Dual phase priming by IL-3 for leukotriene C4 generation in human basophils: difference in characteristics between acute and late priming effects

Basophils beyond allergic and parasitic diseases

Basophils bind IgE via FcεRI-αβγ2, which they uniquely share only with mast cells. In doing so, they can rapidly release mediators that are hallmark of allergic disease. This fundamental similarity, along with some morphological features shared by the two cell types, has long brought into question the biological significance that basophils mediate beyond that of mast cells. Unlike mast cells, which mature and reside in tissues, basophils are released into circulation from the bone marrow (constituting 1% of leukocytes), only to infiltrate tissues under specific inflammatory conditions. Evidence is emerging that basophils mediate non-redundant roles in allergic disease and, unsuspectingly, are implicated in a variety of other pathologies [e.g., myocardial infarction, autoimmunity, chronic obstructive pulmonary disease, fibrosis, cancer, etc.]. Recent findings strengthen the notion that these cells mediate protection from parasitic infections, whereas related studies implicate basophils promoting wound healing. Central to these functions is the substantial evidence that human and mouse basophils are increasingly implicated as important sources of IL-4 and IL-13. Nonetheless, much remains unclear regarding the role of basophils in pathology vs. homeostasis. In this review, we discuss the dichotomous (protective and/or harmful) roles of basophils in a wide spectrum of non-allergic disorders.

Differential Effects of Alarmins on Human and Mouse Basophils

Epithelial-derived alarmins (IL-33, TSLP, and IL-25) play an upstream role in the pathogenesis of asthma. Basophil-derived cytokines are a pivotal component of allergic inflammation. We evaluated the in vitro effects of IL-33, TSLP, and IL-25, alone and in combination with IL-3 on purified peripheral blood human basophils (hBaso) and bone marrow-derived mouse basophils (mBaso) in modulating the production of IL-4, IL-13, CXCL8 or the mouse CXCL8 equivalents CXCL1 and CXCL2. IL-3 and IL-33, but not TSLP and IL-25, concentration-dependently induced IL-4, IL-13, and CXCL8 release from hBaso. IL-3 synergistically potentiated the release of cytokines induced by IL-33 from hBaso. In mBaso, IL-3 and IL-33 rapidly induced IL-4 and IL-13 mRNA expression and protein release. IL-33, but not IL-3, induced CXCL2 and CXCL1 from mBaso. Differently from hBaso, TSLP induced IL-4, IL-13, CXCL1 and CXCL2 mRNA expression and protein release from mBaso. IL-25 had no effect on IL-4, IL-13, and CXCL1/CXCL2 mRNA expression and protein release even in the presence of IL-3. No synergism was observed between IL-3 and either IL-25 or TSLP. IL-3 inhibited both TSLP- and IL-33-induced CXCL1 and CXCL2 release from mBaso. Our results highlight some similarities and marked differences between the effects of IL-3 and alarmins on the release of cytokines from human and mouse basophils.

Granzyme B in Epithelial Barrier Dysfunction and Related Skin Diseases

The predominant function of the skin is to serve as a barrier - to protect against external insults and to prevent water loss. Junctional and structural proteins in the stratum corneum, the outermost layer of the epidermis, are critical to the integrity of the epidermal barrier as it balances ongoing outward migration, differentiation, and desquamation of keratinocytes in the epidermis. As such, epidermal barrier function is highly susceptible to upsurges of proteolytic activity in the stratum corneum and epidermis. Granzyme B is a serine protease scarce in healthy tissues but present at high levels in tissues encumbered by chronic inflammation. Discovered in the 1980s, Granzyme B is currently recognized for its intracellular roles in immune cell-mediated targeted apoptosis as well as extracellular roles in inflammation, chronic injuries, tissue remodeling, and processing of cytokines, matrix proteins, and autoantigens. Increasing evidence has emerged in recent years supporting a role for Granzyme B in promoting barrier dysfunction in the epidermis by direct cleavage of barrier proteins and eliciting immunoreactivity. Likewise, Granzyme B contributes to impaired epithelial function of the airways, retina, gut and vessels. In the present review, the role of Granzyme B in cutaneous epithelial dysfunction is discussed in the context of specific conditions with an overview of underlying mechanisms as well as utility of current experimental and therapeutic inhibitors.

IL-3 in the development and function of basophils

The β common chain (βc) cytokine family includes granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) and IL-5, all of which use βc as key signaling receptor subunit. GM-CSF, IL-3 and IL-5 have specific roles as hematopoietic growth factors. IL-3 binds with high affinity to the IL-3 receptor α (IL-3Rα/CD123) and then associates with the βc subunit. IL-3 is mainly synthesized by different subsets of T cells, but is also produced by several other immune [basophils, dendritic cells (DCs), mast cells, etc.] and non-immune cells (microglia and astrocytes). The IL-3Rα is also expressed by immune (basophils, eosinophils, mast cells, DCs, monocytes, and megacaryocytes) and non-immune cells (endothelial cells and neuronal cells). IL-3 is the most important growth and activating factor for human and mouse basophils, primary effector cells of allergic disorders. IL-3-activated basophils and mast cells are also involved in different chronic inflammatory disorders, infections, and several types of cancer. IL-3 induces the release of cytokines (i.e., IL-4, IL-13, CXCL8) from human basophils and preincubation of basophils with IL-3 potentiates the release of proinflammatory mediators and cytokines from IgE- and C5a-activated basophils. IL-3 synergistically potentiates IL-33-induced mediator release from human basophils. IL-3 plays a pathogenic role in several hematologic cancers and may contribute to autoimmune and cardiac disorders. Several IL-3Rα/CD123 targeting molecules have shown some efficacy in the treatment of hematologic malignancies.

