Relationship between spleen tyrosine kinase and phosphatidylinositol 5' phosphatase expression and secretion from human basophils in the general population

Interleukin-3-dependent potentiation of IgE responsiveness in mouse basophils

Basophils produce interleukins (IL)-4 in response to various stimuli and may contribute to type 2 immune responses to various infections and allergens. We found that resting basophils freshly isolated from mice produce IL-4 in response to IL-3 but not to high-affinity Fc receptor (FcεRI) cross-linking (CL), yet both required the immunoreceptor tyrosine-based activation motif (ITAM) containing adaptor Fc receptor γ-chain (FcRγ), while basophils activated in vitro by IL-3 become responsive to FcεRI CL. Acquisition of responsiveness to FcεRI CL occurred upon infection with Trichinella spiralis or administration of superantigen. Because cultured basophils return to a quiescent state upon starvation with IL-3 with surface FcεRI levels unchanged, this acquisition is reversible and probably reflects intracellular events requiring protein synthesis. Interestingly, similar activation-associated acquisition was observed for responsiveness to other stimuli, including CD200R3 CL, which is known to signal via DAP-12, and the allergen protease papain. This acquisition of responsiveness to FcεRI CL was inhibited by Jak inhibitor. Thus, the IL-3 signal bifurcates downstream of Jak, into two distinct pathway, one leading to IL-4 production and the other to render basophils competent to respond to stimuli dependent on ITAM-containing adaptors DAP12 and FcRγ for IL-4 production.

IgE-dependent human basophil responses are inversely associated with the sarcoplasmic reticulum Ca2+-ATPase (SERCA)

Basophils crucially contribute to allergies and other Th2-driven diseases by rapidly releasing inflammatory and immunomodulatory mediators following high-affinity IgE-receptor crosslinking. Although these basophil-mediated responses depend on sensitization with antigen-specific IgE, this does not necessarily predict clinical symptom severity. It is thought that the balance of early stimulatory (e.g. SYK) and inhibitory (e.g. SHIP-1) intracellular signals are associated with basophil responsiveness, which is also critically dependent on calcium mobilization. Previous studies suggest that the sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2), which regulates cytosolic calcium levels, may be inversely associated with airway smooth muscle reactivity in asthma. Since basophils are implicated in asthma severity, our aims were to address whether SERCA2 is implicated in human basophil responses, especially following IgE-mediated activation. Human basophils were obtained from buffy coats, following research ethics approval, and further purified by immunomagnetic cell sorting. Expressions of SERCA2, and other isoforms, were determined by Western blotting in parallel to measuring IgE-dependent histamine releases from the same donors. The effects of a SERCA-activator and inhibitor were also assessed on their abilities to modulate basophil histamine release. We observed an inverse correlation between basophil responsiveness to IgE-dependent stimulation and SERCA2 expression. Thapsigargin, a highly-specific SERCA inhibitor, stimulated basophil histamine release and potentiated IgE-dependent secretion of the amine. Conversely, disulfiram, a SERCA activator, inhibited IgE-dependent basophil activation. The results obtained from this exploratory study indicate that SERCA2 may be an additional regulator of basophil reactivity alongside early excitatory or inhibitory signal transduction pathways.

Basophil activation test: Mechanisms and considerations for use in clinical trials and clinical practice

The basophil activation test (BAT) is a functional assay that measures the degree of degranulation following stimulation with allergen or controls by flow cytometry. It correlates directly with histamine release. From the dose-response curve resulting from BAT in allergic patients, basophil reactivity (%CD63⁺ basophils) and basophil sensitivity (EC₅₀ or similar) are the main outcomes of the test. BAT takes into account all characteristics of IgE and allergen and thus can be more specific than sensitization tests in the diagnosis of allergic disease. BAT reduces the need for in vivo procedures, such as intradermal tests and allergen challenges, which can cause allergic reactions of unpredictable severity. As it closely reflects the patients' phenotype in most cases, it may be used to support the diagnosis of food, venom and drug allergies and chronic urticaria, to monitor the natural resolution of food allergies and to predict and monitor clinical the response to immunomodulatory treatments, such as allergen-specific immunotherapy and biologicals. Clinical application of BAT requires analytical validation, clinical validation, standardization of procedures and quality assurance to ensure reproducibility and reliability of results. Currently, efforts are ongoing to establish a platform that could be used by laboratories in Europe and in the USA for quality assurance and certification.

Basophil activation test: Assay precision and BI 1002494 SYK inhibition in healthy and mild asthmatics

BACKGROUND

Application of basophil activation test (BAT) in clinical trials requires assay validity. Whether assay variability differs between healthy and asthmatic subjects is mostly unknown. This study compares basophil stimulation using blood from healthy and asthmatic subjects with or without inhibition of spleen tyrosine kinase (SYK).

METHODS

Whole blood of healthy and mild asthmatic subjects was stimulated with anti-dinitrophenyl (DNP) IgE/DNP bovine serum albumin and anti-IgE. Basophil activation was detected by CD63 and CD203c expression. CD63 expression levels were compared with serum IgE levels. Three operators repeated experiments with three subjects each from both groups at 3 days to observe assay precision. The effect of the SYK inhibitor BI 1002494 was assessed in BAT for both healthy and asthmatic subjects.

RESULTS

BAT was reproducible in both groups. Acceptance criteria of <25% CV were mostly fulfilled. Stimulation with anti-DNP (p < 0.001, r = -0.80) but not anti-IgE (p = 0.74, r = 0.05) was related to serum IgE with levels > 200 IU/ml limiting anti-DNP stimulation. BI 1002494 IC₅₀ values were 497 nM and 1080 nM in healthy and 287 nM and 683 nM in asthmatics for anti-DNP and anti-IgE stimulation, respectively.

CONCLUSION

BAT, performed with blood from healthy or asthmatic subjects, is a robust test for the measurement of a physiological response in clinical trials. Blood from asthmatic donors with serum IgE > 200 IU/ml is less feasible when using anti-DNP stimulation. SYK inhibition was not affected by disease status.

Modulating the Human Basophil Phenotype During Its Development and Maturation: Basophils Derived from In Vitro Cultures of CD34+ Progenitor Cells

Historically, the human basophil that is studied experimentally comes from peripheral blood. But there is evidence that only a short portion of the basophil life cycle related to IgE-mediated function occurs in the blood. The same evidence suggests that IgE-mediated functionality is present for 5-7 days in the bone marrow (or other tissues) during which the cell modulates its phenotype according to local conditions. It is suggested that to properly understand the nature of basophil behavior, a better understanding of its biology during maturation would be helpful. For example, one highly suggestive line of evidence for the relevance of understanding the maturation period is related to the change in basophil phenotype that occurs during treatment of patients with omalizumab. During this treatment, the intrinsic reactivity or sensitivity of the basophils is significantly increased despite, or perhaps because of, the dramatic reduction in FcεRI expression that accompanies this treatment. One of the critical signaling enzymes to increase expression selectively in basophils during treatment is SYK, which is one of the earliest signaling tyrosine kinases involved in translating the aggregation of FcεRI into secretion from the cell. Treatment with omalizumab increases SYK expression, and this observation focuses some attention of how SYK expression is regulated. It is possible that the key regulation occurs during maturation of the basophil. Regardless of the mechanisms operative in this particular treatment, understanding the process of maturation and the extrinsic factors that influence it may lead to better understanding of disease processes. Therefore, this chapter will discuss and present techniques to work with maturing human basophils.

