Identification of basophils by a mAb directed against pro-major basic protein 1

Metallothionein 1: A New Spotlight on Inflammatory Diseases

MT1 has been demonstrated to be an essential stress protein in maintaining physiological balance and regulating immune homeostasis. While the immunological involvement of MT1 in central nervous system disorders and cancer has been extensively investigated, mounting evidence suggests that MT1 has a broader role in inflammatory diseases and can shape innate and adaptive immunity. In this review, we will first summarize the biological features of MT1 and the regulators that influence MT1 expression, emphasizing metal, inflammation, and immunosuppressive factors. We will then focus on the immunoregulatory function of MT1 on diverse immune cells and the signaling pathways regulated by MT1. Finally, we will discuss recent advances in our knowledge of the biological role of MT1 in several inflammatory diseases to develop novel therapeutic strategies.

Development and application of novel immunoassays for eosinophil granule major basic proteins to evaluate eosinophilia and myeloproliferative disorders

BACKGROUND

During eosinophil differentiation, the granule eosinophil major basic protein 1 (eMBP1) is synthesized as a 32-kDa precursor form, referred to as proMBP1, which is processed into the 14-kDa mature form of eMBP1. The prevalence of these two forms of MBP1 in most pathological conditions remains unknown.

OBJECTIVE

To develop the immunoassays that differentiate mature eMBP1 and proMBP1 and apply them to analyze their levels in biological fluids from patients with eosinophilia and hematologic disorders.

METHODS

We produced a series of monoclonal antibodies and selected pairs capable of discriminating between the two molecular forms of eMBP1. Radioimmunoassay (RIA) was performed to simultaneously quantitate the levels of mature eMBP1 and proMBP1 in secretions from patients with chronic rhinosinusitis (CRS) and sera from patients with hypereosinophilic syndrome (HES) and other myeloproliferative disorders.

RESULTS

The novel immunoassays possessed less than 1% crossreactivity between mature eMBP1 and proMBP1. Mature eMBP1, but not proMBP1, was found in nasal secretions of CRS patients. In contrast, elevated serum levels of mature eMBP1 and proMBP1 were observed in approximately 60% and 90% of HES patients, respectively, with proMBP1 present in greater quantities than mature eMBP1. Patients with several myeloproliferative disorders also showed high serum levels of proMBP1 while mature eMBP1 remained at basal levels.

CONCLUSION

The novel immunoassays successfully differentiated mature eMBP1 and proMBP1 in human biological fluids. Further studies addressing the clinical correlates of these assays will help to develop biomarkers to diagnose and monitor patients with eosinophilia and myeloproliferative disorders.

Granzyme B inhibition reduces disease severity in autoimmune blistering diseases

Pemphigoid diseases refer to a group of severe autoimmune skin blistering diseases characterized by subepidermal blistering and loss of dermal-epidermal adhesion induced by autoantibody and immune cell infiltrate at the dermal-epidermal junction and upper dermis. Here, we explore the role of the immune cell-secreted serine protease, granzyme B, in pemphigoid disease pathogenesis using three independent murine models. In all models, granzyme B knockout or topical pharmacological inhibition significantly reduces total blistering area compared to controls. In vivo and in vitro studies show that granzyme B contributes to blistering by degrading key anchoring proteins in the dermal-epidermal junction that are necessary for dermal-epidermal adhesion. Further, granzyme B mediates IL-8/macrophage inflammatory protein-2 secretion, lesional neutrophil infiltration, and lesional neutrophil elastase activity. Clinically, granzyme B is elevated and abundant in human pemphigoid disease blister fluids and lesional skin. Collectively, granzyme B is a potential therapeutic target in pemphigoid diseases.

Mass Cytometry Phenotyping of Human Granulocytes Reveals Novel Basophil Functional Heterogeneity

