Multiple defects in Fc epsilon RI signaling in Syk-deficient nonreleaser basophils and IL-3-induced recovery of Syk expression and secretion

Human basophils respond to Ag-induced cross-linking of their high affinity IgE receptor, FcepsilonRI, by releasing histamine and other mediators from granules, producing IL-4 and other cytokines and, as shown in this study, by forming membrane ruffles and showing increased very late Ag-4 (VLA-4)-mediated adhesion to VCAM-1-expressing target cells. We have identified five blood donors whose basophils lack detectable levels of the FcepsilonRI-associated protein tyrosine kinase, Syk. Despite showing no obvious ultrastructural differences from normal basophils, nonreleaser basophils fail to form membrane ruffles, to show increased VLA-4-mediated adhesive activity, or to produce IL-4 in response to FcepsilonRI cross-linking. Although Syk protein levels are suppressed in basophils from all five donors, Syk mRNA is consistently present. Furthermore, culturing nonreleaser basophils for 4 days with IL-3 restores Syk protein expression and FcepsilonRI-mediated histamine release. Understanding the reversible suppression of Syk protein expression in nonreleaser basophils, and learning to replicate this property in patients with allergic inflammation could be a powerful and specific way to limit symptomatic disease.     

IgE modulates neutrophil survival in asthma: role of mitochondrial pathway

The high-affinity IgE receptor (FcepsilonRI) has recently been reported to be expressed by neutrophils in atopic asthmatic individuals, leading to speculations that IgE could influence biological functions of these cells. In this study, we demonstrate that monomeric human IgE delayed spontaneous apoptosis of primary human neutrophils from atopic asthmatics in vitro. This effect was not dependent on FcepsilonRI cross-linking or autocrine release of soluble mediators; however, it was associated with increased expression of the antiapoptotic myeloid cell leukemia-1 protein, retention of the proapoptotic molecule Bax in the cytoplasm, decreased release of Smac from mitochondria, and reduced caspase-3 activity. Taken together, our results indicate that in vitro IgE can delay programmed cell death of neutrophils from allergic asthmatics and this may possibly contribute to neutrophilic inflammation in atopic asthma.     

Recombinant human IL-1 alpha and -1 beta potentiate IgE-mediated histamine release from human basophils

In this study, we have explored the relationship between interleukins and human basophil activation. Previous studies by ourselves and others have found that recombinant human (rh) IL-3 causes histamine release. The ability to release histamine has also been claimed for IL-1 but we cannot confirm this. In experiments with the basophils of 29 donors (excluding one D2O responder), histamine release with 100 ng/ml rhIL-1 alpha was 1.3 +/- 1% (SEM), whereas with rhIL-1 beta, it was 0.8 +/- 1%. Both IL-1 alpha and -1 beta were also used at concentrations of 0.01 to 1000 ng/ml without causing release. Neither increasing the Ca2+ concentration nor adding D2O or cytochalasin B caused IL-1 alpha and -1 beta to become secretagogues. rhIL-1, however, did augment IgE-dependent histamine release. The enhancement was similar with both rhIL-1 alpha and -1 beta, i.e. they were dose-dependent between 0.1 and 3 ng/ml and reached a plateau from 3 to 100 ng/ml. At submaximal histamine release (less than 10%), there was enhancement of three IgE-dependent secretagogues: 125% with goat anti-human IgE (n = 7), 215% with Ag E (n = 10), and 260% with a histamine releasing factor (n = 7). Non-IgE-dependent stimuli (formyl-methionine-leucine-phenylalanine and the ionophore A23187, n = 10) were enhanced less than 5%. rhIL-1-enhancement persisted after cell washing (n = 10). rhIL-1 was active in preparations of 50 to 75% pure basophils in which mononuclear cells were reduced by greater than 95% (n = 4), and mAbH34 to IL-1 beta blocked the enhancement caused by that molecule. We postulate that basophils have an IL-1 receptor which, when occupied, upregulates the response to IgE-related signals. Thus, this work characterizes a second interaction between interleukins and the cells central to the allergic response.     