Response of peripheral blood basophils in subjects with chronic spontaneous urticaria during treatment with omalizumab

BACKGROUND

Treatment of patients with asthma or food allergy with omalizumab results in several consistent changes in circulating basophils. The multiple basophil phenotypes observed in patients with chronic spontaneous urticaria (CSU) present some unique attributes that may not respond in a similar fashion to patients with asthma or food allergy. As part of a clinical study on the therapeutic outcomes of omalizumab treatment in CSU, the basophil compartment was examined for changes in characteristics predicted by prior studies.

OBJECTIVE

This study sought to examine the changes in basophil function and its relationship to auto-antibodies in serum during treatment with omalizumab.

METHODS

At multiple time points before and during omalizumab treatment of patients with CSU, basophil surface IgE and FcεRI expression, cellular spleen tyrosine kinase (SYK) expression, IgE-mediated histamine release (HR), and the presence of auto-antibodies in serum were determined.

RESULTS

Three basophil phenotypes were enumerated in the clinical study and used to group results in this basophil study: subjects with (1) basopenia, (2) normal basophil numbers with normal IgE-mediated HR, and (3) normal basophil numbers with poor HR. Basopenia was highly associated with the presence of auto-antibodies to unoccupied FcεRI and basophil numbers did not change during treatment. Likewise, subjects who are basopenic showed no changes in SYK expression or HR during treatment. In basophils of subjects who are nonbasopenic, increases in SYK expression and HR showed the expected inverse relationship to starting SYK and HR levels. Treatment with omalizumab resulted in similar kinetics for decreases in surface FcεRI and IgE in all 3 groups.

CONCLUSIONS

A unifying interpretation of the results revolves around the presence of auto-antibodies to FcεRI in CSU. If present, basopenia and an absence of changes in basophils during omalizumab treatment are observed. If auto-antibodies are absent, the changes in the basophil compartment are consistent with prior studies of asthma and food allergy. These group differences also are related to efficacy of the treatment for clinical outcomes, as found in the parent clinical study.

The relationship between released soluble FceRI-alpha and its cell surface density on human basophils

Background

The IgE-mediated activation of mast cells and basophils results in the secretion of many substances, including the release of FceRI-alpha subunit. This released alpha subunit can bind IgE and it may act as a down-regulator of subsequent IgE-dependent reactions. However, previous studies do not observe loss of the mass of FceRI-alpha associated with the cells, at least not for human basophils. This study was designed to understand the basis for the discordant observations.

Methods

Purified human basophils were stimulated with multiple activating secretagogues and supernatants were examined for histamine and released FceRI-alpha. In addition, cell surface IgE densities (occupied and unoccupied) were measured by flow cytometry and total cellular content of mature and immature FceRI-alpha determined with Western blots.

Results

Released FceRI-alpha, on average, represented 7% of the total surface FceRI before the reaction. The molecular weight of the soluble FceRI-alpha was approximately 54 kD, larger than immature subunit and somewhat smaller than surface subunit. In addition, 1) release ceased long before internalized FceRI-alpha was processed, 2) release was insensitive to Bafilomycin A, 3) release was independent of the starting density of FceRI and 4) release occurred more effectively with non-IgE-dependent stimuli, FMLP or C5a.

Conclusions

There appears to be relatively constant amount of nearly mature FceRI-alpha that is susceptible to secretion events induced by any form of stimulation. The amount, on average, represents about 7% of the mature form of FceRI-alpha.

Basophils from Cancer Patients Respond to Immune Stimuli and Predict Clinical Outcome

Basophils are involved in manifestations of hypersensitivity, however, the current understanding of their propensity for activation and their prognostic value in cancer patients remains unclear. As in healthy and atopic individuals, basophil populations were identified in blood from ovarian cancer patients (n = 53) with diverse tumor histologies and treatment histories. Ex vivo basophil activation was measured by CD63 expression using the basophil activation test (BAT). Irrespective of prior treatment, basophils could be activated by stimulation with IgE- (anti-FcεRI and anti-IgE) and non-IgE (fMLP) mediated triggers. Basophil activation was detected by ex vivo exposure to paclitaxel, but not to other anti-cancer therapies, in agreement with a clinical history of systemic hypersensitivity reactions to paclitaxel. Protein and gene expression analyses support the presence of basophils (CCR3, CD123, FcεRI) and activated basophils (CD63, CD203c, tryptase) in ovarian tumors. Greater numbers of circulating basophils, cells with greater capacity for ex vivo stimulation (n = 35), and gene signatures indicating the presence of activated basophils in tumors (n = 439) were each associated with improved survival in ovarian cancer. Circulating basophils in cancer patients respond to IgE- and non-IgE-mediated signals and could help identify hypersensitivity to therapeutic agents. Activated circulating and tumor-infiltrating basophils may be potential biomarkers in oncology.

Interspecies differences in protein expression do not impact the spatiotemporal regulation of glycoprotein VI mediated activation

BACKGROUND

Accurate protein quantification is a vital prerequisite for generating meaningful predictions when using systems biology approaches, a method that is increasingly being used to unravel the complexities of subcellular interactions and as part of the drug discovery process. Quantitative proteomics, flow cytometry, and western blotting have been extensively used to define human platelet protein copy numbers, yet for mouse platelets, a model widely used for platelet research, evidence is largely limited to a single proteomic dataset in which the total amount of proteins was generally comparatively higher than those found in human platelets.

OBJECTIVES

To investigate the functional implications of discrepancies between levels of mouse and human proteins in the glycoprotein VI (GPVI) signalling pathway using a systems pharmacology model of GPVI.

METHODS

The protein copy number of mouse platelet receptors was determined using flow cytometry. The Virtual Platelet, a mathematical model of GPVI signalling, was used to determine the consequences of protein copy number differences observed between human and mouse platelets.

RESULTS AND CONCLUSION

Despite the small size of mouse platelets compared to human platelets they possessed a greater density of surface receptors alongside a higher concentration of intracellular signalling proteins. Surprisingly the predicted temporal profile of Syk activity was similar in both species with predictions supported experimentally. Super resolution microscopy demonstrates that the spatial distribution of Syk is similar between species, suggesting that the spatial distribution of receptors and signalling molecules in activated platelets, rather than their copy number, is important for signalling pathway regulation.

