Human cell surface-AAV interactomes identify LRP6 as blood-brain barrier transcytosis receptor and immune cytokine IL3 as AAV9 binder.

Adeno-associated viruses (AAVs) are foundational gene delivery tools for basic science and clinical therapeutics. However, lack of mechanistic insight, especially for engineered vectors created by directed evolution, can hamper their application. Here, we adapt an unbiased human cell microarray platform to determine the extracellular and cell surface interactomes of natural and engineered AAVs. We identify a naturally-evolved and serotype-specific interaction between the AAV9 capsid and human interleukin 3 (IL3), with possible roles in host immune modulation, as well as lab-evolved low-density lipoprotein receptor-related protein 6 (LRP6) interactions specific to engineered capsids with enhanced blood-brain barrier crossing in non-human primates after intravenous administration. The unbiased cell microarray screening approach also allows us to identify off-target tissue binding interactions of engineered brain-enriched AAV capsids that may inform vectors' peripheral organ tropism and side effects. Our cryo-electron tomography and AlphaFold modeling of capsid-interactor complexes reveal LRP6 and IL3 binding sites. These results allow confident application of engineered AAVs in diverse organisms and unlock future target-informed engineering of improved viral and non-viral vectors for non-invasive therapeutic delivery to the brain.

IL-3: key orchestrator of inflammation.

Interleukin (IL)-3 has long been known for its hematopoietic properties. However, recent evidence has expanded our understanding of IL-3 function by identifying IL-3 as a critical orchestrator of inflammation in a wide array of diseases. Depending on the type of disease, the course of inflammation, the cell or the tissue involved, IL-3 promotes either pathologic inflammation or its resolution. Here, we describe the cell-specific functions of IL-3 and summarize its role in diseases. We discuss the current treatments targeting IL-3 or its receptor, and highlight the potential and the limitations of targeting IL-3 in clinics.

Improvement of multilineage hematopoiesis in hematopoietic stem cell-transferred c-kit mutant NOG-EXL humanized mice.

Human hematopoietic stem cell (HSC)-transferred humanized mice are valuable models for exploring human hematology and immunology. However, sufficient recapitulation of human hematopoiesis in mice requires large quantities of enriched human CD34+ HSCs and total-body irradiation for adequate engraftment. Recently, we generated a NOG mouse strain with a point mutation in the c-kit tyrosine kinase domain (W41 mutant; NOGW mice). In this study, we examined the ability of NOGW mice to reconstitute human hematopoietic cells. Irradiated NOGW mice exhibited high engraftment levels of human CD45+ cells in the peripheral blood, even when only 5,000-10,000 CD34+ HSCs were transferred. Efficient engraftment of human CD45+ cells was also observed in non-irradiated NOGW mice transferred with 20,000-40,000 HSCs. The bone marrow (BM) of NOGW mice exhibited significantly more engrafted human HSCs or progenitor cells (CD34+CD38- or CD34+CD38+ cells) than the BM of NOG mice. Furthermore, we generated a human cytokine (interleukin-3 and granulocyte-macrophage colony-stimulating factor) transgenic NOG-W41 (NOGW-EXL) mouse to achieve multilineage reconstitution with sufficient engraftment of human hematopoietic cells. Non-irradiated NOGW-EXL mice showed significantly higher engraftment levels of human CD45+ and myeloid lineage cells, particularly granulocytes and platelets/megakaryocytes, than non-irradiated NOGW or irradiated NOG-EXL mice after human CD34+ cell transplantation. Serial BM transplantation experiments revealed that NOGW mice exhibited the highest potential for long-term HSC compared with other strains. Consequently, c-kit mutant NOGW-EXL humanized mice represent an advanced model for HSC-transferred humanized mice and hold promise for widespread applications owing to their high versatility.

Efficient production of human interleukin-3 from Escherichia coli using protein disulfide isomerase b'a' domain.

