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Neutrophils are critical for the direct eradication of Aspergillus fumigatus conidia, but whether they mediate antifungal defense beyond their role as effectors is unclear. In this study, we demonstrate that neutrophil depletion impairs the activation of protective antifungal CCR2+ inflammatory monocytes. In the absence of neutrophils, monocytes displayed limited differentiation into monocyte-derived dendritic cells, reduced formation of reactive oxygen species, and diminished conidiacidal activity. Upstream regulator analysis of the transcriptional response in monocytes predicted a loss of STAT1-dependent signals as the potential basis for the dysfunction seen in neutrophil-depleted mice. We find that conditional removal of STAT1 on CCR2+ cells results in diminished antifungal monocyte responses, whereas exogenous administration of IFN-γ to neutrophil-depleted mice restores monocyte-derived dendritic cell maturation and reactive oxygen species production. Altogether, our findings support a critical role for neutrophils in antifungal immunity not only as effectors but also as important contributors to antifungal monocyte activation, in part by regulating STAT1-dependent functions.

Neuroimmune interactions are crucial for regulating immunity and inflammation. Recent studies have revealed that the central nervous system (CNS) senses peripheral inflammation and responds by releasing molecules that limit immune cell activation, thereby promoting tolerance and tissue integrity. However, the extent to which this is a bidirectional process, and whether peripheral immune cells also promote tolerance mechanisms in the CNS remains poorly defined. Here we report that helminth-induced type 2 inflammation promotes monocyte responses in the brain that are required to inhibit excessive microglial activation and host death. Mechanistically, infection-induced monocytes express YM1 that is sufficient to inhibit tumor necrosis factor production from activated microglia. Importantly, neuroprotective monocytes persist in the brain, and infected mice are protected from subsequent lipopolysaccharide-induced neuroinflammation months after infection-induced inflammation has resolved. These studies demonstrate that infiltrating monocytes promote CNS homeostasis in response to inflammation in the periphery and demonstrate that a peripheral infection can alter the immunologic landscape of the host brain.

Parasitic helminth infections remain a significant global health issue and are responsible for devastating morbidity and economic hardships. During infection, helminths migrate through different host organs, which results in substantial tissue damage and the release of diverse effector molecules by both hematopoietic and non-hematopoietic cells. Thus, host protective responses to helminths must initiate mechanisms that help to promote worm clearance while simultaneously mitigating tissue injury. The specialized immunity that promotes these responses is termed type 2 inflammation and is initiated by the recruitment and activation of hematopoietic stem/progenitor cells, mast cells, basophils, eosinophils, dendritic cells, neutrophils, macrophages, myeloid-derived suppressor cells, and group 2 innate lymphoid cells. Recent work has also revealed the importance of neuron-derived signals in regulating type 2 inflammation and antihelminth immunity. These studies suggest that multiple body systems coordinate to promote optimal outcomes post-infection. In this review, we will describe the innate immune events that direct the scope and intensity of antihelminth immunity. Further, we will highlight the recent progress made in our understanding of the neuro-immune interactions that regulate these pathways and discuss the conceptual advances they promote.

The role of p53 in tumor suppression has been extensively studied and well-established. However, the role of p53 in parasitic infections and the intestinal type 2 immunity is unclear. Here, we report that p53 is crucial for intestinal type 2 immunity in response to the infection of parasites, such as Tritrichomonas muris and Nippostrongylus brasiliensis. Mechanistically, p53 plays a critical role in the activation of the tuft cell-IL-25-type 2 innate lymphoid cell circuit, partly via transcriptional regulation of Lrmp in tuft cells. Lrmp modulates Ca2+ influx and IL-25 release, which are critical triggers of type 2 innate lymphoid cell response. Our results thus reveal a previously unrecognized function of p53 in regulating intestinal type 2 immunity to protect against parasitic infections, highlighting the role of p53 as a guardian of immune integrity., P53 is a well-known tumour suppressor, however its role in intestinal type 2 immunity is currently unclear. Here authors report that during parasitic infections, p53 triggers tuft cell Ca2+ influx and IL-25 release, and shows a regulatory role for p53 in intestinal type 2 immunity via transcriptional regulation of the Lrmp gene.

Type 2 cytokine responses promote parasitic immunity and initiate tissue repair; however, they can also result in immunopathologies when not properly restricted. Although basophilia is recognized as a common feature of type 2 inflammation, the roles basophils play in regulating these responses are unknown. Here, we demonstrate that helminth-induced group 2 innate lymphoid cell (ILC2) responses are exaggerated in the absence of basophils, resulting in increased inflammation and diminished lung function. Additionally, we show that ILC2s from basophil-depleted mice express reduced amounts of the receptor for the neuropeptide neuromedin B (NMB). Critically, NMB stimulation inhibited ILC2 responses from control but not basophil-depleted mice, and basophils were sufficient to directly enhance NMB receptor expression on ILC2s. These studies suggest that basophils prime ILC2s to respond to neuron-derived signals necessary to maintain tissue integrity. Further, these data provide mechanistic insight into the functions of basophils and identify NMB as a potent inhibitor of type 2 inflammation.

Inflammation is an important component of fibrosis but immune processes that orchestrate kidney fibrosis are not well understood. Here we apply single-cell sequencing to a mouse model of kidney fibrosis. We identify a subset of kidney tubule cells with a profibrotic-inflammatory phenotype characterized by the expression of cytokines and chemokines associated with immune cell recruitment. Receptor-ligand interaction analysis and experimental validation indicate that CXCL1 secreted by profibrotic tubules recruits CXCR2

It has been appreciated that basophilia is a common feature of helminth infections for approximately 50 years. The ability of basophils to secrete IL-4 and other type 2 cytokines has supported the prevailing notion that basophils contribute to antihelminth immunity by promoting optimal type 2 T helper (Th2) cell responses. While this appears to be the case in several helminth infections, emerging studies are also revealing that the effector functions of basophils are extremely diverse and parasite-specific. Further, new reports now suggest that basophils can restrict type 2 inflammation in a manner that preserves the integrity of helminth-affected tissue. Finally, exciting data has also demonstrated that basophils can regulate inflammation by participating in neuro-immune interactions. This article will review the current state of basophil biology and describe how recent studies are transforming our understanding of the role basophils play in the context of helminth infections.