Identifying regulatory pathways of spleen tyrosine kinase expression in human basophils

BACKGROUND

Expression levels of spleen tyrosine kinase (SYK), a critical signaling tyrosine kinase in basophils, are uniquely low relative to all other circulating leukocytes, and levels are highly variable in the population.

OBJECTIVE

We sought to determine whether transcriptional regulation of SYK through unique silencing of the SYK gene determines its basophil-specific expression patterns.

METHODS

Culture-derived basophils (CD34B cells) were derived from cultures of CD34⁺ progenitor cells by using 2 methods (G1 or G3). Peripheral blood basophils (PBBs; relative SYK protein level = 1), B cells (SYK = 8), CD34B-G1 cells (SYK = 11), and CD34B-G3 cells (SYK = 5) were examined by using assay for transposase-accessible chromatin sequencing (ATAC-seq) methods. In addition, the transcriptomes of 6 cell types, PBBs, peripheral blood eosinophils (SYK = 11), plasmacytoid dendritic cells (SYK = 30), CD34⁺ progenitors (SYK = 11), CD34B-G1 cells, and CD34B-G3 cells, were analyzed for patterns that matched patterns of SYK expression in these cells, with a focus on transcription factors.

RESULTS

ATAC-seq showed that PBBs have multiple open regions in the SYK gene, suggesting a nonsilenced state with 1 region unique to PBBs (low SYK expression), 1 region unique to both PBBs (low SYK expression) and both G1 and G3 CD34B cells (high and moderate SYK expression, respectively), and 5 regions unique to B cells (high SYK expression). SYK expression across the 6 cell types explored showed a unique pattern that was matched to expression patterns of 3 transcription factors: Kruppel-like factor 5 (KLF5), zinc-finger protein 608 (ZNF608), and musculoaponeurotic fibrosarcoma protein (c-MAF).

CONCLUSIONS

Two new potential regulatory pathways for SYK expression were identified. One appears independent of transcriptional regulation, and one appears to be dependent on transcriptional control in the SYK gene.

Human mast cells and basophils-How are they similar how are they different?

Mast cells and basophils are key contributors to allergies and other inflammatory diseases since they are the most prominent source of histamine as well as numerous additional inflammatory mediators which drive inflammatory responses. However, a closer understanding of their precise roles in allergies and other pathological conditions has been marred by the considerable heterogeneity that these cells display, not only between mast cells and basophils themselves but also across different tissue locations and species. While both cell types share the ability to rapidly degranulate and release histamine following high-affinity IgE receptor cross-linking, they differ markedly in their ability to either react to other stimuli, generate inflammatory eicosanoids or release immunomodulating cytokines and chemokines. Furthermore, these cells display considerable pharmacological heterogeneity which has stifled attempts to develop more effective anti-allergic therapies. Mast cell- and basophil-specific transcriptional profiling, at rest and after activation by innate and adaptive stimuli, may help to unravel the degree to which these cells differ and facilitate a clearer understanding of their biological functions and how these could be targeted by new therapies.

The Use of Biomarkers to Predict Aero-Allergen and Food Immunotherapy Responses

The incidence of allergic conditions has continued to rise over the past several decades, with a growing body of research dedicated toward the treatment of such conditions. By driving a complex range of changes in the underlying immune response, immunotherapy is the only therapy that modulates the immune system with long-term effects and is presently utilized for the treatment of several atopic conditions. Recent efforts have focused on identifying biomarkers associated with these changes that may be of use in predicting patients with the highest likelihood of positive clinical outcomes during allergen immunotherapy (AIT), providing guidance regarding AIT discontinuation, and predicting symptomatic relapse and the need for booster AIT after therapy. The identification of such biomarkers in food allergy has the additional benefit of replacing oral food challenges, which are presently the gold standard for diagnosing food allergies. While several markers have shown early promise, research has yet to identify a marker that can invariably predict clinical response to AIT. Skin prick testing (SPT) and specific IgE have commonly been used as inclusion criteria for the initiation of AIT and prediction of reactions during subsequent allergen challenge; however, existing data suggests that changes in these markers are not always associated with clinical improvement and can be widely variable, reducing their utility in predicting clinical response. Similar findings have been described for the use of allergen-specific functional IgG4 antibodies, basophil activation and histamine release, and type 2 innate lymphoid cells. There appears to be a promising association between changes in the expression of dendritic cell-associated markers, as well as the use of DNA promoter region methylation patterns in the prediction of allergy status following therapy. The cellular and molecular changes brought about by immunotherapy are still under investigation, but major strides in our understanding are being made.

Can alternative epitope mapping approaches increase the impact of B-cell epitopes in food allergy diagnostics?

In vitro allergy diagnostics are currently based on the detection of specific IgE binding on intact allergens or a mixture thereof. This approach has drawbacks as it may yield false‐negative and/or false‐positive results. Thus, we reviewed the impact of known B‐cell epitopes of food allergens to predict transience or persistence, tolerance or allergy and the severity of an allergic reaction and to examine new epitope mapping strategies meant to improve serum‐based allergy diagnostics. Recent epitope mapping approaches have been worthwhile in epitope identification and may increase the specificity of allergy diagnostics by using epitopes predominately recognized by allergic patients in some cases. However, these approaches did not lead to discrimination between clinically relevant and irrelevant epitopes so far, since the polyclonal serum IgE‐binding epitope spectrum seems to be too individual, independent of the disease status of the patients. New epitope mapping strategies are necessary to overcome these obstacles. The use of patient‐derived monoclonal antibodies instead of patient sera for functional characterization of clinically relevant and irrelevant epitope combinations, distinguished by their ability to induce degranulation, might be a promising approach to gain more insight into the allergic reaction and to improve serum‐based allergy diagnostics.

Dependence of Optimal Histamine Release on Cell Surface IgE Density on Human Basophils: Nature of the Stimulus

BACKGROUND

The characteristics of the aggregation reaction that follows allergen binding to cell surface IgE on basophils and mast cells depend on a variety of factors that include the density of IgE and the affinity of the allergen for IgE. For simple bivalent stimuli, one prediction is that the location of the optimum for aggregation is not dependent on IgE density, only the affinity for IgE. However, this behavior does not occur for stimulation with an anti-IgE antibody (Ab) during the treatment of patients with omalizumab.

METHODS

This study re-examined the stability of the optimum for histamine release, relative to cell surface IgE density, using the simple bivalent penicillin hapten (BPO2) or a bivalent monoclonal anti-IgE Ab.