Human interleukin-3 (IL3) is a multifunctional cytokine essential for both clinical and biomedical research endeavors. However, its production in Escherichia coli has historically been challenging due to its aggregation into inclusion bodies, requiring intricate solubilization and refolding procedures. This study introduces an innovative approach employing two chaperone proteins, maltose binding protein (MBP) and protein disulfide isomerase b'a' domain (PDIb'a'), as N-terminal fusion tags. Histidine tag (H) was added at the beginning of each chaperone protein gene for easy purification. This fusion of chaperone proteins significantly improved IL3 solubility across various E. coli strains and temperature conditions, eliminating the need for laborious refolding procedures. Following expression optimization, H-PDIb'a'-IL3 was purified using two chromatographic methods, and the subsequent removal of the H-PDIb'a' tag yielded high-purity IL3. The identity of the purified protein was confirmed through liquid chromatography coupled with tandem mass spectrometry analysis. Biological activity assays using human erythroleukemia TF-1 cells revealed a unique two-step stimulation pattern for both purified IL3 and the H-PDIb'a'-IL3 fusion protein, underscoring the protein's functional integrity and revealing novel insights into its cellular interactions. This study advances the understanding of IL3 expression and activity while introducing novel considerations for protein fusion strategies.

IL3-Driven T Cell-Basophil Crosstalk Enhances Antitumor Immunity.

Cytotoxic T lymphocytes (CTL) are pivotal in combating cancer, yet their efficacy is often hindered by the immunosuppressive tumor microenvironment, resulting in CTL exhaustion. This study investigates the role of interleukin-3 (IL3) in orchestrating antitumor immunity through CTL modulation. We found that intratumoral CTLs exhibited a progressive decline in IL3 production, which was correlated with impaired cytotoxic function. Augmenting IL3 supplementation, through intraperitoneal administration of recombinant IL3, IL3-expressing tumor cells, or IL3-engineered CD8+ T cells, conferred protection against tumor progression, concomitant with increased CTL activity. CTLs were critical for this therapeutic efficacy as IL3 demonstrated no impact on tumor growth in Rag1 knockout mice or following CD8+ T-cell depletion. Rather than acting directly, CTL-derived IL3 exerted its influence on basophils, concomitantly amplifying antitumor immunity within CTLs. Introducing IL3-activated basophils retarded tumor progression, whereas basophil depletion diminished the effectiveness of IL3 supplementation. Furthermore, IL3 prompted basophils to produce IL4, which subsequently elevated CTL IFNγ production and viability. Further, the importance of basophil-derived IL4 was evident from the absence of benefits of IL3 supplementation in IL4 knockout tumor-bearing mice. Overall, this research has unveiled a role for IL3-mediated CTL-basophil cross-talk in regulating antitumor immunity and suggests harnessing IL3 sustenance as a promising approach for optimizing and enhancing cancer immunotherapy. See related Spotlight, p. 798.

E3 ubiquitin ligase RNF128 negatively regulates the IL-3/STAT5 signaling pathway by facilitating K27-linked polyubiquitination of IL-3Rα.

IL-3/STAT5 signaling pathway is crucial for the development and activation of immune cells, contributing to the cellular response to infections and inflammatory stimuli. Dysregulation of the IL-3/STAT5 signaling have been associated with inflammatory and autoimmune diseases characterized by inflammatory cell infiltration and organ damage. IL-3 receptor α (IL-3Rα) specifically binds to IL-3 and initiates intracellular signaling, resulting in the phosphorylation of STAT5. However, the regulatory mechanisms of IL-3Rα remain unclear. Here, we identified the E3 ubiquitin ligase RNF128 as a negative regulator of IL-3/STAT5 signaling by targeting IL-3Rα for lysosomal degradation. RNF128 was shown to selectively bind to IL-3Rα, without interacting with the common beta chain IL-3Rß, which shares the subunit with GM-CSF. The deficiency of Rnf128 had no effect on GM-CSF-induced phosphorylation of Stat5, but it resulted in heightened Il-3-triggered activation of Stat5 and increased transcription of the Id1, Pim1, and Cd69 genes. Furthermore, we found that RNF128 promoted the K27-linked polyubiquitination of IL-3Rα in a ligase activity-dependent manner, ultimately facilitating its degradation through the lysosomal pathway. RNF128 inhibited the activation and chemotaxis of macrophages in response to LPS stimulation, thereby attenuating excessive inflammatory responses. Collectively, these results reveal that RNF128 negatively regulates the IL-3/STAT5 signaling pathway by facilitating K27-linked polyubiquitination of IL-3Rα. This study uncovers E3 ubiquitin ligase RNF128 as a novel regulator of the IL-3/STAT5 signaling pathway, providing potential molecular targets for the treatment of inflammatory diseases.