Basophils are innate immune cells associated with type 2 immunity, allergic reactions, and host defense against parasite infections. In this study, we show that the transcription factor PLZF, which is known for its essential role in the function and development of several innate lymphocyte subsets, is also important for the myeloid-derived basophil lineage. PLZF-deficient mice had decreased numbers of basophil progenitors in the bone marrow and mature basophils in multiple peripheral tissues. Functionally, PLZF-deficient basophils were less responsive to IgE activation and produced reduced amounts of IL-4. The altered function of basophils resulted in a blunted Th2 T cell response to a protein allergen. Additionally, PLZF-deficient basophils had reduced expression of the IL-18 receptor, which impacted migration to lungs. PLZF, therefore, is a major player in controlling type 2 immune responses mediated not only by innate lymphocytes but also by myeloid-derived cells.

PURPOSE OF REVIEW. Allergic diseases represent a growing global health concern, especially among pediatric populations. Current strategies for the treatment of allergies and asthma focus on limiting the severity of the symptoms; however, additional research investigating the mechanisms promoting inflammation in the context of allergic reactions may lead to the development of more effective therapeutic strategies. RECENT FINDINGS. Novel studies have highlighted the contributions of innate lymphocytes to the induction of inflammatory responses to allergens. Remarkably, neuron-derived signals, hormones, and even vitamins have been suggested to modulate the activity of innate lymphocytes, opening new windows of opportunity for the treatment of allergic inflammation SUMMARY. These studies highlight the complex interactions of the nervous, endocrine and immune system that promote pathology in the context of allergic inflammation. Further studies are required to understand these interactions in order to aid in the development of novel and much-needed therapies to treat allergic conditions.

Macrophages are known to mediate anti-helminth responses, but it remains uncertain which subsets are involved or how macrophages actually kill helminths. Here we show rapid monocyte recruitment to the lung after infection with the nematode parasite,Nippostrongylus brasiliensis. In this inflamed tissue microenvironment these monocytes differentiate into an alveolar-like macrophage (AM) phenotype, expressing both Siglec-F and CD11c, surround invading parasitic larvae and preferentially kill parasites in vitro. Monocyte-derived AMs (Mo-AMs) express type 2-associated markers and show distinct remodeling of the chromatin landscape relative to tissue-derived AMs. In particular, they express high amounts of Arg1 (arginase-1), which we demonstrate mediates helminth killing through L-arginine depletion. These studies indicate that recruited monocytes are selectively programmed in the pulmonary environment to express AM markers and an anti-helminth phenotype.

Anti-helminth responses require robust type 2 cytokine production that simultaneously promotes worm expulsion and initiates the resolution of helminth-induced wounds and hemorrhaging. However, how infection-induced changes in hematopoiesis contribute to these seemingly distinct processes remains unknown. Recent studies have suggested the existence of a hematopoietic progenitor with dual mast cell-erythrocyte potential. Nonetheless, whether and how these progenitors contribute to host protection during an active infection remains to be defined. Here, we employed single cell RNA-sequencing and identified that the metabolic enzyme, carbonic anhydrase (Car) 1 marks a predefined bone marrow-resident hematopoietic progenitor cell (HPC) population. Next, we generated a Car1-reporter mouse model and found that Car1-GFP positive progenitors represent bipotent mast cell/erythrocyte precursors. Finally, we show that Car1-expressing HPCs simultaneously support mast cell and erythrocyte responses during Trichinella spiralis infection. Collectively, these data suggest that mast cell/erythrocyte precursors are mobilized to promote type 2 cytokine responses and alleviate helminth-induced blood loss, developmentally linking these processes. Collectively, these studies reveal unappreciated hematopoietic events initiated by the host to combat helminth parasites and provide insight into the evolutionary pressure that may have shaped the developmental relationship between mast cells and erythrocytes., Author summary Helminth parasites infect approximately 2 billion people and represent a significant public health concern. Helminths undertake complex developmental life cycles through multiple organs and as a result cause substantial tissue damage. To combat this, mammals have evolved mechanisms to initiate balanced immune responses that promote inflammation needed to seclude parasites in granulomas, reduce parasitic burdens and mitigate the consequences of helminth-induced wounds. Despite their clinical importance, the mechanisms that regulate these events remain poorly defined. Here we have uncovered a unique progenitor cell that supports both proinflammatory mast cell responses and red blood cell development, thereby simultaneously initiating both of these host-protective responses. Collectively, these studies reveal unappreciated events initiated by the host to combat pathogens that infect billions of individuals worldwide.

We examined the activation and effector functions of lung macrophages in mediatingimmunity against helminth parasites. Using fate mapping mice, we showed thatmonocytes recruited to the lung assume an alveolar macrophage phenotype andcomprise as many as 10% of alveolar macrophages by 7 days after inoculation.Monocyte-derived alveolar macrophages assume distinct transcriptional and metabolicprofiles that include high levels of arginase expression and preferentially mediatehelminth damage, both of which are dependent on neutrophil help. In further studies,arginase was shown to mediate helminth killing through localized depletion of arginine.

It is well established that T helper type 2 (TH2) immune responses are necessary not only to provide protection against helminth parasites but also to promote the detrimental inflammation associated with allergies and asthma. Given the importance of type 2 immunity and inflammation, many studies have focused on better understanding the factors that regulate TH2 cell development and activation. As a result, significant progress has been made in understanding the signaling pathways and molecular events necessary to promote TH2 cell polarization. In addition to the adaptive compartment, emerging studies are better defining the innate immune pathways needed to promote TH2 cell responses. Given the recent and substantial growth of this field, the purpose of this review is to highlight recent studies defining the innate immune events that promote immunity to helminth parasites and allergic inflammation. Emerging studies have begun to elucidate the importance of cytokine alarmins such as thymic stromal lymphopoietin (TSLP), IL-25 (IL-17E), and IL-33 in promoting type 2 immunity and inflammation following helminth challenge or exposure to allergens. Specifically, recent reports have begun to define the complex cellular networks these alarmins activate and their contribution to type 2 immunity and inflammation. Our increased understanding of the pathways that regulate type 2 cytokine-mediated immunity and inflammation have revealed novel therapeutic targets to treat both helminth infections and allergic disease states.

