaB nuclear translocation. These results suggest that SFWE inhibits the secretion of pro-inflammatory cytokines in HMC-1 cells through blockade of IkappaB degradation and NF-kappaB activation. Taken together, these findings may help elucidate the mechanism of action of this medicine in the modulation of mast cell activation in inflammatory conditions.

Repressible transgenic model of NRAS oncogene–driven mast cell disease in the mouse

To create a model in which to study the effects of RAS dysregulation in hematopoietic disease, we developed separate founder lines of transgenic mice, with the tetracycline transactivator (tTA) driven by the Vav hematopoietic promoter in one line and NRASV12 driven by the tetracycline responsive element (TRE2) in the other. When these lines are crossed, doubly transgenic animals uniformly develop a disease similar to human aggressive systemic mastocytosis (ASM) or mast cell leukemia (MCL) when they are between 2 and 4 months of age. Disease is characterized by tissue infiltrates of large, well-differentiated mast cells in the spleen, liver, skin, lung, and thymus. Analysis of bone sections shows small to large foci of similarly well-differentiated mast cells. Results also show that transgene expression and diseases are repressible through the administration of doxycycline in the drinking water of affected animals, indicating that NRASV12 expression is required to initiate and maintain disease in doubly transgenic mice. Our inducible system of transgenes, developed as a model of mutant NRASV12 oncogene–driven myeloid disease, will be useful for studying the role of RAS dysregulation in hematopoietic disease in general and in discrete human diseases, specifically ASM and MCL.

Response to therapy with interferon alpha-2b and prednisolone in aggressive systemic mastocytosis: report of five cases and review of the literature

Aggressive systemic mastocytosis (ASM) is a hematopoietic neoplasm characterized by infiltration of visceral organs by neoplastic mast cells (MCs) with consecutive organopathy and respective clinical and laboratory findings (so called C-Findings). Whereas, it is generally appreciated that patients with ASM are candidates for pharmacological intervention, no ideal drug or drug combination have been identified yet. One drug proposed to work in ASM is interferon alpha-2b (IFN-alpha2b). However, little is known so far about the quality of responses to IFN-alpha2b and actual response rates. We here report on five ASM patients treated with either a combination of IFN-alpha2b (3x3 million units per week) and prednisolone (n=4), or IFN-alpha2b alone (n=1). During therapy, two of the five patients showed a major response defined by complete resolution of C-Finding(s), one a partial response (partial regression of C-Findings), and one a stable disease (no changes in C-Findings). In one patient, progression to mast cell leukemia was seen after 3 months. In contrast to the other patients, this patient exhibited >10% MCs in his bone marrow (bm) smear at first presentation. In summary, our data confirm beneficial effects of IFN-alpha2b (plus prednisolone) for a group of patients with ASM, whereas patients with mast cell leukemia may require more aggressive therapy. Prospective trials with more patients are now required to further document these drug effects and to better define subgroups of patients with ASM who show good and long-lasting responses to IFN-alpha2b.

Flavones inhibit proliferation and increase mediator content in human leukemic mast cells (HMC-1)

OBJECTIVE

Mast cells are involved in allergic and inflammatory reactions. These cells are also increased in the bone marrow, skin, and other organs in systemic mastocytosis. Flavonoids are naturally occurring molecules with antioxidant, cytoprotective, and anti-inflammatory activities. Some flavonoids, like quercetin, inhibit the growth of certain malignant cells in culture. Quercetin also inhibits histamine release and induces accumulation of secretory granules in rat basophilic leukemia cells.

METHOD

We investigated the effect of five flavonoids: flavone, kaempferol, morin, myricetin, and quercetin at 1, 10, and 100 microM on proliferation and secretory mediator content (beta-hexosaminidase, histamine, and tryptase) in human leukemic mast cells (HMC-1), the doubling time of which was about 2 d.

RESULTS

Flavone and kaempferol at 100 microM inhibited cell proliferation over 80% on either day 3, 4, or 5 of culture. Quercetin showed this level of inhibition only on day 5, myricetin inhibited by 50% at days 3-5, whereas morin's inhibition was < 20%. All flavonoids (except morin) at 100 microm increased histamine and tryptase content, but not beta-hexosaminidase, equally at days 3 and 4 of culture quercetin also increased the development of secretory granules.