EP300-ZNF384 transactivates IL3RA to promote the progression of B-cell acute lymphoblastic leukemia.

The EP300-ZNF384 fusion gene is an oncogenic driver in B-cell acute lymphoblastic leukemia (B-ALL). In the present study, we demonstrated that EP300-ZNF384 substantially induces the transcription of IL3RA and the expression of IL3Rα (CD123) on B-ALL cell membranes. Interleukin 3 (IL-3) supplementation promotes the proliferation of EP300-ZNF348-positive B-ALL cells by activating STAT5. Conditional knockdown of IL3RA in EP300-ZF384-positive cells inhibited the proliferation in vitro, and induced a significant increase in overall survival of mice, which is attributed to impaired propagation ability of leukemia cells. Mechanistically, the EP300-ZNF384 fusion protein transactivates the promoter activity of IL3RA by binding to an A-rich sequence localized at -222/-234 of IL3RA. Furthermore, forced EP300-ZNF384 expression induces the expression of IL3Rα on cell membranes and the secretion of IL-3 in CD19-positive B precursor cells derived from healthy individuals. Doxorubicin displayed a selective killing of EP300-ZNF384-positive B-ALL cells in vitro and in vivo. Collectively, we identify IL3RA as a direct downstream target of EP300-ZNF384, suggesting CD123 is a potent biomarker for EP300-ZNF384-driven B-ALL. Targeting CD123 may be a novel therapeutic approach to EP300-ZNF384-positive patients, alternative or, more likely, complementary to standard chemotherapy regimen in clinical setting.

Possible alternative strategies to implement basophil activation testing in multicentric studies.

The Basophil Activation Test (BAT) enables flow cytometry characterization of basophil reactivity against specific allergenic molecules. The focus now revolves around democratizing this tool, but, as blood sample stability could be challenging, after having developed a simplified approach, herein, we aimed to characterize two strategies for implementing BAT in multicentric studies: store and ship blood before or after sample processing. Fresh heparin- and EDTA-anticoagulated whole blood samples followed both BAT workflows: "collect, store, process & analyze" or "collect, process, store & analyze". Storage temperatures of 18-25 °C or 2-8 °C and preservation times from 0 to 7 days were considered. Interleukin-3 was also evaluated. With the "collect, store, process & analyze" workflow, heparin-anticoagulated blood and 18-25 °C storage were better than other conditions. While remaining possible, basophil activation exhibited a possible reactivity decay after 24 h. Under the conditions tested, interleukin-3 had no role in enhancing basophil reactivity after storage. Conversely, the "collect, process, store & analyze" workflow demonstrated that either heparin- or EDTA-anticoagulated blood can be processed and kept up to 7 days at 18-25 °C or 2-8 °C before being analyzed. Various strategies can be implemented to integrate BAT in multicentric studies. The "collect, store, process & analyze" workflow remains a simplified logistical approach, but depending on time required to ship from the clinical centers to the reference laboratories, it might not be applicable, or should be used with caution. The "collect, process, store & analyze" workflow may constitute a workflow improvement to provide significant flexibility without impact on basophil reactivity.

Structure of the interleukin-5 receptor complex exemplifies the organizing principle of common beta cytokine signaling.