Car enzyme inhibition prevents mast cell responses and inflammation following Trichinella spiralis infection or the induction of food allergy–like disease., Type 2 cytokine responses are necessary for the development of protective immunity to helminth parasites but also cause the inflammation associated with allergies and asthma. Recent studies have found that peripheral hematopoietic progenitor cells contribute to type 2 cytokine–mediated inflammation through their enhanced ability to develop into mast cells. In this study, we show that carbonic anhydrase (Car) enzymes are up-regulated in type 2–associated progenitor cells and demonstrate that Car enzyme inhibition is sufficient to prevent mouse mast cell responses and inflammation after Trichinella spiralis infection or the induction of food allergy–like disease. Further, we used CRISPR/Cas9 technology and illustrate that genetically editing Car1 is sufficient to selectively reduce mast cell development. Finally, we demonstrate that Car enzymes can be targeted to prevent human mast cell development. Collectively, these experiments identify a previously unrecognized role for Car enzymes in regulating mast cell lineage commitment and suggest that Car enzyme inhibitors may possess therapeutic potential that can be used to treat mast cell–mediated inflammation.

Innate cells are responsible for the rapid recognition of infection and mediate essential mechanisms of pathogen elimination, and also facilitate adaptive immune responses. We review here the numerous intricate interactions among innate cells that initiate protective immunity. The efficient eradication of pathogens depends on the coordinated actions of multiple cells, including innate cells and epithelial cells. Rather than acting as isolated effector cells, innate cells are in constant communication with other responding cells of the immune system, locally and distally. These interactions are critically important for the efficient control of primary infections as well for the development of ‘trained’ innate cells that facilitate the rapid elimination of homologous or heterologous infections.

Helminth parasites are responsible for some of the most common human infections and cause significant health problems and economic difficulties in the developing areas of the world. The type 2 immune response, characteristic of helminth infections, has been associated with the development of protective immunity and reduced worm burdens in infected humans. Further, animal model systems have demonstrated that type 2 cytokine production and signalling are necessary to promote inflammation and parasite clearance. Despite significant advances in our understanding of the mammalian immune response to helminths, the molecular and cellular mechanisms that promote type 2 immunity remain to be fully defined. Emerging studies suggest that a series of highly coordinated events including the production of epithelial cell-derived alarmins, the activation of innate immune cells (innate lymphoid cells, haematopoietic progenitor cells, mast cells, basophils, eosinophils, neutrophils and macrophages) and the subsequent activation of lymphocytes are required to promote antihelminth immunity. This article will review these recent advances and highlight how these studies may inform the development of new therapeutic strategies to treat helminth infections and their associated morbidities. Key Concepts Helminths trigger a specific type of immune response different from that induced by microbial pathogens. This response to helminths includes many of the same immune cell populations activated by microbial pathogens; however, the activation state and effector functions of the individual immune cell populations are quite different. The immune cell effector functions stimulated by helminths include innate and adaptive components that mediate resistance and elimination of the parasite. Effector functions of the helminth-induced type 2 immune response also include tolerance mechanisms that mitigate tissue damage associated with trafficking of these large multicellular parasites. The type 2 immune response is initiated through release of endogenous danger signals triggered by tissue damage and through release of specific parasite products that can modulate the immune response. Keywords: type 2 immune response; alarmins; helminths; endogenous danger signals; cytokines; innate immunity; adaptive immunity

Breaches in the skin barrier initiate an inflammatory immune response that is critical for successful wound healing. Innate lymphoid cells (ILCs) are a recently identified population of immune cells that reside at epithelial barrier surfaces such as the skin, lung and gut and promote pro-inflammatory or epithelial repair functions following exposure to allergens, pathogens or chemical irritants. However, the potential role of ILCs in regulating cutaneous wound healing remains undefined. Here, we demonstrate that cutaneous injury promotes an IL-33-dependent group 2 ILC (ILC2) response and that abrogation of this response impairs re-epithelialization and efficient wound closure. Additionally, we provide evidence suggesting that an analogous ILC2 response is operational in acute wounds of human skin. Together, these results indicate that IL-33-responsive ILC2s are an important link between the cutaneous epithelium and the immune system, acting to promote the restoration of skin integrity following injury.

We have reported that alternatively activated neutrophils (N2) enhance lung anti-helminth trained macrophage effector function in response to infection with N. brasiliensis(Fei Chen, et al., NI, 2014). However, it is not clear how these neutrophils develop and what lung macrophage subsets actually mediate resistance. We report here that IL-4R signaling is required for the polarization of neutrophils within 2 days after N. brasiliensisinfection and that this characteristic N2 phenotype can develop in Rag−/− but not Rag2cg−/− mice, suggesting a role for innate lymphoid cells in initiating N2 cell differentiation. N2 neutrophils further showed significant proliferative capacity and oxidative phosphorylation at day 2 after N. brasiliensisinfection. Using CD45 congenic transfers and fate mapping Cx3cr1creER-YFP/+R26tdTomato/+ mice, we further show that monocyte-derived alveolar macrophages are the major effector macrophage subset mediating parasite killing through Arginase 1 dependent mechanisms. In vivo depletion of neutrophils with anti-Ly6G Ab blocked the development of this anti-helminth pulmonary macrophage subset and RNAseq analyses show marked differences from tissue resident alveolar macrophages. These studies demonstrate heterogeneity in lung macrophage and neutrophil subsets during helminth infection resulting in distinct activation pathways required for helminth resistance.

Helminth infections represent a significant public health concern resulting in devastating morbidity and economic consequences across the globe. Helminths migrate through mucosal sites causing tissue damage and the induction of type 2 immune responses. Antihelminth protection relies on the mobilization and activation of multiple immune cells, including type 2 innate lymphocytes (ILC2s), basophils, mast cells, macrophages, and hematopoietic stem/progenitor cells. Further, epithelial cells and neurons have been recognized as important regulators of type 2 immunity. Collectively, these pathways stimulate host-protective responses necessary for worm expulsion and the healing of affected tissues. In this review we focus on the innate immune pathways that regulate immunity to helminth parasites and describe how better understanding of these pathways may lead to the development of new therapeutic strategies.

Summary B cells thwart antigenic aggressions by releasing immunoglobulin M (IgM), IgG, IgA, and IgE, which deploy well-understood effector functions. In contrast, the role of secreted IgD remains mysterious. We found that some B cells generated IgD-secreting plasma cells following early exposure to external soluble antigens such as food proteins. Secreted IgD targeted basophils by interacting with the CD44-binding protein galectin-9. When engaged by antigen, basophil-bound IgD increased basophil secretion of interleukin-4 (IL-4), IL-5, and IL-13, which facilitated the generation of T follicular helper type 2 cells expressing IL-4. These germinal center T cells enhanced IgG1 and IgE but not IgG2a and IgG2b responses to the antigen initially recognized by basophil-bound IgD. In addition, IgD ligation by antigen attenuated allergic basophil degranulation induced by IgE co-ligation. Thus, IgD may link B cells with basophils to optimize humoral T helper type 2-mediated immunity against common environmental soluble antigens.