Basophils, the rarest granulocyte, play critical roles in parasite- and allergen-induced inflammation. We applied mass cytometry (CyTOF) to simultaneously asses 44 proteins to phenotype and functionally characterize neutrophils, eosinophils, and basophils from 19 healthy donors. There was minimal heterogeneity seen in eosinophils and neutrophils, but data-driven analyses revealed four unique subpopulations within phenotypically basophilic granulocytes (PBG; CD45⁺HLA-DR⁻CD123⁺). Through CyTOF and fluorescence-activated cell sorting (FACS), we classified these four PBG subpopulations as (I) CD16^lowFcεRI^highCD244^high (88.5 ± 1.2%), (II) CD16^highFcεRI^highCD244^high (9.1 ± 0.4%), (III) CD16^lowFcεRI^lowCD244^low (2.3 ± 1.3), and (IV) CD16^highFcεRI^lowCD244^low (0.4 ± 0.1%). Prospective isolation confirmed basophilic-morphology of PBG I–III, but neutrophilic-morphology of PBG IV. Functional interrogation via IgE-crosslinking or IL-3 stimulation demonstrated that PBG I–II had significant increases in CD203c expression, whereas PBG III–IV remained unchanged compared with media-alone conditions. Thus, PBG III–IV could serve roles in non-IgE-mediated immunity. Our findings offer new perspectives in human basophil heterogeneity and the varying functional potential of these new subsets in health and disease.

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Unsupervised clustering revealed 4 basophil populations, driven by CD16, CD244, and FcεRI

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The rarest basophil subpopulation IV was morphologically neutrophils

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Anti-IgE and IL-3 stimulation did not induce functional responses in III and IV

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Basophil subpopulation heterogeneity was observed in healthy and CML samples

IL-33-Induced Atopic Dermatitis-Like Inflammation in Mice Is Mediated by Group 2 Innate Lymphoid Cells in Concert with Basophils

IL-33 is a proinflammatory cytokine that plays a pivotal role in allergic disorders. In a transgenic mouse expressing IL-33 driven by a keratin-14 promoter (IL33tg), atopic dermatitis (AD)-like inflammation develops spontaneously with the activation of group 2 innate lymphoid cells (ILC2s). However, it remains unknown how effector cells, such as T helper type 2 cells, ILC2s, and basophils, contribute to the inflammatory process induced by IL-33. To address the question, we examined the phenotype of IL33tg mice lacking each of these cells. AD-like inflammation still developed in Rag2KO IL33tg mice lacking T and B cells; in contrast, when ILC2s were depleted in IL33tg mice via bone marrow transplantation from ILC2-lacking, RAR-related orphan receptor alpha-deficient mice, the development of AD-like inflammation was almost completely suppressed. Basophils were accumulated in the inflamed skin of IL33tg mice, and AD-like inflammation was alleviated by the conditional depletion of basophils using anti-FcεRIα antibodies or a Bas-TRECK transgenic mouse system. In these basophil-depleted IL33tg skins, ILC2s were decreased, and cytokines and chemokines such as IL-5, IL-13, and CCL5 were reduced. From these results, we suggest that IL-33-induced AD-like inflammation is dependent on innate immune responses that are mediated by ILC2s in concert with basophils.

Basophils are increased and express increased levels of interleukin-4 in the parotid lesions of Kimura disease

Background

Kimura disease (KD) is a systemic soft-tissue disease that leads to formation of painless masses in lymph nodes, with the highest predilection for the head and neck and especially the parotid gland. KD lesions are characterized by marked eosinophil infiltration, production of IgE and increased expression of T-helper type 2 (Th2) cytokines (interleukin [IL]-4, IL-5, etc.). Skewing to a Th2 inflammation is also demonstrated in the peripheral blood, with elevated eosinophils and high IgE levels. It is thought that basophils may play important roles in orchestrating this Th2 inflammation via IL-4 production leading to the induction of IgE synthesis as well as eosinophil infiltration. However, there are no reports as yet on the role of basophils in KD.

Objective

The present study was performed to investigate the potential role of basophils in the pathogenesis of KD. In this context we also examined the expression of IL-4 in basophils in the KD lesions.

Methods

By immunohistochemistry using a monoclonal antibody against a basophil marker ProMBP1 we investigated the number and distribution of basophils in the KD lesions. By double immunohistochemistry we analyzed the colocalization of IL-4 in basophils.

Results

There was an increased number of basophils infiltrating the KD parotid gland lesions as compared to that in normal control parotid tissue. By double-immunofluorescence we found that approximately 7% of IL-4-positive cells in KD patients' parotid glands were basophils.

Conclusion

Basophils may also play a role in the pathogenesis of KD, leading to the induction of IgE synthesis and eosinophil infiltration.

Inducible urticaria: Case series and literature review

Inducible urticaria is a heterogeneous group of skin disorders characterized by the appearance of wheals, pruritus and/or angioedema, sometimes accompanied by systemic symptoms caused by innocuous stimuli (cold, heat, pressure, etc.). This group of disorders compromises people's quality of life and most of the literature in this regard comes from case reports and case series since its epidemiology has been poorly studied and some cases are very rare. The aim of this review is to show an up-to-date overview of the available literature for various types of inducible urticarias, always beginning with an illustrative case and then describing their pathophysiological mechanisms, clinical manifestations, and treatment.