Cytokines regulate immune responses by binding to cell surface receptors, including the common subunit beta (ßc), which mediates signaling for GM-CSF, IL-3, and IL-5. Despite known roles in inflammation, the structural basis of IL-5 receptor activation remains unclear. We present the cryo-EM structure of the human IL-5 ternary receptor complex, revealing architectural principles for IL-5, GM-CSF, and IL-3. In mammalian cell culture, single-molecule imaging confirms hexameric IL-5 complex formation on cell surfaces. Engineered chimeric receptors show that IL-5 signaling, as well as IL-3 and GM-CSF, can occur through receptor heterodimerization, obviating the need for higher-order assemblies of ßc dimers. These findings provide insights into IL-5 and ßc receptor family signaling mechanisms, aiding in the development of therapies for diseases involving deranged ßc signaling.

Altered TLR7 Expression-Mediated Immune Modulation Is Supportive of Persistent Replication and Intrauterine Transmission of HBV.

Hepatitis B Virus (HBV) is posing as a serious public health threat mainly due to its asymptomatic nature of infection in pregnancy and vertical transmission. Viral sensing toll-like receptors (TLR) and Interleukins (IL) are important molecules in providing an antiviral state. The study aimed to assess the role of TLR7-mediated immune modulation, which might have an impact in the intrauterine transmission of HBV leading to mother to child transmission of the virus. We investigated the expression pattern of TLR7, IL-3, and IL-6 by RT-PCR in the placentas of HBV-infected pregnant women to see their role in the intrauterine transmission of HBV. We further validated the expression of TLR7 in placentas using Immunohistochemistry. Expression analysis by RT-PCR of TLR7 revealed significant downregulation among the Cord blood (CB) HBV DNA positive and negative cases with mean ± standard deviation (SD) of 0.43 ± 0.22 (28) and 1.14 ± 0.57 (44) with p = 0.001. IL-3 and IL-6 expression revealed significant upregulation in the CB HBV DNA-positive cases with p = 0.001. Multinomial logistic regression analysis revealed that TLR7 and IL-3 fold change and mother HBeAg status are important predictors for HBV mother to child transmission. Immunohistochemistry revealed the decreased expression of TLR7 in CB HBV DNA-positive cases. This study reveals that the downregulation of TLR7 in the placenta along with CB HBV DNA-positive status may lead to intrauterine transmission of HBV, which may lead to vertical transmission of HBV.

Interleukin 3 Inhibits Glutamate-Cytotoxicity in Neuroblastoma Cell Line.

Interleukin 3 (IL-3) is a well-known pleiotropic cytokine that regulates the proliferation and differentiation of hematopoietic progenitor cells, triggering classical signaling pathways such as JAK/STAT, Ras/MAPK, and PI3K/Akt to carry out its functions. Interestingly, the IL-3 receptor is also expressed in non-hematopoietic cells, playing a crucial role in cell survival. Our previous research demonstrated the expression of the IL-3 receptor in neuron cells and its protective role in neurodegeneration. Glutamate, a principal neurotransmitter in the central nervous system, can induce cellular stress and lead to neurotoxicity when its extracellular concentrations surpass normal levels. This excessive glutamate presence is frequently observed in various neurological diseases. In this study, we uncover the protective role of IL-3 as an inhibitor of glutamate-induced cell death, analyzing the cytokine's signaling pathways during its protective effect. Specifically, we examined the relevance of JAK/STAT, Ras/MAPK, and PI3 K signaling pathways in the molecular mechanism triggered by IL-3. Our results show that the inhibition of JAK, ERK, and PI3 K signaling pathways, using pharmacological inhibitors, effectively blocked IL-3's protective role against glutamate-induced cell death. Additionally, our findings suggest that Bcl-2 and Bax proteins may be involved in the molecular mechanism triggered by IL-3. Our investigation into IL-3's ability to protect neuronal cells from glutamate-induced damage offers a promising therapeutic avenue with potential clinical implications for several neurological diseases characterized by glutamate neurotoxicity.

NFIL3 contributes to cytotoxic T lymphocyte-mediated killing.