RESULTS

The results validated one prediction for one bivalent hapten, BPO2. Across a range of BPO-specific IgE density of 270-23,500/cell, optimal histamine release remained constant (10 nM BPO2). In contrast, across a range of approximately 6,000-110,000/cell, optimal histamine release shifted 8- to 30-fold for anti-IgE Ab. The distinguishing characteristic between the 2 bivalent stimuli was the difference in their crosslink re-equilibration. Recent modeling of histamine release suggested that the SYK-to-receptor ratio could determine the position of histamine release optimum. The study showed that there were significant shifts in the SYK-to-receptor ratio (from 1: 6 to 5: 1) but the basophil's ability to sense this ratio was restricted to transient crosslinks, as occurred with anti-IgE Ab.

CONCLUSIONS

The results suggest that ligand crosslinking dynamics couple with SYK and receptor expression levels to determine qualitative characteristics of the dose response curve for secretion.

Autoantibodies to IgE and FcεRI and the natural variability of spleen tyrosine kinase expression in basophils

BACKGROUND

Secretion from human basophils and mast cells requires spleen tyrosine kinase (SYK) activity, but SYK expression is highly variable in the general population, and this variability predicts the magnitude of IgE-mediated secretion. One known mechanism of modulating SYK expression in human basophils is aggregation of FcεRI.

OBJECTIVE

This study examines the possibility that functional autoantibodies are present in a wide variety of subjects and, in particular, subjects whose basophils poorly express SYK. It also tests whether any found antibodies could modulate SYK expression in maturing basophils and whether interaction with FcγRIIb/CD32b modulates the effect.

METHODS

An experimental algorithm for classifying the nature of histamine release induced by serum from 3 classes of subjects was developed.

RESULTS

The frequency of functional autoantibodies that produce characteristics concordant with FcεRI-mediated secretion was zero in 34 subjects without chronic spontaneous urticaria (CSU). In patients with CSU, the frequency was lower than expected, approximately 7%. For the 5 of 68 unique sera from patients with CSU tested that contained anti-FcεRI or anti-IgE antibodies, these antibodies were found to induce downregulation of SYK in both peripheral blood basophils and basophils developed from CD34⁺ progenitors. Blocking interaction of these antibodies with CD32b did not alter their ability to downregulate SYK expression.

CONCLUSIONS

This study establishes that functional autoantibodies to IgE/FcεRI do not provide a good explanation for the variability in SYK expression in basophils in the general population. They do show that if antibodies with these characteristics are present, they are capable of modulating SYK expression in developing basophils.

Histamine Release from Mast Cells and Basophils

Mast cells and basophils represent the most relevant source of histamine in the immune system. Histamine is stored in cytoplasmic granules along with other amines (e.g., serotonin), proteases, proteoglycans, cytokines/chemokines, and angiogenic factors and rapidly released upon triggering with a variety of stimuli. Moreover, mast cell and basophil histamine release is regulated by several activating and inhibitory receptors. The engagement of different receptors can trigger different modalities of histamine release and degranulation. Histamine released from mast cells and basophils exerts its biological activities by activating four G protein-coupled receptors, namely H1R, H2R, H3R (expressed mainly in the brain), and the recently identified H4R. While H1R and H2R activation accounts mainly for some mast cell- and basophil-mediated allergic disorders, the selective expression of H4R on immune cells is uncovering new roles for histamine (possibly derived from mast cells and basophils) in allergic, inflammatory, and autoimmune disorders. Thus, the in-depth knowledge of mast cell and basophil histamine release and its biologic effects is poised to uncover new therapeutic avenues for a wide spectrum of disorders.

Beyond IgE-When Do IgE-Crosslinking and Effector Cell Activation Lead to Clinical Anaphylaxis?

Anaphylaxis in humans is inherently difficult to study due to the acuteness of symptoms and the lack of biomarkers serving as risk predictors. Most cases are related to IgE sensitizations to foods, insect venoms, and drugs with mastocytosis patients forming a smaller risk group. However, identifying the relatively small fraction of persons at risk has been exceedingly difficult. In this review, we propose to describe anaphylaxis in a broader context than defined by IgE sensitization alone. Exposure to a trigger, such as an allergen, may lead to anaphylaxis, but in particular, the internal dose sensed by the immune system needs to be established. Moreover, intrinsic patient factors as well as the specific circumstances of the exposure, i.e., the extrinsic factors, need to be thoroughly accounted for. More controversially, other triggers of anaphylaxis, such as increased sensitivity to or reduced catabolism of histamine (“histamine intolerance”) or mast cell activation syndrome also named mast cell activation disorder have been suggested, but still with very limited epidemiological evidence that a significant proportion of the observed reactions are caused by these alleged conditions. Thus, when all conditions are considered, it seems as if IgE-mediated reactions are responsible for the vast majority of anaphylactic conditions.

Pros and Cons of Clinical Basophil Testing (BAT)

PURPOSE OF REVIEW

We review basophil testing by flow cytometry with an emphasis on advantages and disadvantages.

RECENT FINDINGS

There are many tools available to assess the presence and severity of allergic diseases in patients. For 50 years, peripheral blood basophils have been used as tools to study these diseases. It is a very accessible cell that binds IgE antibody and secretes the classical mediators responsible for the symptoms of allergic reactions. In the last decade, an even more accessible methodology, using flow cytometry, has been developed to enhance the ability to use basophils for both mechanistic and clinical diagnostics. Basophil testing has been included in diagnostics for different forms of allergies as well as to monitor disease status. A variety of studies have begun to establish both precise methods and their clinical relevance for disease diagnosis, but there remain some important questions on how to take optimal advantage of the behaviours of basophils.

FceRI density and spontaneous secretion from human basophils

Mast cells and basophils depend on aggregation of the high-affinity IgE receptor, FceRI, to initiate secretion. A variety of studies have shown that FceRI densities vary 100 fold among subjects' basophils and it has been speculated that high densities might be responsible for unusual behaviors of the cells, notably sensitivity to certain monomeric IgE antibodies or spontaneous release. These studies experimentally examined the density dependence of spontaneous release and signaling element expression in subjects' basophils with FceRI densities ranging from approximately 6000 to 600,000 per cell. Through the use of numerical simulation, this study examined the expectations for spontaneous receptor aggregation and aggregate persistence at densities of FceRI ranging from 5000 to 500,000. Experimentally, FceRI density was not associated with greater spontaneous histamine release even when secretion was enhanced by the inclusion of deuterium oxide in the buffers. There was also no association of 15 activating or de-activating signaling elements with FceRI density. The numerical simulations demonstrated that at densities of ≈500,000 receptors, 13% of receptors were involved in transient aggregates at any given moment but that these aggregates rarely persisted for greater than 10 milliseconds. In contrast, a weak linear antigen aggregator, with ligand affinities known to induce secretion, would generate aggregates persisting for an average of ≈60 milliseconds. These results suggest that although a high density of FceRI likely produces a large number of transient aggregates, these aggregates do not persist long enough to induce signaling that results in secretion and do not induce the cells to alter their expression of several signaling elements known to be important in regulating secretion from human basophils. The results set some boundaries on the aggregation requirements for inducing histamine release from human basophils.

