Eosinophils exhibit a unique transcriptional signature and increased sensitivity to IL-3-induced activation in response to colorectal cancer cells.

Eosinophils have been mainly studied in allergic diseases and parasitic infections. Nonetheless, eosinophils accumulate in a variety of solid tumors, including colorectal cancer, where their presence is associated with improved prognosis. Eosinophils can promote anti-tumor immunity through various mechanisms, including direct cytotoxicity towards tumor cells and promoting T cell activation. However, the mechanisms by which tumor cells regulate eosinophil activities are largely unknown. Herein, we characterized the potential interactions between eosinophils and colorectal cancer cells using an unbiased transcriptomic and proteomic analyses approach. Human eosinophils were stimulated with colorectal cancer cell-conditioned media, containing tumor cell-secreted factors from multiple cancer cell lines. RNA sequencing analysis identified a "core" signature consisting of 101 genes that characterize a baseline transcriptional program for the response of human eosinophils to colorectal cancer cells. Among these, the increased expression of IL-3Rα and its ßc chain was identified and validated at the protein level. Secreted factors from tumor cells potentiated IL-3-induced expression of the adhesion molecule CD11a in eosinophils. Combining proteomics analysis of tumor cell-secreted factors with RNA sequencing revealed potential ligand-receptor pairs between tumor cells and eosinophils and the potential involvement of the adhesion molecule CD18 and F2RL3/PAR4. Subsequent functional analyses demonstrated that F2RL3/PAR4 suppresses eosinophil migration in response tumor cell-secreted factors. These findings add to the growing body of evidence that eosinophils are conditioned by their local microenvironment. Identifying mechanisms by which eosinophils interact with tumor cells could lead to the development of new immunotherapies for colorectal cancer and other solid tumors.

A Mouse Model for Eosinophilic Esophagitis (EoE).

Eosinophilic esophagitis (EoE) is an emerging chronic T helper type 2 (Th2)-associated, allergic, and immune-mediated disease, characterized histologically by eosinophil-predominant mucosal inflammation and clinically by esophageal dysfunction. Over the past years, the prevalence of EoE has dramatically increased globally. Until recently, most studies of EoE focused on using human biopsies, which are also used for diagnostic purposes, or esophageal epithelial cell lines, which led to major advances in the understanding of EoE. Despite this, a robust mouse model that mimics human disease is still crucial for both understanding disease pathogenesis and as a preclinical model for testing future therapeutics. Herein, we describe a highly reproducible and robust model of EoE that can be performed using wild-type mice by ear sensitization with oxazolone (OXA) followed by intraesophageal challenges. Experimental EoE elicited by OXA mimics the main histopathological features of human EoE, including intraepithelial eosinophilia, epithelial and lamina propria thickening, basal cell hyperplasia, and fibrosis. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Induction of EoE in mice using oxazolone Support Protocol 1: Preparing the mouse esophagus for histological analysis Support Protocol 2: Assessment of epithelial and lamina propria thickness using H&E staining Support Protocol 3: Assessment of eosinophilic infiltration using anti-MBP and basal cell proliferation using anti-Ki-67 staining Support Protocol 4: Flow cytometry of mouse esophageal samples Support Protocol 5: ELISA on protein lysates of esophageal samples.

CD300b regulates intestinal inflammation and promotes repair in colitis.

Chronic inflammation is a hallmark charataristic of various inflammatory diseases including inflammatory bowel disease. Subsequently, current therapeutic approaches target immune-mediated pathways as means for therapeutic intervention and promotion of mucosal healing and repair. Emerging data demonstrate important roles for CD300 receptor family members in settings of innate immunity as well as in allergic and autoimmune diseases. One of the main pathways mediating the activities of CD300 family members is via promotion of resolution through interactions with ligands expressed by viruses, bacteria, or dead cells (e.g., phospholipids such as PtdSer and/or ceramide). We have recently shown that the expression of CD300a, CD300b and CD300f were elevated in patients with IBD and that CD300f (but not CD300a) regulates colonic inflammation in response to dextran sodium sulphate (DSS)-induced colitis. Whether CD300b has a role in colitis or mucosal healing is largely unknown. Herein, we demonstrate a central and distinct role for CD300b in colonic inflammation and subsequent repair. We show that Cd300b-/- mice display defects in mucosal healing upon cessation of DSS treatment. Cd300b-/- mice display increased weight loss and disease activity index, which is accompanied by increased colonic histopathology, increased infiltration of inflammatory cells and expression of multiple pro-inflammatory upon cessation of DSS cytokines. Furthermore, we demonstrate that soluble CD300b (sCD300b) is increased in the colons of DSS-treated mice and establish that CD300b can bind mouse and human epithelial cells. Finally, we show that CD300b decreases epithelial EpCAM expression, promotes epithelial cell motility and wound healing. These data highlight a key role for CD300b in colonic inflammation and repair processes and suggest that CD300b may be a future therapeutic target in inflammatory GI diseases.