Regulatory T cells (Tregs) are a subset of CD4+ T cells with suppressive function and are critical for limiting inappropriate activation of T cells. Hence, the expansion of Tregs is an attractive strategy for the treatment of autoimmune diseases. Here, we demonstrate that the skin possesses the remarkable capacity to systemically expand Treg numbers by producing thymic stromal lymphopoietin (TSLP) in response to vitamin D receptor stimulation. An ∼2-fold increase in the proportion and absolute number of Tregs was observed in mice treated topically but not systemically with the Vitamin D3 analog MC903. This expansion of Tregs was dependent on TSLP receptor signaling but not on VDR signaling in hematopoietic cells. However, TSLP receptor expression by Tregs was not required for their proliferation. Rather, skin-derived TSLP promoted Treg expansion through dendritic cells. Importantly, treatment of skin with MC903 significantly lowered the incidence of autoimmune diabetes in non-obese diabetic mice and attenuated disease score in experimental autoimmune encephalomyelitis. Together, these data demonstrate that the skin has the remarkable potential to control systemic immune responses and that Vitamin D-mediated stimulation of skin could serve as a novel strategy to therapeutically modulate the systemic immune system for the treatment of autoimmunity.

Immunization with human papillomavirus (HPV) L1 virus-like particles (VLPs) prevents infection with HPV. However, the expense and logistical demands of current VLP vaccines will limit their widespread use in resource-limited settings, where most HPV-induced cervical cancer occurs. Live oral adenovirus vaccines have properties that are well-suited for use in such settings. We have described a live recombinant adenovirus vaccine prototype that produces abundant HPV16 L1 protein from the adenovirus major late transcriptional unit and directs the assembly of HPV16 VLPs in tissue culture. Recombinant-derived VLPs potently elicit neutralizing antibodies in mice. Here, we characterize the immune response to the recombinant after dual oral and intranasal immunization of pigtail macaques, in which the virus replicates as it would in immunized humans. The immunization of macaques induced vigorous humoral responses to adenovirus capsid and nonstructural proteins, although, surprisingly, not against HPV L1. In contrast, immunization elicited strong T-cell responses to HPV VLPs as well as adenovirus virions. T-cell responses arose immediately after the primary immunization and were boosted by a second immunization with recombinant virus. T-cell immunity contributes to protection against a wide variety of pathogens, including many viruses. The induction of a strong cellular response by the recombinant indicates that live adenovirus recombinants have potential as vaccines for those agents. These studies encourage and will inform the continued development of viable recombinant adenovirus vaccines.

Basophils have been implicated in promoting the early development of TH 2 cell responses in some murine models of TH 2 cytokine-associated inflammation. However, the specific role of basophils in allergic asthma remains an active area of research. Recent studies in animal models and human subjects suggest that IgE may regulate the homeostasis of human basophil populations. Here, we examine basophil populations in children with severe asthma before and during therapy with the IgE-directed monoclonal antibody omalizumab. Omalizumab therapy was associated with a significant reduction in circulating basophil numbers, a finding that was concurrent with improved clinical outcomes. The observation that circulating basophils are reduced following omalizumab therapy supports a mechanistic link between IgE levels and circulating basophil populations, and may provide new insights into one mechanism by which omalizumab improves asthma symptoms.

SummaryExtramedullary hematopoiesis (EMH) refers to the differentiation of hematopoietic stem cells (HSCs) into effector cells that occurs in compartments outside of the bone marrow. Previous studies linked pattern-recognition receptor (PRR)-expressing HSCs, EMH, and immune responses to microbial stimuli. However, whether EMH operates in broader immune contexts remains unknown. Here, we demonstrate a previously unrecognized role for thymic stromal lymphopoietin (TSLP) in promoting the population expansion of progenitor cells in the periphery and identify that TSLP-elicited progenitors differentiated into effector cells including macrophages, dendritic cells, and granulocytes and that these cells contributed to type 2 cytokine responses. The frequency of circulating progenitor cells was also increased in allergic patients with a gain-of-function polymorphism in TSLP, suggesting the TSLP-EMH pathway might operate in human disease. These data identify that TSLP-induced EMH contributes to the development of allergic inflammation and indicate that EMH is a conserved mechanism of innate immunity.

Asthma is a heterogeneous disorder that results in recurrent attacks of breathlessness, coughing, and wheezing that affects millions of people worldwide. Although the precise causes of asthma are unclear, studies suggest that a combination of genetic predisposition and environmental exposure to various allergens and pathogens contribute to its development. Currently, the most common treatment to control asthma is a dual combination of β2-adrenergic receptor agonists and corticosteroids. However, studies have shown that some patients do not respond well to these medications, while others experience significant side effects. It is reported that the majority of asthmas are associated with T helper type 2 (TH2) responses. In these patients, allergen challenge initiates the influx of TH2 cells in the airways leading to an increased production of TH2-associated cytokines and the promotion of allergy-induced asthma. Therefore, biologics that target this pathway may provide an alternative method to treat the allergic airway inflammation associated with asthma. As of now, only two biologics (omalizumab and mepolizumab), which target immunoglobulin E and interleukin-5, respectively, are FDA-approved and being prescribed to asthmatics. However, recent studies have reported that targeting other components of the TH2 response also show great promise. In this review, we will briefly describe the immunologic mechanisms underlying allergic asthma. Furthermore, we will discuss the current therapeutic strategies used to treat asthma including their limitations. Finally, we will highlight the benefits of using biologics to treat asthma-associated allergic airway inflammation with an emphasis on the potential of targeting cytokine alarmins, especially thymic stromal lymphopoietin.

Basophils are rare immune cells that were originally identified by the German scientist Paul Ehrlich over a century ago. Similar to mast cells, basophils are known to possess granules containing preformed effector molecules, bind immunoglobulin E (IgE), and expand in number in the context of type 2 cytokine responses. Despite these advances, the specific contributions of basophils to the induction of type 2 cytokine-mediated inflammation and protective immunity remain to be fully defined. Recent advances in flow cytometric techniques and murine model systems have allowed investigators to, for the first time, define the nonredundant functions of basophils in the context of several infectious insults. Here we will review these recent studies and discuss how they have significantly informed our greater understanding of basophil biology. Further, we will highlight how these recent conceptual advances may inform new therapeutic strategies to treat clinically important infections.