Ultrastructural cytochemical and autoradiographic demonstration of nonspecific esterase(s) in guinea pig basophils

We used ultrastructural autoradiographic and cytochemical methods to localize esterase activities in unstimulated guinea pig basophils and in basophils undergoing degranulation or recovery from degranulation. We used tritium-labeled diisopropylfluorophosphate (DFP) as a probe for serine enzymes and localized this probe by ultrastructural autoradiography to cytoplasmic granules of immature or mature unstimulated basophils, as well as to granules released by degranulating basophils. Ultrastructural cytochemistry using alpha naphthyl acetate (ANA) as substrate localized nonspecific esterase activity to extruded granules, either within the interiors of degranulation sacs or within granules completely separated from degranulating basophils. Extruded granules retained their esterase activity for as long as 24 hr after antigen-induced degranulation. The plasma membranes of unstimulated or degranulating basophils, as well as of basophils recovering from degranulation, displayed prominent cell surface ANA esterase ectoenzyme activity. Lipid bodies, organelles present in the cytoplasm of both control and recovering basophils, were also alpha naphthyl acetate esterase (ANAE)-positive. Thus, cytochemical and autoradiographic techniques localized esterase and/or [3H]-DFP-binding activities to cytoplasmic granules, lipid bodies, and cell surface of basophils, and these enzyme activities persisted during both degranulation and recovery from degranulation.     

The effect of salbutamol on histamine release from basophils in vivo and in vitro]

In vivo and in vitro basophil histamine release inhibition by salbutamol was investigated in patients with bronchial asthma. The study involved 14 patients in stable period of the disease: FEV1 = 66-84% of the normal values. Histamine release was determined following an incubation of the isolated basophils with concanavalin A (Sigma Co., USA) or specific allergens (dust, grass pollens, mites; Bencard, UK). Histamine was assayed with isotope-enzymatic technique according to Shaff and Beaven with histamine N-methyltransferase. Salbutamol administered intravenously in the dose of 1 mg inhibited allergen-induced histamine release from the basophils isolated from patient's blood within 30 minutes. Salbutamol in the concentration of 8 X 10(-6) M inhibited in vitro histamine release induced by an allergen and concanavalin A.     

Test of a theory relating to the cross-linking of IgE antibody on the surface of human basophils

Recent mathematical models of bivalent hapten-induced histamine release from basophils predict that under appropriate conditions histamine release is maximum when cross-link formation is maximum, at a hapten concentration equal to 1/(2Ka), where Ka is the average affinity constant of the hapten for a single IgE binding site. To test this prediction we sensitized human basophils with a monoclonal anti-dinitrophenol IgE and generated histamine release dose-response curves with a bivalent hapten, alpha, epsilon-DNP-lysine. The monoclonal IgE has a published affinity constant of 7.1 X 10(7) M-1 for epsilon-DNP-lysine as determined by equilibrium dialysis. From the position of the maximum of the histamine dose-response curves, both in the presence and in the absence of monovalent DNP hapten, we determine that the sensitizing IgE has an intrinsic affinity constant of 6.9 +/- 0.5 X 10(7) M-1 for epsilon-DNP-lysine and 1.2 +/- 0.6 X 10(6) M-1 for alpha-DNP-lysine. The agreement between the two estimates of the epsilon-DNP-lysine affinity constant, one from histamine release experiments involving surface bound IgE and one from binding experiments involving IgE free in solution, 1) is consistent with a central prediction of the theory of cross-linking and 2) indicates that the hapten-binding properties of the IgE are unaffected by its being bound to Fc epsilon receptors on the basophil surface.     

Involvement of CCL18 in allergic asthma

Allergic asthma is associated with a pulmonary recruitment of Th type 2 cells, basophils, and eosinophils, mainly linked to chemokine production. CCL18 is a chemokine preferentially expressed in the lung, secreted by APCs, induced by Th2-type cytokines, and only present in humans. Therefore, CCL18 may be involved in allergic asthma. PBMC from asthmatics allergic to house dust mite cultured in the presence of Dermatophagoides pteronyssinus 1 (Der p 1) allergen secreted CCL18, 48 and 72 h after stimulation, whereas those from healthy donors did not. Part of CCL18 was directly derived from Der p 1-stimulated plasmacytoid dendritic cells, whereas the other part was linked to monocyte activation by IL-4 and IL-13 produced by Der p 1-stimulated T cells. In bronchoalveolar lavages from untreated asthmatic allergic patients, CCL18 was highly increased compared with controls. Functionally, CCL18 preferentially attracted in vitro-polarized Th2 cells and basophils, but not eosinophils and Th1 cells, and induced basophil histamine and intracellular calcium release. These data show a new function for CCL18, i.e., the recruitment of Th2 cells and basophils, and suggest that CCL18 may play a predominant role in allergic asthma.     

