The history of mast cell and basophil research - some lessons learnt from the last century

The ontogenesis and heterogeneity of basophils

Basophils are the rarest leukocytes, but they have essential roles in protection against helminths, allergic disorders, autoimmune diseases, and some cancers. For years, the clinical significance of basophils has been neglected because of the lack of proper experimental tools to study them. The development of basophil-specific antibodies and animal models, along with genomic advances like single-cell transcriptomics, has greatly enhanced our understanding of basophil biology. Recent discoveries regarding basophils prompted us to write this review, emphasizing the basophil developmental pathway. In it, we chronologically examine the steps of basophil development in various species, which reveals the apparent advent of basophils predating IgE and basophil's IgE-independent regulatory role in primitive vertebrates. Then, we cover studies of basophil development in adult bone marrow, and compare those of murine and human basophils, introducing newly identified basophil progenitors and mature basophil subsets, as well as the transcription factors that regulate the transitions between them. Last, we discuss the heterogeneity of tissue-resident basophils, which may develop through extramedullary hematopoiesis. We expect that this review will contribute to a deeper understanding of basophil biology from the intricate aspects of basophil development and differentiation, offering valuable insights for both researchers and clinicians.

Quantification of Mucosal Mast Cells in the Gastrointestinal Tract: A Primer for Practicing Pathologists

CONTEXT.—

Mast cells are essential components of the immune system and play crucial pathogenetic roles in several digestive diseases, including mastocytic enterocolitis and eosinophilic gastrointestinal disorders. Pathologists have rarely been asked to evaluate the distribution and density of mast cells in gastrointestinal (GI) biopsy specimens. However, such requests are becoming more common because of an increasing awareness of the role of mast cells in functional GI disease and in both esophageal and nonesophageal eosinophilic gastrointestinal disorders.

OBJECTIVE.—

To provide pathologists with tools to incorporate the assessment of mast cells in the evaluation of esophageal, gastric, and intestinal specimens by developing a systematic approach to their evaluation, counting, and reporting.

DESIGN.—

This study consisted of a review of the literature followed by multiple consensus sessions to decide where to count mast cells and what a countable mast cell is.

RESULTS.—

We reviewed 135 papers addressing the content of mast cells in the digestive tract, selected 21 that detailed how cells were counted (microscope lens, area of high-power fields, locations evaluated, type of cells considered as countable), and summarized their data in a table. Then, drawing from both the acceptable literature and our own extensive experience, we reached a tentative consensus on: (1) the normal numbers in the different segments of the GI tract; (2) the morphology of countable mast cells; and (3) the locations and strategies for counting them.

CONCLUSIONS.—

The result is a set of suggestions for reporting mast cell counts, their distribution, and their location in a way clinicians can understand and use for management decisions.

Effects of Dietary Components on Mast Cells: Possible Use as Nutraceuticals for Allergies?

Allergic diseases affect an estimated 30 percent of the world's population. Mast cells (MC) are the key effector cells of allergic reactions by releasing pro-inflammatory mediators such as histamine, lipid mediators, and cytokines/chemokines. Components of the daily diet, including certain fatty acids, amino acids, and vitamins, as well as secondary plant components, may have effects on MC and thus may be of interest as nutraceuticals for the prevention and treatment of allergies. This review summarizes the anti-inflammatory effects of dietary components on MC, including the signaling pathways involved, in in vitro and in vivo models. Butyrate, calcitriol, kaempferol, quercetin, luteolin, resveratrol, curcumin, and cinnamon extract were the most effective in suppressing the release of preformed and de novo synthesized mediators from MC or in animal models. In randomized controlled trials (RCT), vitamin D, quercetin, O-methylated epigallocatechin gallate (EGCG), resveratrol, curcumin, and cinnamon extract improved symptoms of allergic rhinitis (AR) and reduced the number of inflammatory cells in patients. However, strategies to overcome the poor bioavailability of these nutrients are an important part of current research.