Expression profiling of human basophils: modulation by cytokines and secretagogues

Human basophils are an accessible participant of the human allergic reaction. There is natural variation in various functional endpoints and in signaling molecule expression but there has been only a limited effort to place this information in the context of mRNA expression profiles. This study examined the hypothesis that unique mRNA signatures could be identified during the response of human basophils to several known forms of stimulation. Highly purified human basophils were cultured in vitro and exposed to IL-3, IL-5, NGF, IL-33, IL-2, anti-IgE Ab, or FMLP and the mRNA profiles examined by microarrays. The response to IL-3 and anti-IgE Ab were examined on 2–3 time frames and the response to IL-3 examined at several concentrations. In addition, the mRNA signatures of 3 different potential phenotypes were examined. These included basophils with the so-called non-releaser phenotype, and basophils from atopic and non-atopic subjects. Given the role of IL-3 in basophil maturation and the known profound effects on mature basophil function, it was not surprising that IL-3 showed the greatest influence on the basophil transcriptome. However, it also became apparent that the act of isolating and culturing basophils was sufficient to induce a large number of changes in the transcriptome, despite high viability and recovery. These “culture-effect” changes dominated the changes in mRNA profiles induced by other stimuli. Unique signatures for anti-IgE antibody and IL-33 could be identified although the number of gene transcripts (6–30) that were unique to these two stimuli was very limited. There were no apparent unique profiles for IL-5, NGF, IL-2 or FMLP. Therefore, a potential tool for screening basophil phenotypes was limited to changes that could be induced by IL-3 (or no IL-3), IL-33 and anti-IgE Ab.

In human basophils, IL-3 selectively induces RANKL expression that is modulated by IgER-dependent and IgER-independent stimuli

BACKGROUND

Receptor activator of NF-κB ligand (RANKL) is expressed as either surface (hRANKL1, hRANKL2) or soluble (hRANKL3) form. RANKL is involved in multifaceted processes of immunoregulation and bone resorption such as they occur in rheumatoid arthritis (RA). Interestingly, activated basophils, which are effector cells in allergic inflammation, contribute to the progress of collagen-induced arthritis (CIA), a mouse model for RA. Here, we investigate under which conditions human basophils express RANKL.

METHODS

Among other stimuli, basophils were cultured with IL-3 alone. Alternatively, as a secondary stimulus, IgER-dependent or IgER-independent agents were added simultaneously either with IL-3 or after prolonged IL-3 culturing. Expression of RANKL protein and mRNA was analyzed by flow cytometry, ELISA, and real-time PCR. A coculture system was applied to investigate biological activity of basophil-derived RANKL.

RESULTS

We show that in human basophils, IL-3 but no other stimulus induces de novo expression of soluble and surface RANKL, of which the latter enhances survival of MoDC. Upon simultaneous stimulation, IgER cross-linking reduces surface RANKL expression, while IgER-independent stimuli have no effect. This is in contrast to consecutive stimulation, as triggering with both IgER-dependent and IgER-independent stimuli enhances RANKL expression, particularly in its soluble form. Real-time PCR analysis shows that RANKL expression is mainly regulated at the mRNA level.

CONCLUSION

This study identifies IL-3 as a potent inducer of RANKL expression in human basophils, suggesting them to interact with bone physiology and activation of immune cells. IgER-dependent and IgER-independent stimuli modulate the IL-3-mediated RANKL expression in a time- and stimulus-dependent fashion.

Omalizumab increases the intrinsic sensitivity of human basophils to IgE-mediated stimulation

BACKGROUND

Treatment of allergic patients with omalizumab results in a paradoxical increase in their basophil histamine release (HR) response ex vivo to cross-linking anti-IgE antibody. It is not known whether this change in response is associated with an increase in intrinsic cellular sensitivity, which would be a paradoxical response.

OBJECTIVE

We sought to determine whether the increase in response to anti-IgE antibody is a reflection of an increased cellular sensitivity expressed as molecules of antigen-specific IgE per basophil required to produce 50% of the maximal response.

METHODS

Patients were treated with omalizumab or placebo for 12 weeks (NCT01003301 at ClinicalTrials.gov), and the metric of basophil sensitivity was assessed at 4 time points: baseline, 6 to 8 weeks, 12 weeks (after which treatment stopped), and 24 weeks (12 weeks after the end of treatment).

RESULTS

As observed previously, treatment with omalizumab resulted in a marked increase in the maximal HR induced by cross-linking anti-IgE antibody. This change was accompanied by a marked shift in intrinsic basophil sensitivity, ranging from 2.5- to 125-fold, with an average of 6-fold at the midpoint of the treatment to 12-fold after 12 weeks. The magnitude of the increase in cellular sensitivity was inversely related to the starting sensitivity or the starting maximum HR. The increased cellular sensitivity also occurred when using leukotriene C4 secretion as a metric of the basophil response. Twelve weeks after the end of treatment, cellular sensitivity was found to shift toward the baseline value, although the return to baseline was not yet complete at this time point.