Regulation of immune cell signaling by SHIP1: A phosphatase, scaffold protein, and potential therapeutic target

The phosphoinositide phosphatase SHIP is a critical regulator of immune cell activation. Despite considerable study, the mechanisms controlling SHIP activity to ensure balanced cell activation remain incompletely understood. SHIP dampens BCR signaling in part through its association with the inhibitory coreceptor Fc gamma receptor IIB, and serves as an effector for other inhibitory receptors in various immune cell types. The established paradigm emphasizes SHIP's inhibitory receptor-dependent function in regulating phosphoinositide 3-kinase signaling by dephosphorylating the phosphoinositide PI(3,4,5)P₃ ; however, substantial evidence indicates that SHIP can be activated independently of inhibitory receptors and can function as an intrinsic brake on activation signaling. Here, we integrate historical and recent reports addressing the regulation and function of SHIP in immune cells, which together indicate that SHIP acts as a multifunctional protein controlled by multiple regulatory inputs, and influences downstream signaling via both phosphatase-dependent and -independent means. We further summarize accumulated evidence regarding the functions of SHIP in B cells, T cells, NK cells, dendritic cells, mast cells, and macrophages, and data suggesting defective expression or activity of SHIP in autoimmune and malignant disorders. Lastly, we discuss the biological activities, therapeutic promise, and limitations of small molecule modulators of SHIP enzymatic activity.

Therapeutic effects of Euphorbia Pekinensis and Glycyrrhiza glabra on Hepatocellular Carcinoma Ascites Partially Via Regulating the Frk-Arhgdib-Inpp5d-Avpr2-Aqp4 Signal Axis

To clarify unknown rationalities of herbaceous compatibility of Euphorbia Pekinensis (DJ) and Glycyrrhiza glabra (GC) acting on hepatocellular carcinoma (HCC) ascites, peritoneum transcriptomics profiling of 15 subjects, including normal control (Con), HCC ascites mouse model (Mod), DJ-alone, DJ/GC-synergy and DJ/GC-antagonism treatment groups were performed on OneArray platform, followed by differentially expressed genes (DEGs) screening. DEGs between Mod and Con groups were considered as HCC ascites-related genes, and those among different drug treatment and Mod groups were identified as DJ/GC-combination-related genes. Then, an interaction network of HCC ascites-related gene-DJ/GC combination-related gene-known therapeutic target gene for ascites was constructed. Based on nodes’ degree, closeness, betweenness and k-coreness, the Frk-Arhgdib-Inpp5d-Avpr2-Aqp4 axis with highly network topological importance was demonstrated to be a candidate target of DJ/GC combination acting on HCC ascites. Importantly, both qPCR and western blot analyses verified this regulatory effects based on HCC ascites mice in vivo and M-1 collecting duct cells in vitro. Collectively, different combination designs of DJ and GC may lead to synergistic or antagonistic effects on HCC ascites partially via regulating the Frk-Arhgdib-Inpp5d-Avpr2-Aqp4 axis, implying that global gene expression profiling combined with network analysis can offer an effective way to understand pharmacological mechanisms of traditional Chinese medicine prescriptions.

Allergen Valency, Dose, and FcεRI Occupancy Set Thresholds for Secretory Responses to Pen a 1 and Motivate Design of Hypoallergens

Ag-mediated crosslinking of IgE-FcεRI complexes activates mast cells and basophils, initiating the allergic response. Of 34 donors recruited having self-reported shrimp allergy, only 35% had significant levels of shrimp-specific IgE in serum and measurable basophil secretory responses to rPen a 1 (shrimp tropomyosin). We report that degranulation is linked to the number of FcεRI occupied with allergen-specific IgE, as well as the dose and valency of Pen a 1. Using clustered regularly interspaced palindromic repeat-based gene editing, human RBL^rαKO cells were created that exclusively express the human FcεRIα subunit. Pen a 1-specific IgE was affinity purified from shrimp-positive plasma. Cells primed with a range of Pen a 1-specific IgE and challenged with Pen a 1 showed a bell-shaped dose response for secretion, with optimal Pen a 1 doses of 0.1-10 ng/ml. Mathematical modeling provided estimates of receptor aggregation kinetics based on FcεRI occupancy with IgE and allergen dose. Maximal degranulation was elicited when ∼2700 IgE-FcεRI complexes were occupied with specific IgE and challenged with Pen a 1 (IgE epitope valency of ≥8), although measurable responses were achieved when only a few hundred FcεRI were occupied. Prolonged periods of pepsin-mediated Pen a 1 proteolysis, which simulates gastric digestion, were required to diminish secretory responses. Recombinant fragments (60-79 aa), which together span the entire length of tropomyosin, were weak secretagogues. These fragments have reduced dimerization capacity, compete with intact Pen a 1 for binding to IgE-FcεRI complexes, and represent a starting point for the design of promising hypoallergens for immunotherapy.

Distinct Contributory Factors Determine Basophil-Allergen Sensitivity in Grass Pollen Rhinitis and in Anaphylactic Wasp Venom Allergy

BACKGROUND

We sought to determine whether basophil-allergen sensitivity could be transferred to donor basophils by passive IgE sensitisation in allergic rhinitis and anaphylactic Hymenoptera venom hypersensitivity.

METHODS

We studied 15 wasp venom-, 19 grass pollen- and 2 house dust mite-allergic patients, 2 healthy donors, and 8 wasp venom-allergic donors. In all subjects, we first evaluated the initial basophil response to wasp venom, grass pollen, or house dust mite allergen. Donor basophils were then stripped, sensitised with the different patients' serum IgE, and challenged with the corresponding allergen. The CD63 response of donor basophils was then compared with initial basophil responses.

RESULTS

In wasp venom-allergic subjects, the IgE transfer did not reflect the initial basophil-allergen sensitivity, because the venom IgE of subjects with high or low basophil sensitivity induced comparable responsiveness in healthy donor basophils. Furthermore, vice versa, when we sensitised the donor basophils of wasp venom-allergic individuals with different wasp venom or house dust mite IgE, we demonstrated that their response was predictable by their initial basophil allergen sensitivity. In the rhinitis allergy model, the IgE transfer correlated with the patients' initial basophil responsiveness because the grass pollen IgE of the subjects with high basophil allergen sensitivity induced significantly higher responsiveness of donor basophils than the IgE of subjects with initially low basophil allergen sensitivity.

CONCLUSIONS

Our results suggest that basophil allergen sensitivity evaluated by flow-cytometric CD63 analysis depends on two distinct contribution factors. In anaphylactic Hymenoptera allergy, the major factor was intrinsic cellular sensitivity, whereas in pollen allergy, the major factor was allergen-specific IgE on the cell surface.