CD4+ Th2 cytokine responses promote the development of allergic inflammation and are critical for immunity to parasitic helminth infection. Recent studies highlighted that basophils can promote Th2 cytokine-mediated inflammation and that phenotypic and functional heterogeneity exists between classical IL-3–elicited basophils and thymic stromal lymphopoietin (TSLP)-elicited basophils. However, whether distinct basophil populations develop after helminth infection and their relative contributions to anti-helminth immune responses remain to be defined. After Trichinella spiralis infection of mice, we show that basophil responses are rapidly induced in multiple tissue compartments, including intestinal-draining lymph nodes. Trichinella-induced basophil responses were IL-3–IL-3R independent but critically dependent on TSLP–TSLPR interactions. Selective depletion of basophils after Trichinella infection impaired infection-induced CD4+ Th2 cytokine responses, suggesting that TSLP-dependent basophils augment Th2 cytokine responses after helminth infection. The identification and functional classification of TSLP-dependent basophils in a helminth infection model, coupled with their recently described role in promoting atopic dermatitis, suggests that these cells may be a critical population in promoting Th2 cytokine-associated inflammation in a variety of inflammatory or infectious settings. Collectively, these data suggest that the TSLP–basophil pathway may represent a new target in the design of therapeutic intervention strategies to promote or limit Th2 cytokine-dependent immunity and inflammation.

Commensal bacteria that colonize mammalian barrier surfaces are reported to influence T helper type 2 (T(H)2) cytokine-dependent inflammation and susceptibility to allergic disease, although the mechanisms that underlie these observations are poorly understood. In this report, we find that deliberate alteration of commensal bacterial populations via oral antibiotic treatment resulted in elevated serum IgE concentrations, increased steady-state circulating basophil populations and exaggerated basophil-mediated T(H)2 cell responses and allergic inflammation. Elevated serum IgE levels correlated with increased circulating basophil populations in mice and subjects with hyperimmunoglobulinemia E syndrome. Furthermore, B cell-intrinsic expression of myeloid differentiation factor 88 (MyD88) was required to limit serum IgE concentrations and circulating basophil populations in mice. Commensal-derived signals were found to influence basophil development by limiting proliferation of bone marrow-resident precursor populations. Collectively, these results identify a previously unrecognized pathway through which commensal-derived signals influence basophil hematopoiesis and susceptibility to T(H)2 cytokine-dependent inflammation and allergic disease.

CD4(+) T-helper type 2 (T(H)2) cells, characterized by their expression of interleukin (IL)-4, IL-5, IL-9 and IL-13, are required for immunity to helminth parasites and promote the pathological inflammation associated with asthma and allergic diseases. Polymorphisms in the gene encoding the cytokine thymic stromal lymphopoietin (TSLP) are associated with the development of multiple allergic disorders in humans, indicating that TSLP is a critical regulator of T(H)2 cytokine-associated inflammatory diseases. In support of genetic analyses, exaggerated TSLP production is associated with asthma, atopic dermatitis and food allergies in patients, and studies in murine systems demonstrated that TSLP promotes T(H)2 cytokine-mediated immunity and inflammation. However, the mechanisms through which TSLP induces T(H)2 cytokine responses remain poorly defined. Here we demonstrate that TSLP promotes systemic basophilia, that disruption of TSLP-TSLPR interactions results in defective basophil responses, and that TSLPR-sufficient basophils can restore T(H)2-cell-dependent immunity in vivo. TSLP acted directly on bone-marrow-resident progenitors to promote basophil responses selectively. Critically, TSLP could elicit basophil responses in both IL-3-IL-3R-sufficient and -deficient environments, and genome-wide transcriptional profiling and functional analyses identified heterogeneity between TSLP-elicited versus IL-3-elicited basophils. Furthermore, activated human basophils expressed TSLPR, and basophils isolated from eosinophilic oesophagitis patients were distinct from classical basophils. Collectively, these studies identify previously unrecognized heterogeneity within the basophil cell lineage and indicate that expression of TSLP may influence susceptibility to multiple allergic diseases by regulating basophil haematopoiesis and eliciting a population of functionally distinct basophils that promote T(H)2 cytokine-mediated inflammation.

Recent studies indicate that basophils perform essential functions in multiple models of Th2 cytokine-dependent immunity and inflammation. In addition to their role as late phase effector cells, basophil populations can express MHC class II and costimulatory molecules, migrate into draining lymph nodes, present antigen to naive CD4(+) T cells, and promote Th2 cell differentiation. In this context, basophils have been shown to contribute to the induction and propagation of Th2 cytokine responses following exposure to some helminth parasites or allergens. In this review, we discuss recent studies that provide new insights into basophil development, regulation, and effector function. In addition, we discuss the ability of basophils to act both independently and cooperatively with dendritic cells to support Th2 cytokine-mediated inflammation.

Recent studies have identified several previously unrecognized functions of basophils in multiple models of Th2 cytokine-dependent immunity and inflammation. In addition to their established role as effector cells in inflamed tis- sues, findings now indicate that basophils express MHC class II and co-stimulatory molecules, can migrate into draining lymph nodes, present antigen to naive CD4 + T cells and promote Th2 cell differentiation. In this context, basophils have been shown to be critically important for the induction and propagation of Th2 cytokine responses following exposure to helminth parasites and allergens. This article reviews recent conceptual advances in our understanding of basophil biology in the context of allergy and helminth infection.

