BACKGROUND: 5-10% of patients with asthma have severe disease. Many patients experience persistent symptoms despite being T2-low. Obesity is associated with increased asthma symptoms. Eicosanoids have well-described roles in the pathophysiology of asthma and may contribute to persistent symptoms in T2-low severe asthma. OBJECTIVE: To examine the relationship between urinary eicosanoids, asthma symptoms, obesity and T2-biomarkers in severe asthma. METHODS: Urine samples were collected during a randomized controlled trial assessing corticosteroid optimization using T2-biomarker directed care at scheduled study visits (n=728) and at exacerbation (n=103). Eicosanoid concentrations were quantified from urine samples using mass-spectrometry. Metabolite concentrations were log 2-transformed, z-scored and concentrated by pathway to generate 6 pathway scores. Results were stratified by T2-biomarker status (T2-Low: fractional-exhaled nitric-oxide [FeNO]<20ppb AND blood eosinophil count [BEC]<0.15x10 9cells/L) vs T2-high: (FeNO≥20ppb AND BEC≥0.15x10 9cells/L), symptoms (symptom-low: Asthma control Questionnaire-7 (ACQ-7)<1.5)] vs symptom-high [ACQ-7≥1.5]), and obesity. RESULTS: The cysteinyl-leukotriene (CysLT) pathway score was elevated in T2-high versus T2-low participants (P=0.0007), regardless of symptom burden. The isoprostane pathway score was higher in symptom-high versus symptom-low participants, regardless of T2-status (P=0.01). Higher isoprostane (P=0.02) and thromboxane (P=0.04) pathway scores were associated with increased symptoms in T2-low participants. Corticosteroid exposure, obesity and exacerbations were not associated with raised pathway scores (P≥0.05). CONCLUSION: Thromboxane pathway metabolites were elevated in symptom-high/T2-low participants whereas isoprostane pathway metabolites were associated with increased symptoms, regardless of T2-status. These pathways are not affected by CS exposure. Further research is needed to define the role of eicosanoids in T2-low severe asthma using interventions to perturb these pathways.

Background Activation of mast cells through IgE results in secretion and shedding of mast cell proteins and in vivo models suggest that these processes are governed by IgE antibody affinity. Methods We passively sensitized cultured primary human mast cells with recombinant human IgE clones with either high or low affinity for Der p 2, with a 200-fold affinity difference, and activated them with recombinant allergen. Activation was assessed by CD63 upregulation and PGD 2 secretion. Supernatants collected from mast cells activated for 0, 3, 6 and 24 hours were assessed for PGD 2 and inflammatory mediators on the OLINK platform at repeated time points. Results CD63 upregulation and PGD 2 synthesis scaled with affinity, as did secretion of cytokines like IL-8 and IL-13. Secretion of chemokines like CCL3 and CCL4 appeared to depend less on affinity, whereas shedding of surface markers CD40, SLAMF4 and CD5, and secretion of intracellular markers SIRT2 and CASP-8, were elevated by stimulation through low affinity IgE compared with high affinity IgE, illustrating differential responses dependent on the affinity of IgE. Conclusion Cytokine secretion and shedding of surface receptors of sensitized, cultured primary human mast cells is differentially regulated depending on the affinity of IgE for the Der p 2 allergen and may shape the chronic response to repeated allergic activation.