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[This corrects the article DOI: 10.3389/fimmu.2023.1151468.].

Mepolizumab, an IL-5-blocking antibody, reduces exacerbations in patients with severe eosinophilic asthma. Mepolizumab arrests eosinophil maturation; however, the functional phenotype of eosinophils that persist in the blood and airway after administration of IL-5 neutralizing antibodies has not been reported. To determine the effect of anti-IL-5 antibody on the numbers and phenotypes of allergen-induced circulating and airway eosinophils. Airway inflammation was elicited in participants with mild allergic asthma by segmental allergen challenge before and 1 month after a single intravenous 750-mg dose of mepolizumab. Eosinophils were examined in blood, bronchoalveolar lavage, and endobronchial biopsies 48 hours after challenge. Segmental challenge without mepolizumab induced a rise in circulating eosinophils, bronchoalveolar lavage eosinophilia, and eosinophil peroxidase deposition in bronchial mucosa. IL-5 neutralization before allergen challenge abolished the allergen-induced rise in circulating eosinophils and expression of IL-3 receptors, whereas airway eosinophilia and eosinophil peroxidase deposition were blunted but not eliminated. Before mepolizumab treatment, bronchoalveolar lavage eosinophils had more surface IL-3 and granulocyte-monocyte colony-stimulating factor receptors, CD69, CD44, and CD23 and decreased IL-5 and eotaxin receptors than blood eosinophils. This activation phenotype indicated by bronchoalveolar lavage eosinophil surface markers, as well as the release of eosinophil peroxidase by eosinophils in the bronchial mucosa, was maintained after mepolizumab. Mepolizumab reduced airway eosinophil numbers but had a limited effect on airway eosinophil activation markers, suggesting that these cells retain functionality. This observation may explain why IL-5 neutralization reduces but does not completely eradicate asthma exacerbations. Clinical trial registered with www.clinicaltrials.gov (NCT00802438).

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and inteleukin-3 (IL-3) have long been known as mediators of emergency myelopoiesis, but recent evidence has highlighted their critical role in modulating innate immune effector functions in mice and humans. This new wealth of knowledge has uncovered novel aspects of the pathogenesis of a range of disorders, including infectious, neoplastic, autoimmune, allergic and cardiovascular diseases. Consequently, GM-CSF and IL-3 are now being investigated as therapeutic targets for some of these disorders, and some phase I/II clinical trials are already showing promising results. There is also pre-clinical and clinical evidence that GM-CSF can be an effective immunostimulatory agent when being combined with anti-cytotoxic T lymphocyte-associated protein 4 (anti-CTLA-4) in patients with metastatic melanoma as well as in novel cancer immunotherapy approaches. Finally, GM-CSF and to a lesser extent IL-3 play a critical role in experimental models of trained immunity by acting not only on bone marrow precursors but also directly on mature myeloid cells. Altogether, characterizing GM-CSF and IL-3 as central mediators of innate immune activation is poised to open new therapeutic avenues for several immune-mediated disorders and define their potential in the context of immunotherapies.

Background Triple negative breast cancer (TNBC) remains one of the most aggressive subtypes of cancer with a poor prognosis and limited treatment options. Building on our previous findings of elevated Interleukin-3-Receptor-α (IL-3Rα) expression in TNBC, this study investigates the mechanisms underpinning IL-3-mediated actions in TNBC. Methods GEO database (GSE25066) was interrogated to evaluate the expression of IL-3. RNAseq data were acquired from the TCGA-BRCA (Breast Carcinoma) project. Seven TNBC cell lines were used to validate the expression of IL-3 by ELISA assay. Chromatin immunoprecipitation assay was performed to evaluate the binding of STAT5A to the miR-155-5p promoter in TNBC cells. FACS analysis and ALDH activity were performed to evaluate the expansion of ALDH-1A1 + and CD44 high /CD24 low subpopulations. Mammosphere formation efficiency (MFE) was evaluated using the standard assay, while chemoresistance by applying the incucyte cell viability assay. miR155-5p silencing served to validate the expression of all target proteins both in vitro and in vivo. Results Bioinformatic analysis of breast cancer patient gene datasets revealed significant upregulation of the IL-3 gene in TNBC patient samples compared to the non-TNBC group (GEO: p  = 0.004: TCGA p  = 2.7e−30 respectively). We also found that TNBC cells secrete IL-3, which activates STAT5A promoting miR-155-5p expression by binding to its promoter in TNBC cells. Correlation analysis based on TCGA-BRCA confirmed elevated miR-155-5p levels in TNBC compared to non-tumoral tissues ( p  = 2.1e−33) and non-TNBC ( p  = 6.5e−30), with positive correlations between the IL-3 and miR-155-5p ( r  = 0.157, p  < 0.001), as well as between miR-155-5p and miR-155-3p and STAT5A ( r  = 0.250, p  = 0.002; r  = 0.245, p  < 0.005 respectively). Functional studies demonstrated that miR-155-5p downregulates programmed cell death 4, APC, and GSK-3β, enhancing β-catenin nuclear translocation and c-myc expression. Silencing miR-155-5p reversed all these effects. IL-3, via miR-155-5p, also drives ALDH-1A1 + and CD44 high /CD24 low subpopulation expansion and ALDH activity, enhances MFE and chemoresistance. Notably, blocking IL-3 impaired MFE, suggesting an autocrine loop sustaining IL-3 action in TNBC. In vivo, IL-3 promoted tumour growth, β-catenin activity, and metastasis, while miR-155-5p silencing mitigated these effects. Conclusions Overall, our results underscore the crucial role of IL-3 in tumour progression, thereby advocating IL-3/IL-3Rα axis targeting as a promising therapeutic approach for TNBC. Graphical abstract