Blood cell traits and risk of glaucoma: A two-sample mendelian randomization study

Importance: Glaucoma is the second leading cause of blindness in the world. The causal direction and magnitude of the association between blood cell traits and glaucoma is uncertain because of the susceptibility of observational studies to confounding and reverse causation. Objective: To explore whether there is a causal relationship of blood cell traits including white blood cell (WBC) count (WBCC) and its subtypes [basophil cell count (BASO), monocyte cell count (MONO), lymphocyte cell count (LYMPH), eosinophil cell count (EOS), neutrophil cell count (NEUT)], red blood cell (RBC) count (RBCC), red blood distribution width (RDW), platelet count (PLT), and plateletcrit (PCT) on glaucoma risk. Methods: A two-sample Mendelian randomization (MR) analysis was conducted. Genome-wide significant single nucleotide polymorphisms (SNPs) from published genome-wide association studies (GWAS) on human blood cell traits were utilized as exposure instruments and the dataset for outcome was from the GWAS summary data of glaucoma. In the univariable MR analysis, we examined the association between genetic evidence of blood cell traits and glaucoma. To further investigate the potential causal mechanisms underlying the observed association, we performed multivariable MR analysis with three models, taking into account the mediator effect of inflammation and oxidative stress. According to Bonferroni-corrected for the 10 exposures in 3 methods, the MR study yielded a statistically significant p-value of 0.0017. Results: Genetically BASO, PCT, LYMPH, and PLT were potentially positively associated with glaucoma in the European ancestry [BASO: Odds ratio (OR) = 1.00122, 95% confidence interval (CI), 1.00003-1.00242, p = 0.045; PCT: OR = 1.00078, 95% CI, 1.00012-1.00143, p = 0.019; LYMPH: OR = 1.00076, 95% CI, 1.00002-1.00151, p = 0.045; PLT: OR = 1.00065, 95% CI, 1.00006-1.00123, p = 0.030], There was insufficient evidence to support a causal association of MONO, NEUT, EOS, WBCC, RBCC and RDW (MONO: OR = 1.00050, p = 0.098; NEUT: OR = 1.00028, p = 0.524; EOS: OR = 1.00020, p = 0.562; WBCC: OR = 1.00008, p = 0.830; RBCC: OR = 0.99996, p = 0.920; RDW: OR = 0.99987, p = 0.734) with glaucoma. The multivariable MR with model 1, 2, and 3 demonstrated that BASO, PCT, LYMPH, and PLT were still potentially genetically associated with the risk of glaucoma. Conclusion: Our study reveals a genetic predisposition to higher LYMPH, BASO, PLT, and PCT are associated with a higher risk of glaucoma, whereas WBCC, MONO, EOS, NEUT, RBCC, and RDW are not associated with the occurrence of glaucoma. This finding also supports previous observational studies associating immune components with glaucoma, thus provide guidance on the predication and prevention for glaucoma.

Mast Cells and Acupuncture Analgesia

Mast cells are widely distributed in various parts of the human body and play a vital role in the progression of many diseases. Recently, the close relationship between mast cells and acupoints was elucidated, and the role of mast cells in acupuncture analgesia has attracted the attention of researchers worldwide. Using mast cells, acupuncture analgesia and acupoint as key words to search CNKI, PubMed, Web of Science and other databases, combining the representative articles in these databases with the published research papers of our group, we summarized: The enrichment of mast cells and the dense arrangement of collagen fibers, microvessels, and nerves form the basis for acupoints as the reaction sites of acupuncture; acupuncture can cause the deformation of collagen fibers and activate TRPV channels on mast cells membrane, so as to stimulate mast cells to release bioactive substances and activate nerve receptors to generate analgesic effect; system biology models are set up to explain the quantitative process of information initiation and transmission at acupuncture points, and indicate that the acupuncture effect depends on the local mast cells density. In a conclusion, this review will give a scientific explanation of acupuncture analgesia from the material basis of acupoints, the local initiation, and afferent biological mechanism.

