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

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.

The Role of Crosstalk of Immune Cells in Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is defined as recurrent episodes of spontaneous wheal development and/or angioedema for more than six weeks and at least twice a week. The core link in the pathogenesis of CSU is the activation of mast cells, T cells, eosinophils, and other immune cells infiltrating around the small venules of the lesion. Increased vascular permeability, vasodilatation, and recruitment of inflammatory cells directly depend on mast cell mediators’ release. Complex regulatory systems tightly influence the critical roles of mast cells in the local microenvironment. The bias toward Th2 inflammation and autoantibodies derived from B cells, histamine expressed by basophils, and initiation of the extrinsic coagulation pathway by eosinophils or monocytes exerts powerful modulatory influences on mast cells. Cell-to-cell interactions between mast cells and eosinophils/T cells also are regulators of their function and may involve CSU’s pathomechanism. This review summarizes up-to-date knowledge regarding the crosstalk between mast cells and other immune cells, providing the impetus to develop new research concepts and treatment strategies for CSU.

Diagnosis, Classification and Management of Mast Cell Activation Syndromes (MCAS) in the Era of Personalized Medicine

Mast cell activation (MCA) is seen in a variety of clinical contexts and pathologies, including IgE-dependent allergic inflammation, other immunologic and inflammatory reactions, primary mast cell (MC) disorders, and hereditary alpha tryptasemia (HAT). MCA-related symptoms range from mild to severe to life-threatening. The severity of MCA-related symptoms depends on a number of factors, including genetic predisposition, the number and releasability of MCs, organs affected, and the type and consequences of comorbid conditions. In severe systemic reactions, MCA is demonstrable by a substantial increase of basal serum tryptase levels above the individual’s baseline. When, in addition, the symptoms are recurrent, involve more than one organ system, and are responsive to therapy with MC-stabilizing or mediator-targeting drugs, the consensus criteria for the diagnosis of MCA syndrome (MCAS) are met. Based on the etiology of MCA, patients can further be classified as having i) primary MCAS where KIT-mutated, clonal, MCs are detected; ii) secondary MCAS where an underlying IgE-dependent allergy or other reactive MCA-triggering pathology is found; or iii) idiopathic MCAS, where neither a triggering reactive state nor KIT-mutated MCs are identified. Most severe MCA events occur in combined forms of MCAS, where KIT-mutated MCs, IgE-dependent allergies and sometimes HAT are detected. These patients may suffer from life-threatening anaphylaxis and are candidates for combined treatment with various types of drugs, including IgE-blocking antibodies, anti-mediator-type drugs and MC-targeting therapy. In conclusion, detailed knowledge about the etiology, underlying pathologies and co-morbidities is important to establish the diagnosis and develop an optimal management plan for MCAS, following the principles of personalized medicine.

Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Mast cell activation syndromes: definition and classification

Mast cell activation (MCA) occurs in a number of different clinical conditions, including IgE-dependent allergies, other inflammatory reactions, and mastocytosis. MCA-related symptoms may be mild, moderate, severe, or even life-threatening. The severity of MCA depends on a number of different factors, including genetic predisposition, the number and releasability of mast cells involved in the reaction, the type of allergen, presence of specific IgE, and presence of certain comorbidities. In severe reactions, MCA can be documented by a substantial increase in the serum tryptase level above baseline. When symptoms are recurrent, are accompanied by an increase in mast cell-derived mediators in biological fluids, and are responsive to treatment with mast cell-stabilizing or mediator-targeting drugs, the diagnosis of mast cell activation syndrome (MCAS) is appropriate. Based on the underlying condition, these patients can further be classified into i) primary MCAS where KIT-mutated, clonal mast cells are detected, ii) secondary MCAS where an underlying inflammatory disease, often in the form of an IgE-dependent allergy, but no KIT-mutated mast cells, is found, and iii) idiopathic MCAS, where neither an allergy or other underlying disease, nor KIT-mutated mast cells are detectable. It is important to note that in many patients with MCAS, several different factors act together to lead to severe or even life-threatening anaphylaxis. Detailed knowledge about the pathogenesis and complexity of MCAS, and thus establishing the exact final diagnosis, may greatly help in the management and therapy of these patients.