CONCLUSIONS

Treatment with omalizumab results in a markedly increased sensitivity of basophils to IgE-mediated stimulation in terms of the number of IgE molecules required to produce a given response. These results provide a better quantitative sense of the phenotypic change that occurs in basophils during omalizumab treatment, which has both mechanistic and clinical implications.

Carbon dioxide-enriched water inhalation in patients with allergic rhinitis and its relationship with nasal fluid cytokine/chemokine release

BACKGROUND AND AIMS

Allergic rhinitis is characterized by eosinophil infiltration and accumulation in the nasal mucosa mainly due to IL-3, IL-5, and eotaxin activities. We undertook this study to investigate a possible in vivo effect of carbon dioxide-enriched water inhalation in patients with allergic rhinitis.

METHODS

Twenty five consecutive patients inhaled carbon dioxide-enriched water at Fonti di Rabbi Spa Centre (Trento, Italy). Symptom scores for nasal obstruction, itching and sneezing were obtained before and after treatment. Nasal lavage was collected, and IL-3, IL-5, and eotaxin levels were assessed using the quantitative sandwich enzyme immunoassay technique. Cytometric analysis was performed on samples to measure total cell count, CD45+ cells, and percentages of polymorphonucleates and lymphocytes.

RESULTS

There were statistically significant differences in chemokine levels and in cell populations between patients and healthy controls before treatment. After carbon dioxide-enriched water inhalation, we observed statistically significant improvements in symptom scores, chemokine levels, and percentages of cell populations.

CONCLUSIONS

Our results seem to confirm the role of IL-3, IL-5, and eotaxin in the pathophysiology of allergy and the beneficial effect of carbon dioxide-enriched water inhalation in patients affected by allergic rhinitis.

Regulation of human mast cell and basophil function by anaphylatoxins C3a and C5a

Allergic diseases such as asthma result from inappropriate immunologic responses to common environmental allergens in genetically susceptible individuals. Following allergen exposure, interaction of dendritic cells (DC) with CD4(+) T cells leads to the production of Th2 cytokines, which induce B cells to synthesize IgE molecules (sensitization phase). These IgE molecules bind to their high affinity receptors (FcvarepsilonRI) on the surface of mast cells and basophils and their subsequent cross-linking by allergen results in the release of preformed and newly synthesized mediators, which cause bronchoconstriction, lung inflammation and airway hyperresponsiveness (AHR) in asthma (effector phase). The complement components C3a and C5a levels are increased in the lungs of patients with asthma and are likely generated via the actions of both allergen and mast cell proteases. In vivo studies with rodents have shown that while C3a facilitates allergen sensitization in some models C5a inhibits this response. Despite this difference, both anaphylatoxins promote lung inflammation and AHR in vivo indicating that cells other than DC and T cells likely mediate the functional effects of C3a and C5a in asthma. This review focuses on the contribution of C3a and C5a in the pathogenesis of asthma with a particular emphasis on mast cells and basophils. It discusses the mechanisms by which anaphylatoxins activate mast cells and basophils and the associated signaling pathways via which their receptors are regulated by priming and desensitization.

C5a-induced in vitro basophil activation in patients with chronic urticaria: a pilot study

BACKGROUND

Complement component 5a (C5a) might be involved in the formation of wheals in patients with chronic urticaria (CU). We sought to compare the in vitro responsiveness of basophils to C5a in patients with CU and in a control group.

METHODS

Basophil surface expression of activation marker CD63 induced by C5a, anti-FcepsilonRI mAb or anti-IgE pAb was measured using flow cytometry in 17 patients with CU and in 10 healthy controls.

RESULTS

Patients with CU showed significantly greater basophil CD63 surface expression induced by C5a (median [interquartile range]; 16.4% [13-25.1]; P = 0.011) than the group of healthy controls (10.7% [7.2-16.8]). In contrast, basophil CD63 response to anti-IgE and anti-FcepsilonRI was lower in the CU group (12.3% [6-36.3]; 25.9% [12.5-60.5]) than in the control group (51.7% [6.7-84.3]; 62.1% [9.7-89.2]), although not statistically significant.

CONCLUSION

Results of this pilot study suggest that patients with CU might have an enhanced basophil response to stimulation with C5a, indicating that further studies in CU basophil responsiveness are needed.

IL-3 is required for increases in blood basophils in nematode infection in mice and can enhance IgE-dependent IL-4 production by basophils in vitro

Basophils represent potential effector and immunoregulatory cells, as well as a potential source of IL-4, during the immune response elicited by infection with the nematode Nippostrongylus brasiliensis (N.b.), and in other settings. However, the factors which regulate the numbers of blood basophils in mice, or the ability of these cells to produce IL-4, are not fully understood. We found that infection of mice with the nematodes N.b. or Strongyloides venezuelensis (S.v.) induced substantial increases in the numbers of blood basophils (to as high as 18% of circulating blood leukocytes). Experiments in IL-3-/- vs IL-3+/+ mice, and in IL-3-treated IL-3-/- mice, showed that essentially all of the increases in blood or bone marrow basophils during N.b. or S.v. infection were IL-3 dependent. Many of the blood, bone marrow or liver-derived basophils from IL-3-/- or IL-3+/+ mice expressed intracellular IL-4 upon stimulation with anti-IgE in vitro. However, after incubation of the cells with exogenous IgE in vitro, blood- or liver-derived basophils from IL-3+/+ mice exhibited higher levels of intracellular IL-4 after stimulation with anti-IgE than did basophils derived from IL-3-/- mice. Thus, IL-3 is a major regulator of the marked increases in blood basophil levels observed during infection of mice with N.b. or S.v. and also can enhance levels of intracellular IL-4 upon activation of basophils with anti-IgE in vitro.