Harnessing the Power of Mast Cells in unconventional Immunotherapy Strategies and Vaccine Adjuvants

Mast cells are long-lived, granular, myeloid-derived leukocytes that have significant protective and repair functions in tissues. Mast cells sense disruptions in the local microenvironment and are first responders to physical, chemical and biological insults. When activated, mast cells release growth factors, proteases, chemotactic proteins and cytokines thereby mobilizing and amplifying the reactions of the innate and adaptive immune system. Mast cells are therefore significant regulators of homeostatic functions and may be essential in microenvironmental changes during pathogen invasion and disease. During infection by helminths, bacteria and viruses, mast cells release antimicrobial factors to facilitate pathogen expulsion and eradication. Mast cell-derived proteases and growth factors protect tissues from insect/snake bites and exposure to ultraviolet radiation. Finally, mast cells release mediators that promote wound healing in the inflammatory, proliferative and remodelling stages. Since mast cells have such a powerful repertoire of functions, targeting mast cells may be an effective new strategy for immunotherapy of disease and design of novel vaccine adjuvants. In this review, we will examine how certain strategies that specifically target and activate mast cells can be used to treat and resolve infections, augment vaccines and heal wounds. Although these strategies may be protective in certain circumstances, mast cells activation may be deleterious if not carefully controlled and any therapeutic strategy using mast cell activators must be carefully explored.

Basophil counting in hematology analyzers: time to discontinue?

Basophils (basophilic granulocytes) are the least abundant cells in blood. Nowadays, basophils are included in the complete blood count performed by hematology analyzers and therefore reported in practically all patients in whom hematologic investigations are requested. However, hematology analyzers are not reliable enough to report clinically useful results. This is due to a combination of very high analytical imprecision and poor specificity, because the chemical and physical methods used for basophil counting in hematology analyzers are ill-defined and thus basophils are not well recognized by the analyzers. As a result, false basophil counts are quite common. In view of increasing analytical performance demands, hematology laboratories should stop reporting basophil counts produced by hematology analyzers. Suggestions for alternative pathways are presented for those situations where basophils are of clinical relevance.

Signal Transduction Pathways Activated by Innate Immunity in Mast Cells: Translating Sensing of Changes into Specific Responses

Mast cells (MCs) constitute an essential cell lineage that participates in innate and adaptive immune responses and whose phenotype and function are influenced by tissue-specific conditions. Their mechanisms of activation in type I hypersensitivity reactions have been the subject of multiple studies, but the signaling pathways behind their activation by innate immunity stimuli are not so well described. Here, we review the recent evidence regarding the main molecular elements and signaling pathways connecting the innate immune receptors and hypoxic microenvironment to cytokine synthesis and the secretion of soluble or exosome-contained mediators in this cell type. When known, the positive and negative control mechanisms of those pathways are presented, together with their possible implications for the understanding of mast cell-driven chronic inflammation. Finally, we discuss the relevance of the knowledge about signaling in this cell type in the recognition of MCs as central elements on innate immunity, whose remarkable plasticity converts them in sensors of micro-environmental discontinuities and controllers of tissue homeostasis.

Cell-bound IgE and plasma IgE as a combined clinical diagnostic indicator for allergic patients

Allergic responses are mainly caused by IgE, which is often located on the cell surface. The current diagnostic method detects both allergen-specific IgE and total IgE levels, but a number of allergic patients have a normal serum IgE level, which is a poor clinical correlate for allergy. Here, we developed a simple method to detect the level of cell-bound IgE by dissociating it from blood cells with lactic acid. Dissociated cell-bound IgE and plasma IgE levels were detected using the same ELISA kit at the same time. We established two clinical cohorts: an allergic patient group and a healthy participant group. In general, cell-bound IgE correlated well with plasma IgE; however, some patients exhibited high cell-bound IgE levels but low plasma IgE levels. We recommended 350 ng/mL peripheral blood total IgE (cell-bound IgE + plasma IgE) as the cut-off value for allergy diagnosis. Using this indicator, 90.32% of our allergic patients were correctly diagnosed. The peripheral blood total IgE level is a promising clinical diagnostic indicator in allergic patients and will provide more guidance for allergy diagnosis and therapeutic evaluation.