Inhibitory effect of polyphenol-enriched apple extracts on mast cell degranulation in vitro targeting the binding between IgE and FcepsilonRI

Extracts from immature fruit of the apple (Rosaceae, Malus sp.), which contain procyanidins (polymers of catechins) as the major ingredients, are known to inhibit histamine release from mast cells. We analyzed in this study the mechanism for the anti-allergic activity of two polyphenol-enriched apple extracts. These extracts, termed "crude apple polyphenol (CAP)" and "apple condensed tannin (ACT)", reduced the degranulation of mast cells caused by cross-linking of the high-affinity receptor for IgE (FcepsilonRI) with IgE and the antigen in a dose-dependent manner. Furthermore, western blotting revealed that phosphorylation of the intracellular signal-transduction molecules caused by cross-linking of FcepsilonRI was markedly decreased by the addition of CAP or ACT. We then analyzed the effects of CAP and ACT on the binding of the IgE antibody to FcepsilonRI on mast cells, which is the first key step in the allergic reaction mediated by mast cells, and found that this binding was markedly inhibited by both CAP and ACT. These results indicate that the inhibition of binding between FcepsilonRI and IgE by either CAP or ACT was the probable cause of the suppression of mast cell activation. This is the first report demonstrating the molecular mechanism for the anti-allergic effect of procyanidin-enriched extracts from apples.     

Dysregulated FcepsilonRI signaling and altered Fyn and SHIP activities in Lyn-deficient mast cells

Studies in B cells from Lyn-deficient mice have identified Lyn as both a kinetic accelerator and negative regulator of signaling through the BCR. The signaling properties of bone marrow-derived mast cells from Lyn(-/-) mice (Lyn(-/-) BMMCs) have also been explored, but their signaling phenotype remains controversial. We confirm that Lyn(-/-) BMMCs release more beta-hexosaminidase than wild-type BMMCs following FcepsilonRI cross-linking and show that multiple mast cell responses to FcepsilonRI cross-linking (the phosphorylation of receptor subunits and other proteins, the activation of phospholipase Cgamma isoforms, the mobilization of Ca(2+), the synthesis of phosphatidylinositol 3,4,5-trisphosphate, the activation of the alpha(4)beta(1) integrin, VLA-4) are slow to initiate in Lyn(-/-) BMMCs, but persist far longer than in wild-type cells. Mechanistic studies revealed increased basal as well as stimulated phosphorylation of the Src kinase, Fyn, in Lyn(-/-) BMMCs. Conversely, there was very little basal or stimulated tyrosine phosphorylation or activity of the inositol phosphatase, SHIP, in Lyn(-/-) BMMCs. We speculate that Fyn may substitute (inefficiently) for Lyn in signal initiation in Lyn(-/-) BMMCs. The loss of SHIP phosphorylation and activity very likely contributes to the increased levels of phosphatidylinositol 3,4,5-trisphosphate and the excess FcepsilonRI signaling in Lyn(-/-) BMMCs. The unexpected absence of the transient receptor potential channel, Trpc4, from Lyn(-/-) BMMCs may additionally contribute to their altered signaling properties.     