Cytotoxic T lymphocytes (CTLs) are key effectors of the adaptive immune system that recognize and eliminate virally infected and cancerous cells. In naive CD8+ T cells, T-cell receptor (TCR) engagement drives a number of transcriptional, translational and proliferation changes over the course of hours and days leading to differentiation into CTLs. To gain a better insight into this mechanism, we compared the transcriptional profiles of naive CD8+ T cells to those of activated CTLs. To find new regulators of CTL function, we performed a selective clustered regularly interspaced short palindromic repeats (CRISPR) screen on upregulated genes and identified nuclear factor IL-3 (NFIL3) as a potential regulator of cytotoxicity. Although NFIL3 has established roles in several immune cells including natural killer, Treg, dendritic and CD4+ T cells, its function in CD8+ CTLs is less well understood. Using CRISPR/Cas9 editing, we found that removing NFIL3 in CTLs resulted in a marked decrease in cytotoxicity. We found that in CTLs lacking NFIL3 TCR-induced extracellular signal-regulated kinase phosphorylation, immune synapse formation and granule release were all intact while cytotoxicity was functionally impaired in vitro. Strikingly, NFIL3 controls the production of cytolytic proteins as well as effector cytokines. Thus, NFIL3 plays a cell intrinsic role in modulating cytolytic mechanisms in CTLs.

Ginsenoside RH4 inhibits Ang II-induced myocardial remodeling by interfering with NFIL3.

Ventricular remodeling refers to the structural and functional changes of the heart under various stimuli or disease influences and may also be accompanied by myocardial fibrosis, where an excessive amount of fibrous tissue appears in the myocardial tissue, affecting the heart's normal contraction and relaxation. Hypertension is posing the potential risk of causing myocardial injury and remodeling. The significance of the renin-angiotensin-aldosterone system (RAAS) in myocardial remodeling cannot be overlooked. Drug targeting of RAAS can effectively lower blood pressure and reduce left ventricular mass. Studies have shown that ginsenoside Rh4 can inhibit oxidative stress and inflammatory responses. In this study, a myocardial remodeling model was established using angiotensin (Ang) II, and the inhibitory effect of RH4 on myocardial hypertrophy and remodeling induced by Ang II was investigated using pathological staining and quantitative polymerase chain reaction (qPCR). Immunofluorescence and qPCR demonstrated that Rh4 causes myocardial hypertrophy and the generation of reactive oxygen species (ROS) in vitro. The Rh4 target was identified using transcriptomics. The findings indicated that RH4 could inhibit myocardial hypertrophy, inflammatory fibrosis, and oxidative stress induced by Ang II, suggesting potential cardiovascular protection effects. In vitro experiments have shown that Rh4 inhibits myocardial hypertrophy. Transcriptomics revealed that nuclear factor interleukin-3 (NFIL3) is a downstream regulator of Rh4. By constructing AAV9-NFIL3 and injecting it into mice, it was found that NFIL3 overexpression interfered with anti-Ang II-induced myocardial remodeling of Rh4. These results indicate that Rh4 demonstrates potential therapeutic effects on myocardial hypertrophy and fibrosis.

TRPV1 Channel in Human Eosinophils: Functional Expression and Inflammatory Modulation.

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel expressed on sensory neurons and immune cells. We hypothesize that TRPV1 plays a role in human eosinophil function and is modulated by inflammatory conditions. TRPV1 expression on human eosinophils was examined by qPCR, flow cytometry, and immunohistochemistry, respectively. TRPV1 functionality was analyzed by investigating calcium flux, apoptosis, modulation by cytokines and acidic pH, and CD69 externalization using flow cytometry. Activation of TRPV1 induced calcium influx and prolonged survival. Although eosinophils were not directly activated by TRPV1 agonists, activation by IL-3 or GM-CSF was mainly restricted to TRPV1-positive eosinophils. TRPV1 surface content was increased by acidic pH, IL-3, IL-31, IL-33, TSLP, TNF-α, BDNF, and NGF-ß. Interestingly, TRPV1 was also expressed by eosinophils located in proximity to peripheral nerves in atopic dermatitis (AD) skin. In conclusion, eosinophils express functional TRPV1 channels which are increased by extracellular acidification and AD-related cytokines. Since eosinophils also express TRPV1 in AD skin, our results indicate an important role of TRPV1 for neuroimmune interaction mechanisms in itchy, inflammatory skin diseases, like AD.