Flow cytometry for basophil activation markers: the measurement of CD203c up-regulation is as reliable as CD63 expression in the diagnosis of cat allergy

The flow cytometric basophil activation test (BAT), based on the detection of allergen-induced CD63 expression, has been proved effective in the diagnosis of various IgE-mediated allergies. However, there is not yet consensus about the suitability of CD203c expression as a specific basophil activation marker and its diagnostic reliability. The goal of the present study was to compare measurement of CD63 and CD203c expression using BAT in a model of cat allergy and to determine optimal experimental conditions for both markers. Heparinized whole blood samples from 20 cat allergic patients and 19 controls were incubated with Fel d1 (relevant allergen) or anti-FcepsilonRI (positive control) either in IL-3 or IL-3-free conditions. An optimal gating of basophils was achieved in triple staining protocols: anti-IgE PE/anti-CD45 PerCP/anti-CD63 FITC or anti-IgE FITC/anti-CD45 PerCP/anti-CD203c PE. We demonstrated that IL-3 significantly enhanced CD63-induced expression by basophils obtained from cat allergic patients in response to Fel d1. Sensitivity was found to be 100%. The CD203c protocol, when performed under IL-3-free conditions, also demonstrated 100% sensitivity. Only one of the control subjects was positive in both tests. In conclusion, using well-defined experimental conditions, the measurement of CD203c up-regulation on basophils in response to specific allergens is as reliable as CD63-BAT for the in vitro diagnosis of patients with IgE-mediated allergy.

Granzyme B, a novel mediator of allergic inflammation: its induction and release in blood basophils and human asthma

Histamine, leukotriene C4, IL-4, and IL-13 are major mediators of allergy and asthma. They are all formed by basophils and are released in particularly large quantities after stimulation with IL-3. Here we show that supernatants of activated mast cells or IL-3 qualitatively change the makeup of granules of human basophils by inducing de novo synthesis of granzyme B (GzmB), without induction of other granule proteins expressed by cytotoxic lymphocytes (granzyme A, perforin). This bioactivity of IL-3 is not shared by other cytokines known to regulate the function of basophils or lymphocytes. The IL-3 effect is restricted to basophil granulocytes as no constitutive or inducible expression of GzmB is detected in eosinophils or neutrophils. GzmB is induced within 6 to 24 hours, sorted into the granule compartment, and released by exocytosis upon IgE-dependent and -independent activation. In vitro, there is a close parallelism between GzmB, IL-13, and leukotriene C4 production. In vivo, granzyme B, but not the lymphoid granule marker granzyme A, is released 18 hours after allergen challenge of asthmatic patients in strong correlation with interleukin-13. Our study demonstrates an unexpected plasticity of the granule composition of mature basophils and suggests a role of granzyme B as a novel mediator of allergic diseases.

Acute IL-3 priming up-regulates the stimulus-induced Raf-1-Mek-Erk cascade independently of IL-3-induced activation of Erk

IL-3 is a potent priming cytokine for human basophils, inducing an increase of mediator release after stimulation. The mechanism of IL-3 priming of the basophil response to FcepsilonRI aggregating stimuli remains unknown. We explored the regulation of several elements of IgE-mediated signaling by a short priming with IL-3. Early signaling events such as phosphorylation of Syk, Shc, linker for activation of T cells, and the calcium signal were not statistically affected by acute IL-3 priming. Downstream in the signaling cascade, a point of up-regulation was found at the level of Raf-1-Mek-Erk. Although the phosphorylation of Raf-1 was not changed by IL-3 priming, IL-3-primed anti-IgE-stimulated basophils showed a strong synergism for Mek and Erk phosphorylation when compared with either IL-3 or anti-IgE alone; pre-exposure to IL-3 induced a final 13-fold average increase over anti-IgE-induced Erk phosphorylation (6-fold above the sum of anti-IgE and IL-3 alone). The kinetics, dose response, and pharmacologic characteristics of the IL-3 priming of stimulus-induced Erk phosphorylation support the involvement of a yet unknown mechanism that is independent of IL-3-induced Erk and PI3K activation. This type of preactivation can be mimicked by incubation with the Ser-Thr kinase inhibitors, Ro-81-3220, or bisindoylmaleimide II.

Assessment of determinants of optimum performance of the CAST-2000 ELISA procedure

The Cellular Antigen Stimulation Test (CAST), a recent innovation in the laboratory detection of allergen sensitivity, is a functional assay based on the release of sulphidoleukotrienes (LTs) from allergen-activated circulating basophils. The current study was undertaken to establish optimum determinants of this procedure. The results demonstrate that treatment of blood with preservative-free heparin in polypropylene containers, and removal of erythrocytes by selective lysis with 0.83% ammonium chloride are excellent alternatives to the use of CAST venepuncture tubes and dextran, respectively. Similarly, decreasing and increasing the leucocyte concentration by 0.5- and 4-fold, respectively, as well as omission of interleukin-3 (IL-3) were also without significant effect. However, treatment of leucocyte suspensions with bacterial endotoxin (>1 microg/ml) activated the release of sulphidoleukotrienes from basophils and/or other types of leucocytes. The findings of this study are clearly relevant, both with respect to cost and performance, when implementing the CAST in clinical immunology laboratories.