Co-aggregation of FcgammaRII with FcepsilonRI on human mast cells inhibits antigen-induced secretion and involves SHIP-Grb2-Dok complexes

Signaling through the high affinity IgE receptor FcepsilonRI on human basophils and rodent mast cells is decreased by co-aggregating these receptors to the low affinity IgG receptor FcgammaRII. We used a recently described fusion protein, GE2, which is composed of key portions of the human gamma1 and the human epsilon heavy chains, to dissect the mechanisms that lead to human mast cell and basophil inhibition through co-aggregation of FcgammaRII and FcepsilonRI. Unstimulated human mast cells derived from umbilical cord blood express the immunoreceptor tyrosine-based inhibitory motif-containing receptor FcgammaRII but not FcgammaRI or FcgammaRIII. Interaction of the mast cells with GE2 alone did not cause degranulation. Co-aggregating FcepsilonRI and FcgammaRII with GE2 1) significantly inhibited IgE-mediated histamine release, cytokine production, and Ca(2+) mobilization, 2) reduced the antigen-induced morphological changes associated with mast cell degranulation, 3) reduced the tyrosine phosphorylation of several cellular substrates, and 4) increased the tyrosine phosphorylation of the adapter protein downstream of kinase 1 (p62(dok); Dok), growth factor receptor-bound protein 2 (Grb2), and SH2 domain containing inositol 5-phosphatase (SHIP). Tyrosine phosphorylation of Dok was associated with increased binding to Grb2. Surprisingly, in non-stimulated cells, there were complexes of phosphorylated SHIP-Grb2-Dok that were lost upon IgE receptor activation but retained under conditions of Fcepsilon-Fcgamma co-aggregation. Finally, studies using mast cells from Dok-1 knock-out mice showed that IgE alone triggers degranulation supporting an inhibitory role for Dok degranulation. Our results demonstrate how human FcepsilonRI-mediated responses can be inhibited by co-aggregation with FcgammaRIIB and implicate Dok, SHIP, and Grb2 as key intermediates in regulating antigen-induced mediator release.     

Inhibitory effect of xanthones isolated from the pericarp of Garcinia mangostana L. on rat basophilic leukemia RBL-2H3 cell degranulation

Mangostin, Garcinia mangostana L. is used as a traditional medicine in southeast Asia for inflammatory and septic ailments. Hitherto we indicated the anticancer activity induced by xanthones such as alpha-, beta-, and gamma-mangostin which were major constituents of the pericarp of mangosteen fruits. In this study, we examined the effect of xanthones on cell degranulation in rat basophilic leukemia RBL-2H3 cells. Antigen (Ag)-mediated stimulation of high affinity IgE receptor (FcepsilonRI) activates intracellular signal transductions resulting in the release of biologically active mediators such as histamine. The release of histamine and other inflammatory mediators from mast cell or basophils is the primary event in several allergic responses. These xanthones suppressed the release of histamine from IgE-sensitized RBL-2H3 cells. In order to reveal the inhibitory mechanism of degranulation by xanthones, we examined the activation of intracellular signaling molecules such as Lyn, Syk, and PLCgammas. All the xanthones tested significantly suppressed the signaling involving Syk and PLCgammas. In Ag-mediated activation of FcepsilonRI on mast cells, three major subfamilies of mitogen-activated protein kinases were activated. The xanthones decreased the level of phospho-ERKs. Furthermore, the levels of phospho-ERKs were observed to be regulated by Syk/LAT/Ras/ERK pathway rather than PKC/Raf/ERK pathway, suggesting that the inhibitory mechanism of xanthones was mainly due to suppression of the Syk/PLCgammas/PKC pathway. Although intracellular free Ca(2+) concentration ([Ca(2+)](i)) was elevated by FcepsilonRI activation, it was found that alpha- or gamma-mangostin treatment was reduced the [Ca(2+)](i) elevation by suppressed Ca(2+) influx.     

Antigen receptor engagement selectively induces macrophage inflammatory protein-1 alpha (MIP-1 alpha) and MIP-1 beta chemokine production in human B cells