Type-2 immunity, the ancient defence mechanism that provides protection against gastrointestinal helminth infections, involves the recruitment of T helper (TH) cells that produce immune mediators or cytokines to coordinate an immune response involving IgE antibody production, the recruitment of eosinophils and goblet cell hyperplasia. Two groups reporting in this issue have characterized innate type 2 effector leukocyte populations that promote TH2 cytokine responses. Saenz et al. describe multipotent progenitor type-2 (MPPtype2) cells that accumulate in response to the cytokine IL-25 (interleukin-25) and give rise to macrophage or granulocyte lineages promoting TH2 differentiation. Neill et al. describe 'nuocytes', induced by IL25 and IL33, which are the predominant early source of IL13 during a helminth infection. In News & Views, Gerard Eberl discusses how these two papers — and a third in Nature Reviews Immunology ( http://go.nature.com/sJ9D77 ) — influence current thinking on the role of innate immunity. Several non-haematopoietic-cell-derived cytokines, including interleukin (IL)25, have been implicated in inducing T helper 2 (TH2) cell-dependent inflammation, but their precise role has been unclear. Here, IL25 is shown to promote the accumulation of multipotent progenitor cells in gut-associated lymphoid tissue. These cells can give rise to macrophage or granulocyte lineages that promote the differentiation of TH2 cells and contribute to protective immunity against helminth infections. CD4+ T helper 2 (TH2) cells secrete interleukin (IL)4, IL5 and IL13, and are required for immunity to gastrointestinal helminth infections1. However, TH2 cells also promote chronic inflammation associated with asthma and allergic disorders2. The non-haematopoietic-cell-derived cytokines thymic stromal lymphopoietin, IL33 and IL25 (also known as IL17E) have been implicated in inducing TH2 cell-dependent inflammation at mucosal sites3,4,5,6, but how these cytokines influence innate immune responses remains poorly defined. Here we show that IL25, a member of the IL17 cytokine family, promotes the accumulation of a lineage-negative (Lin-) multipotent progenitor (MPP) cell population in the gut-associated lymphoid tissue that promotes TH2 cytokine responses. The IL25-elicited cell population, termed MPPtype2 cells, was defined by the expression of Sca-1 (also known as Ly6a) and intermediate expression of c-Kit (c-Kitint), and exhibited multipotent capacity, giving rise to cells of monocyte/macrophage and granulocyte lineages both in vitro and in vivo. Progeny of MPPtype2 cells were competent antigen presenting cells, and adoptive transfer of MPPtype2 cells could promote TH2 cytokine responses and confer protective immunity to helminth infection in normally susceptible Il25-/- mice. The ability of IL25 to induce the emergence of an MPPtype2 cell population identifies a link between the IL17 cytokine family and extramedullary haematopoiesis, and suggests a previously unrecognized innate immune pathway that promotes TH2 cytokine responses at mucosal sites.

Dendritic cells can prime naive CD4(+) T cells; however, here we demonstrate that dendritic cell-mediated priming was insufficient for the development of T helper type 2 cell-dependent immunity. We identify basophils as a dominant cell population that coexpressed major histocompatibility complex class II and interleukin 4 message after helminth infection. Basophilia was promoted by thymic stromal lymphopoietin, and depletion of basophils impaired immunity to helminth infection. Basophils promoted antigen-specific CD4(+) T cell proliferation and interleukin 4 production in vitro, and transfer of basophils augmented the population expansion of helminth-responsive CD4(+) T cells in vivo. Collectively, our studies suggest that major histocompatibility complex class II-dependent interactions between basophils and CD4(+) T cells promote T helper type 2 cytokine responses and immunity to helminth infection

Most of our understanding of the development and phenotype of alternatively activated macrophages (AAMs) has been obtained from studies investigating the response of bone marrow- and peritoneal-derived cells to IL-4 or IL-13 stimulation. Comparatively little is known about the development of AAMs in the lungs, and how the complex signals associated with pulmonary inflammation influence the AAM phenotype. Here, we use Nippostrongylus brasiliensis to initiate AAM development and define the dynamics of surface molecules, gene expression, and cell function of macrophages isolated from lung tissue at different times postinfection (PI). Initially, lung macrophages take on a foamy phenotype, up-regulate MHC and costimulatory molecules, express reduced levels of TNF and IL-12, and undergo proliferation. Cells isolated between days 8 and 15 PI adopt a dense, granular phenotype and exhibit reduced levels of costimulatory molecules and elevated levels of programmed death ligand-1 (PDL-1) and PDL-2 and an increase in IL-10 expression. Functionally, AAMs isolated on days 13–15 PI demonstrate an enhanced capacity to take up and sequester antigen. However, these same cells did not mediate antigen-specific T cell proliferation and dampened the proliferation of CD3/CD28-activated CD4+ T cells. These data indicate that the alternative activation of macrophages in the lungs, although initiated by IL-4/IL-13, is a dynamic process that is likely to be influenced by other immune and nonimmune factors in the pulmonary environment.

A number of important helminth parasites of humans have incorporated short-term residence in the lungs as an obligate phase of their life cycles. The significance of this transient pulmonary exposure to the infection and immunity is not clear. Employing a rodent model of infection with hookworm (Nippostrongylus brasiliensis), we characterized the long-term changes in the immunological status of the lungs induced by parasite infection. At 36 days after infection, alterations included a sustained increase in the transcription of both Th2 and Th1 cytokines as well as a significant increase in the number and frequency of alveolar macrophages displaying an alternatively activated phenotype. WhileN. brasiliensisdid not induce alternate activation of lung macrophages in STAT6−/−animals, the parasite did induce a robust Th17 response in the pulmonary environment, suggesting that STAT6 signaling plays a role in modulating Th17 immunity and pathology in the lungs. In the context of the cellular and molecular changes induced byN. brasiliensisinfection, there was a significant reduction in overall airway responsiveness and lung inflammation in response to allergen. In addition, theN. brasiliensis-altered pulmonary environment showed dramatic alterations in the nature and number of genes that were up- and downregulated in the lung in response to allergen challenge. The results demonstrate that even a transient exposure to a helminth parasite can effect significant and protracted changes in the immunological environment of the lung and that these complex molecular and cellular changes are likely to play a role in modulating a subsequent allergen-induced inflammatory response.

Estrogens increase aspects of innate immunity and contribute to sex differences in the prevalence of autoimmune diseases and in response to infection. The goal of the present study was to assess whether exposure to 17β-estradiol (E2) affects the development and function of bone marrow-derived dendritic cells and to determine whether similar changes are observed in CD11c+ splenocytes exposed to E2 in vivo. E2 facilitated the differentiation of BM precursor cells into functional CD11c+CD11b+MHC class II+ dendritic cells (DCs) with increased expression of the costimulatory molecules CD40 and CD86. Exposure of bone marrow-derived dendritic cells to E2 also enhanced production of IL-12 in response to the TLR ligands, CpG and LPS. In contrast, CD11c+ cells isolated from the spleens of female C57BL/6 mice that were intact, ovariectomized, or ovariectomized with E2 replacement exhibited no differences in the number or activity of CD11c+CD11b+MHC class II+ DCs. The presence of E2 in vivo, however, increased the number of CD11c+CD49b+NK1.1low cells and reduced numbers of CD11c+CD49b+NK1.1high cells, a surface phenotype for IFN-producing killer DCs (IKDCs). Ultrastructural analysis demonstrated that CD11c+NK1.1+ populations were comprised of cells that had the appearance of both DCs and IKDCs. CD11c+ splenocytes isolated from animals with supplemental E2 produced more IFN-γ in response to IL-12 and IL-18. These data illustrate that E2 has differential effects on the development and function of DCs and IKDCs and provide evidence that E2 may strengthen innate immunity by enhancing IFN-γ production by CD11c+ cells.