Biomarkers of the involvement of mast cells, basophils and eosinophils in asthma and allergic diseases

Biomarkers of disease activity have come into wide use in the study of mechanisms of human disease and in clinical medicine to both diagnose and predict disease course; as well as to monitor response to therapeutic intervention. Here we review biomarkers of the involvement of mast cells, basophils, and eosinophils in human allergic inflammation. Included are surface markers of cell activation as well as specific products of these inflammatory cells that implicate specific cell types in the inflammatory process and are of possible value in clinical research as well as within decisions made in the practice of allergy-immunology.

Basophils and allergic inflammation

Basophils were discovered by Paul Ehrlich in 1879 and represent the least abundant granulocyte population in mammals. The relative rarity of basophils and their phenotypic similarities with mast cells resulted in this cell lineage being historically overlooked, both clinically and experimentally. However, recent studies in human subjects and murine systems have shown that basophils perform nonredundant effector functions and significantly contribute to the development and progression of TH2 cytokine-mediated inflammation. Although the potential functions of murine and human basophils have provoked some controversy, recent genetic approaches indicate that basophils can migrate into lymphoid tissues and, in some circumstances, cooperate with other immune cells to promote optimal TH2 cytokine responses in vivo. This article provides a brief historical perspective on basophil-related research and discusses recent studies that have identified previously unappreciated molecules and pathways that regulate basophil development, activation, and function in the context of allergic inflammation. Furthermore, we highlight the unique effector functions of basophils and discuss their contributions to the development and pathogenesis of allergic inflammation in human disease. Finally, we discuss the therapeutic potential of targeting basophils in preventing or alleviating the development and progression of allergic inflammation.

Accumulation of eosinophils, mast cells, and basophils in the spleen in anaphylactic deaths

Death in anaphylactic shock cannot be diagnosed by autopsy alone. Morphological diagnosis of anaphylactic death by counting mast cells in the lung and airways have failed to give consistent results. Previously it has been observed that eosinophils seem to accumulate in the spleen in anaphylaxis. The purpose of this study was to investigate if it is possible to safely diagnose anaphylactic deaths by counting eosinophils, mast cells, and basophils in the spleen. In 43 forensic autopsy cases specific antibodies to mast cells, eosinophil-, and basophil granulocytes were used on sections from lung and splenic tissue. The cells were counted in 20 × 40 fields in a Leica photo-microscope. Presumed deaths in anaphylaxis were compared with sudden deaths after intravenous injection of opiates, and sudden cardiac deaths (control group). The main result was that significant (p < 0.05) increases of both eosinophil granulocytes (mean 26.6 ± 17.8/SD/)and mast cells (3.2 ± 2.0/SD/) versus controls (eosinophils mean 7.0 ± 10.5 and mast cells mean 0.9 ± 1.1) were seen in splenic tissue in anaphylactic deaths. Comparing cases with high and low concentrations of mast cell tryptase in serum showed a similar increase in eosinophils and mast cells in the spleen in cases with elevated tryptase, but not in the lung. The numbers of pulmonary mast cells and eosinophils were not different in anaphylactic deaths compared with controls. It is concluded that by quantifying eosinophil granulocytes and mast cells in the spleen in combination with tryptase measurements in serum it is possible to diagnose anaphylaxis with a high degree of certainty.

Basophils in allergic immune responses

Basophils are rare effector cells of the innate immune system. They are generally associated with type 2 immune responses that develop during helminth infections and allergic reactions. The role of basophils for initiation and execution of allergic immune responses is not well understood. Over the past few years new tools have been generated to study the function of basophils in mouse models. Depending on the experimental systems used conflicting results were obtained with regard to the role of basophils for initiation and execution of immune responses against allergens and helminths. This review highlights the current knowledge about basophil in vivo functions with a focus on the role of basophils for allergic responses like asthma, allergic skin diseases and anaphylaxis.

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.