Adaptive immune response to BNT162b2 mRNA vaccine in immunocompromised adolescent patients.

Protective immunity against COVID-19 is orchestrated by an intricate network of innate and adaptive anti-viral immune responses. Several vaccines have been rapidly developed to combat the destructive effects of COVID-19, which initiate an immunological cascade that results in the generation of neutralizing antibodies and effector T cells towards the SARS-CoV-2 spike protein. Developing optimal vaccine-induced anti-SARS- CoV-2 protective immunity depends on a fully competent immune response. Some evidence was gathered on the effects of vaccination outcomes in immunocompromised adult individuals. Nonetheless, protective immunity elicited by the Pfizer Biontech BNT162b2 vaccine in immunocompromised adolescents received less attention and was mainly focused on the antibody response and their neutralization potential. The overall immune response, including T-cell activities, was largely understudied. In this study, we characterized the immune response of vaccinated immunocompromised adolescents. We found that immunocompromised adolescents, which may fail to elicit a humoral response and develop antibodies, may still develop cellular T-cell immunity towards SARS-CoV-2 infections. Furthermore, most immunocompromised adolescents due to genetic disorders or drugs (Kidney and liver transplantation) still develop either humoral, cellular or both arms of immunity towards SARS-CoV-2 infections. We also demonstrate that most patients could mount a cellular or humoral response even after six months post 2nd vaccination. The findings that adolescents immunocompromised patients respond to some extent to vaccination are promising. Finally, they question the necessity for additional vaccination boosting regimens for this population who are not at high risk for severe disease, without further testing of their post-vaccination immune status.

Epithelial cell-expressed type II IL-4 receptor mediates eosinophilic esophagitis.

BACKGROUND: Eosinophilic esophagitis (EoE) is a chronic, food-driven allergic disease, characterized by eosinophil-rich inflammation in the esophagus. The histopathological and clinical features of EoE have been attributed to overproduction of the type 2 cytokines IL-4 and IL-13, which mediate profound alterations in the esophageal epithelium and neutralizing of their shared receptor component (IL-4Rα) with a human antibody drug (dupilumab) demonstrates clinical efficacy. Yet, the relative contribution of IL-4 and IL-13 and whether the type II IL-4 receptor (comprised of the IL-4Rα chain in association with IL-13Rα1) mediates this effect has not been determined. METHODS: Experimental EoE was induced in WT, Il13ra1-/- , and Krt14Cre /Il13ra1fl/fl mice by skin-sensitized using 4-ethoxymethylene-2-phenyl-2-oxazolin (OXA) followed by intraesophageal challenges. Esophageal histopathology was determined histologically. RNA was extracted and sequenced for transcriptome analysis and compared with human EoE RNAseq data. RESULTS: Induction of experimental EoE in mice lacking Il13ra1 and in vivo IL-13 antibody-based neutralization experiments blocked antigen-induced esophageal epithelial and lamina propria thickening, basal cell proliferation, eosinophilia, and tissue remodeling. In vivo targeted deletion of Il13ra1 in esophageal epithelial cells rendered mice protected from experimental EoE. Single-cell RNA sequencing analysis of human EoE biopsies revealed predominant expression of IL-13Rα1 in epithelial cells and that EoE signature genes correlated with IL-13 expression compared with IL-4. CONCLUSIONS: We demonstrate a definitive role for IL-13 signaling via IL-13Rα1 in EoE. These data provide mechanistic insights into the mode of action of current therapies in EoE and highlight the type II IL-4R as a future therapeutic target.

Differential regulation of Type 1 and Type 2 mouse eosinophil activation by apoptotic cells.