Background An ecological correlation between invasive cervical cancer incidence and burden of soil-transmitted helminths (STH) is hypothesized to explain the excess in detectable human papillomavirus (HPV) infection in Latin America, via a global T-helper type 2 (Th2)-biased mucosal immune response secondary to STH infection. Methods The association between current STH infection and HPV prevalence was compared in regions of Peru where STH is or is not endemic. Adjusted prevalence ratios (PRs) with robust variance were estimated as an effect measure of STH infection on HPV prevalence in each study site. Soluble immune marker profiles in STH-infected and STH-uninfected women were compared using Spearman rank correlation with the Sidak correction. Results Among women in the helminth-endemic region of the Peruvian Amazon, those with STH infection women had a 60% higher prevalence of HPV, compared with those without STH infection (PR, 1.6; 95% confidence interval, 1.0-2.7). Non-STH parasitic/protozoal infections in the non-STH-endemic population of Peru were not associated with HPV prevalence. In Iquitos, A Th2 immune profile was observed in cervical fluid from helminth-infected women but not helminth-uninfected women. Conclusions A proportion of the increased HPV prevalence at older ages observed in Latin America may be due to a population-level difference in the efficiency of immunological control of HPV across the lifespan due to endemic STH infection.

Type 2 cytokine responses are necessary for the development of protective immunity to helminth parasites but also cause the inflammation associated with allergies and asthma. Recent studies have found that peripheral hematopoietic progenitor cells contribute to type 2 cytokine-mediated inflammation through their enhanced ability to develop into mast cells. Here we show that carbonic anhydrase (Car) enzymes are upregulated in type 2-associated progenitor cells and demonstrate that Car enzyme inhibition is sufficient to prevent murine mast cell responses and inflammation following Trichinella spiralis infection or the induction of food allergy-like disease. Further, we employed CRISPR/Cas9 technology and illustrate that genetically editing Car1 is sufficient to selectively reduce mast cell development. Finally, we demonstrate that Car enzymes can be targeted to prevent human mast cell development. Collectively these studies identify a previously unrecognized role for Car enzymes in regulating mast cell lineage commitment and suggest that Car enzyme inhibitors may possess therapeutic potential that can be employed to treat mast cell-mediated inflammation.

Hematopoiesis refers to the development of blood cells in the body through the differentiation of pluripotent stem cells. Although hematopoiesis is a multifocal process during embryonic development, under homeostatic conditions it occurs exclusively within the bone marrow. There, a limited number of hematopoietic stem cells differentiate into a rapidly proliferating population of lineage-restricted progenitors that serve to replenish circulating blood cells. However, emerging reports now suggest that under inflammatory conditions, alterations in hematopoiesis that occur outside of the bone marrow appear to constitute a conserved mechanism of innate immunity. Moreover, recent reports have identified previously unappreciated pathways that regulate the egress of hematopoietic progenitor cells from the bone marrow, alter their activation status, and skew their developmental potential. These studies suggest that progenitor cells contribute to inflammatory response by undergoing in situ hematopoiesis (ISH). In this review, we highlight the differences between homeostatic hematopoiesis, which occurs in the bone marrow, and ISH, which occurs at mucosal surfaces. Further, we highlight factors produced at local sites of inflammation that regulate hematopoietic progenitor cell responses and the development of TH2 cytokine-mediated inflammation. Finally, we discuss the therapeutic potential of targeting ISH in preventing the development of inflammation at mucosal sites.

Type 2 inflammation underlies allergic diseases such as atopic dermatitis, which is characterized by the accumulation of basophils and group 2 innate lymphoid cells (ILC2s) in inflamed skin lesions. Although murine studies have demonstrated that cutaneous basophil and ILC2 responses are dependent on thymic stromal lymphopoietin, whether these cell populations interact to regulate the development of cutaneous type 2 inflammation is poorly defined. In this study, we identify that basophils and ILC2s significantly accumulate in inflamed human and murine skin and form clusters not observed in control skin. We demonstrate that murine basophil responses precede ILC2 responses and that basophils are the dominant IL-4–enhanced GFP-expressing cell type in inflamed skin. Furthermore, basophils and IL-4 were necessary for the optimal accumulation of ILC2s and induction of atopic dermatitis–like disease. We show that ILC2s express IL-4Rα and proliferate in an IL-4–dependent manner. Additionally, basophil-derived IL-4 was required for cutaneous ILC2 responses in vivo and directly regulated ILC2 proliferation ex vivo. Collectively, these data reveal a previously unrecognized role for basophil-derived IL-4 in promoting ILC2 responses during cutaneous inflammation.

Parasites make it hard to fight viruses Microbial co-infections challenge the immune system—different pathogens often require different flavors of immune responses for their elimination or containment (see the Perspective by Maizels and Gause). Two teams studied what happens when parasitic worms and viruses infect mice at the same time. Reese et al. found that parasite co-infection woke up a dormant virus. Osborne et al. found that mice already infected with parasitic worms were worse at fighting off viruses. In both cases, worms skewed the immune response so that the immune cells and the molecules they secreted created an environment favorable for the worm at the expense of antiviral immunity. Science , this issue p. 573 and p. 578 ; see also p. 517

Interleukin-25 preferentially elicits multipotent progenitor type 2 cells, which are distinct from other populations of type 2 innate lymphoid cells., The predominantly epithelial cell–derived cytokines IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) can promote CD4+ Th2 cell–dependent immunity, inflammation, and tissue repair at barrier surfaces through the induction of multiple innate immune cell populations. IL-25 and IL-33 were previously shown to elicit four innate cell populations, named natural helper cells, nuocytes, innate type 2 helper cells, and multipotent progenitor type 2 (MPPtype2) cells, now collectively termed group 2 innate lymphoid cells (ILC2). In contrast to other types of ILC2, MPPtype2 cells exhibit multipotent potential and do not express T1/ST2 or IL-7Rα, suggesting that MPPtype2 cells may be a distinct population. Here, we show that IL-33 elicits robust ILC2 responses, whereas IL-25 predominantly promotes MPPtype2 cell responses at multiple tissue sites with limited effects on ILC2 responses. MPPtype2 cells were distinguished from ILC2 by their differential developmental requirements for specific transcription factors, distinct genome-wide transcriptional profile, and functional potential. Furthermore, IL-25–induced MPPtype2 cells promoted Th2 cytokine–associated inflammation after depletion of ILC2. These findings indicate that IL-25 simultaneously elicits phenotypically and functionally distinct innate lymphoid– and nonlymphoid-associated cell populations and implicate IL-25–elicited MPPtype2 cells and extramedullary hematopoiesis in the promotion of Th2 cytokine responses at mucosal surfaces.