Stability of Syk protein and mRNA in human peripheral blood basophils

In human basophils, Syk expression is 10-fold lower than most other types of leukocytes. There are indirect studies that suggest that Syk protein is highly unstable (a calculated half-life less than 15 min) in human peripheral blood basophils. Therefore, in these studies, Syk stability was directly examined. Purified basophils were metabolically labeled and a pulse-chase experimental design showed Syk protein to be stable in the time frame of 12 h (95% likelihood that half-life is more than 12 h). However, its synthetic rate was very slow (∼10-fold slower) compared with CD34-derived basophils, which have been shown to express levels of Syk consistent with other mature circulating leukocytes. Syk mRNA expression was found to be 5-30-fold lower than other cell types (CD34-derived basophils, peripheral blood eosinophils, and plasmacytoid dendritic cells). Syk protein and mRNA levels, across cell types, were relatively concordant. Syk mRNA in basophils showed a half-life of 3.5 h, which was greater than that of interleukin-4 or Fc epsilon receptor I-α mRNA (∼2 h), but somewhat shorter than Fc epsilon receptor I-β mRNA (8 h). A comparison of miR expression between CD34-derived and peripheral blood basophils demonstrated only 1 significant increase, in miR-150 (77-fold). Transfection in human embryonic kidney cells of a stabilized form of miR-150 showed that it modified expression of c-Myb mRNA but not of Syk mRNA or protein. These results suggest that low Syk expression in basophils results, not from protein instability and perhaps not from mRNA stability. Instead, the results point to the transcriptional nature of an important point of regulation.

Phenotypic variability in human skin mast cells

Mast cells (MCs) are unique constituents of the human body. While inter-individual differences may influence the ways by which MCs operate in their skin habitat, they have not been surveyed in a comprehensive manner so far. We therefore set out to quantify skin MC variability in a large cohort of subjects. Pathophysiologically relevant key features were quantified and correlated: transcripts of c-kit, FcεRIα, FcεRIβ, FcεRIγ, histidine decarboxylase, tryptase, and chymase; surface expression of c-Kit, FcεRIα; activity of tryptase, and chymase; histamine content and release triggered by FcεRI and Ca(2+) ionophore. While there was substantial variability among subjects, it strongly depended on the feature under study (coefficient of variation 33-386%). Surface expression of FcεRI was positively associated with FcεRIα mRNA content, histamine content with HDC mRNA, and chymase activity with chymase mRNA. Also, MC signature genes were co-regulated in distinct patterns. Intriguingly, histamine levels were positively linked to tryptase and chymase activity, whereas tryptase and chymase activity appeared to be uncorrelated. FcεRI triggered histamine release was highly variable and was unrelated to FcεRI expression but unexpectedly tightly correlated with histamine release elicited by Ca(2+) ionophore. This most comprehensive and systematic work of its kind provides not only detailed insights into inter-individual variability in MCs, but also uncovers unexpected patterns of co-regulation among signature attributes of the lineage. Differences in MCs among humans may well underlie clinical responses in settings of allergic reactions and complex skin disorders alike.

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.

The future of biologics: applications for food allergy

Allergic diseases affect millions worldwide, with growing evidence of an increase in allergy occurrence over the past few decades. Current treatments for allergy include corticosteroids to reduce inflammation and allergen immunotherapy; however, some subjects experience treatment-resistant inflammation or adverse reactions to these treatments, and there are currently no approved therapeutics for the treatment of food allergy. There is a dire need for new therapeutic approaches for patients with poorly controlled atopic diseases and a need to improve the safety and effectiveness of allergen immunotherapy. Improved understanding of allergy through animal models and clinical trials has unveiled potential targets for new therapies, leading to the development of several biologics to treat allergic diseases. This review focuses on the mechanisms that contribute to allergy, with an emphasis on future targets for biologics for the treatment of food allergy. These biologics include immunotherapy with novel anti-IgE antibodies and analogs, small-molecule inhibitors of cell signaling, anti-type 2 cytokine mAbs, and TH1-promoting adjuvants.

Regulation of IgE-mediated signalling in human basophils by CD32b and its role in Syk down-regulation: basic mechanisms in allergic disease

BACKGROUND

CD32b has been previously demonstrated to modulate IgE-mediated secretion from human basophils. However, exploration of the implications of this regulation has been limited. One unstudied area is whether regulation of signalling by CD32 also alters some of the phenotypic changes induced by IgE-mediated activation. The reported character of CD32-mediated signal transduction is not clear for human basophils and the two primary mechanisms considered important in this reaction predict different long-term outcomes, notably predicting different outcomes for down-regulation of syk expression.

OBJECTIVE

Syk expression was considered a unique point of phenotypic control in human basophils and the role of CD32b in its regulation is explored in this study. However, initial pilot studies discovered that IL-3 could markedly up-regulate CD32 expression and first describing the consequences of this up-regulation became an additional focus of this study.

METHODS

Human basophils were examined for the changes in IgE-mediated signalling during simultaneous engagement of CD32b.

RESULTS

Preliminary experiments noted that CD32b could be up-regulated by IL-3 (3- to 12-fold). Both natural variation and induced up-regulation of CD32b modulated the efficacy of this receptor to inhibit IgE-mediated release. Signalling induced by engagement of CD32b (lyn, syk, SHP-1, or SHIP1 phosphorylation) was more consistent with a mode of action involving SHIP1 rather than SHP-1. IgE-mediated down-regulation of syk expression was not altered by co-engagement of CD32b, a result also consistent with a SHIP1-dependent mechanism of inhibition.

CONCLUSIONS

Taken together these results suggest that the combined action of IgE and IgG could generate a natural mechanism, whereby the significant variation in syk expression in allergic subjects occurs without necessarily also inducing mediator release.

Infection with human rhinovirus 16 promotes enhanced IgE responsiveness in basophils of atopic asthmatics

BACKGROUND

Rhinovirus and IgE act in concert to promote asthma exacerbations. While basophils are the principal cell type in the blood that is activated by IgE, their role in virus-induced asthma episodes remains elusive.

OBJECTIVE

To monitor IgE responsiveness in circulating basophils of rhinovirus-infected atopic asthmatics during acute infection and convalescence.

METHODS

The capacity for basophils to respond to IgE was assessed by testing the effects of allergen, or cross-linking anti-FcεRI and anti-IgE antibodies, on surface TSLP receptor in 24-hour PBMC cultures. Activation profiles of basophils from atopic asthmatics challenged intranasally with human rhinovirus 16 were monitored directly ex vivo or else in 24-hour cultures, at baseline (day 0), and then at days 4 and 21 post-challenge.

