Allergic diseases, including asthma, atopic dermatitis, and food allergy, are a widespread health issue. The prevalence of these diseases has been increasing, but the mechanism behind this increase and how allergies develop is not well understood. Although the immune system is central to the pathology of allergy, recent work has begun to focus on the contributions of nonimmune processes, including the epithelial barrier, microbiome, and stem cells. IL-33 is a Type 2-associated cytokine that has been described as an “epithelial-derived cytokine”, along with TLSP and IL-25, and has been shown to act as an adjuvant to promote sensitization and elicit eosinophilic inflammation. My work demonstrates two novel functions for IL-33 that contribute to our understanding of allergic disease: supporting the development of eosinophils in the bone marrow and shaping the intestinal microbiome. >It was recently described that the receptor for IL-33, ST2, is expressed on hematopoietic stem cells, where its function remains unclear. Here I demonstrate that IL-33 regulates eosinophil development in bone marrow by supporting early lineage commitment. Initially, I observed that basal eosinophilopoiesis in naïve mice requires IL-33 and ST2. While both IL-33 and IL-5 can expand mature eosinophils (EoM), I found that IL-33 specifically expanded a pool of eosinophil precursors (EoPre) as well as induced upregulation of IL-5Rα on EoPre and expression of IL-5 by bone marrow cells. Serum levels of IL-5 were also increased under this treatment, and neutralizing IL-5 with a blocking antibody ablated the IL-33-induced EoM expansion. The homeostatic hypereosinophilia seen in IL-5–transgenic mice was significantly lower with ST2 deficiency. These findings establish a basal defect in eosinophilopoiesis in IL-33– and ST2-deficient mice and a mechanism whereby IL-33 supports mature eosinophils by driving both systemic IL-5 production and the expansion of IL-5Rα–expressing precursor cells. In addition to the effects seen in the bone marrow, I found that the same IL-33 treatment is sufficient to significantly alter the cecal microbiome. At the phylum level, IL-33 increases the Bacteriodetes and decreases the Firmicutes. Overall, IL-33 significantly altered 69 operational taxon units (OTUs). To determine how IL-33 alters the microbiome, I used a microarray of mast cells treated with IL-33 and identified that the antimicrobial protein lipocalin 2 (Lcn2) is increased. Then I confirmed that IL-33 induces Lcn2 in the serum, lung, and small intestine in vivo as well as dendritic cells and mast cells, but not neutrophils, in vitro. By examining the microbiome of IL-33-treated Lcn2 KO mice and comparing it to WT mice, I determined that there are 29 OTUs that appear to be significantly altered by IL-33 in a Lcn2-dependent fashion. Thus, Lcn2 appears to be one mechanism by which IL-33 alters the microbiome. These data provide a mechanism by which IL-33 disrupts homeostasis of the microbiome by decreasing potentially beneficial bacteria. Collectively, my work defines two novel functions for IL-33 outside of any disease. In the bone marrow, IL-33 acts on eosinophil precursors to promote homeostatic development of eosinophils. In the intestine, IL-33 shapes the microbiome. Thus, IL-33 is central to two distinct processes that can both affect allergic disease. Future work is needed to determine if these novel functions are important in the development of allergy and maintenance of detrimental immune processes within disease.</

Last modified

• 01/29/2019

Creator

• Laura Katrina Ng Johnston

DOI

• https://doi.org/10.21985/N2VT8K

Subject

• Driskill Graduate Training Program in Life Sciences

Keyword

• microbiome
• eosinophils
• ST2
• IL-33
• stem cells
• allergy

Date created

• 2017-01-01

Resource type

• Dissertation

Rights statement

• In Copyright