Role of SHIP-1 in the adaptive immune responses to aeroallergen in the airway

Background

Th2-dominated inflammatory response in the airway is an integral component in the pathogenesis of allergic asthma. Accumulating evidence supports the notion that the phosphoinositide 3-kinase (PI3K) pathway is involved in the process. We previously reported that SHIP-1, a negative regulator of the PI3K pathway, is essential in maintaining lung immunohomeostasis, potentially through regulation of innate immune cells. However, the function of SHIP-1 in adaptive immune response in the lung has not been defined. We sought to determine the role of SHIP-1 in adaptive immunity in response to aeroallergen stimulation in the airway.

Methodology/Principal Findings

SHIP-1 knockout (SHIP-1^−/−) mice on BALB/c background were immunized with ovalbumin (OVA) plus aluminum hydroxide, a strong Th2-inducing immunization, and challenged with OVA. Airway and lung inflammation, immunoglobulin response, Th2 cytokine production and lymphocyte response were analyzed and compared with wild type mice. Even though there was mild spontaneous inflammation in the lung at baseline, SHIP-1^−/− mice showed altered responses, including less cell infiltration around the airways but more in the parenchyma, less mucus production, decreased Th2 cytokine production, and diminished serum OVA-specific IgE, IgG1, but not IgG2a. Naïve and OVA sensitized SHIP-1^−/− T cells produced a lower amount of IL-4. In vitro differentiated SHIP-1^−/− Th2 cells produced less IL-4 compared to wild type Th2 cells upon T cell receptor stimulation.

Conclusions/Significance

These findings indicate that, in contrast to its role as a negative regulator in the innate immune cells, SHIP-1 acts as a positive regulator in Th2 cells in the adaptive immune response to aeroallergen. Thus any potential manipulation of SHIP-1 activity should be adjusted according to the specific immune response.

Role of SHIP in cancer

The SH2-containing inositol-5'-phosphatase, SHIP (or SHIP1), is a hematopoietic-restricted phosphatidylinositide phosphatase that translocates to the plasma membrane after extracellular stimulation and hydrolyzes the phosphatidylinositol-3-kinase-generated second messenger PI-3,4,5-P(3) to PI-3,4-P(2). As a result, SHIP dampens down PI-3,4,5-P(3)-mediated signaling and represses the proliferation, differentiation, survival, activation, and migration of hematopoietic cells. There are multiple lines of evidence suggesting that SHIP may act as a tumor suppressor during leukemogenesis and lymphomagenesis. Because of its ability to skew macrophage progenitors toward M1 macrophages and naïve T cells toward T helper 1 and T helper 17 cells, SHIP may play a critical role in activating the immune system to eradicate solid tumors. In this review, we will discuss the role of SHIP in hematopoietic cells and its therapeutic potential in terms of suppressing leukemias and lymphomas and manipulating the immune system to combat cancer.

Alternaria alternata TCTP, a novel cross-reactive ascomycete allergen

Defining more comprehensively the allergen repertoire of the ascomycete Alternaria alternata is undoubtedly of immense medical significance since this mold represents one of the most important, worldwide occurring fungal species responsible for IgE-mediated hypersensitivity reactions ranging from rhinitis and ocular symptoms to severe involvement of the lower respiratory tract including asthma with its life-threatening complications. Performing a hybridization screening of an excised A. alternata cDNA library with a radioactively labeled Cladosporium herbarum TCTP probe, we were able to identify, clone and purify the respective A. alternata homologue of TCTP which again represents a multifunctional protein that has been evolutionarily conserved from unicellular eukaryotes like yeasts to humans and appears, summarizing current literature, to be involved in housekeeping processes such as cell growth as well as cell-cycle progression, the protection of cells against various stress conditions including for instance apoptosis, and in higher organisms even in the allergic response. In this context, our present study characterizes recombinant A. alternata TCTP as a novel minor allergen candidate that displays a prevalence of IgE reactivity of approximately 4% and interestingly shares common, cross-reactive IgE epitopes with its C. herbarum and human counterparts as determined via Western blotting and in vitro inhibition approaches.