Mast cell disorders: From infancy to maturity

Mast cells are typically linked to immediate hypersensitivity and anaphylaxis. This review looks beyond this narrow role, focusing on how these cells have evolved and diversified via natural selection promoting serine protease gene duplication, augmenting their innate host defense function against helminths and snake envenomation. Plasticity of mast cell genes has come at a price. Somatic activating mutations in the mast cell growth factor KIT gene cause cutaneous mastocytosis in young children and systemic mastocytosis with a more guarded prognosis in adults who may also harbor other gene mutations with oncogenic potential as they age. Allelic TPSAB1 gene duplication associated with higher basal mast cell tryptase is possibly one of the commonest autosomal dominantly inherited multi-system diseases affecting the skin, gastrointestinal tract, circulation and musculoskeletal system. Mast cells are also establishing a new-found importance in severe asthma, and in remodeling of blood vessels in cancer and atherosclerotic vascular disease. Furthermore, recent evidence suggests that mast cells sense changes in oxygen tension, particularly in neonates, and that subsequent degranulation may contribute to common lung, eye, and brain diseases of prematurity classically associated with hypoxic insults. One hundred and forty years since Paul Ehrlich's initial description of "mastzellen," this review collates and highlights the complex and diverse roles that mast cells play in health and disease.

An investigation of the distribution and location of mast cells affected by the stiffness of substrates as a mechanical niche

The distribution and location of mast cells are closely related to their physiological and pathological functions, such as allergic responses, immunity, and fibrosis, and are used in acupuncture. In this study, the distribution of mast cells in vivo was observed, and mechanical clues for understanding their distribution based on mechanical niches were explored. By toluidine blue staining and immunohistochemical staining, we examined the distribution and location of mast cells in rat skin and found that mast cells are distributed in a spatially nonuniform manner, preferring to locate at regions in the tissue and extracellular matrix with stiffness changes. In vitro experiments for studying the distribution of rat basophilic leukemia (RBL-2H3) mast cell line on poly-di-methyl-siloxane (PDMS) substrates with stiffness variations were performed. It was found that RBL-2H3 cells migrate and tend to remain in the areas with stiffness variations. The present research suggests that changing the stiffness of local tissues may stimulate mast cell recruitment, which may be the method by which some traditional Chinese medicine treatments, such as acupuncture. On the basis of the origin of mast cells and our experimental results, we predict that mast cells exist in tissues that contain permeable capillaries and prefer regions with stiffness changes. We discussed this prediction using examples of specific tissues from some cases.

Mast cells acquire MHCII from dendritic cells during skin inflammation

Dudeck et al. demonstrate that inflammatory conditions induce dynamic interactions between mast cells (MCs) and dendritic cells (DCs) culminating in protein exchange. Resident MCs are equipped with DC MHCII and empowered to initiate T cell–driven inflammation during migration-based DC absence.

Mast cells (MCs) and dendritic cells (DCs) are essential innate sentinels populating host-environment interfaces. Using longitudinal intravital multiphoton microscopy of DC^GFP/MC^RFP reporter mice, we herein provide in vivo evidence that migratory DCs execute targeted cell-to-cell interactions with stationary MCs before leaving the inflamed skin to draining lymph nodes. During initial stages of skin inflammation, DCs dynamically scan MCs, whereas at a later stage, long-lasting interactions predominate. These innate-to-innate synapse-like contacts ultimately culminate in DC-to-MC molecule transfers including major histocompatibility complex class II (MHCII) proteins enabling subsequent ex vivo priming of allogeneic T cells with a specific cytokine signature. The extent of MHCII transfer to MCs correlates with their T cell priming efficiency. Importantly, preventing the cross talk by preceding DC depletion decreases MC antigen presenting capacity and T cell–driven inflammation. Consequently, we identify an innate intercellular communication arming resident MCs with key DC functions that might contribute to the acute defense potential during critical periods of migration-based DC absence.

