Activation of Human Basophils by A549 Lung Epithelial Cells Reveals a Novel IgE-Dependent Response Independent of Allergen

Exploiting innate immunity for cancer immunotherapy

Immunotherapies have revolutionized the treatment paradigms of various types of cancers. However, most of these immunomodulatory strategies focus on harnessing adaptive immunity, mainly by inhibiting immunosuppressive signaling with immune checkpoint blockade, or enhancing immunostimulatory signaling with bispecific T cell engager and chimeric antigen receptor (CAR)-T cell. Although these agents have already achieved great success, only a tiny percentage of patients could benefit from immunotherapies. Actually, immunotherapy efficacy is determined by multiple components in the tumor microenvironment beyond adaptive immunity. Cells from the innate arm of the immune system, such as macrophages, dendritic cells, myeloid-derived suppressor cells, neutrophils, natural killer cells, and unconventional T cells, also participate in cancer immune evasion and surveillance. Considering that the innate arm is the cornerstone of the antitumor immune response, utilizing innate immunity provides potential therapeutic options for cancer control. Up to now, strategies exploiting innate immunity, such as agonists of stimulator of interferon genes, CAR-macrophage or -natural killer cell therapies, metabolic regulators, and novel immune checkpoint blockade, have exhibited potent antitumor activities in preclinical and clinical studies. Here, we summarize the latest insights into the potential roles of innate cells in antitumor immunity and discuss the advances in innate arm-targeted therapeutic strategies.

Basophils beyond allergic and parasitic diseases

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

Basophils from allergy to cancer

Human basophils, first identified over 140 years ago, account for just 0.5-1% of circulating leukocytes. While this scarcity long hampered basophil studies, innovations during the past 30 years, beginning with their isolation and more recently in the development of mouse models, have markedly advanced our understanding of these cells. Although dissimilarities between human and mouse basophils persist, the overall findings highlight the growing importance of these cells in health and disease. Indeed, studies continue to support basophils as key participants in IgE-mediated reactions, where they infiltrate inflammatory lesions, release pro-inflammatory mediators (histamine, leukotriene C₄: LTC₄) and regulatory cytokines (IL-4, IL-13) central to the pathogenesis of allergic diseases. Studies now report basophils infiltrating various human cancers where they play diverse roles, either promoting or hampering tumorigenesis. Likewise, this activity bears remarkable similarity to the mounting evidence that basophils facilitate wound healing. In fact, both activities appear linked to the capacity of basophils to secrete IL-4/IL-13, with these cytokines polarizing macrophages toward the M2 phenotype. Basophils also secrete several angiogenic factors (vascular endothelial growth factor: VEGF-A, amphiregulin) consistent with these activities. In this review, we feature these newfound properties with the goal of unraveling the increasing importance of basophils in these diverse pathobiological processes.

IgG Autoantibodies Against IgE from Atopic Dermatitis Can Induce the Release of Cytokines and Proinflammatory Mediators from Basophils and Mast Cells

IgE-mediated release of proinflammatory mediators and cytokines from basophils and mast cells is a central event in allergic disorders. Several groups of investigators have demonstrated the presence of autoantibodies against IgE and/or FcεRI in patients with chronic spontaneous urticaria. By contrast, the prevalence and functional activity of anti-IgE autoantibodies in atopic dermatitis (AD) are largely unknown. We evaluated the ability of IgG anti-IgE from patients with AD to induce the in vitro IgE-dependent activation of human basophils and skin and lung mast cells. Different preparations of IgG anti-IgE purified from patients with AD and rabbit IgG anti-IgE were compared for their triggering effects on the in vitro release of histamine and type 2 cytokines (IL-4, IL-13) from basophils and of histamine and lipid mediators (prostaglandin D₂ and cysteinyl leukotriene C₄) from human skin and lung mast cells. One preparation of human IgG anti-IgE out of six patients with AD induced histamine release from basophils, skin and lung mast cells. This preparation of human IgG anti-IgE induced the secretion of cytokines and eicosanoids from basophils and mast cells, respectively. Human monoclonal IgE was a competitive antagonist of both human and rabbit IgG anti-IgE. Human anti-IgE was more potent than rabbit anti-IgE for IL-4 and IL-13 production by basophils and histamine, prostaglandin D₂ and leukotriene C₄ release from mast cells. Functional anti-IgE autoantibodies rarely occur in patients with AD. When present, they induce the release of proinflammatory mediators and cytokines from basophils and mast cells, thereby possibly contributing to sustained IgE-dependent inflammation in at least a subset of patients with this disorder.