Newly appreciated roles for basophils in allergy and protective immunity

Basophils are evolutionarily conserved in many animal species, in spite of the fact that they account for <1% of peripheral blood leukocyte. This suggests that basophils have an indispensable and nonredundant role in vivo, even though they show some phenotypic similarity with tissue-resident mast cells. However, their functional significance remained uncertain long after Paul Ehrlich discovered them as blood-circulating cells with basophilic granules more than 130 years ago. The study of basophils has been far behind that of mast cells, owing to the rarity of basophils and the paucity of tools for their detection and functional analysis. Recent development of novel analytical tools, including basophil-depleting antibodies and genetically engineered mice deficient only in basophils, has greatly advanced basophil research and illuminated previously unrecognized roles of basophils. We now appreciate that basophils and mast cells play distinct roles in immune responses. Basophils have crucial roles in the development of acute and chronic allergic responses, the protective immunity against ecto- and endoparasites, and the regulation of acquired immunity, including the augmentation of humoral memory responses and the initiation of Th2 responses. Thus, basophils are no longer the neglected minority and are key players in the immune system.

FcεRI, but not FcγR, signals induce prostaglandin D2 and E2 production from basophils

Prostaglandin (PG) D2 and PGE2 are arachidonic acid metabolites that are generated though an isomerization reaction catalyzed by PG synthases. PGs have been implicated in immunologic reactions in addition to a wide range of physiological functions. It has long been thought that basophils, in contrast to mast cells, do not synthesize PGs, although they do release leukotrienes and platelet-activating factor. Here, we show that basophils function as a source of PGD2 and PGE2. In vitro-cultured basophils from mouse bone marrow produced both PGD2 and PGE2 in response to IgE + antigen (Ag), but not to IgG + Ag. Release of PGs was almost completely abrogated in cultured basophils from FcRγ-chain(-/-) mice, indicating the involvement of FcεRI. Basophils freshly isolated from bone marrow cells (primary basophils) were also capable of secreting PGD2 and PGE2. Although the amount of PGD2 released from primary basophils was lower than that from mast cells, the capability of primary basophils to generate PGE2 was more potent than that of mast cells. Transcripts and proteins for both hematopoietic-type PGD synthase and PGE synthase were detected in basophils. In addition, human basophils, like mouse basophils, also produced PGD2 through IgE-mediated stimulation. Thus, basophils could be an important source of PGD2/PGE2 and may contribute to allergic inflammation and immune responses.

Basophils preferentially express mouse Mast Cell Protease 11 among the mast cell tryptase family in contrast to mast cells

Tryptases and chymases are the major proteins stored and secreted by mast cells, and they have various biological functions. However, the nature of proteases produced by basophils has been poorly characterized, particularly in mice. mMCP-11 is the most recently discovered mast cell tryptase in mice and was originally identified as Prss34, which is transcribed in some mast cell-like cell lines and at the early stage in the culture of BMMC with IL-3. Curiously, Prss34 is preferentially expressed in the BM and spleen among normal tissues in contrast to other mast cell tryptases. Therefore, it remains elusive what types of cells express mMCP-11 in vivo. Here, we show that mMCP-11 is highly expressed by primary basophils and to a much lesser extent, by some mast cells. Prss34 transcripts were detected abundantly in primary and cultured basophils and very weakly in peritoneal mast cells or cultured BMMC. Conversely, transcripts for mMCP-6 and mMCP-7 tryptases were preferentially expressed by cultured and peritoneal mast cells but not basophils. We established a mMCP-11-specific mAb and showed that mMCP-11 proteins are indeed expressed by primary basophils and those infiltrating the affected tissues during allergic inflammation and parasitic infections. Some primary mast cells also expressed mMCP-11 proteins, albeit at a much lower level. Thus, basophils rather than mast cells are the major source of mMCP-11. This is the first study to demonstrate that mouse basophils produce a trypsin-like protease.

The role of basophils in helminth infection

Protective immunity against gastrointestinal and tissue dwelling helminths is coordinated by interaction of different effector cells of the innate and adaptive immune system. Helminths induce a strong type 2 immune response which is characterized by high levels of IgE and increased numbers of Th2 cells, eosinophils, mast cells and basophils. Basophils are rapidly mobilized after helminth infection and can be efficiently recruited into lymphoid and peripheral tissues where they execute their effector functions. Recent work demonstrated that basophils contribute to initiation and execution of type 2 immunity. This review discusses the potential role of basophils for protective immunity against helminths.