Allergen-specific basophil suppression associated with clinical tolerance in patients with milk allergy

BACKGROUND

Children with milk allergy who tolerate heat-denatured milk (HM) have less severe reactions and outgrow the condition earlier than those who react to HM, which might be related to differences in IgE-dependent effector cell function.

OBJECTIVE

We sought to apply a novel assay to test the hypothesis that HM-tolerant children have suppressed IgE-mediated basophil responses.

METHODS

Allergic, HM-tolerant, outgrown, or control subjects were defined based on oral food challenges. Whole blood cells were stimulated in vitro with a range of milk allergen doses in the presence or absence of autologous serum or with dilutions of autologous serum. Activated basophils were identified by means of flow cytometry as CD63(bright)CD123+CD203c+HLA-DR(-)CD41a(-).

RESULTS

HM-tolerant subjects' basophils were significantly less responsive to milk allergen stimulation at all doses than were basophils from HM-reactive (allergic) individuals. In the absence of autologous serum, HM-tolerant subjects' basophils were significantly more reactive at low allergen concentrations. To a lesser extent, autologous serum also inhibited IL-3- and anti-IgE-induced, but not N-formyl-methionyl-leucyl-phenylalanine-induced, responses. The allergen-specific responsiveness of HM-tolerant subjects' basophils increased with dilution of autologous serum with normal pooled serum.

CONCLUSION

Children with milk allergy with a favorable prognosis have evidence of extrinsically suppressed allergen-specific effector cell reactivity.

Src homology 2 domain-containing inositol 5-phosphatase 1 deficiency leads to a spontaneous allergic inflammation in the murine lung

BACKGROUND

Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP-1) controls the intracellular level of the phosphoinositide 3-kinase product phosphotidylinositol-3,4,5-trisphosphate and functions as a negative regulator of cytokine and immune receptor signaling. Emerging evidence suggests that the phosphoinositide 3-kinase pathway might be involved in allergic inflammation in the lung. However, the functional relevance of SHIP-1 in the T(H)2 activation pathway has not been established. SHIP-1(-/-) mice have spontaneous myeloproliferative inflammation in the lung, the nature of which has not been elucidated. We hypothesized that SHIP-1 plays an important role as a regulator in pulmonary allergic inflammation and in maintaining lung homeostasis.

OBJECTIVE

To test our hypothesis, we characterized the pulmonary phenotype of SHIP-1(-/-) mice.

RESULTS

Analyses of lung histopathology and bronchoalveolar lavage cellularity revealed that the majority of SHIP-1(-/-) mice had progressive and severe pulmonary inflammation of macrophages, lymphocytes, neutrophils, and eosinophils; mucous hyperplasia; airway epithelial hypertrophy; and subepithelial fibrosis. These pathologic changes were accompanied by exaggerated production of T(H)2 cytokines and chemokines, including IL-4, IL-13, eotaxin, and monocyte chemoattractant protein 1, in the lung. Furthermore, the number of mast cells significantly increased, and many of these cells were undergoing degranulation, which was correlated with increased content and spontaneous release of histamine in the lung tissue of SHIP-1(-/-) mice.

CONCLUSION

These findings provide strong evidence that mice lacking SHIP-1 have an allergic inflammation in the lung, suggesting that SHIP-1 plays an important role in regulating the T(H)2 signaling pathway and in maintaining lung homeostasis.

CLINICAL IMPLICATIONS

SHIP-1 as a regulator might be a potential therapeutic target for controlling allergic inflammation in diseases such as asthma.