Eosinophils are multifunctional, evolutionary conserved leukocytes that are involved in a plethora of responses ranging from regulation of tissue homeostasis, host defense and cancer. Although eosinophils have been studied mostly in the context of Type 2 inflammatory responses, it is now evident that they participate in Type 1 inflammatory responses and can respond to Type 1 cytokines such as IFN-γ. Notably, both Type 1- and Type 2 inflammatory environments are characterized by tissue damage and cell death. Collectively, this raises the possibility that eosinophils can interact with apoptotic cells, which can alter eosinophil activation in the inflammatory milieu. Herein, we demonstrate that eosinophils can bind and engulf apoptotic cells. We further show that exposure of eosinophils to apoptotic cells induces marked transcriptional changes in eosinophils, which polarize eosinophils towards an anti-inflammatory phenotype that is associated with wound healing and cell migration. Using an unbiased RNA sequencing approach, we demonstrate that apoptotic cells suppress the inflammatory responses of eosinophils that were activated with IFN-γ + E. coli (e.g., Type 1 eosinophils) and augment IL-4-induced eosinophil activation (e.g., Type 2 eosinophils). These data contribute to the growing understanding regarding the heterogeneity of eosinophil activation patterns and highlight apoptotic cells as potential regulators of eosinophil polarization.

Metastasis-Entrained Eosinophils Enhance Lymphocyte-Mediated Antitumor Immunity.

The recognition of the immune system as a key component of the tumor microenvironment (TME) led to promising therapeutics. Because such therapies benefit only subsets of patients, understanding the activities of immune cells in the TME is required. Eosinophils are an integral part of the TME especially in mucosal tumors. Nonetheless, their role in the TME and the environmental cues that direct their activities are largely unknown. We report that breast cancer lung metastases are characterized by resident and recruited eosinophils. Eosinophil recruitment to the metastatic sites in the lung was regulated by G protein-coupled receptor signaling but independent of CCR3. Functionally, eosinophils promoted lymphocyte-mediated antitumor immunity. Transcriptome and proteomic analyses identified the TME rather than intrinsic differences between eosinophil subsets as a key instructing factor directing antitumorigenic eosinophil activities. Specifically, TNFα/IFNγ-activated eosinophils facilitated CD4+ and CD8+ T-cell infiltration and promoted antitumor immunity. Collectively, we identify a mechanism by which the TME trains eosinophils to adopt antitumorigenic properties, which may lead to the development of eosinophil-targeted therapeutics. SIGNIFICANCE: These findings demonstrate antitumor activities of eosinophils in the metastatic tumor microenvironment, suggesting that harnessing eosinophil activity may be a viable clinical strategy in patients with cancer.

Analysis of Mouse Eosinophil Migration and Killing of Tumor Cells.

Eosinophils are bone marrow-derived cells that differentiate in the bone marrow and migrate into the peripheral blood primarily under the regulation of interleukin (IL)-5. Despite the fact that eosinophils have been mostly studied in the context of allergic inflammatory diseases, eosinophils accumulate in multiple tumors. In fact, recent data highlight key anti-tumorigenic activities for eosinophils. Thus, developing simple assays that will dissect the interactions between eosinophils and tumor cells is important since these assays will provide tools to study eosinophils in the tumor microenvironment. In this chapter, we provide detailed methods for isolating eosinophils from Il5 transgenic mice. Furthermore, we provide methodology to assess eosinophil chemotaxis in response to tumor-secreted factors. Finally, we describe a co-culture system of eosinophils and tumor cells aimed to determine the cytotoxic capabilities of eosinophils.

A new dawn for eosinophils in the tumour microenvironment.

Eosinophils are evolutionarily conserved, pleotropic cells that display key effector functions in allergic diseases, such as asthma. Nonetheless, eosinophils infiltrate multiple tumours and are equipped to regulate tumour progression either directly by interacting with tumour cells or indirectly by shaping the tumour microenvironment (TME). Eosinophils can readily respond to diverse stimuli and are capable of synthesizing and secreting a large range of molecules, including unique granule proteins that can potentially kill tumour cells. Alternatively, they can secrete pro-angiogenic and matrix-remodelling soluble mediators that could promote tumour growth. Herein, we aim to comprehensively outline basic eosinophil biology that is directly related to their activity in the TME. We discuss the mechanisms of eosinophil homing to the TME and examine their diverse pro-tumorigenic and antitumorigenic functions. Finally, we present emerging data regarding eosinophils as predictive biomarkers and effector cells in immunotherapy, especially in response to immune checkpoint blockade therapy, and highlight outstanding questions for future basic and clinical cancer research.

A key role for IL-13 signaling via the type 2 IL-4 receptor in experimental atopic dermatitis.