Basophils and mast cells in renal injury

Until recently, basophils and mast cells were considered mainly effector cells with an innate immune response linked to allergy and parasite infection. Only in the past few years they were recognized as important regulators of adaptive immunity. The development of new methods and reagents has enabled detection and functional analysis of these rare cells in patients and murine disease models. Basophils are normally present in the peripheral blood, spleen, and bone marrow, but migrate into lymph nodes and tissues during inflammation. They are rapidly activated by cytokines (e.g., interleukin (IL)-3) and intact antigens that cross-link surface-bound immunoglobulins. Activated basophils change the phenotype of T cells toward Th2 and markedly support humoral memory responses. Mast cells also migrate into lymph nodes and interact with dendritic cells, T cells, and B cells. In this review, we describe how mast cells and basophils affect immune responses and discuss implications for renal diseases and transplant rejection.

New insights into the roles for basophils in acute and chronic allergy

Basophils represent less than 1% of peripheral blood leukocytes. They are often recruited to the site of allergic inflammation, albeit in small numbers. However, it remained uncertain whether basophils play any significant role in allergic reactions or act as minor and redundant 'circulating mast cells'. We have recently demonstrated that basophils play critical roles in systemic anaphylaxis and chronic allergic inflammation, distinctively from mast cells. Basophils are one of the major players in the IgG- but not IgE-mediated systemic anaphylaxis, in contrast to mast cells. In response to the allergen-IgG immune complexes, basophils release the platelet-activating factor rather than histamine as the major chemical mediator to induce the systemic anaphylaxis. The depletion of basophils protects mice from death due to anaphylactic shock. Basophils also play a crucial role in the development of the IgE-mediated chronic allergic inflammation with massive eosinophil infiltration in the skin, independently of T cells and mast cells, even though basophils account for only approximately 2% of the infiltrates. The basophil depletion shows a therapeutic effect on on-going allergic inflammation. Accumulating evidence suggests that basophils function as initiators rather than effectors of the chronic allergic inflammation. Thus, basophils and their products seem to be promising therapeutic targets for allergic disorders.

Basophils are essential initiators of a novel type of chronic allergic inflammation

Basophils represent less than 1% of peripheral blood leukocytes and have often been considered as minor and possibly redundant circulating mast cells. The recent finding that basophils readily generate large quantities of T helper 2 (Th2) cytokines such as IL-4 provided new insights into the possible role of basophils in allergic disorders and immunity to pathogens. However, in-depth studies on basophils, particularly their functions in vivo, have been hampered by the lack of appropriate animal models, such as mutant animals deficient only in basophils. Here, we established a mAb that reacted with mouse basophils and depleted them when administered in vivo. The mAb treatment of mice did not show any significant effect on classical allergic reactions such as passive cutaneous anaphylaxis and contact hypersensitivity. In contrast, it completely abolished the development of IgE-mediated chronic allergic dermatitis that is characterized by massive eosinophil infiltration, even though basophils accounted for only approximately 2% of the infiltrates. The treatment during the progression of the dermatitis resulted in drastic reduction in numbers of infiltrating eosinophils and neutrophils, concomitantly with elimination of basophils from the skin lesions. Thus, basophils play a pivotal role in the development of IgE-mediated chronic allergic inflammation, as an initiator rather than as an effector.

The 21st century renaissance of the basophil? Current insights into its role in allergic responses and innate immunity

Basophils and mast cells express all the three subchains of the high-affinity immunoglobulin E (IgE) receptor Fc epsilon RI and contain preformed histamine in the cytoplasmic granules. However, it is increasingly clear that these cells play distinct roles in allergic inflammatory disease. Despite their presence throughout much of the animal kingdom, the physiological function of basophils remains obscure. As rodent mast cells are more numerous than basophils, and generate an assortment of inflammatory cytokines, basophils have often been regarded as minor players in allergic inflammation. In humans, however, basophils are the prime early producers of interleukin (IL)-4 and IL-13, T helper (Th)2-type cytokines crucial for initiating and maintaining allergic responses. Basophils also express CD40 ligand which, in combination with IL-4 and IL-13, facilitates IgE class switching in B cells. They are the main cellular source for early IL-4 production, which is vital for the development of Th2 responses. The localization of basophils in various tissues affected by allergic inflammation has now been clearly demonstrated by using specific staining techniques and the new research is shedding light on their selective recruitment to the tissues. Finally, recent studies have shown that basophil activation is not restricted to antigen-specific IgE crosslinking, but can be caused in non-sensitized individuals by a growing list of parasitic antigens, lectins and viral superantigens, binding to non-specific IgE antibodies. This, together with novel IgE-independent routes of activation, imparts important new insights into the potential role of basophils in both adaptive and innate immunity.