Extracellular DNA Traps: Origin, Function and Implications for Anti-Cancer Therapies

Extracellular DNA may serve as marker in liquid biopsies to determine individual diagnosis and prognosis in cancer patients. Cell death or active release from various cell types, including immune cells can result in the release of DNA into the extracellular milieu. Neutrophils are important components of the innate immune system, controlling pathogens through phagocytosis and/or the release of neutrophil extracellular traps (NETs). NETs also promote tumor progression and metastasis, by modulating angiogenesis, anti-tumor immunity, blood clotting and inflammation and providing a supportive niche for metastasizing cancer cells. Besides neutrophils, other immune cells such as eosinophils, dendritic cells, monocytes/macrophages, mast cells, basophils and lymphocytes can also form extracellular traps (ETs) during cancer progression, indicating possible multiple origins of extracellular DNA in cancer. In this review, we summarize the pathomechanisms of ET formation generated by different cell types, and analyze these processes in the context of cancer. We also critically discuss potential ET-inhibiting agents, which may open new therapeutic strategies for cancer prevention and treatment.

The S1 Subunit of the SARS-CoV-2 Spike Protein Activates Human Monocytes to Produce Cytokines Linked to COVID-19: Relevance to Galectin-3

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), rapidly evolved into a pandemic –the likes of which has not been experienced in 100 years. While novel vaccines show great efficacy, and therapeutics continue to be developed, the persistence of disease, with the concomitant threat of emergent variants, continues to impose massive health and socioeconomic issues worldwide. Studies show that in susceptible individuals, SARS-CoV-2 infection can rapidly progress toward lung injury and acute respiratory distress syndrome (ARDS), with evidence for an underlying dysregulated innate immune response or cytokine release syndrome (CRS). The mechanisms responsible for this CRS remain poorly understood, yet hyper-inflammatory features were also evident with predecessor viruses within the β-coronaviridae family, namely SARS-CoV-1 and the Middle East Respiratory Syndrome (MERS)-CoV. It is further known that the spike protein (S) of SARS-CoV-2 (as first reported for other β-coronaviruses) possesses a so-called galectin-fold within the N-terminal domain of the S1 subunit (S1-NTD). This fold (or pocket) shows structural homology nearly identical to that of human galectin-3 (Gal-3). In this respect, we have recently shown that Gal-3, when associated with epithelial cells or anchored to a solid phase matrix, facilitates the activation of innate immune cells, including basophils, DC, and monocytes. A synthesis of these findings prompted us to test whether segments of the SARS-CoV-2 spike protein might also activate innate immune cells in a manner similar to that observed in our Gal-3 studies. Indeed, by immobilizing S components onto microtiter wells, we show that only the S1 subunit (with the NTD) activates human monocytes to produce a near identical pattern of cytokines as those reported in COVID-19-related CRS. In contrast, both the S1-CTD/RBD, which binds ACE2, and the S2 subunit (stalk), failed to mediate the same effect. Overall, these findings provide evidence that the SARS-CoV-2 spike protein can activate monocytes for cytokines central to COVID-19, thus providing insight into the innate immune mechanisms underlying the CRS and the potential for therapeutic interventions.

The Prognostic Value of Multiple Systemic Inflammatory Biomarkers in Preoperative Patients With Non-small Cell Lung Cancer

Introduction

The preoperative inflammatory and nutrient status of the patient are closely correlated to the outcome of surgery-based treatment for non-small cell lung cancer (NSCLC). We aimed to investigate the prognostic value of inflammation and nutrient biomarkers in preoperative patients with non-small cell lung cancer (NSCLC) by constructing a prognostic predictive model.