Autophagy and apoptosis are two important and interconnected stress-response mechanisms. However, the molecular interplay between these two pathways is not fully understood. To study the fate and function of autophagic proteins at the onset of apoptosis, we used a cellular model system in which autophagy precedes apoptosis. IL-3 depletion of Ba/F3 cells caused caspase (casp)-mediated cleavage of Beclin-1 and PI3KC3, two crucial components of the autophagy-inducing complex. We identified two casp cleavage sites in Beclin-1, TDVD 133 and DQLD 149 , cleavage at which yields fragments lacking the autophagy-inducing capacity. Noteworthy, the C-terminal fragment, Beclin-1-C, localized predominantly at the mitochondria and sensitized the cells to apoptosis. Moreover, on isolated mitochondria, recombinant Beclin-1-C was able to induce the release of proapoptotic factors. These findings point to a mechanism by which casp-dependent generation of Beclin-1-C creates an amplifying loop enhancing apoptosis upon growth factor withdrawal.

Mast cells have been implicated in allergic diseases such as asthma, rhinitis, conjunctivitis, atopic dermatitis, urticaria, and anaphylaxis. However, it is now well established that they also fulfill critical roles in tissue homeostasis, repair, and defense. Despite considerable progress, their ontogeny, proliferation, and differentiation remain subjects of debate, as does their involvement in a wide spectrum of diseases, including cancer and cardiovascular disorders. What remains indisputable is their essential contribution to both innate and adaptive immune responses. Importantly, the activity of their effector molecules can elicit either protective or deleterious outcomes. A complete absence of mast cells (MCs) in humans would undoubtedly provide valuable insight into their fundamental role in immunity, much as neutropenia and agranulocytosis have historically clarified the functions of neutrophils. In this review, we provide a comprehensive overview of mast cell (MC) biology, emphasizing their functional diversity and pathogenic potential. Furthermore, we highlight emerging therapeutic strategies, particularly the use of inhibitors and monoclonal antibodies, which are reshaping current approaches to conditions such as allergy, mastocytosis, and related disorders.

Interleukin 3 (IL-3) plays an important role in hematopoiesis and immune regulation, brain IL-3/IL-3R signaling has been shown to involve in the physiological and pathological processes of a variety of neurodegenerative diseases, but its role in prion diseases is rarely described. Here, the changes of IL-3/IL-3R and its downstream signaling pathways in a scrapie-infected cell line and in the brains of several scrapie - infected rodent models were evaluated by various methods. Markedly decreased IL-3Rα were observed in the brains of scrapie-infected rodents at terminal stage and in the prion-infected cell model, which showed increased in the brain samples collected at early and middle stage of infection. The IL-3 levels were almost unchanged in the brains of scrapie-infected mice and in the prion-infected cell line. Morphological assays identified close co-localization of the increased IL-3Rα signals with NeuN- and Iba1-positive cells, whereas co-localization of IL-3 signals with NeuN- and GFAP-positive cells in the scrapie-infected brain tissues. Some downstream components of IL-3/IL-3R pathways, including JAK2-STAT5 and PI3K/AKT/mTOR pathways, were downregulated in the brains of scrapie-infected rodents at terminal stage and in the prion-infected cells. Stimulation of recombinant IL-3 on the cultured cells showed prion that the prion-infected cells displayed markedly more reluctant responses of JAK2-STAT5 and PI3K/AKT/mTOR pathways than the normal partner cells. These data suggest that although prion infection or PrP Sc accumulation in brain tissues does not affect IL-3 expression, it significantly downregulates IL-3R levels, thereby inhibiting the downstream pathways of IL-3/IL-3R and blocking the neuroregulatory and neuroprotective activities of IL-3.