Actin cytoskeleton-dependent down-regulation of early IgE-mediated signaling in human basophils

Two regions of down-regulation of FcepsilonRI [high-affinity immunogloublin E (IgE) receptor] signaling have been localized recently in basophils. An early down-regulatory step is located proximal to syk and appears responsible for a transient syk phosphorylation in antigen-stimulated basophils. A second, more distal region appears responsible for the transient activation of the ras-extracellular-regulated kinase (Erk) pathway when syk phosphorylation is sustained in anti-IgE-stimulated basophils. As the actin cytoskeleton has been demonstrated to inhibit the early FcepsilonRI signaling in rat basophilic leukemia cells, we explored the hypothesis that the actin cytoskeleton was responsible for the transience of syk phosphorylation in antigen-stimulated basophils. The inhibition of F-actin polymerization with latrunculin A induced a sustained syk phosphorylation in basophils stimulated with an optimal dose of the antigen benzyl penicilloyl-human serum albumin. However, in the presence of latrunculin A, Erk phosphorylation remained transient after stimulation with the antigen or anti-IgE. Latrunculin A also increased downstream events such as histamine release, leukotriene C(4) release, and the intracellular calcium signal, although some of these effects were not specific for an immunologic stimulus. Our results suggest that the actin cytoskeleton is responsible for down-regulation of FcepsilonRI signaling at a point located proximal to syk phosphorylation. Moreover, the fact that latrunculin A did not result in sustained Erk phosphorylation supports the presence of a second down-regulatory step between syk and Erk that cannot be overcome by a sustained early signal.

IFN-alpha inhibits IL-3 priming of human basophil cytokine secretion but not leukotriene C4 and histamine release

BACKGROUND

Innate immune responses play a critical role in determining the course of acquired immunity, including that associated with allergic disease. Type I interferons, which are generated early in these reactions, are important soluble factors that prime for TH1-like activity.

OBJECTIVE

Because human basophils secrete IL-4 and IL-13 in response to both IgE-dependent and IgE-independent stimuli, we tested whether IFN-alpha, a major type I IFN, affects the production of these TH2 cytokines and/or mediator release from these cells.

METHODS

Basophils isolated from blood were treated with IFN-alpha in the presence and absence of IL-3 priming before stimulating through the IgE receptor to release histamine, leukotriene C4, and IL-4. Effects of IFN-alpha on IL-3-mediated IL-13 secretion and basophil survival were also tested. IFN-alpha receptor expression was determined by RT-PCR.

RESULTS

IFN-alpha specifically inhibited the effects IL-3 has on basophil cytokine secretion. Enhanced secretion of IL-4 resulting from IL-3 priming was significantly inhibited in cells concurrently cultured with IFN-alpha. This effect was specific for cytokine generation, because histamine and leukotriene C4 were unaffected. Furthermore, IFN-alpha blocked IL-13 secretion directly induced by IL-3. Although IFN-beta also possessed some inhibitory activity, IFN-gamma (a type II IFN) had no effect on basophil cytokine secretion. Basophils constitutively expressed mRNA for the type I IFN receptor, and IFN-alpha did not affect basophil viability with regard to inhibition of cytokine secretion.

CONCLUSIONS

These results support the belief that early innate immune responses resulting in IFN-alpha production negatively regulate allergic responses by also inhibiting priming of basophil cytokine release.

IL3 effect on basophils histamine release upon stimulation with chronic urticaria sera

BACKGROUND

Chronic urticaria is thought to be an autoimmune disorder in 35-40% of patients because of the presence of an immunoglobulin G (IgG) antibody reactive with the IgE receptor. Patients possessing this antibody are identified by the ability of serum to degranulate donor basophils to release histamine. We questioned whether priming of basophils with interleukin 3 (IL3) would facilitate identification of patients and/or alter the percentage of patients who have a positive assay.

METHODS

We incubated 37 chronic urticaria sera with basophils from donors with no urticaria with and without priming with IL3 and compared histamine release in each instance. We also preincubated basophils from a 'non-releaser' with IL3, used these cells to assay chronic urticaria sera, and assessed the contribution of complement.

RESULTS

Interleukin 3 increases the amount of histamine release by the sera which is able to activate basophils, but it does not convert negative sera into positive releasers. Interleukin 3 is able to partially reverse 'non-releaser' basophils into cells that respond to chronic urticaria sera, and complement cannot account for the augmentation seen.

CONCLUSIONS

Preincubating basophils with IL3 facilitates the identification of sera with anti-IgE receptor antibody but does not affect the percentage of sera designated as positive.