Methods

We retrospectively studied 995 patients with NSCLC who underwent surgery in the Shandong Provincial Hospital and randomly allocated them into the training and validation group with a ratio of 7:3. We then compared their prognostic performance and conducted univariate Cox analyses with several clinicopathological variables. Based on the performance of the receiver operating characteristic (ROC) curves and decision curves analysis (DCA), the prognostic model was optimized and validated.

Result

The median overall overall survival (OS) of patients was 74 months. Univariate Cox analysis indicated that fifteen inflammatory biomarkers were significantly correlated with OS (p < 0.100). Multivariate Cox analysis revealed that the model incorporating grade, age, stage, basophil-to-lymphocyte ratio (BLR, ≥0.00675 vs. < 0.00675) and albumin-to-globulin ratio (AGR, ≥1.40 vs. <1.40) showed the maximum area under the curve (AUC, 0.744). The C-index in the training and validation group was 0.690 and 0.683, respectively. The 3-year integrated discrimination improvement (IDI) compared to TNM (Tumor Node Metastasis) stage was 0.035 vs. 0.011 in the training and validation group, respectively.

Conclusions

Lower AGR, ANRI, and higher BLR were associated with a worse outcome for patients with NSCLC. We constructed a prognostic nomogram with risk stratification based on inflammatory and nutrient biomarkers. The discrimination and calibration abilities of the model were evaluated to confirm its validity, indicating the potential utility of this prognostic model for clinical guidance.

SARS-CoV-2 Induces Cytokine Responses in Human Basophils

Basophils play a key role in the orientation of immune responses. Though the interaction of SARS-CoV-2 with various immune cells has been relatively well studied, the response of basophils to this pandemic virus is not characterized yet. In this study, we report that SARS-CoV-2 induces cytokine responses and in particular IL-13, in both resting and IL-3 primed basophils. The response was prominent under IL-3 primed condition. However, either SARS-CoV-2 or SARS-CoV-2-infected epithelial cells did not alter the expression of surface markers associated with the activation of basophils, such as CD69, CD13 and/or degranulation marker CD107a. We also validate that human basophils are not permissive to SARS-CoV-2 replication. Though increased expression of immune checkpoint molecule PD-L1 has been reported on the basophils from COVID-19 patients, we observed that SARS-CoV-2 does not induce PD-L1 on the basophils. Our data suggest that basophil cytokine responses to SARS-CoV-2 might help in reducing the inflammation and also to promote antibody responses to the virus.

Clinical and Translational Significance of Basophils in Patients with Cancer

Despite comprising a very small proportion of circulating blood leukocytes, basophils are potent immune effector cells. The high-affinity receptor for IgE (FcɛRI) is expressed on the basophil cell surface and powerful inflammatory mediators such as histamine, granzyme B, and cytokines are stored in dense cytoplasmic granules, ready to be secreted in response to a range of immune stimuli. Basophils play key roles in eliciting potent effector functions in allergic diseases and type 1 hypersensitivity. Beyond allergies, basophils can be recruited to tissues in chronic and autoimmune inflammation, and in response to parasitic, bacterial, and viral infections. While their activation states and functions can be influenced by Th2-biased inflammatory signals, which are also known features of several tumor types, basophils have received little attention in cancer. Here, we discuss the presence and functional significance of basophils in the circulation of cancer patients and in the tumor microenvironment (TME). Interrogating publicly available datasets, we conduct gene expression analyses to explore basophil signatures and associations with clinical outcomes in several cancers. Furthermore, we assess how basophils can be harnessed to predict hypersensitivity to cancer treatments and to monitor the desensitization of patients to oncology drugs, using assays such as the basophil activation test (BAT).

Basophils as a potential therapeutic target in cancer

Basophils, which are considered as redundant relatives of mast cells and the rarest granulocytes in peripheral circulation, have been neglected by researchers in the past decades. Previous studies have revealed their vital roles in allergic diseases and parasitic infections. Intriguingly, recent studies even reported that basophils might be associated with cancer development, as activated basophils synthesize and release a variety of cytokines and chemokines in response to cancers. However, it is still subject to debate whether basophils function as tumor-protecting or tumor-promoting components; the answer may depend on the tumor biology and the microenvironment. Herein, we reviewed the role of basophils in cancers, and highlighted some potential and promising therapeutic strategies.