Astrocyte-derived IL-3 activates the corresponding receptor IL-3Rα in microglia. This cross-talk between astrocytes and microglia ameliorates the pathology of Alzheimer’s disease in mice. In this study we investigated the role of IL-3/IL-3Rα cross-talk and its regulatory mechanisms in ischemic stroke. Ischemic stroke was induced in mice by intraluminal occlusion of the right middle cerebral artery (MCA) for 60 min followed by reperfusion (I/R). Human astrocytes or microglia subjected to oxygen-glucose deprivation and reoxygenation (OGD/Re) were used as in vitro models of brain ischemia. We showed that both I/R and OGD/Re significantly induced decreases in astrocytic IL-3 and microglial IL-3Rα protein levels, accompanied by pro-inflammatory activation of A1-type astrocytes and M1-type microglia. Importantly, astrocyte-derived VEGFD acting on VEGFR3 of astrocytes and microglia contributed to the cross-talk dysfunction and pro-inflammatory activation of the two glial cells, thereby mediating neuronal cell damage. By using metabolomics and multiple biochemical approaches, we demonstrated that IL-3 supplementation to microglia reversed OGD/Re-induced lipid metabolic reprogramming evidenced by upregulated expression of CPT1A, a rate-limiting enzyme for the mitochondrial β-oxidation, and increased levels of glycerophospholipids, the major components of cellular membranes, causing reduced accumulation of lipid droplets, thus reduced pro-inflammatory activation and necrosis, as well as increased phagocytosis of microglia. Notably, exogenous IL-3 and the VEGFR antagonist axitinib reestablished the cross-talk of IL-3/IL-3Rα, improving microglial lipid metabolic levels via upregulation of CPT1A, restoring microglial phagocytotic function and attenuating microglial pro-inflammatory activation, ultimately contributing to brain recovery from I/R insult. Our results demonstrate that VEGFD/VEGFR3 signaling contributes to the dysfunction of the astrocyte IL-3/microglia IL-3Rα cross-talk and drives pro-inflammatory activation, causing lipid metabolic reprogramming of microglia. These insights suggest VEGFR3 antagonism or restoring IL-3 levels as a potential therapeutic strategy for ischemic stroke.

Basophils have been recognized as a characterized cellular player for Th2 immune responses implicated in allergic diseases, but the mechanisms responsible for basophil recruitment to allergic skin remain not well understood. Using a hapten fluorescein isothiocyanate (FITC)-induced allergic contact dermatitis (ACD) mouse model, we show that basophils in FITC-treated IL-3-knockout mice are defective in crossing the vascular endothelium to enter the inflamed skin. By generating mice in which IL-3 is selectively ablated in T cells, we further demonstrate that IL-3 produced by T cells mediates basophil extravasation. Moreover, basophils sorted from FITC-treated IL-3-knockout mice exhibit a decreased expression of integrins Itgam, Itgb2, Itga2b and Itgb7, which are potentially implicated in extravasation process. Interestingly, we observed that these basophils had a reduced expression of retinaldehyde dehydrogenase 1 family member A2 (Aldh1a2), an enzyme responsible for the production of retinoic acid (RA), and administration of all-trans RA restored partially the extravasation of basophils in IL-3-knockout mice. Finally, we validate that IL-3 induces the expression of ALDH1A2 in primary human basophils, and provide further evidence that IL-3 stimulation induces the expression of integrins particularly ITGB7 in an RA-dependent manner. Together, our data propose a model that IL-3 produced by T cells activates ALDH1A2 expression by basophils, leading to the production of RA, which subsequently induces the expression of integrins crucially implicated in basophil extravasation to inflamed ACD skin.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an extremely rare hematologic malignancy with an aggressive course and poor prognosis. Treatment remains challenging particularly in patients who are ineligible for stem cell transplantation due to resistance to conventional chemotherapy. The introduction of tagraxofusp, a CD123-directed cytotoxin, has significantly expanded therapeutic options and improved outcomes for patients with BPDCN. However, its use can be accompanied by notable adverse events, especially capillary leak syndrome, underscoring the need for careful patient selection and monitoring. Up to date, no data is available regarding the safety of tagraxofusp in patients with chronic kidney failure and cardiovascular co-morbidities. We present the case of a 79-year-old male who developed a solitary, rapidly progressing skin lesion on his lower back. The lesion represented the first manifestation of BPDCN with bone marrow infiltration and concomitant myelodysplastic syndrome (MDS). Molecular analysis identified mutations in CBL, TET2, ZRSR2 and KRAS. Non-eligible for stem cell transplantation, the patient was admitted to treatment with tagraxofusp in a dose-reduced protocol due to concomitant chronic kidney disease (CKD). After three doses of the first cycle, treatment needed to be stopped due to acute-on-chronic renal failure. After treatment disruption, kidney failure was completely restituted to pre-treatment levels. Notably, skin and bone marrow biopsies demonstrated a dermatologic complete response and partial remission of bone marrow infiltration. A watch and wait concept was followed, and prolonged therapy response was obtained for 8 months before relapse. To our knowledge, this is the first reported case demonstrating the use of tagraxofusp in a patient with BPDCN and advanced chronic kidney disease, showing that even a minimum of tolerated treatment dose can induce a sustained response. Despite the risk of adverse events, tagraxofusp should be considered a viable treatment option for elderly patients with poor performance status and significant comorbidities who are ineligible for intensive chemotherapy or stem cell transplantation, as even limited exposure may achieve meaningful clinical responses.