Association of the Src homology 2 domain-containing inositol 5' phosphatase (SHIP) to releasability in human basophils

During the study of the biology of the Human recombinant Histamine Releasing Factor (HrHRF), we uncovered a hyperreleasable phenotype of basophils from HrHRF-responder donors. Basophils from these donors released histamne to HrHRF, IL-3 and D(2)O. While there has been a significant amount of work elucidating signal transduction events in human basophils, the reason for this hyperreleasable phenotype remained illusive. A clue to the releasability of these highly allergic, asthmatic HrHRF-responder donor basophils was demonstrated in studies using SHIP knockout mice. Bone marrow-derived mast cells from the SHIP knockout mice demonstrated hyperreleasability to stimuli through the IgE receptor and alteration of subsequent signal transduction events. We have demonstrated a highly significant negative correlation between the amount of SHIP protein per cell equivalent and maximum histamine release to HrHRF. These results provide a clue to the hyperreleasable phenotype and implicate SHIP as an additional regulator of secretion in human basophils.

Localizing a control region in the pathway to leukotriene C(4) secretion following stimulation of human basophils with anti-IgE antibody

Mediator release from human basophils is a self-limited process, but down-regulation of the signaling cascades leading to secretion of leukotriene C(4) (LTC(4)) is controlled independently of the pathway leading to IL-4 secretion. In the current studies, we have explored the regulation of upstream signaling events leading to activation of extracellular signal-related kinases (ERKs; previously shown to be required for LTC(4) generation) in human basophils. IgE-, but not FMLP-mediated activation, induced sustained tyrosine phosphorylation of syk, of shc, and an association of shc to the Grb2/son of sevenless 2 complex. In contrast, IgE-mediated activation resulted in transient activation of p21(ras) and mitogen-activated protein/ERK kinase 1, which were kinetically associated with phosphorylation of ERKs. The canonical Shc/Grb2/son of sevenless pathway to activation of p21(ras) is therefore sustained, while p21(ras) activity is not. We have previously shown that phosphatidylinositol 3 kinase activity is required for p21(ras) activity and, in the current studies, we show that of the p85-sensitive forms of p110 possible, basophils express only p110 delta and that there are no changes in association between p21(ras) and p110 delta in stimulated basophils. We used the generation of phospho-Akt as a marker of the presence of phosphatidylinositol-3,4,5-trisphosphate and found that phospho-Akt is transient on a time scale consistent with p21(ras) activity. On the basis of information obtained in these and other studies, we localize down-regulation of IgE-mediated LTC(4) secretion to a region of the signaling cascade antecedent to p21(ras) activation, downstream of phosphatidylinositol 3 kinase activity and probably involving regulation of phosphatidylinositol-3,4,5-trisphosphate levels.

Src homology 2 domain-containing inositol 5' phosphatase is negatively associated with histamine release to human recombinant histamine-releasing factor in human basophils

BACKGROUND

The human recombinant histamine-releasing factor (HrHRF) acts as a complete stimulus for histamine release and IL-4 secretion from a subpopulation of highly allergic donor basophils, termed IgE(+) basophils. Additionally, IgE(+) basophils release histamine to other secretogues, IL-3, and deuterium oxide. We hypothesized that IgE(+) basophils were hyperreleasable.

OBJECTIVE

Deficiencies in early signal transduction events associated with Fc(epsilon)RI lead to a nonreleasable phenotype, whereas the Src homology 2 domain--containing inositol 5' phosphatase (SHIP) knockout mice have hyperreleasable mast cells. The purpose of this study was to ascertain whether a difference in intracellular signaling molecules could explain the hyperreleasable phenotype of human IgE(+) basophils.

METHODS

Basophils were purified by means of double Percoll gradients and negative selection with magnetic beads. Cell lysates were Western blotted for the tyrosine kinases Lyn and Syk and the phosphatase SHIP. Additionally, histamine release to HrHRF was performed in addition to real-time RT-PCR to investigate mRNA for SHIP.

RESULTS

We show a striking negative correlation between the amount of SHIP protein per cell equivalent, but not Lyn or Syk, and maximum histamine release to HrHRF. This deficiency of SHIP was observed in basophils, but not lymphocytes or monocytes, of these IgE(+) donors. Additionally, levels of mRNA for SHIP did not differ between IgE(+) and IgE(-) donor basophils, which is consistent with a posttranscriptional mechanism of protein regulation. SHIP and phosphatidylinositol 3-kinase reciprocally regulate phosphatidylinositol (3,4,5) triphosphate levels. We also demonstrated that Ly294002, the phosphatidylinositol 3 kinase inhibitor, prevented HrHRF-induced histamine release in IgE(+) donor basophils.

CONCLUSION

Taken together, these data suggest that the hyperreleasability of IgE(+) donors is associated with low levels of SHIP and implicate SHIP as an additional regulator of secretion in human basophils.

Cutting edge: Differential regulation of chemoattractant receptor-induced degranulation and chemokine production by receptor phosphorylation

Phosphorylation of G protein-coupled receptors and the subsequent recruitment of beta-arrestin play an important role in desensitization of receptor-mediated responses, including degranulation in leukocytes. In this study, we report that receptor phosphorylation also provides a stimulatory signal for CCR ligand 2 (CCL2) production. C3a stimulated degranulation in a basophilic leukemia RBL-2H3 cell expressing wild-type C3aR or a phosphorylation-deficient mutant (DeltaST-C3aR). In contrast, C3a caused CCL2 production only in C3aR but not DeltaST-C3aR cells. Furthermore, overexpression of G protein-coupled receptor kinase 2 resulted in enhancement of both ligand-induced receptor phosphorylation and CCL2 production but inhibition of degranulation. Agonist activation of C3aR, but not DeltaST-C3aR, led to the translocation of green fluorescent protein tagged beta-arrestin 2 from the cytoplasm to the plasma membrane. These data demonstrate that receptor phosphorylation, which provides a turn off signal for degranulation, is essential for CCL2 production.