IL-3 in the development and function of basophils

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

Long-acting muscarinic antagonist regulates group 2 innate lymphoid cell-dependent airway eosinophilic inflammation

BACKGROUND

Tiotropium bromide, a long-acting muscarinic antagonist, reduces the frequency of exacerbation in patients with moderate to severe asthma, but its underlying mechanism is not clear. Asthma exacerbations are associated with exposure to external stimuli, and group 2 innate lymphoid cells (ILC2s) are considered to be involved in the pathophysiology of asthma exacerbation. We investigated whether tiotropium modulates airway inflammation through ILC2 functions.

METHODS

Mice were administered papain intranasally to induce innate-type airway inflammation with or without tiotropium pretreatment, and bronchoalveolar lavage fluids (BALF) and lung tissues were collected. Lung-derived ILC2s and bone marrow-derived basophils were stimulated in vitro with IL-33 in the presence or absence of tiotropium. Muscarinic M3 receptor (M3R) expression on immune cells was assessed by RNA sequence.

RESULTS

Papain induced airway eosinophilic inflammation, and tiotropium reduced the numbers of eosinophils in BALF. The concentrations of IL-4, IL-5, and IL-13, and the numbers of ILC2s in BALF were also reduced by tiotropium treatment. However, tiotropium did not affect IL-33-induced IL-5 and IL-13 production from ILC2s, suggesting that tiotropium regulates ILC2s indirectly. Gene-expression analysis showed that basophils predominantly expressed M3R mRNA among murine immune cells. Tiotropium reduced IL-4 production from basophils derived from mouse bone marrow and human basophils after stimulation with IL-33.

CONCLUSIONS

These findings suggest that tiotropium attenuates ILC2-dependent airway inflammation by suppressing IL-4 production from basophils and, subsequently, regulating ILC2 activation. The inhibitory effects of long-acting muscarinic antagonists on the innate response may contribute to reducing asthma exacerbation.

Basophils Orchestrating Eosinophils' Chemotaxis and Function in Allergic Inflammation

Eosinophils are well known to contribute significantly to Th2 immunity, such as allergic inflammations. Although basophils have often not been considered in the pathogenicity of allergic dermatitis and asthma, their role in Th2 immunity has become apparent in recent years. Eosinophils and basophils are present at sites of allergic inflammations. It is therefore reasonable to speculate that these two types of granulocytes interact in vivo. In various experimental allergy models, basophils and eosinophils appear to be closely linked by directly or indirectly influencing each other since they are responsive to similar cytokines and chemokines. Indeed, basophils are shown to be the gatekeepers that are capable of regulating eosinophil entry into inflammatory tissue sites through activation-induced interactions with endothelium. However, the direct evidence that eosinophils and basophils interact is still rarely described. Nevertheless, new findings on the regulation and function of eosinophils and basophils biology reported in the last 25 years have shed some light on their potential interaction. This review will focus on the current knowledge that basophils may regulate the biology of eosinophil in atopic dermatitis and allergic asthma.

Mechanisms of Allergen Immunotherapy in Allergic Rhinitis

PURPOSE OF REVIEW

Allergic rhinitis (AR) is a chronic inflammatory immunoglobulin (Ig) E-mediated disease of the nasal mucosa that can be triggered by the inhalation of seasonal or perennial allergens. Typical symptoms include sneezing, rhinorrhea, nasal itching, nasal congestion and symptoms of allergic conjunctivitis. AR affects a quarter of the population in the United States of America and Europe.

RECENT FINDINGS

AR has been shown to reduce work productivity in 36-59% of the patients with 20% reporting deteriorated job attendance. Moreover, 42% of children with AR report reduced at-school productivity and lower grades. Most importantly, AR impacts the patient's quality of life, due to sleep deprivation. However, a proportion of patients fails to respond to conventional medication and opts for the allergen immunotherapy (AIT), which currently is the only disease-modifying therapeutic option. AIT can be administered by either subcutaneous (SCIT) or sublingual (SLIT) route. Both routes of administration are safe, effective, and can lead to tolerance lasting years after treatment cessation. Both innate and adaptive immune responses that contribute to allergic inflammation are suppressed by AIT. Innate responses are ameliorated by reducing local mast cell, basophil, eosinophil, and circulating group 2 innate lymphoid cell frequencies which is accompanied by decreased basophil sensitivity. Induction of allergen-specific blocking antibodies, immunosuppressive cytokines, and regulatory T and B cell phenotypes are key pro-tolerogenic adaptive immune responses.