CONCLUSION

These results indicate that certain flavonoids can inhibit HMC-1 proliferation, induce secretory granule development and the accumulation of mediators.

Voltage-dependent and calcium-activated ion channels in the human mast cell line HMC-1

The mechanisms underlying the recruitment, differentiation, and sustained activation of mast cells in disease are likely to include modulation of ion channels. Specific Ca(2+), K(+), and Cl(-) conductances have been identified in rodent mast cells, but there are no equivalent data on human mast cells. We have used the whole-cell patch-clamp technique to characterize macroscopic ion currents in both the human mast cell line HMC-1 and human skin mast cells (HSMCs) at rest and in HMC-1 after activation with calcium ionophore. HSMCs were electrically silent at rest. In contrast, HMC-1 expressed a strong outwardly rectifying voltage-dependent Cl(-) conductance characteristic of ClC-4 or ClC-5 and a small inwardly rectifying K(+) current not carried by the classical Kir family of K(+) channels. Calcium ionophore induced the appearance of outwardly rectifying Ca(2+)-activated Cl(-) and K(+) currents, while hypotonicity induced another outwardly rectifying conductance typical of ClC-3. Reverse transcription-PCRs confirmed that mRNAs for the voltage-dependent Cl(-) channels ClC-3 and -5 were expressed. This is the first definitive description of a ClC-4/5-like current in a native leukocyte. We suggest that this current may contribute to the malignant phenotype while the Ca(2+)-activated K(+) and Cl(-) currents may be involved in cell activation.

Matrix metalloproteinase-9 production, a newly identified function of mast cell progenitors, is downregulated by c-kit receptor activation

Mast cell precursors invade from the peripheral blood into local tissues where they differentiate to their mature phenotypes. However, the mechanism of this migration process has been unclear. We clearly demonstrated here the production and release of matrix metalloproteinase-9 (MMP-9), a matrix-degrading enzyme necessary for leukocyte transmigration, by interleukin-3-dependent mouse mast cell progenitors: bone marrow-derived cultured mast cells and IC-2 mast cells. Because several interleukin-3-independent mast cell lines with active mutations in the c-kit gene did not release MMP-9, the possible involvement of c-kit receptor activation in downregulation of MMP-9 production was predicted. c-kit receptor activation by stem cell factor led to a significant decrease in MMP-9 production of cultured mast cells and IC-2 mast cells transfected with the c-kit gene. Thus, the present results suggest that mast cell precursors are able to produce MMP-9, which may be essential for mast cell migration into tissues, and that stem cell factor may downregulate the MMP-9 production, resulting in engagement of mast cells to matrix components.

CD43 (leukosialin, sialophorin) expression is differentially regulated by retinoic acids

CD43 (leukosialin, sialophorin), a cell-surface associated mucin that is constitutively expressed at high levels on most leukocytes, is thought to be involved in cell activation and adhesion. We here provide evidence that the vitamin A metabolites all-trans and 13-cis retinoic acid up-regulate CD43 on human leukemic (HMC-1) mast cells, as determined by flow cytometry, Western blot analysis, and by semiquantitative reverse transcriptase-polymerase chain reaction. Enhanced CD43 expression was accompanied by a strong increase in anti-CD43-mediated, LFA-1-dependent homotypic aggregation of HMC-1 cells, demonstrating that newly synthesized CD43 is functionally active in transmitting signals across the plasma membrane which result in enhanced cellular adhesion. CD43 expression was also enhanced in response to retinoic acids on isolated human skin mast cells and human monocytes, but not on cells of the basophilic cell line KU-812 and promyelocytic HL-60 cells, indicating that these agents might act in a cell-type specific manner. These combined result-point to a novel aspect in the regulation of CD43. Possibly, vitamin A metabolites act directly on the CD43 gene, since putative retinoic acid response elements have been detected within its regulatory regions.