BH3 mimetics efficiently induce apoptosis in mouse basophils and mast cells

Basophil granulocytes and mast cells are recognized for their roles in immunity and are central effectors of diverse immunological disorders. Despite their similarities, there is emerging evidence for non-redundant roles of the circulating yet scarce basophils and tissue-resident mast cells, respectively. Because of their importance in allergic pathogenesis, specific induction of apoptosis in basophils and mast cells may represent an interesting novel treatment strategy. The pro-inflammatory cytokine interleukin-3 serves as a key factor for basophil and mouse mast cell survival. Interleukin-3 increases the expression of anti-apoptotic BCL-2 family members, such as BCL-2, BCL-X_L or MCL-1; however, little is known how strongly these individual proteins contribute to basophil survival. Here, we were applying small molecule inhibitors called BH3 mimetics, some of which show remarkable success in cancer treatments, to neutralize the function of anti-apoptotic BCL-2 family members. We observed that expression levels of anti-apoptotic BCL-2 proteins do not necessarily correlate with their respective importance for basophil survival. Whereas naive in vitro-differentiated mouse basophils efficiently died upon BCL-2 or BCL-X_L inhibition, interleukin-3 priming rendered the cells highly resistant toward apoptosis, and this could only be overcome upon combined targeting of BCL-2 and BCL-X_L. Of note, human basophils differed from mouse basophils as they depended on BCL-2 and MCL-1, but not on BCL-X_L, for their survival at steady state. On the other hand, and in contrast to mouse basophils, MCL-1 proved critical in mediating survival of interleukin-3 stimulated mouse mast cells, whereas BCL-X_L seemed dispensable. Taken together, our results indicate that by choosing the right combination of BH3 mimetic compounds, basophils and mast cells can be efficiently killed, even after stimulation with potent pro-survival cytokines such as interleukin-3. Because of the tolerable side effects of BH3 mimetics, targeting basophils or mast cells for apoptosis opens interesting possibilities for novel treatment approaches.

The Evolution of Human Basophil Biology from Neglect towards Understanding of Their Immune Functions

Being discovered long ago basophils have been neglected for more than a century. During the past decade evidence emerged that basophils share features of innate and adaptive immunity. Nowadays, basophils are best known for their striking effector role in the allergic reaction. They hence have been used for establishing new diagnostic tests and therapeutic approaches and for characterizing natural and recombinant allergens as well as hypoallergens, which display lower or diminished IgE-binding activity. However, it was a long way from discovery in 1879 until identification of their function in hypersensitivity reactions, including adverse drug reactions. Starting with a historical background, this review highlights the modern view on basophil biology.

The Role of Mast Cells in Molding the Tumor Microenvironment

Mast cells (MCs) are granulocytic immune cells that reside in tissues exposed to the external environment. MCs are best known for their activity in allergic reactions, but they have been involved in different physiological and pathological conditions. In particular, MC infiltration has been shown in several types of human tumors and in animal cancer models. Nevertheless, the role of MCs in the tumor microenvironment is still debated because they have been associated either to good or poor prognosis depending on tumor type and tissue localization. This dichotomous role relies on MC capacity to secrete a broad spectrum of molecules with modulatory functions, which may condition the final tumor outcome also promoting angiogenesis and tissue remodeling. In this review, we analyze the multifaceted role of mast cell in tumor progression and inhibition considering their ability to interact with: i) immune cells, ii) tumor cells and iii) the extracellular matrix. Eventually, the current MC targeting strategies to treat cancer patients are discussed. Deciphering the actual role of MCs in tumor onset and progression is crucial to identify MC-targeted treatments aimed at killing cancer cells or at making the tumor vulnerable to selected anti-cancer drugs.

Helminth Allergens, Parasite-Specific IgE, and Its Protective Role in Human Immunity

The Th2 immune response, culminating in eosinophilia and IgE production, is not only characteristic of allergy but also of infection by parasitic worms (helminths). Anti-parasite IgE has been associated with immunity against a range of helminth infections and many believe that IgE and its receptors evolved to help counter metazoan parasites. Allergens (IgE-antigens) are present in only a small minority of protein families and known IgE targets in helminths belong to these same families (e.g., EF-hand proteins, tropomyosin, and PR-1 proteins). During some helminth infection, especially with the well adapted hookworm, the Th2 response is moderated by parasite-expressed molecules. This has been associated with reduced allergy in helminth endemic areas and worm infection or products have been proposed as treatments for allergic conditions. However, some infections (especially Ascaris) are associated with increased allergy and this has been linked to cross-reactivity between worm proteins (e.g., tropomyosins) and highly similar molecules in dust-mites and insects. The overlap between allergy and helminth infection is best illustrated in Anisakis simplex, a nematode that when consumed in under-cooked fish can be both an infective helminth and a food allergen. Nearly 20 molecular allergens have been isolated from this species, including tropomyosin (Ani s 3) and the EF-hand protein, Ani s troponin. In this review, we highlight aspects of the biology and biochemistry of helminths that may have influenced the evolution of the IgE response. We compare dominant IgE-antigens in worms with clinically important environmental allergens and suggest that arrays of such molecules will provide important information on anti-worm immunity as well as allergy.