We show herein that B cell Ag receptor (BCR) triggering, but not stimulation by CD40 mAb and/or IL-4, rapidly induced the coordinated expression of two closely related T cell chemoattractants, macrophage inflammatory protein-1 beta (MIP-1 beta) and MIP-1 alpha, by human B cells. Naive, memory, and germinal center B cells all produced MIP-1 alpha/beta in response to BCR triggering. In contrast to MIP-1 alpha/beta, IL-8, which is spontaneously produced by germinal center B cells but not by naive and memory B cells, was not regulated by BCR triggering. Culturing follicular dendritic cell-like HK cells with activated B cells did not regulate MIP-1 alpha/beta production, but it did induce production of IL-8 by HK cells. Microchemotaxis assays showed that CD4+CD45RO+ T cells of the effector/helper phenotype actively migrated along a chemotactic gradient formed by BCR-stimulated B cells. This effect was partially blocked by anti-MIP-1 beta and anti-CC chemokine receptor 5 Ab, but not by anti-MIP-1 alpha Ab suggesting that MIP-1 beta plays a major role in this chemoattraction. Since maturation of the B cell response to a peptide Ag is mostly dependent on the availability of T cell help, the ability of Ag-stimulated B cells to recruit T cells via MIP-1 alpha/beta, may represent one possible mechanism enabling cognate interactions between rare in vivo Ag-specific T and B cells.     

Histamine-containing cells obtained from the nose hours after antigen challenge have functional and phenotypic characteristics of basophils.

The pattern of mediators and appearance of cells that stain with alcian blue during human experimental early and late phase allergic reactions suggest that basophils accumulate in nasal secretions within hours of local Ag stimulation. To further explore whether the histamine containing cells that enter the nose after Ag challenge are mast cells or basophils, we studied their functional and phenotypic characteristics. Approximately 24 h after intranasal Ag provocation of subjects with allergic rhinitis, nasal lavage was performed, and the cells were isolated for degranulation studies, analysis of surface Ag, and viability. The average histamine content per alcian blue staining cell was 0.78 +/- 0.2 pg (n = 7), similar to that reported for peripheral blood basophils. Nasal cells were challenged in vitro with anti-IgE, ragweed Amb a I, and FMLP and their responses were compared to those of peripheral blood basophils isolated simultaneously from the same donors. Nasal leukocytes released histamine maximally at 0.1 micrograms/ml of anti-IgE (35.8 +/- 7.8%, n = 7) and responded to FMLP (25.4 +/- 9.9%, n = 7). The response of the cells to ragweed Amb a I and anti-IgE was attenuated compared to peripheral blood basophils. Anti-IgE-induced histamine release was calcium and temperature dependent. Dual color immunofluorescence and flow cytometric analysis of the recovered nasal cells coexpressed CD18, a leukocyte marker not expressed by mast cells. The nasal cells consistently had high levels of spontaneous histamine release (19.5 +/- 2.0%, n = 22). The viability of all cells, assessed by erythrosin B dye exclusion, was 70 +/- 2% (n = 15). However, the viability of IgE-bearing cells was only 28.3 +/- 5.7% (n = 4). The characteristics of histamine release and the nature of the cellular surface markers provide functional proof that the histamine-containing cells accumulating after nasal Ag challenge are basophils and not mast cells.     

Metabolic comparison between basophils and other leukocytes from human blood

Basophilic granulocytes were purified from the blood of normal individuals by successive isopyknic centrifugation and elutriation centrifugation. Starting with the leukocyte-rich fraction of 500 ml of blood, we recovered 31 to 80% (mean 51%, n = 20) of the basophils in 45 to 87% purity (mean 69%, n = 23). The contaminating cells were mainly lymphocytes. The basophils were greater than 98% vital (exclusion of ethidium bromide and hydrolysis of fluorescein diacetate). The histamine content of the basophils was 1.1 to 2 pg/cell (mean 1.6 pg/cell, n = 22). With anti-IgE, 30 to 50% of the histamine was released; with phorbol myristic acetate (PMA) or the calcium ionophore A23187, 70 to 100% of the histamine was released. Serum-opsonized zymosan (STZ) did not induce histamine release. Reactions with monoclonal antibodies revealed that the basophils expressed the C3bi receptor (CR3) and the leukocyte function-associated antigen 1 (LFA1), but not the gp 150,95 antigen, the C3b receptor (CR1), or the low avidity Fc gamma receptor. Basophils carry class I but not class II HLA antigens. During incubation of the basophils with serum-opsonized Staphylococcus aureus or Escherichia coli, these bacteria were neither phagocytized nor killed. STZ, PMA, A23187, or anti-IgE did not initiate an "oxidative burst" in the basophils. This was tested with oxygen consumption, cytochrome c reduction, NBT reduction, chemiluminescence, and release of hydrogen peroxide. Moreover, we did not detect cytochrome b558, superoxide dismutase, catalase, or peroxidase in the basophils. Of the typical granule-associated enzymes lysozyme, Vitamin B12-binding protein, and beta-glucuronidase, only beta-glucuronidase was present in the basophils in detectable amounts. This enzyme was released, together with histamine, on incubation of the cells with PMA, A23187, or anti-IgE, but not with STZ. We conclude that basophils from normal human blood are not phagocytes and are probably not involved in the oxidative defense of the host against foreign antigens.     