Analysis of the genes encoding the mast cell function-associated antigen and its alternatively spliced transcripts

The mast cell function-associated Ag (MAFA) is a C-type lectin that, upon being clustered, inhibits the Fc epsilon RI stimulation-induced mast cell secretory response. We here report that MAFA is encoded by a single-copy gene that spans 13 kb in the rat genome and is composed of five exons. Three separate exons encode the carbohydrate recognition domain of the MAFA, defining its close homology to the genes of CD23, CD69, CD72, NKR-P1, and Ly49. Functional analysis of the 5' flanking region of the gene reveals that a cell type-specific promoter is located within the first 664 bp upstream of the transcription origin. The promoter lacks any obvious TATA box and drives gene transcription originating from multiple start sites. Examination for possible polymorphism of the MAFA transcripts revealed two novel transcripts, generated by alternative splicing. Deletion of the transmembranal exon in one of them does not result in a frameshift and would, upon translation, give rise to a soluble MAFA molecule. Splicing of two exons in a second transcript results in a new reading frame encoding a putative protein containing MAFA's cytoplasmic domain. The transcription of the MAFA gene was detected in normal rat lungs, where both transmembranal and soluble MAFA appear to be expressed. Lung immunohistochemical analysis further suggests that MAFA expression is restricted to mast cells.

Mechanisms of constitutive activation of c-kit receptor tyrosine kinase

We investigated the mechanism of constitutive activation of c-kit receptor tyrosine kinase (KIT) found in the FMA3 murine mastocytoma cell line, and compared it with the mechanisms observed in other tumor mast cell lines (the HMC-1 human mast cell leukemia cell line, the RBL-2H3 rat mast cell leukemia cell line, and the P-815 murine mastocytoma cell line). The c-kit gene obtained from FMA3 cells was found to have 21-base deletion at the juxtamembrane domain of KIT, thereby leading to the constitutive activation of KIT. The deletion at the juxtamembrane domain resulted in constitutive dimerization of c-kit proteins, whereas the point mutation that were detected at the kinase domain of KIT in HMC-1, RBL-2H3, and P-815 cells caused constitutive activation of KIT without dimerization. These constitutively activating mutations of c-kit may play a role in development of mast cell tumors.

Modulation of intercellular adhesion molecule 1 (ICAM-1) expression on the human mast-cell line (HMC)-1 by inflammatory mediators

The effect of inflammatory mediators on the expression of several surface adhesion molecules on the human mast-cell line (HMC)-1 was studied. By flow cytometry, it could be shown that among several surface adhesion molecules (ICAM-1/CD54, VLA-4/CD49d, Mac-1/CD11b, LFA-1/CD11a, LFA-2/CD2, LFA-3/CD58, VCAM-1), only the constitutively expressed immunoglobulin family member intercellular adhesion molecule-1 (ICAM-1) is modulated by proinflammatory cytokines on HMC-1 mast cells. Stimulation with tumor necrosis factor-a (TNF-alpha) and interferon-gamma (IFN-gamma) resulted, in addition to interleukin-(IL-)4, in selective upregulation of ICAM-1 expression. Costimulation of either IL-4 or IFN-gamma with TNF-alpha further increased the ICAM-1 expression as compared to the stimuli alone. In contrast, stem-cell factor (SCF), granulocyte/macrophage colony-stimulating factor (GM-CSF), IL-10, IL-8, monocyte chemotactic and activating factor (MCAF), and the complement split product C5a failed to modulate the expression of any adhesion molecule examined. The levels of cytoplasmic free calcium in HMC-1 mast cells were not altered by cross-linking surface ICAM-1, suggesting linkage of other intracellular signaling pathways. This cytokine-induced upregulation of ICAM-1 expression might reveal a putative regulatory mechanism of mast-cell interaction with effector cells bearing the counterparts of ICAM-1 (CD54), the molecules Mac-1 (CD11b/CD18) and leukosialin (CD43), and the principal ligand LFA-1 (CD11a/CD18).

Phenylarsine oxide (PAO)-mediated activation of phospholipase D in rat basophilic leukemia (RBL-2H3) cells: possible involvement of calcium and protein kinase C