Eosinophilic esophagitis (EoE) is a food allergy-associated inflammatory disease characterized by esophageal eosinophilia. Current management strategies for EoE are nonspecific, and thus there is a need to identify specific immunological pathways that could be targeted to treat this disease. EoE is associated with polymorphisms in the gene that encodes thymic stromal lymphopoietin (TSLP), a cytokine that promotes allergic inflammation, but how TSLP might contribute to EoE disease pathogenesis has been unclear. Here, we describe a new mouse model of EoE-like disease that developed independently of IgE, but was dependent on TSLP and basophils, as targeting TSLP or basophils during the sensitization phase limited disease. Notably, therapeutic TSLP neutralization or basophil depletion also ameliorated established EoE-like disease. In human subjects with EoE, we observed elevated TSLP expression and exaggerated basophil responses in esophageal biopsies, and a gain-of-function TSLP polymorphism was associated with increased basophil responses in patients with EoE. Together, these data suggest that the TSLP-basophil axis contributes to the pathogenesis of EoE and could be therapeutically targeted to treat this disease.

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 T H 2 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 T H 2 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.

Innate lymphoid cells (ILCs) are a recently identified family of heterogeneous immune cells that can be divided into three groups based on their differential developmental requirements and expression of effector cytokines. Among these, group 2 ILCs produce the type 2 cytokines IL-5 and IL-13 and promote type 2 inflammation in the lung and intestine. However, whether group 2 ILCs reside in the skin and contribute to skin inflammation has not been characterized. Here, we identify for the first time a population of skin-resident group 2 ILCs present in healthy human skin that are enriched in lesional human skin from atopic dermatitis (AD) patients. Group 2 ILCs were also found in normal murine skin and were critical for the development of inflammation in a murine model of AD-like disease. Remarkably, in contrast to group 2 ILC responses in the intestine and lung, which are critically regulated by IL-33 and IL-25, ILC responses in the skin and skin-draining lymph nodes were independent of these canonical cytokines but were critically dependent on thymic stromal lymphopoietin (TSLP). Collectively, these results demonstrate an essential role for IL-33– and IL-25–independent group 2 ILCs in promoting skin inflammation.

Type 2 cytokine responses are necessary for the development of protective immunity to helminth parasites but also cause the detrimental inflammation associated with allergies and asthma. Recent studies have found that peripheral hematopoietic progenitor cell populations contribute to type 2 cytokine-mediated inflammation through their enhanced ability to develop into mast cells. Here we identify that carbonic anhydrase (Car) enzymes are upregulated in type 2-asscoaited progenitor cells and demonstrate that Car enzyme inhibition was sufficient to prevent murine mast cell development, type 2 cytokine-mediated inflammation and protective immunity to Trichinella spiralis. Moreover, we show that Car enzyme inhibition was also sufficient to prevent intestinal mast cell responses in a murine model of food allergy-like disease. Finally, we performed translational studies and demonstrated that Car enzymes can be targeted with an FDA-approved inhibitor to prevent human mast cell development. Collectively these studies identify a previously unrecognized role for Car enzymes in regulating mast cell lineage commitment and suggest that FDA-approved Car enzyme inhibitors may possess additional off-label therapeutic potential that can be employed to treat mast cell-mediated inflammation.

Basophils are the most rare granulocyte population, accounting for less than 1% of circulating leukocytes in mice and human. Recent studies have shown that basophils are associated with multiple immunological processes, such as allergic diseases, autoimmunity, and protective immunity against parasites. It has been show that the rapid secretion of Th2 cytokines by basophils in response to various stimuli plays key roles in immunity against parasitic infections. Basophils also release histamine and, therefore, are key contributors to allergy. In addition, basophil responses are associated with multiple human diseases such as asthma, atopic dermatitis and cancer. Given their important roles in inflammatory signaling and human diseases, remarkably little is known about the molecular regulation of basophil effector functions. Therefore, we have been exploring transcription factors that may play a direct role in controlling basophil development and effector functions. In this study, we have developed multiple in vitro and in vivo systems to study the influence of the loss of a potentially key transcription factor on the basophil response to allergen-induced Th2 immunity. We are in the process of performing gene expression arrays to understand the molecular mechanisms underlying the transcriptional regulation. Collectively, our studies provide new insight into the transcriptional network controlling basophil effector functions in Th2 immune response and lead to potential therapies that modulate basophil activities during the treatment of allergic diseases.

Neutropenia is a significant risk factor for life threatening invasive fungal infections (IFI). Neutrophils are well known as important innate cells that promote the direct eradication of fungal pathogens but whether they mediate antifungal defense beyond their role as effectors is unclear. Here we demonstrate that a pulmonary infection with the clinically relevant fungal pathogen Aspergillus fumigatus induces the diversification of specialized antifungal neutrophils that are required for antifungal CCR2+ monocyte-derived dendritic cell (mo-DC) function. Selective depletion of neutrophils resulted in global transcriptional alterations of the antifungal CCR2+ monocyte response, limited mo-DC differentiation, and diminished conidiacidal activity. Impaired mo-DC antifungal activity in neutropenic mice was accompanied by significant upregulation of carbonic anhydrase 4 (Car4) expression in CCR2+ monocyte precursors. Pharmacological inhibition of Car4 with the FDA-approved drug methazolamide (MZ) rescued the antifungal response of mo-DC and protected neutropenic mice from invasive apergillosis. Thus, beyond their role as effectors, antifungal neutrophils facilitate antifungal mo-DC functions by regulating Car4 activity. Moreover, our data provide proof-of-principle evidence for the importance of carbonic anhydrases in shaping innate cell differentiation as well as for the off-label therapeutic benefit of carbonic anhydrase inhibitors to boost antifungal immunity in susceptible patient populations.