Jacobsen, Elizabeth A.

Inflammatory bowel disease (IBD) is driven by a breakdown in immune regulation and epithelial barrier function, yet the contribution of eosinophils to this process has remained poorly defined and controversial. While eosinophils infiltrate the intestinal mucosa during both flares and remission, their role in shaping disease outcomes is unclear. Our RNA-seq analyses of colonic eosinophils isolated from dextran sulfate sodium (DSS)-treated mice revealed a significant upregulation of cyclooxygenase (COX)-2 (gene name, Ptgs2 ). Eosinophil-specific deletion of COX-2 (Ptgs2 fl/fl eoCre +/− ) reduced IL-22 production and exacerbated DSS- and trinitrobenzene sulfonic acid (TNBS)-induced colitis, characterized by greater weight loss, higher disease activity, colon shortening, and epithelial injury. Administration of recombinant IL-22 reversed these phenotypes. Mechanistically, eosinophil-derived COX-2 enhanced IL-22 production by type 3 Innate lymphoid cells (ILC3s) through prostaglandin E2 (PGE 2 ) signaling. Consistently, Ptgs2 fl/fl eoCre +/− mice exhibited reduced colonic PGE 2 levels, while PGE 2 analog treatment restored IL-22 production and mucosal protection. Our findings identify eosinophil-derived COX-2 and PGE 2 as a critical regulator of IL-22 production during colitis, uncovering a eosinophil–ILC3 cross talk that safeguards the intestinal barrier and represents a promising therapeutic target in IBD.

Abstract The immune mechanisms underlying Kawasaki disease (KD), a febrile systemic vasculitis in children, are poorly understood. Reports indicate elevated levels of circulating IL-33 in acute KD patients; however, if IL-33 contributes to the pathogenesis of KD vasculitis remains unclear. Here, we used the Lactobacillus casei cell wall extract (LCWE)-induced murine model of KD to determine the contribution of IL-33 to vasculitis development. We observed increased expression of Il33 transcripts and IL-33 protein in LCWE-induced cardiovascular lesions. Bone marrow chimera experiments suggest that IL-33 production by both hematopoietic and stromal cells is important for LCWE-induced KD vasculitis; however, single-cell RNA sequencing, spatial transcriptomics, and flow cytometric analysis revealed that stromal cells were the predominant sources of IL-33. Furthermore, immune cells infiltrating LCWE-induced cardiovascular lesions expressed Il1rl1 transcripts, coding for the IL-33 receptor ST2. In vitro stimulation of bone marrow-derived macrophages with IL-33 enhanced their production of IL-1b and TNF-α. In vivo blockade of IL-33, using either neutralizing IL-33 antibody or Il33-/- mice, effectively attenuated LCWE-induced cardiovascular inflammation. Our results indicate that IL-33 contributes to LCWE-induced vascular inflammation through redundant mechanisms across multiple immune cell subsets rather than a single population and highlight IL-33 as a potential therapeutic target.

Abstract Eosinophils play an important role in mediating itch and inflammation in dermatitis. The role of the eosinophil granule protein eosinophil peroxidase (EPX) in mediating inflammation and itch was tested in a dermatitis mouse model. Mice were sensitized to trimellitic anhydride (TMA) and subsequently challenged chronically on the ear to establish dermatitis. Loss of EPX (in EPX−/− mice) or blocking EPX with the drug resorcinol significantly reduced dermatitis in mice exposed to TMA. Resorcinol also reduced levels of thymic stromal lymphopoietin protein (TSLP) in skin. Further studies showed that EPX increased different cytokines in keratinocytes in cell culture via 2 distinct mechanisms. EPX-induced TSLP expression requires lysophosphatidic acid signaling while EPX-induced expression of TNF-α, CSF2, CSF3, and IL1a required IL-1 signaling. We also showed that blocking IL-1 reduced inflammation in skin following TMA exposure in mice. Thus, EPX is an important mediator of inflammation and itch, that are mediated via at least 2 pathways. This suggests that both EPX and its signaling pathways may provide novel therapeutic strategies in dermatitis.