Effects of rhinovirus infection on histamine and cytokine production by cell lines from human mast cells and basophils

To understand the biochemical events that occur in the airways after rhinovirus (RV) infection, we developed for the first time a model in which the cell lines from human mast cells (HMC-1) and basophils (KU812) can be infected with RV14, a major group RV. Viral infection was confirmed by demonstrating that viral titers in culture supernatants, and RV RNA increased with time. RV14 infection alone and a combination of PMA plus calcium ionophore A23187, did not increase histamine production by these cells, although IgE plus anti-IgE increased the histamine production. However, histamine content in the supernatants increased in response to PMA plus A23187, or IgE plus anti-IgE after RV14 infection. PMA plus A23187 or IgE plus anti-IgE induced the production of IL-8 and GM-CSF in supernatants of HMC-1 cells and IL-4 and IL-6 in supernatants of KU812 cells. RV14 infection further increased the production of the cytokines, whereas RV14 infection alone did not alter the production of the cytokines by these cells. An Ab to ICAM-1 inhibited RV14 infection of the cells and decreased the production of cytokines and histamine after RV14 infection. RV14 infection enhanced the increases in intracellular calcium concentration and activation of NF-kappaB by PMA plus A23187 in the cells. These findings suggest that RV14 infection may prime the cytokine and histamine production from mast cells and basophils and may cause airway inflammation in asthma.     

Activation of Syk tyrosine kinase is required for c-Cbl-mediated ubiquitination of Fcepsilon RI and Syk in RBL cells

Engagement of the high affinity receptor for IgE (FcepsilonRI) on mast cells and basophils results in FcepsilonRI beta and gamma subunits ubiquitination by an as yet undefined mechanism. Here we show that, upon FcepsilonRI engagement on RBL-2H3 cells Syk undergoes ubiquitination and Syk kinase activity is required for its own ubiquitination and that of FcepsilonRI beta and gamma chains. This requirement was demonstrated by overexpression of Syk wild-type or its kinase-dead mutant in RBL cells or using an Syk-deficient RBL-derived cell line transfected with wild-type or a kinase inactive form of Syk. We also identify c-Cbl as the E3 ligase responsible for both Syk and receptor ubiquitination. Furthermore, we demonstrate that Syk controls tyrosine phosphorylation of Syk-associated Cbl induced after receptor engagement. These data suggest a mutual regulation between Syk and Cbl activities. Finally, we show that a selective inhibitor of proteasome degradation induces persistence of tyrosine-phosphorylated receptor complexes, of activated Syk, and of FcepsilonRI-triggered degranulation. Our results provide a molecular mechanism for down-regulation of engaged receptor complexes by targeting ubiquitinated FcepsilonRI and activated Syk to the proteasome for degradation.     

HIV-1 Nef promotes migration and chemokine synthesis of human basophils and mast cells through the interaction with CXCR4

Background

The Nef protein can be detected in plasma of HIV-1-infected patients and plays a role in the pathogenesis of HIV-1. Nef produced during the early stages of infection is fundamental in creating the ideal environment for viral replication, e.g. by reducing the ability of infected cells to induce an immune response.

Aim

Based on previous experience showing that both Tat and gp41 of HIV-1 are potent chemotactic factors for basophils and mast cells, and gp120 is a powerful stimulus for the release of histamine and cytokines (IL-4 and IL-13) from basophils, in this study we aimed to verify if the HIV Nef protein can exert some effects on basophils and mast cells purified from healthy volunteers through the interaction with the CXCL12 receptor, CXCR4.