IL-13 and IL-4 are potent mediators of type 2-associated inflammation such as those found in atopic dermatitis (AD). IL-4 shares overlapping biological functions with IL-13, a finding that is mainly explained by their ability to signal via the type 2 IL-4 receptor (R), which is composed of IL-4Rα in association with IL-13Rα1. Nonetheless, the role of the type 2 IL-4R in AD remains to be clearly defined. Induction of two distinct models of experimental AD in Il13ra1 -/- mice, which lack the type 2 IL-4R, revealed that dermatitis, including ear and epidermal thickening, was dependent on type 2 IL-4R signaling. Expression of TNF-α was dependent on the type 2 IL-4R, whereas induction of IL-4, IgE, CCL24, and skin eosinophilia was dependent on the type 1 IL-4R. Neutralization of IL-4, IL-13, and TNF-α as well as studies in bone marrow-chimeric mice revealed that dermatitis, TNF-α, CXCL1, and CCL11 expression were exclusively mediated by IL-13 signaling via the type 2 IL-4R expressed by nonhematopoietic cells. Conversely, induction of IL-4, CCL24, and eosinophilia was dependent on IL-4 signaling via the type 1 IL-4R expressed by hematopoietic cells. Last, we pharmacologically targeted IL-13Rα1 and established a proof of concept for therapeutic targeting of this pathway in AD. Our data provide mechanistic insight into the differential roles of IL-4, IL-13, and their receptor components in allergic skin and highlight type 2 IL-4R as a potential therapeutic target in AD and other allergic diseases such as asthma and eosinophilic esophagitis.

Primary tumors from mucosal barrier organs drive unique eosinophil infiltration patterns and clinical associations.

Eosinophils are bone marrow-derived granulocytes that display key effector functions in allergic diseases. Nonetheless, recent data highlight important roles for eosinophils in the tumor microenvironment (TME). Eosinophils have been attributed with pleiotropic and perhaps conflicting functions, which may be attributed at least in part to variations in eosinophil quantitation in the TME. Thus, a reliable, quantitative, and robust method for the assessment of eosinophilic infiltration in the TME is required. This type of methodology could standardize the identification of these cells and promote the subsequent generation of hypothesis-driven mechanistic studies. To this end, we conducted a comprehensive analysis of multiple primary tumors from distinct anatomical sites using a standardized method. Bioinformatics analysis of 10,469 genomically profiled primary tumors revealed that eosinophil abundance within different tumors can be categorized into three groups representing tumors with high, intermediate, and low eosinophil levels. Consequently, eosinophil abundance, as well as spatial distribution, was determined in tissue tumor arrays of six tumors representing all three classifications (colon and esophagus - high; lung - intermediate; cervix, ovary, and breast - low). With the exception of breast cancer, eosinophils were mainly localized in the tumor stroma. Importantly, the tumor anatomical site was identified as the primary predictive factor of eosinophil stromal density highlighting a distinction between mucosal-barrier organs versus non-mucosal barrier organs. These findings enhance our understanding of eosinophil diversity in the TME and provide a compelling rationale for future experiments assessing the activity of these cells.

Activated Eosinophils Exert Antitumorigenic Activities in Colorectal Cancer.

Immunotherapies targeting T lymphocytes are revolutionizing cancer therapy but only benefit a subset of patients, especially in colorectal cancer. Thus, additional insight into the tumor microenvironment (TME) is required. Eosinophils are bone marrow-derived cells that have been largely studied in the context of allergic diseases and parasite infections. Although tumor-associated eosinophilia has been described in various solid tumors including colorectal cancer, knowledge is still missing regarding eosinophil activities and even the basic question of whether the TME promotes eosinophil recruitment without additional manipulation (e.g., immunotherapy) is unclear. Herein, we report that eosinophils are recruited into developing tumors during induction of inflammation-induced colorectal cancer and in mice with the Apcmin /+ genotype, which develop spontaneous intestinal adenomas. Using adoptive transfer and cytokine neutralization experiments, we demonstrate that the TME supported prolonged eosinophil survival independent of IL5, an eosinophil survival cytokine. Tumor-infiltrating eosinophils consisted of degranulating eosinophils and were essential for tumor rejection independently of CD8+ T cells. Transcriptome and proteomic analysis revealed an IFNγ-linked signature for intratumoral eosinophils that was different from that of macrophages. Our data establish antitumorigenic roles for eosinophils in colorectal cancer. These findings may facilitate the development of pharmacologic treatments that could unleash antitumor responses by eosinophils, especially in colorectal cancer patients displaying eosinophilia.