CONCLUSION

A comprehensive understanding of these mechanisms is necessary for optimal selection of AIT-responsive patients and monitoring treatment efficacy. Moreover, it could inspire novel and more efficient AIT approaches.

Epithelial Cell-Associated Galectin-3 Activates Human Dendritic Cell Subtypes for Pro-Inflammatory Cytokines

There is mounting evidence that galectin-3 is a prognostic and diagnostic biomarker associated with diverse diseases and conditions, including cancer, cardiovascular disease, autoimmunity, wound healing, allergic disease, and chronic inflammation in general. Yet, whether and exactly how galectin-3 may participate in the pathogenesis of these diseases remains poorly understood. Recently, we have linked the expression of galectin-3 on the A549 epithelial cell line –an adenocarcinoma, to the activation of human basophils for the release of histamine and secretion of IL-4 and IL-13. These responses proved dependent on cell-to-cell contact, basophil expression of IgE, were inhibited by n-acetyllactosamine, and were ablated when basophils were co-cultured with A549 clones lacking galectin-3 expression. While recombinant galectin-3 failed to activate basophils when in solution, microspheres expressing this lectin did so by mimicking the responses seen when using A549 cells. Given the IgE dependency of the basophil responses, and the fact that galectin-3 is long known to bind this immunoglobulin, we hypothesize that a similar mode of activation extends to other IgE-bearing cells. To investigate this possibility, we tested epithelial cell-associated galectin-3 for its capacity to activate human dendritic cells, including the plasmacytoid and myeloid subtypes as well as monocytes, all of which bind IgE. Indeed, results indicate that epithelial cell-associated galectin-3 activated these cells for robust production of TNF-α and IL-6 and up-regulated the expression of activation markers found on dendritic cells. Moreover, many of the same parameters previously observed for basophils applied to the findings herein, including evidence that matrix-bound galectin-3 (whether on epithelial cells or microspheres) facilitates this mode of activation. In contrast, IgE expression was dispensable for these galectin-3-dependent cytokine responses, implying that this lectin activates dendritic cells (and monocytes) by binding to a glycoprotein other than this immunoglobulin. Overall, these findings further demonstrate how galectin-3 mediates immune cell activation, providing novel insight into how this lectin may promote chronic inflammation underlying the pathogenesis of many diseases.

Is There a Role for Basophils in Cancer?

Basophils were identified in human peripheral blood by Paul Ehrlich over 140 years ago. Human basophils represent <1% of peripheral blood leukocytes. During the last decades, basophils have been described also in mice, guinea pigs, rabbits, and monkeys. There are many similarities, but also several immunological differences between human and mouse basophils. There are currently several strains of mice with profound constitutive or inducible basophil deficiency useful to prove that these cells have specific roles in vivo. However, none of these mice are solely and completely devoid of all basophils. Therefore, the relevance of these findings to humans remains to be established. It has been known for some time that basophils have the propensity to migrate into the site of inflammation. Recent observations indicate that tissue resident basophils contribute to lung development and locally promote M2 polarization of macrophages. Moreover, there is increasing evidence that lung-resident basophils exhibit a specific phenotype, different from circulating basophils. Activated human and mouse basophils synthesize restricted and distinct profiles of cytokines. Human basophils produce several canonical (e.g., VEGFs, angiopoietin 1) and non-canonical (i.e., cysteinyl leukotriene C₄) angiogenic factors. Activated human and mouse basophils release extracellular DNA traps that may have multiple effects in cancer. Hyperresponsiveness of basophils has been demonstrated in patients with JAK2^V617F-positive polycythemia vera. Basophils are present in the immune landscape of human lung adenocarcinoma and pancreatic cancer and can promote inflammation-driven skin tumor growth. The few studies conducted thus far using different models of basophil-deficient mice have provided informative results on the roles of these cells in tumorigenesis. Much more remains to be discovered before we unravel the hitherto mysterious roles of basophils in human and experimental cancers.