Technological innovations have improved many barriers in lung transplantation, but high rates of acute and chronic rejection still limit lung allograft survival. This may be explained by the unique environment of the lung. As a mucosal barrier organ, the lung is constantly exposed to the external environment, leading to unique immunological features that are not seen in other transplantable solid organ allografts such as hearts, kidneys, and livers. Thus, the higher rates of rejection and poor long-term survival of lung transplant recipients may stem from the global immunosuppression strategies that are indiscriminately used for all solid organ grafts. Data from our laboratory, and others, have demonstrated that the unique immunoregulatory pathways of the lung may require different strategies for long-term graft survival. For example, depletion of CD8 + T cells typically contributes to the acceptance of transplanted organs. However, these cells facilitate lung allograft acceptance through interferon gamma mediated nitric oxide production. Interestingly CD8 + T cells modify and polarize eosinophils to produce nitric oxide as a means of tolerance induction. Such eosinophils also function to maintain long-term lung allograft acceptance by interfering with humoral alloimmunity. For most other organs eosinophils are suspected to contribute to graft rejection. In this review, we aim to describe the cytokine pathways involved in lung allograft rejection or tolerance, contrast such pathways to those evident in other solid organs, and discuss the need for further studies that can be used to design rational methods for altering the cytokine environment to improve lung allograft survival.

Abstract Food allergy can be life threatening and often develops early in life, especially in infants and children with atopic dermatitis. Food allergy is induced in neonatal mice with skin barrier mutations (Flaky Tail, FT+/− mice with filaggrin and mattrin gene mutations) by epicutaneous sensitization with co-exposures to the food allergen peanut extract (PNE), the environmental allergen Alternaria alternata (Alt), and detergent (4% SDS); oral PNE-challenge induces anaphylaxis. Sensitization in these neonates also induces eosinophil infiltration into the skin and elevates skin expression of eotaxins (CCL11 and CCL24). However, roles for eosinophils in food allergy are not known. In this study, the iPhil+/− FT+/− pups, which have an inducible eosinophil-deficiency upon injection of diphtheria toxin (DTX), were sensitized and then received PNE by gavage to assess anaphylaxis. DTX depletion of eosinophils, during sensitization and oral PNE-challenge, blocked the recruitment and activation of mast cells, blocked the Alt+PNE-induced increase in plasma IL-33 and OSM, attenuated serum PNE-specific IgE/IgG1/IgG2b, and blocked oral-PNE-induced anaphylaxis. Anti-IL-5 depletion of eosinophils during sensitization/challenge also blocked anaphylaxis. When eosinophils were depleted during allergen-skin-sensitization and restored before oral PNE-challenge, anaphylaxis was blocked. In contrast, when eosinophils were present during allergen-skin-sensitization but then depleted during oral PNE-challenge, anaphylaxis was not blocked. Together, these data indicate that although eosinophils are not necessary during oral food allergen-induced anaphylaxis, eosinophils have a critical role during the development of food allergy early in life by regulating the sensitization-induced increase in mast cell numbers and food allergen-specific IgE.

Respiratory failure occurs more frequently after thoracic surgery than abdominal surgery. Although the etiology for this complication is frequently attributed to underlying lung disease present in patients undergoing thoracic surgery, this notion is often unfounded because many patients with normal preoperative pulmonary function often require prolonged oxygen supplementation even after minimal resection of lung tissue. Using a murine model of pulmonary resection and peripheral blood samples from patients undergoing resection of the lung or abdominal organs, we demonstrated that lung surgery initiates a proinflammatory loop that results in damage to the remaining lung tissue, noncardiogenic pulmonary edema, hypoxia, and even death. Specifically, we demonstrated that resection of murine lung tissue increased concentrations of the homeostatic cytokine interleukin-7, which led to local and systemic activation of type 2 innate lymphoid cells. This process activated lung-resident eosinophils and facilitated stress-induced eosinophil maturation in the bone marrow in a granulocyte-macrophage colony-stimulating factor–dependent manner, resulting in systemic eosinophilia in both mice and humans. Up-regulation of inducible nitric oxide synthase in lung-resident eosinophils led to tissue nitrosylation, pulmonary edema, hypoxia, and, at times, death. Disrupting this activation cascade at any stage ameliorated deleterious outcomes and improved survival after lung resection in the mouse model. Our data suggest that repurposing US Food and Drug Administration–approved eosinophil-targeting strategies may potentially offer a therapeutic intervention to improve outcomes for patients who require lung resection for benign or malignant etiology.