Eosinophils support adipocyte maturation and promote glucose tolerance in obesity.

Accumulating data have indicated a fundamental role of eosinophils in regulating adipose tissue homeostasis. Here, we performed whole-genome RNA sequencing of the small intestinal tract, which suggested the presence of impaired lipid metabolism in eosinophil-deficient ΔdblGATA mice. ΔdblGATA mice fed a high-fat diet (HFD) showed reduced body fat mass, impaired enlargement of adipocytes, decreased expression of adipogenic genes, and developed glucose intolerance. HFD induced accumulation of eosinophils in the perigonadal white adipose tissue. Concordantly, adipocyte-differentiated 3T3-L1 cells promoted the migration of eosinophils through the expression of CCL11 (eotaxin-1) and likely promoted their survival through the expression of interleukin (IL)-3, IL-5, and granulocyte-macrophage colony-stimulating factor. HFD-fed ΔdblGATA mice showed increased infiltration of macrophages, CD4+ T-cells, and B-cells, increased expression of interferon-γ, and decreased expression of IL-4 and IL-13 in white adipose tissue. Interferon-γ treatment significantly decreased lipid deposition in adipocyte-differentiated 3T3-L1 cells, while IL-4 treatment promoted lipid accumulation. Notably, HFD-fed ΔdblGATA mice showed increased lipid storage in the liver as compared with wild-type mice. We propose that obesity promotes the infiltration of eosinophils into adipose tissue that subsequently contribute to the metabolic homeostasis by promoting adipocyte maturation.

Author Correction: Transcriptome profiling of mouse colonic eosinophils reveals a key role for eosinophils in the induction of s100a8 and s100a9 in mucosal healing.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Transcriptome profiling of mouse colonic eosinophils reveals a key role for eosinophils in the induction of s100a8 and s100a9 in mucosal healing.

Eosinophils are bone marrow-derived cells that have been largely implicated in Th2-associated diseases. Recent data highlights a key role for eosinophils in mucosal innate immune responses especially in the gastrointestinal (GI) tract, which is one of the largest eosinophil reservoirs in the body. Although eosinophils express and synthesize a plethora of proteins that can mediate their effector activities, the transcriptome signature of eosinophils in mucosal inflammation and subsequent repair has been considerably overlooked. We demonstrate that eosinophils are recruited to the colon in acute inflammatory stages where they promote intestinal inflammation and remain in substantial numbers throughout the mucosal healing process. Microarray analysis of primary colonic eosinophils that were sorted at distinct stages of mucosal inflammation and repair revealed dynamic regulation of colonic eosinophil mRNA expression. The clinically relevant genes s100a8 and s100a9 were strikingly increased in colonic eosinophils (up to 550-fold and 80-fold, respectively). Furthermore, local and systemic expression of s100a8 and s100a9 were nearly diminished in eosinophil-deficient ΔdblGATA mice, and were re-constituted upon adoptive transfer of eosinophils. Taken together, these data may provide new insight into the involvement of eosinophils in colonic inflammation and repair, which may have diagnostic and therapeutic implications.

CD300f:IL-5 cross-talk inhibits adipose tissue eosinophil homing and subsequent IL-4 production.

Eosinophils and their associated cytokines IL-4 and IL-5 are emerging as central orchestrators of the immune-metabolic axis. Herein, we demonstrate that cross-talk between the Ig-superfamily receptor CD300f and IL-5 is a key checkpoint that modifies the ability of eosinophils to regulate metabolic outcomes. Generation of Il5 Tg /Cd300f -/- mice revealed marked and distinct increases in eosinophil levels and their production of IL-4 in the white and brown adipose tissues. Consequently, Il5 Tg /Cd300f -/- mice had increased alternatively activated macrophage accumulation in the adipose tissue. Cd300f -/- mice displayed age-related accumulation of eosinophils and macrophages in the adipose tissue and decreased adipose tissue weight, which was associated with decreased diet-induced weight gain and insulin resistance. Notably, Il5 Tg /CD300f -/- were protected from diet-induced weight gain and glucose intolerance. These findings highlight the cross-talk between IL-5 receptor and CD300f as a novel pathway regulating adipose tissue eosinophils and offer new entry points for therapeutic intervention for obesity and its complications.

CD300f associates with IL-4 receptor α and amplifies IL-4-induced immune cell responses.