RESULTS

Basophils in atopic asthmatics, but not in non-atopic controls, upregulated TSLP receptor upon IgE receptor ligation. The magnitude of this response was correlated with the proportion of serum total IgE that was allergen-specific (r = 0.615, P < 0.05). Following rhinovirus infection, all subjects developed nasal symptoms that peaked 3-5 days after viral challenge. Basophils displayed maximal IgE responsiveness 3 weeks post-challenge as judged by TSLP receptor levels in 24-hour cultures. No significant change in total IgE or specific IgE antibodies was detected during rhinovirus infection. By contrast, levels of IgE receptor-associated spleen tyrosine kinase, Syk, were increased on day 4 (P < 0.05), and elevated levels were also detected three weeks post-challenge.

CONCLUSIONS AND CLINICAL RELEVANCE

Circulating basophils display increased IgE responsiveness 3 weeks after rhinovirus infection in atopic asthmatics. This observation, coupled with increased expression of Syk, implicates basophils in promoting, or else prolonging, rhinovirus-induced inflammation in atopic asthmatics.

Immunopharmacological modulation of mast cells

Mast cells produce a wide spectrum of mediators and they have been implicated in several physiopathological conditions (e.g. allergic reactions and certain tumors). Pharmacologic agents that modulate the release of mediators from mast cells has helped to elucidate the biochemical mechanisms by which immunological and non-immunological stimuli activate these cells. Furthermore, the study of surface receptors and signaling pathways associated with mast cell activation revealed novel pharmacologic targets. Thus, the development of pharmacologic agents based on this new wave of knowledge holds promise for the treatment of several mast cell-mediated disorders.

Pathogenesis of chronic urticaria: an overview

The pathogenesis of chronic urticaria is not well delineated and the treatment is palliative as it is not tied to the pathomechanism. The centrality of mast cells and their inappropriate activation and degranulation as the key pathophysiological event are well established. The triggering stimuli and the complexity of effector mechanisms remain speculative. Autoimmune origin of chronic urticaria, albeit controversial, is well documented. Numerical and behavioral alterations in basophils accompanied by changes in signaling molecule expression and function as well as aberrant activation of extrinsic pathway of coagulation are other alternative hypotheses. It is also probable that mast cells are involved in the pathogenesis through mechanisms that extend beyond high affinity IgE receptor stimulation. An increasing recognition of chronic urticaria as an immune mediated inflammatory disorder related to altered cytokine-chemokine network consequent to immune dysregulation resulting from disturbed innate immunity is emerging as yet another pathogenic explanation. It is likely that these different pathomechanisms are interlinked rather than independent cascades, acting either synergistically or sequentially to produce clinical expression of chronic urticaria. Insights into the complexities of pathogenesis may provide an impetus to develop safer, efficacious, and targeted immunomodulators and biological treatment for severe, refractory chronic urticaria.

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.

Basophil activation testing

Both the treatment of patients with allergic diseases and the study of allergic disease mechanisms depend on a wide variety of assays that in various ways assess the presence and function of IgE antibody. The study of allergic diseases could benefit from the study of its 2 principle cellular participants, mast cells and basophils, but the basophil is more accessible than mast cells for ex vivo studies. Its functionality is tested by using 2 predominant methodologies: the secretion of mediators of allergic inflammation and the expression of proteins on the plasma membrane after stimulation. Each approach has benefits. There are also many operational details to consider regardless of which general approach is taken, and proper interpretation of the methods requires a good understanding of the reagents used and the receptors expressed on basophils and a detailed understanding of the factors regulating aggregation of cell-surface IgE.

Subthreshold desensitization of human basophils re-capitulates the loss of Syk and FcεRI expression characterized by other methods of desensitization

BACKGROUND

Clinical desensitization of patients to drugs involves progressive exposure to escalating doses of drug over a period of 24 h. In prior studies, this method was re-capitulated in vitro to also demonstrate loss of mast cell or basophil responsiveness. However, most signalling studies of human basophils have identified changes in signalling by using other methods of inducing cellular desensitization.

OBJECTIVE

This study examined two well-described endpoints of basophil desensitization, loss of syk or FcεRI expression, under conditions of subthreshold desensitization.

METHODS

The loss of FcεRI and syk was examined in human basophils.

RESULTS

It was shown that both loss of syk and FcεRI/IgE occurred during an escalating series of stimulation (anti-IgE Ab) and that expression loss occurred despite the presence of little histamine release. If basophils were first cultured for 3 days in 10 ng/mL IL-3, the concentration-dependence of histamine release shifted to 100-fold lower concentrations of stimulus. However, loss of syk did not show any change in its EC50 while loss of FcεRI also shifted 100-fold. From the perspective of early signal element activation, the marked shift in the EC50 for histamine release was not accompanied by similar shifts in the EC50s for several signalling elements. The EC50s for phospho-Src, phospho-SHIP1, phospho-Syk, or phospho-Cbl did not change while the EC50s for phospho-Erk and the cytosolic calcium response did shift 100-fold.

CONCLUSIONS

These studies show that under normal conditions, subthreshold desensitization leads to loss of two critical signalling molecules (FcεRI and syk) but under at least one condition, treatment with IL-3, it is possible to markedly blunt the loss of syk, but not FcεRI, while executing a proper subthreshold titration. These data also suggest that IL-3 modifies only the sensitivity of signalling elements that are downstream of syk activation.

IgE-dependent signaling as a therapeutic target for allergies

Atopic diseases are complex, with many immunological participants, but the central element in their expression is IgE antibody. In an atopic individual, the immune system pathologically reacts to environmental substances by producing IgE, and these allergen-specific IgE antibodies confer to IgE receptor-bearing cells responsiveness to the environmental substances. Mast cells and basophils are central to the immediate hypersensitivity reaction that is mediated by IgE. In humans, there are various other immune cells, notably dendritic cells and B cells, which can also bind IgE. For mast cells, basophils and dendritic cells, the receptor that binds IgE is the high-affinity receptor, FcɛRI. For B cells and a few other cell types, the low affinity receptor, FcɛRII, provides the cell with a means to sense the presence of IgE. This overview will focus on events following activation of the high-affinity receptor because FcɛRI generates the classical immediate hypersensitivity reaction.

Development of a microarray-based method to detect exposure of human basophils to IL-3

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. The goal of these studies was to develop gene transcript profiles associated with IL-3 exposure for use in probing basophil phenotypes. Highly purified human basophils were cultured under several conditions and the cells subsequently analyzed by microarray analysis of gene transcript expression. Basophils were cultured with or without IL-3 for 24 h and the expression profile, relative to pre-culture, analyzed for transcripts that act in a reciprocal fashion depending on the condition. A 51-gene transcript set was identified that was composed of 34 transcripts that increased with IL-3 and decreased without IL-3 and a further 17 transcripts that did the reverse. This set of transcripts was validated on two microarray chips. The changes induced by IL-3 were stable in time, with 3 day cultures generating a signature concordant with 1 day cultures. The inverted nature of the response to ±IL-3 suggested that the normal circulating basophil is balanced between a state of high and low IL-3 exposure and thus is very sensitive to changes in IL-3. For example, the basophil could detect the early generation of IL-3 that follows IgE-mediated stimulation of basophils. When this signature tool was applied to freshly isolated basophils, it was observed that the signature was similar for the same subjects' basophil sampled weeks apart. It was also shown that the 51-gene transcript was insensitive to the method of preparing purified basophils. Finally, these studies provided an estimate for the normal in vivo exposure of circulating basophils to IL-3 or IL-3-like functionality. These studies identified an IL-3 signature to probe changes in basophils occurring in vivo.