Objective Previous studies indicate that eosinophils are recruited into the allograft following orthotopic liver transplantation and protect from ischaemia reperfusion (IR) injury. In the current studies, we aim to explore whether their protective function could outlast during liver repair. Design Eosinophil-deficient mice and adoptive transfer of bone marrow-derived eosinophils (bmEos) were employed to investigate the effects of eosinophils on tissue repair and regeneration after hepatic IR injury. Aside from exogenous cytokine or neutralising antibody treatments, mechanistic studies made use of a panel of mouse models of eosinophil-specific IL-4/IL-13-deletion, cell-specific IL-4rα-deletion in liver macrophages and hepatocytes and macrophage-specific deletion of heparin-binding epidermal growth factor-like growth factor (hb-egf). Result We observed that eosinophils persisted over a week following hepatic IR injury. Their peak accumulation coincided with that of hepatocyte proliferation. Functional studies showed that eosinophil deficiency was associated with a dramatic delay in liver repair, which was normalised by the adoptive transfer of bmEos. Mechanistic studies demonstrated that eosinophil-derived IL-4, but not IL-13, was critically involved in the reparative function of these cells. The data further revealed a selective role of macrophage-dependent IL-4 signalling in liver regeneration. Eosinophil-derived IL-4 stimulated macrophages to produce HB-EGF. Moreover, macrophage-specific hb-egf deletion impaired hepatocyte regeneration after IR injury. Conclusion Together, these studies uncovered an indispensable role of eosinophils in liver repair after acute injury and identified a novel crosstalk between eosinophils and macrophages through the IL-4/HB-EGF axis.

BACKGROUND Obesity is a multifactorial disease with adverse health implications including insulin resistance (IR). In patients with obesity, the presence of high circulating levels of leptin, deemed hyperleptinemia, is associated with IR. Recent data in mice with diet-induced obesity (DIO) show that a partial reduction in leptin levels improves IR. Additional animal studies demonstrate that IL-4 decreases leptin levels. In rodents, resident adipose tissue eosinophils (AT-EOS) are the main source of IL-4 and are instrumental in maintaining metabolic homeostasis. A marked reduction in AT-EOS content is observed in animal models of DIO. These observations have not been explored in humans. METHODS We analyzed AT from individuals with obesity and age-matched lean counterparts for AT-EOS content, IL-4, circulating leptin levels, and measures of IR. RESULTS Our results show that individuals with obesity ( n = 15) had a significant reduction in AT-EOS content ( P < 0.01), decreased AT–IL-4 gene expression ( P = 0.02), and decreased IL-4 plasma levels ( P < 0.05) in addition to expected IR ( P < 0.001) and hyperleptinemia ( P < 0.01) compared with lean subjects ( n = 15). AT-EOS content inversely correlated with BMI ( P = 0.002) and IR ( P = 0.005). Ex vivo AT explants and in vitro cell culture of primary human mature adipocytes exposed to either IL-4 or EOS conditioned media produced less leptin ( P < 0.05). CONCLUSION Our results suggest that IL-4 acts as a link between EOS, AT, and leptin production. Future studies exploring this interaction may identify an avenue for the treatment of obesity and its complications through amelioration of hyperleptinemia. TRIAL REGISTRATION Clinicaltrials.gov NCT02378077 & NCT04234295.

While the function of many leukocytes in transplant biology has been well defined, the role of eosinophils is controversial and remains poorly explored. Conflicting data exist regarding eosinophils’ role in alloimmunity. Due to their prevalence in the lung, and their defined role in other pulmonary pathologies such as asthma, we set out to explore the role of eosinophils in the long-term maintenance of the lung allograft. We noted that depletion of eosinophils results in the generation of donor-specific antibodies. Eosinophil depletion increased memory B cell, plasma cell, and antibody-secreting cell differentiation and resulted in de novo generation of follicular germinal centers. Germinal center formation depended on the expansion of CD4 + Foxp3 – Bcl6 + CXCR5 + PD-1 + T follicular helper (Tfh) cells, which increase in number after eosinophil depletion. Mechanistically, we demonstrate that eosinophils prevent Tfh cell generation by acting as the dominant source of IFN-γ in an established lung allograft, thus facilitating Th1 rather than Tfh polarization of naive CD4 + T cells. Our data thus describe what we believe is a unique and previously unknown role for eosinophils in maintaining allograft tolerance and suggest that indiscriminate administration of eosinophil-lytic corticosteroids for treatment of acute cellular rejection may inadvertently promote humoral alloimmunity.