Differences in functional consequences and signal transduction induced by IL-3, IL-5, and nerve growth factor in human basophils

Previous studies have indicated a redundancy in the effects of the cytokines, IL-3, IL-5, and nerve growth factor (NGF) on acute priming of human basophils. In the current study, we have examined the effects of these three cytokines on 18-h priming for leukotriene C4 generation, their ability to induce Fc(epsilon)RIbeta mRNA expression, or their ability to sustain basophil viability in culture. We also examine a variety of the signaling steps that accompany activation with these cytokines. In contrast with the ability of IL-3 to alter secretagogue-mediated cytosolic calcium responses following 18-h cultures, 18-h treatment with IL-5 or NGF did not affect C5a-induced leukotriene C4 generation or alter C5a-induced intracellular Ca2+ concentration elevations. IL-3 and IL-5, but not NGF, induced Fc(epsilon)RIbeta mRNA expression and all three improved basophil viability in culture with a ranking of IL-3 > IL-5 > or = NGF. All three cytokines acutely activated the extracellular signal-regulated kinase pathway and the signaling elements that preceded extracellular signal-regulated kinase and cytosolic phospholipase A2 phosphorylation, consistent with their redundant ability to acutely prime basophils. However, only IL-3 and IL-5 induced Janus kinase 2 and STAT5 phosphorylation. This pattern of signal element activation among the three cytokines most closely matched their ability to induce expression of Fc(epsilon)RIbeta mRNA. Induction of the sustained calcium signaling that follows overnight priming with IL-3 appeared to be related to the strength of the early signals activated by these cytokines but the relevant pathway required was not identified. None of the signaling patterns matched the ability of the cytokines to promote basophil survival.

Expression and modulation of FcepsilonRIalpha and FcepsilonRIbeta in human blood basophils

BACKGROUND

The IgE receptor (FcepsilonRI) may exist as a tetramer (alphabetagamma2) or a trimer (alphagamma2) because FcepsilonRIbeta is dispensable for membrane expression of FcepsilonRIalpha. FcepsilonRIbeta amplifies signaling of FcepsilonRI so that regulation of FcepsilonRIalpha:beta stoichiometry would affect cellular responsiveness.

OBJECTIVE

We examined basophils from a variety of donors for differences in their expression of FcepsilonRIalpha and FcepsilonRIbeta protein.

METHODS

Enriched blood basophils were assessed at baseline and after IL-3 culture for FcepsilonRIalpha and FcepsilonRIbeta protein by Western blotting, surface FcepsilonRIalpha by flow cytometry, and FcepsilonRIbeta mRNA by real-time PCR. Basophil functional response was measured by allergen-triggered histamine release.

RESULTS

For the FcepsilonRIalpha subunit, 2 protein bands with molecular weights of 50 kd and 60 kd were identified by Western blots. The 60-kd band correlated to surface-expressed FcepsilonRIalpha detected by flow cytometry (Spearman R = 0.78, P <.01). Surface FcepsilonRIalpha also correlated with FcepsilonRIbeta protein (Spearman R = 0.92, P <.01). FcepsilonRIbeta protein levels increased disproportionately with higher surface FcepsilonRIalpha expression. The ratio of FcepsilonRIbeta to FcepsilonRIalpha varied 10-fold among donors and correlated with surface FcepsilonRIalpha. Basophil 50-kd alpha protein levels were similar despite a 10-fold range in surface FcepsilonRIalpha expression, implying stores of this protein such as those found in eosinophils. Unlike eosinophils, the basophil 50-kd protein was lost with culture and was absent from supernatants. Levels of beta protein and mRNA were enhanced by IL-3 culture, whereas FcepsilonRIalpha expression (by flow cytometry and 60 kd) was not.

CONCLUSION

These findings demonstrate variable stoichiometry of FcepsilonRIalpha:beta in whole cells and that this stoichiometry can be altered by IL-3 culture. With the assumption that all detected beta protein is surface expressed, these findings suggest a variable stoichiometry for FcepsilonRIalpha:beta that is also related to FcepsilonRIalpha surface expression.

Systemic activation of basophils and eosinophils: markers and consequences

Basophils and eosinophils are important effector cells in human allergic diseases; they play a significant role in promoting allergic inflammation through the release of proinflammatory mediators (such as histamine, leukotriene C(4), major basic protein, eosinophil cationic protein, IL-4, and IL-13, among others). Notably, in allergic subjects, these cells exist in higher numbers and in a more activated state compared with nonatopic control subjects. Evidence for the greater activation state includes increased expression of intracellular and surface markers and hyperreleasability of allergy mediators. We have been interested in the phenotypic markers of effector-cell activation for many years. There is considerable overlap among activation markers, and few activation markers have been found that define a unique phenotype that is quantifiable in the assessment of the presence and severity of allergic disease. This review summarizes the existing evidence for systemic activation of human basophils and eosinophils in allergic diseases. The potential mechanisms responsible for functional and morphologic alterations in these effector cells and the specificity and utility of surface markers in the assessment of allergic disease activity or severity are also discussed.