IL-4 receptor (R) α, the common receptor chain for IL-4 and IL-13, is a critical component in IL-4- and IL-13-mediated signaling and subsequent effector functions such as those observed in type 2 inflammatory responses. Nonetheless, the existence of intrinsic pathways capable of amplifying IL-4Rα-induced responses remains unknown. In this study, we identified the myeloid-associated Ig receptor CD300f as an IL-4-induced molecule in macrophages. Subsequent analyses demonstrated that CD300f was colocalized and physically associated with IL-4Rα. Using Cd300f(-/-) cells and receptor cross-linking experiments, we established that CD300f amplified IL-4Rα-induced responses by augmenting IL-4/IL-13-induced signaling, mediator release, and priming. Consistently, IL-4- and aeroallergen-treated Cd300f(-/-) mice displayed decreased IgE production, chemokine expression, and inflammatory cell recruitment. Impaired responses in Cd300f(-/-) mice were not due to the inability to generate a proper Th2 response, because IL-4/IL-13 levels were markedly increased in allergen-challenged Cd300f(-/-) mice, a finding that is consistent with decreased cytokine consumption. Finally, CD300f expression was increased in monocytes and eosinophils obtained from allergic rhinitis patients. Collectively, our data highlight a previously unidentified role for CD300f in IL-4Rα-induced immune cell responses. These data provide new insights into the molecular mechanisms governing IL-4Rα-induced responses, and may provide new therapeutic tools to target IL-4 in allergy and asthma.

MicroRNA profiling reveals opposing expression patterns for miR-511 in alternatively and classically activated macrophages.

BACKGROUND: Macrophages are heterogeneous cells, which possess pleotropic effector and immunoregulatory functions. The phenotypic diversity of macrophages is best exemplified by the ability of IL-4 or IL-13, two key cytokines in asthma to promote macrophages into a suppressive/anti-inflammatory phenotype (e.g. alternatively activated or M2) whereas exposure to IFN-γ followed by microbial trigger renders macrophages pro-inflammatory (e.g. classically activated or M1). Intriguingly, only limited data exists regarding the expression of miRNA in M2 macrophages. OBJECTIVE: To define the miRNA profile of M2 and M1 macrophages. METHODS: Bone marrow-derived macrophages were activated to classically and alternatively activated states using IL-4, IL-13 or IFN-γ followed by Escherichia coli stimulation. Thereafter, an unbiased miRNA "mining" approach was utilized and the expression of several miRNAs was validated following in-vitro and in-vivo macrophage activation (qPCR). miR-511 over-expression was performed followed by global transcriptional and bioinformatic analyses. RESULTS: We report unique miRNA expression profiles in M2 and M1 macrophages involving multiple miRNAs. Among these miRNAs, we established that miR-511 is increased in macrophages following IL-4- and IL-13-stimulation and decreased in M1 macrophages both in-vitro and in-vivo. Increased miR-511 expression was sufficient to induce marked transcriptional changes in macrophages. Interestingly, bioinformatics analyses revealed that miR-511 altered the expression of gene products that are associated with hallmark alternatively activated macrophage functions, such as cellular proliferation, wound healing responses and inflammation. CONCLUSIONS: Our data establish miR-511 as a bona fide M2-associated miRNA. These data may have significant implications in asthma where the expression of IL-4 and IL-13 are highly increased.

Paired immunoglobulin-like receptor A is an intrinsic, self-limiting suppressor of IL-5-induced eosinophil development.

Eosinophilia is a hallmark characteristic of T helper type 2 (TH2) cell-associated diseases and is critically regulated by the central eosinophil growth factor interleukin 5 (IL-5). Here we demonstrate that IL-5 activity in eosinophils was regulated by paired immunoglobulin-like receptors PIR-A and PIR-B. Upon self-recognition of ß2-microglobulin (ß2M) molecules, PIR-B served as a permissive checkpoint for IL-5-induced development of eosinophils by suppressing the proapoptotic activities of PIR-A, which were mediated by the Grb2-Erk-Bim pathway. PIR-B-deficient bone marrow eosinophils underwent compartmentalized apoptosis, resulting in decreased blood eosinophilia in naive mice and in mice challenged with IL-5. Subsequently, Pirb(-/-) mice displayed impaired aeroallergen-induced lung eosinophilia and induction of lung TH2 cell responses. Collectively, these data uncover an intrinsic, self-limiting pathway regulating IL-5-induced expansion of eosinophils, which has broad implications for eosinophil-associated diseases.