Suppression of the basophil response to allergen during treatment with omalizumab is dependent on 2 competing factors

BACKGROUND

A recent study of subjects with peanut allergy treated with omalizumab generated some results that were concordant with a study of subjects with cat allergy treated with omalizumab. However, there were differences that provided additional insight into the nature of the cellular responses in allergic subjects.

OBJECTIVE

We sought to determine the cause for failure to suppress the allergen-induced basophil response during treatment with omalizumab.

METHODS

Patients with peanut allergy were treated with omalizumab. Clinical, serologic, and cellular indices relevant to the response of the subjects and their peripheral blood basophil values (specific/total IgE ratio, cell-surface FcεRI expression, and histamine release responses to anti-IgE antibody or peanut allergen) were obtained at 3 times.

RESULTS

After treatment, approximately 60% of the subjects' basophil responses to peanut allergen did not significantly decrease. In 40% of cases, the in vitro basophil response to peanut allergen increased 2- to 7-fold. The increases were associated with 2 primary factors: a high (>10%) specific/total IgE ratio and an increase in the intrinsic response of the basophil to IgE-mediated stimulation. The extent to which the basophil response to peanut allergen increased was inversely correlated with improvement in the patient's ability to tolerate ingestion of peanut.

CONCLUSION

The basophil response during treatment with omalizumab is a consequence of 2 competing factors: suppression of allergen-specific IgE on the cell surface versus increased intrinsic sensitivity to IgE-mediated stimulation. In subjects with peanut allergy, the basophil response appears to mitigate against the ability of omalizumab to improve the patient's tolerance of oral allergen.

The potential use of tyrosine kinase inhibitors in severe asthma

PURPOSE OF REVIEW

Severe asthma comprises heterogeneous phenotypes that share in common a poor response to traditional therapies. Recent and ongoing work with tyrosine kinase inhibitors suggests a potential beneficial role in treatment of severe asthma.

RECENT FINDINGS

Various receptor and nonreceptor tyrosine kinase pathways contribute to aspects of airway inflammation, airway hyperresponsiveness, and remodeling of asthma. Selective and nonselective tyrosine kinase inhibitors may be useful to block pathways that are pathologically overactive or overexpressed in severe asthma. Recent in-vivo studies have demonstrated the utility of inhibitors against specific tyrosine kinases (epidermal growth factor receptor, c-kit/platelet derived growth factor receptor, vascular endothelial growth factor receptor, spleen tyrosine kinase, and janus kinase) in altering key aspects of severe asthma.

SUMMARY

Asthma and even severe asthma does not consist of a single phenotype. Targeting key inflammatory and remodeling pathways engaged across subphenotypes with tyrosine kinase inhibitors appears to hold promise.

House dust mite-specific immunotherapy alters the basal expression of T regulatory and FcεRI pathway genes

BACKGROUND

Regulatory T (Treg) cells and IgE-mediated signaling pathways could play important roles in the induction of allergen tolerance during house dust mite-specific subcutaneous immunotherapy (HDM-SCIT). Our aim was to compare the basal expression levels of Treg, T helper 1 (Th1) and Th2 transcription factors and components involved in IgE-mediated signaling in healthy subjects with those in HDM-allergic patients both untreated and successfully treated with HDM-SCIT.

METHODS

Thirty-nine HDM-allergic patients who completed a 3- to 5-year course of mite extract SCIT, 20 mite-allergic controls and 25 healthy controls participated in this study. The efficacy of SCIT was monitored using skin-prick tests (SPTs), total immunoglobulin E (tIgE), specific IgE (sIgE), sIgG(4), nasal challenge and visual analog scale (VAS) scores at several time points. The mRNA levels of forkhead box protein 3 (FOXP3), T-BET, GATA-3, FcεRI, spleen tyrosine kinase (Syk), phosphatidylinositol 3 kinase (PI3K) and SH2 domain-containing inositol phosphatase (SHIP) were quantified by real-time RT-PCR using nonstimulated whole blood samples.

RESULTS

Decreased wheal sizes and VAS scores, negative challenges and increased sIgG(4) levels indicated that SCIT was effective in the treated patients. Basal expression levels of FOXP3 and GATA-3 decreased and T-BET levels increased in both treated patients and in healthy controls compared to untreated patients. The IgE-mediated pathway kinases Syk and PI3K exhibited reduced expression, whereas SHIP phosphatase levels were elevated in both treated patients and healthy controls relative to untreated patients. The expression levels of FcεRI were not significantly altered.

CONCLUSIONS

Immunotherapy using HDM extracts results in a modification of the basal expression levels of several IgE-related signaling factors and induces a highly significant upregulation of Th1-response and downregulation of Th2-response transcription factors. Interestingly, this therapy also appears to reduce the basal expression of FOXP3.

Immunology in the Clinic Review Series; focus on allergies: basophils as biomarkers for assessing immune modulation

Allergen-specific immunotherapy is an effective clinical treatment for hypersensitivity to many allergens. Studies of basophils during immunotherapy have provided insight into underlying immune mechanisms and support the potential use of basophil activation as a biomarker of clinical outcomes. This review examines the evidence for different pathways of basophil modulation associated with various forms of immunotherapy. Better understanding the molecular mechanisms of basophil activation and desensitization and the relationship between suppression of these effector cells to clinical outcomes holds promise for further development and improvement in potential therapies for allergic diseases.

Basophils: emerging roles in the pathogenesis of allergic disease

After approximately 130 years since their discovery as rare granulocytes that circulate in blood, basophils are just now gaining respect as significant contributors in the pathogenesis underlying allergic inflammation and disease. While long known for secreting preformed and newly synthesized mediators and for selectively infiltrating tissue during immunoglobulin E (IgE)-mediated inflammation, their role has largely been viewed as redundant to that of tissue mast cells in functioning as effector cells. This line of thought has persisted even though it has been known in humans for approximately 20 years that basophils additionally produce relatively large quantities of cytokines, e.g. interleukin-4 (IL-4)/IL-13, that are central for the manifestations of allergic disease. Studies using novel IL-4 reporter mice have significantly added to the in vivo importance of basophils as IL-4 producing cells, with recent findings indicating that these cells also function as antigen-presenting cells essential in initiating T-helper 2 responses. If confirmed and translated to humans, these provocative findings will give new meaning to the role basophils have in allergic disease, and in immunology overall.