Methods

Basophils purified from peripheral blood cells of 30 healthy volunteers and mast cells obtained from lung tissue of ten healthy volunteers were tested by flow cytometric analysis, chemotaxis and chemokine production by ELISA assays.

Results

Nef is a potent chemoattractant for basophils and lung mast cells obtained from healthy, HIV-1 and HIV-2 seronegative individuals. Incubation of basophils and mast cells with Nef induces the release of chemokines (CXCL8/IL-8 and CCL3/MIP-1α). The chemotactic activity of Nef on basophils and mast cells is mediated by the interaction with CXCR4 receptors, being blocked by preincubation of FcεRI⁺ cells with an anti-CXCR4 Ab. Stimulation with Nef or CXCL12/SDF-1α, a CXCR4 ligand, desensitizes basophils to a subsequent challenge with an autologous or heterologous stimulus.

Conclusions

These results indicate that Nef, a HIV-1-encoded α-chemokine homolog protein, plays a direct role in basophils and mast cell recruitment and activation at sites of HIV-1 replication, by promoting directional migration of human FcεRI⁺ cells and the release of chemokines from these cells. Together with our previous results, these data suggest that FcεRI⁺ cells contribute to the dysregulation of the immune system in HIV-1 infection.

     

Positive and negative regulation of mast cell activation by Lyn via the FcepsilonRI

Aggregation of the high affinity receptor for IgE (FcepsilonRI) induces activation of mast cells. In this study we show that upon low intensity stimulation of FcepsilonRI with monomeric IgE, IgE plus anti-IgE, or IgE plus low Ag, Lyn (a Src family kinase) positively regulates degranulation, cytokine production, and survival, whereas Lyn works as a negative regulator of high intensity stimulation with IgE plus high Ag. Low intensity stimulation suppressed Lyn kinase activity and its association with FcepsilonRI beta subunit, whereas high intensity stimulation enhanced Lyn activity and its association with FcepsilonRI beta. The latter induced much higher levels of FcepsilonRI beta phosphorylation and Syk activity than the former. Downstream positive signaling molecules, such as Akt and p38, were positively and negatively regulated by Lyn upon low and high intensity stimulations, respectively. In contrast, the negative regulators, SHIP and Src homology 2 domain-containing protein tyrosine phosphatase-1, interacted with FcepsilonRI beta, and their phosphorylation was controlled by Lyn. Therefore, we conclude that Lyn-mediated positive vs negative regulation depends on the intensity of the stimuli. Studies of mutant FcepsilonRI beta showed that FcepsilonRI beta subunit-ITAM (ITAM motif) regulates degranulation and cytokine production positively and negatively depending on the intensity of FcepsilonRI stimulation. Furthermore, Lyn-mediated negative regulation was shown to be exerted via the FcepsilonRI beta-ITAM.     

Imbalance production between interleukin-1beta (IL-1beta) and IL-1 receptor antagonist (IL-1Ra) in bronchial asthma

Genes of the IL-1 family encode three different peptides, IL-1alpha, IL-1beta, and IL-1Ra, respectively. IL-1 operates through IL-1RI, and is involved in airway inflammation in asthmatic subjects, whereas IL-1Ra appears to be a specific competitive inhibitor of IL-1. All genes are on chromosome 2q12-21 where genomewide searches have identified linkage for asthma. To test whether variants of IL-1 relate to asthma, we conducted a genetic association study in a Japanese population. We show that the A2 allele of IL1RN (encoding IL-1Ra) associates with nonatopic asthma [OR = 5.71, 95% CI: 1.63-19. 8, Pc = 0.007]. Both atopic and nonatopic asthmatics with the A2 allele had significantly lower serum IL-1Ra levels in both types of asthmatics. Peripheral blood cells from asthmatics with A2 alleles, however, produced as much IL-1 as did those with A1 homozygotes. Since Th1 and Th2 cytokines differentially regulate the ratio between IL-1beta and IL-1Ra, these findings suggest that dysregulation of IL-1beta/IL-1Ra, probably due to interaction between epithelium and immuno-competent cells in the airway, is important in asthma inflammation.