Phosphatidylinositol-3 kinase regulates p21ras activation during IgE-mediated stimulation of human basophils

Cross-linking of IgE or a bacterial product (f-Met-Leu-Phe; FMLP) induces the release of leukotriene C4 (LTC4) and histamine in human basophils. However, the signaling mechanisms in human basophils are only partially understood. It has been demonstrated that extracellular signal-regulated kinases (ERK1/2) specifically regulate the pathway for LTC4 generation, but not for histamine release and interleukin-4 production. More recent studies have suggested that tyrosine kinase (syk)-mediated phosphorylation of shc is responsible for the ras-ERK cascade via the formation of shc-Grb2-Sos2 following stimulation with anti-IgE antibody, but not FMLP, in human basophils. However, while characterizing the role of phosphatidylinositol (PI)-3 kinase in signaling pathways leading to basophil mediator release, it was noted that this pathway might also regulate p21ras activation. Anti-IgE antibody, but not FMLP, resulted in phosphorylation of p85 (regulatory subunit of PI3 kinase), suggesting activation of PI3 kinase. Inhibition of PI3 kinase by selective inhibitor (LY294002) abolished anti-IgE antibody- but not FMLP-induced phosphorylation of MEK1 (MAPK kinase/ERK kinase) and ERKs while inhibiting LTC4 generation as well as histamine release. IgE-mediated activation of ras (upstream of MEK-ERK) was also inhibited. But, further upstream, phosphorylation of syk and of shc and inducible association between shc and Grb2 were not affected. Furthermore, the IgE-mediated cytosolic calcium response ([Ca++]i) was also diminished. These results suggest that functional responses may be dependent on the activity of PI3 kinase, which regulates at least 2 important signaling pathways: by regulating activation of ras for the MEK-ERK pathway and the increase in [Ca++]i.

Phosphatidylinositol-3 kinase regulates p21ras activation during IgE-mediated stimulation of human basophils

Cross-linking of IgE or a bacterial product (f-Met-Leu-Phe; FMLP) induces the release of leukotriene C4 (LTC4) and histamine in human basophils. However, the signaling mechanisms in human basophils are only partially understood. It has been demonstrated that extracellular signal-regulated kinases (ERK1/2) specifically regulate the pathway for LTC4 generation, but not for histamine release and interleukin-4 production. More recent studies have suggested that tyrosine kinase (syk)-mediated phosphorylation of shc is responsible for the ras-ERK cascade via the formation of shc-Grb2-Sos2 following stimulation with anti-IgE antibody, but not FMLP, in human basophils. However, while characterizing the role of phosphatidylinositol (PI)-3 kinase in signaling pathways leading to basophil mediator release, it was noted that this pathway might also regulate p21ras activation. Anti-IgE antibody, but not FMLP, resulted in phosphorylation of p85 (regulatory subunit of PI3 kinase), suggesting activation of PI3 kinase. Inhibition of PI3 kinase by selective inhibitor (LY294002) abolished anti-IgE antibody- but not FMLP-induced phosphorylation of MEK1 (MAPK kinase/ERK kinase) and ERKs while inhibiting LTC4 generation as well as histamine release. IgE-mediated activation of ras (upstream of MEK-ERK) was also inhibited. But, further upstream, phosphorylation of syk and of shc and inducible association between shc and Grb2 were not affected. Furthermore, the IgE-mediated cytosolic calcium response ([Ca++]i) was also diminished. These results suggest that functional responses may be dependent on the activity of PI3 kinase, which regulates at least 2 important signaling pathways: by regulating activation of ras for the MEK-ERK pathway and the increase in [Ca++]i.

Requirements for C5a receptor-mediated IL-4 and IL-13 production and leukotriene C4 generation in human basophils

Anaphylatoxin derived from the fifth complement component (C5a) in the presence of IL-3 induces continuous leukotriene C4 generation and IL-4 and IL-13 expression in human basophils for a period of 16-18 h. This indicates that the G protein-coupled C5a receptor (C5aR) can induce long-lasting cellular responses. Using anti-N-terminal C5aR Abs, C-terminal C5a hexapeptide analogs, and pertussis toxin, we demonstrate that the putative activation site of the C5aR is both necessary and sufficient for these late cellular responses. Furthermore, continuous pertussis toxin-sensitive G protein-coupled receptor activation and receptor-ligand interaction is ongoing and required during the entire period of product release. However, the late basophil responses have a more stringent requirement for optimal receptor activation. Leukotriene C4 generation appears to be influenced mostly by the way the receptor is activated, because the most active hexapeptide is a superagonist for this response. By contrast, C5adesarg, lacking the C-terminal arginine, induces minimal lipid mediator formation but is fully active to induce IL-4 production and is even a superagonist for IL-13 release. Nevertheless, IL-4/IL-13 synthesis in response to C5adesarg could be blocked by both C-terminal antagonistic peptide as well as anti-N-terminal C5aR Abs, indicating only minor differences of ligand-receptor interactions between C5a and C5adesarg. Taken together, our data demonstrate that long-lasting and continuous signaling occurs through a limited activation domain of the C5aR, which can differentially promote separate basophil functions.