Addition of phenylarsine oxide (PAO) to [3H]oleic acid-labeled rat basophilic leukemia (RBL-2H3) cells gave rise to the remarkable formation of [3H]phosphatidylbutanol (PBut), a specific product of phospholipase D (PLD) activation. Preincubation of cells with 2,3-dimercaptopropanol (DMP) or dithiothreitol (DTT), compounds containing sulfhydryls, prevented PAO-stimulated [3H]PBut formation, indicating that PAO-stimulated PLD through interacting with vicinal thiol groups. Treatment of cells with PAO resulted in increase in intracellular Ca2+ concentration without significant production of inositol phosphates. Removal of extracellular free Ca2+ by chelating with EGTA was found to inhibit [3H]PBut formation by PAO. Incubation of cells with 20 nM phorbol 12-myristate 13-acetate (PMA) for 6 h caused down-regulation of protein kinase C (PKC) alpha and beta isozymes, whereas it had no effect on PKC delta, epsilon and zeta isozymes. Under this condition, decrease in PAO-stimulated [3H]PBut formation was observed to occur with a concomitant decrease in the level of PKC alpha and beta isozymes. These results suggest that a covalent bridge between vicinal thiol groups of cell surface proteins induced by PAO potentiates PLD activation and that PAO-induced PLD activation is regulated by Ca2+ and PKC alpha and/or beta isozymes.

Effects of cyclosporin A and FK-506 on stem cell factor-induced histamine secretion and growth of human mast cells

Stem cell factor (SCF) is a key regulator of human mast cells (MCs) and a potential mediator of allergy. In this study the effects of cyclosporin A (CSA) and FK-506, two potent immunosuppressive drugs, on SCF-dependent histamine release and growth of human MCs were analyzed. Preincubation of tissue MCs with CSA (3 micrograms/ml) resulted in inhibition of histamine release provoked by either recombinant human (rh) SCF (70.3% +/- 20.6% inhibition, p < 0.001) or anti-IgE (76.7% +/- 21.9%, p < 0.001) or by rhSCF+ anti-IgE (77.4% +/- 13.9%, p < 0.001). Almost the same inhibition was produced by FK-506 (rhSCF: 82.0% +/- 18.9% inhibition, p < 0.001; anti-IgE: 71.5% +/- 16.7%, p < 0.001; rhSCF+ anti-IgE: 70.0% +/- 7.3%, p < 0.001). The effects of CSA and FK-506 on SCF-dependent release of histamine were dose-dependent (IC50: CSA, 1 to 10 ng/ml; FK-506, 0.3 to 3 ng/ml). IC50 values about three to 10 times higher were found for MCs preincubated with rhSCF before anti-IgE activation, compared with anti-IgE or SCF alone. SCF-dependent differentiation of human MCs was analyzed in a long-term suspension culture system (n = 6). Unexpectedly, CSA and FK-506 were unable to suppress, but even enhanced SCF-dependent growth of MCs and formation of MC tryptase in long-term culture. Together, CSA and FK-506 inhibit SCF-dependent release of histamine from human MCs and even augment SCF-dependent growth of human MCs in long-term culture.

Anti-allergic activity of cyclosporin-A metabolites and their interaction with the parent compound and FK 506

The ability of cyclosporin-A (CSA) and four of its metabolites M1, M17, M18 and M21, to inhibit antigen-stimulated release of beta-hexoseaminidase from IgE-sensitized rat basophilic leukemia cells (RBL-2H3), as an in vitro correlate of anti-allergic effect, was studied Metabolites M17, M1 and M21 were effective in inhibiting enzyme release, though less potent than the parent compound. The concentrations achieving 50% inhibition (IC50 values) were 53.3, 315.5 and 875.7 ng/ml for CSA, M17 and M1, respectively. M21 had approximately same IC50 as M1 while M18 was essentially inactive. At the highest concentration tested (1000 ng/ml) the mean maximum percentage inhibitions were 98.6, 79.5, 53.9, 48.6 and 12.2 for CSA, M17, M1, M21 and M18, respectively. The relative anti-allergic potency of the metabolites was similar to their reported relative immunosuppressive potency. Combinations of low concentrations of CSA and its metabolites were synergistic in inhibiting enzyme release whereas at higher concentrations interactions were either additive or antagonistic. Even the concentrations of the metabolites that have little or no activity when used alone also potentiated the effect of CSA. The immunosuppressor FK 506 was found to be about three times more potent than CSA in this system and the interactions between FK 506 (3, 10 and 30 ng/ml) and CSA (10, 30 and 100 ng/ml) or M17 (20, 100 and 500 ng/ml) were synergistic at all combinations. Both CSA and M17 synergized more strongly with FK 506 than they did between themselves. These results show that some metabolites of CSA, like the parent compound, possess anti-allergic effects and that at concentrations that are obtainable in transplant patients, synergistic interaction occurs between CSA and its metabolites, and this may be of some therapeutic significance.