IgE Autoreactivity in Atopic Dermatitis: Paving the Road for Autoimmune Diseases?

Atopic dermatitis (AD) is a common skin disease affecting 20% of the population beginning usually before one year of age. It is associated with the emergence of allergen-specific IgE, but also with autoreactive IgE, whose function remain elusive. This review discusses current knowledge relevant to the mechanisms, which leads to the secretion of autoreactive IgE and to the potential function of these antibodies in AD. Multiple autoantigens have been described to elicit an IgE-dependent response in this context. This IgE autoimmunity starts in infancy and is associated with disease severity. Furthermore, the overall prevalence of autoreactive IgE to multiple auto-antigens is high in AD patients. IgE-antigen complexes can promote a facilitated antigen presentation, a skewing of the adaptive response toward type 2 immunity, and a chronic skin barrier dysfunction and inflammation in patients or AD models. In AD, skin barrier defects and the atopic immune environment facilitate allergen sensitization and the development of other IgE-mediated allergic diseases in a process called the atopic march. AD is also associated epidemiologically with several autoimmune diseases showing autoreactive IgE secretion. Thus, a potential outcome of IgE autoreactivity in AD could be the development of further autoimmune diseases.

Basophils in Tumor Microenvironment and Surroundings

Basophils represent approximately 1% of human peripheral blood leukocytes. Their effector functions were initially appreciated in the 1970s when basophils were shown to express the high-affinity receptor (FcεRI) for IgE and to release proinflammatory mediators (histamine and cysteinyl leukotriene C₄) and immunoregulatory cytokines (i.e., IL-4 and IL-13). Basophils in the mouse were subsequently identified and immunologically characterized. There are many similarities but also several differences between human and mouse basophils. Basophil-deficient mice have enabled to examine the in vivo roles of basophils in several immune disorders and, more recently, in tumor immunity. Activated human basophils release several proangiogenic molecules such as vascular endothelial growth factor-A (VEGF-A), vascular endothelial growth factor-B (VEGF-B), CXCL8, angiopoietin 1 (ANGPT1), and hepatocyte growth factor (HGF). On the other side, basophils can exert anti-tumorigenic effects by releasing granzyme B, TNF-α, and histamine. Circulating basophils have been associated with certain human hematologic (i.e., chronic myeloid leukemia) and solid tumors. Basophils have been found in tumor microenvironment (TME) of human lung adenocarcinoma and pancreatic cancer. Basophils played a role in melanoma rejection in basophil-deficient mouse model. By contrast, basophils appear to play a pro-tumorigenic role in experimental and human pancreatic cancer. In conclusion, the roles of basophils in experimental and human cancers have been little investigated and remain largely unknown. The elucidation of the roles of basophils in tumor immunity will demand studies on increasing complexity beyond those assessing basophil density and their microlocalization in TME. There are several fundamental questions to be addressed in experimental models and clinical studies before we understand whether basophils are an ally, adversary, or even innocent bystanders in cancers.

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.

Possible roles of basophils in chronic itch

Basophils are blood granulocytes and normally constitute <1% of blood peripheral leucocytes. Basophils share some morphological and functional similarities with mast cells, and basophils were once regarded as redundant and negligible circulating mast cells. However, recent studies reveal the indispensable roles of basophils in various diseases, including allergic and pruritic diseases. Basophils may be involved in itch through the mediation of a Th2 immune response, interaction with other cells in the skin and secretion of a wide variety of itch-related mediators, for example histamine, cytokines and chemokines (IL-4, IL-13, IL-31 and TSLP), proteases (cathepsin S), prostaglandins (PGE2 and PGD2), substance P and platelet-activating factor. Not only pruritic skin diseases (eg, atopic dermatitis, irritant contact dermatitis, chronic urticaria, prurigo, papulo-erythroderma of Ofuji, eosinophilic pustular folliculitis, scabies, tick bites and bullous pemphigoid) but also pruritic systemic diseases (eg, primary sclerosing cholangitis and polycythemia vera) may be affected by basophils.