ETV6::ACSL6 translocation-driven super-enhancer activation leads to eosinophilia in acute lymphoblastic leukemia through IL-3 overexpression.

ETV6::ACSL6 represents a rare genetic aberration in hematopoietic neoplasms and is often associated with severe eosinophilia, which confers an unfavorable prognosis requiring additional anti-inflammatory treatment. However, since the translocation is unlikely to produce a fusion protein, the mechanism of ETV6::ACSL6 action remains unclear. Here, we performed multi-omics analyses of primary leukemia cells and patient-derived xenografts from an acute lymphoblastic leukemia (ALL) patient with ETV6::ACSL6 translocation. We identified a super-enhancer located within the ETV6 gene locus, and revealed translocation and activation of the super-enhancer associated with the ETV6::ACSL6 fusion. The translocated super-enhancer exhibited intense interactions with genomic regions adjacent to and distal from the breakpoint at chromosomes 5 and 12, including genes coding inflammatory factors such as IL-3. This led to modulations in DNA methylation, histone modifications, and chromatin structures, triggering transcription of inflammatory factors leading to eosinophilia. Furthermore, the bromodomain and extraterminal domain (BET) inhibitor synergized with standard-of-care drugs for ALL, effectively reducing IL-3 expression and inhibiting ETV6::ACSL6 ALL growth in vitro and in vivo. Overall, our study revealed for the first time a cis-regulatory mechanism of super-enhancer translocation in ETV6::ACSL6ALL, leading to an ALL-accompanying clinical syndrome. These findings may stimulate novel treatment approaches for this challenging ALL subtype.

Interleukin-3 production by basal-like breast cancer cells is associated with poor prognosis.

Breast cancer represents a collection of pathologies with different molecular subtypes, histopathology, risk factors, clinical behavior, and responses to treatment. "Basal-like" breast cancers predominantly lack the receptors for estrogen and progesterone (ER/PR), lack amplification of human epidermal growth factor receptor 2 (HER2) but account for 10-15% of all breast cancers, are largely insensitive to targeted treatment and represent a disproportionate number of metastatic cases and deaths. Analysis of interleukin (IL)-3 and the IL-3 receptor subunits (IL-3RA + CSF2RB) reveals elevated expression in predominantly the basal-like group. Further analysis suggests that IL-3 itself, but not the IL-3 receptor subunits, associates with poor patient outcome. Histology on patient-derived xenografts supports the notion that breast cancer cells are a significant source of IL-3 that may promote disease progression. Taken together, these observations suggest that IL-3 may be a useful marker in solid tumors, particularly triple negative breast cancer, and warrants further investigation into its contribution to disease pathogenesis.

Recent Advances in the Biology and CD123-Directed Treatment of Blastic Plasmacytoid Dendritic Cell Neoplasm.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive myeloid malignancy of the dendritic cell lineage that affects patients of all ages, though the incidence appears to be highest in patients over the age of 60 years. Diagnosis is based on the presence of plasmacytoid dendritic cell precursors expressing CD123, the interleukin-3 (IL-3) receptor alpha, and a distinct histologic appearance. Timely diagnosis remains a challenge, due to lack of disease awareness and overlapping biologic and clinical features with other hematologic malignancies. Prognosis is poor with a median overall survival of 8 to 14 months, irrespective of disease presentation pattern. Historically, the principal treatment was remission induction therapy followed by a stem cell transplant (SCT) in eligible patients. However, bridging to SCT is often not achieved with induction chemotherapy regimens. The discovery that CD123 is universally expressed in BPDCN and is considered to have a pathogenetic role in its development paved the way for the successful introduction of tagraxofusp, a recombinant human IL-3 fused to a truncated diphtheria toxin payload, as an initial treatment for BPDCN. Tagraxofusp was approved in 2018 by the United States Food and Drug Administration for the treatment of patients aged 2 years and older with newly diagnosed and relapsed/refractory BPDCN, and by the European Medicines Agency in 2021 for first-line treatment of adults. The advent of tagraxofusp has opened a new era of precision oncology in the treatment of BPDCN. Herein, we present an overview of BPDCN biology, its diagnosis, and treatment options, illustrated by clinical cases.