Tumor necrosis factor alpha and interleukin-1 beta mRNA expression in HMC-1 cells: differential regulation of gene product expression by recombinant interleukin-4

Cytokine-activation pathways in mast cells are supposed to play a significant role in host defense mechanisms and allergic reactions. Interleukin-4 (IL-4) is a well-characterized regulator of growth and function of mast cells. The human mast cell line HMC-1 was established from a patient suffering from mast cell leukemia and was shown to expose IL-4 binding sites. In the present study, the effects of recombinant human (rh) IL-4 and other rh cytokines (IL-2, IL-3, IL-6, IL-8) on expression of cytokine mRNA in HMC-1 cells were examined by Northern blot analysis using oligonucleotide probes. Tumor necrosis factor alpha (TNF-alpha) and IL-1 beta transcripts were found to be expressed constitutively in HMC-1 cells, whereas transcripts for IL-3, IL-4, IL-5, IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF) could not be detected. Of all cytokines tested, rhIL-4 was found to down-regulate IL-1 beta mRNA expression and formation of immunoreactive IL-1 beta protein in HMC-1 cells. The effect of IL-4 on IL-1 beta gene product expression was time- and dose-dependent (maximum effects obtained with 100 U/mL of rhIL-4). No effect of IL-4 on expression of TNF-alpha mRNA in HMC-1 cells was observed. These results raise the possibility that human mast cells are a source of both TNF-alpha and IL-1 beta. Furthermore, our study provides evidence that IL-4 regulates IL-1 beta gene product expression in HMC-1 cells. The HMC-1 cell line should be a useful tool for studying cytokine activation pathways in human mast cells.

Interleukin 4 promotes expression of mast cell ICAM-1 antigen

Cell recognition molecules play a crucial role in the regulation of immune cells. We recently found that mast cells (MCs) express leukocyte recognition molecules, including ICAM-1 antigen, a natural ligand of LFA-1. We here report that interleukin 4 (IL-4), a pleiotropic cytokine and mast cell differentiation factor, selectively promotes expression of surface ICAM-1 antigen and ICAM-1 mRNA in human MCs. IL-4 also up-regulates ICAM-1 antigen in cells of monocyte/macrophage lineage but has no effect on ICAM-1 antigen expressed on basophils, fibroblasts, or lymphocytes. The increase in expression of mast cell/macrophage ICAM-1 antigen induced by IL-4 may contribute to the accumulation of leukocytes and facilitate cell-contact-dependent regulation of immune cells in inflamed tissues.

Calcium specificity of the antigen-induced channels in rat basophilic leukemia cells

Ion channels, activated upon IgE-Fc epsilon receptor aggregation by specific antigen, were studied in micropipet-supported lipid bilayers. These bilayers were reconstituted with purified IgE-Fc epsilon receptor complex and the intact 110-kDa channel-forming protein, both isolated from plasma membranes of rat basophilic leukemia cells (line RBL-2H3). In order to identify the current carrier through these ion channels and to determine their ion selectivity, we investigated the currents flowing through the IgE-Fc epsilon receptor gated channels in the presence of a gradient of Ca2+ ions. Thus, the solution in which the micropipet-supported bilayer was immersed contained 1.8 mM CaCl2, while the interior of the micropipet contained 0.1 microM Ca2+ (buffered with EGTA). Both solutions also contained 150 mM of a monovalent cation chloride salt (either K+ or Na+). The currents induced upon specific aggregation of the IgE (by either antigen or anti-IgE antibodies) were examined over a range of potentials imposed on the bilayer. The type of conductance event most frequently observed under the employed experimental conditions was a channel that has a slope conductance of 3 pS and a reversal potential practically identical with the calculated value for the reversal potential of calcium (134 +/- 11 mV in the presence of sodium, 125 +/- 13 mV in the presence of potassium). These results indicate that this channel is highly selective for calcium against the monovalent cations sodium and potassium. This same channel has a conductance of 4-5 pS in the presence of symmetrical solutions containing only 100 mM CaCl2 and 8 pS in the presence of 0.5 M NaCl with no calcium.(ABSTRACT TRUNCATED AT 250 WORDS)