Sequential engagement of adhesion molecules and cytokine receptors impacts both piecemeal and anaphylactic degranulation of human basophils.

Basophils are rare granulocytes in circulation which home to tissues in a process depending on rolling, adhesion and cytokine exposure. However, it is still unclear how these steps affect basophil degranulation. Our aim was to imitate these processes associated with homing by sequential crosslinking of adhesion molecules and cytokine exposure and evaluate the effect on basophil piecemeal (PMD) and anaphylactic degranulation (AND). Blood donors with or without allergic asthma were recruited from an ongoing cohort study. Basophils were subjected to CD62L-, CD49d- or CD11b crosslinking and IL-3 or IL-33 stimulation in different orders followed by anti-IgE and fMLP stimulation. Basophil CD203c and CD63 expression were analysed by flow cytometry to determine PMD and AND, respectively. IL-3 induced PMD in basophils and combined with CD62L- or CD11b crosslinking, IL-3 potentiated the degranulation regardless of sequential order. IL-3 priming followed by adhesion molecule crosslinking induced AND and potentiated the effect of anti-IgE. CD62L- and CD11b crosslinking did not further potentiate this effect. CD49d crosslinking followed by IL-3 increased CD63 expression following anti-IgE. IL-3 potentiated the effect of fMLP on AND while adhesion molecule crosslinking did not. IL-33 had impact on PMD only when followed by adhesion molecule crosslinking but did not potentiate neither IgE-dependent nor IgE-independent degranulation. Our data indicate that sequential interactions between basophils, cytokines and adhesion molecule ligands have a decisive effect on basophil degranulation and that these interactions are operational for fine-tuning the activity of tissue dwelling basophils. These data should be considered when the effect of different pharmaceutical on basophil function is studied.

The transcription factor NFIL3/E4BP4 regulates the developmental stage-specific acquisition of basophil function.

BACKGROUND: Basophils are rare but important effector cells in many allergic disorders. Contrary to their early progenitors, the terminal developmental processes of basophils in which they gain their unique functional properties are unknown. OBJECTIVE: We sought to identify a novel late-stage basophil precursor and a transcription factor regulating the terminal maturation of basophils. METHODS: Using flow cytometry, transcriptome analysis, and functional assays, we investigated the identification and functionality of the basophil precursors as well as basophil development. We generated mice with basophil-specific deletion of nuclear factor IL-3 (NFIL3)/E4BP4 and analyzed the functional impairment of NFIL3/E4BP4-deficient basophils in vitro and in vivo using an oxazolone-induced murine model of allergic dermatitis. RESULTS: We report a new mitotic transitional basophil precursor population (referred to as transitional basophils) that expresses the FcεRIα chain at higher levels than mature basophils. Transitional basophils are less responsive to IgE-linked degranulation but produce more cytokines in response to IL-3, IL-33, or IgE cross-linking than mature basophils. In particular, we found that the expression of NFIL3/E4BP4 gradually rises as cells mature from the basophil progenitor stage. Basophil-specific deletion of NFIL3/E4BP4 reduces the expression of genes necessary for basophil function and impairs IgE receptor signaling, cytokine secretion, and degranulation in the context of murine atopic dermatitis. CONCLUSIONS: We discovered transitional basophils, a novel late-stage mitotic basophil precursor cell population that exists between basophil progenitors and postmitotic mature basophils. We demonstrated that NFIL3/E4BP4 augments the IgE-mediated functions of basophils, pointing to a potential therapeutic regulator for allergic diseases.