Blood Leukocyte Characterisation in Eosinophilic Granulomatosis with Polyangiitis (EGPA)

<p dir="ltr">Introduction: Eosinophilic Granulomatosis with Polyangiitis (EGPA) is a rare, autoimmune condition, preceded by asthma and/or chronic rhinosinusitis symptoms, later developing blood and tissue eosinophilia, along with vasculitis and granuloma formation, with multi-organ involvement. Type 2 (T2) immunological processes have not been fully described in EGPA, with functional outputs, such as activation status and cytokine production, only partially investigated.</p><p dir="ltr">Hypothesis: The underlying Type 2 immunological environment in EGPA with Anti-Neutrophil Cytoplasmic Antibody (ANCA) -ve disease is different from Severe Eosinophilic Asthma (SEA) and healthy controls.</p><p dir="ltr">Methods: Cytometry of whole blood was used to assess T2 and non-T2 leukocyte counts and proportions. Intracellular cytokine cytometry of stimulated T2 T cells and Luminex on stimulated PBMC supernatants was used to assess the functional output of these cells. Extracellular markers (CD45RO, CD45RA and Leukocyte Function-associated Antigen-1 (LFA-1)) assessed the activation levels of Innate Lymphoid Cell (ILC) subsets and granulocytes.</p><p dir="ltr">Results: In whole blood, T2 leukocytes were similar between groups, with non-T2 leukocyte populations (B cells, neutrophils, non-Th2 CD183+ CCR6+ cells) being altered in EGPA vs health. Investigation into ILC subsets saw ILC2s and CD183+-expressing ILC1s were significantly decreased in EGPA vs health, with a larger proportion of ILC2s being CD45RO+-matured cells. A greater proportion of PMA/ionomycin-stimulated Th2 cells produced IL-5 and TNFα together in EGPA vs SEA. Lastly, fewer resting blood basophils were activated in EGPA, with trends showing a greater proportion of Prostaglandin D2-stimulated basophils were activated vs health. This was significant for FMLP-stimulated basophils in SEA vs health.</p><p dir="ltr">Discussion: Despite immunosuppressive treatment, T2 cells (Th2, ILC2, basophils) were more activated in EGPA compared to SEA/health. Changes in non-T2 leukocytes (ILC1s, neutrophils, B cells) were also seen in EGPA compared to health. Further research should focus on the contribution of these cells, particularly ILCs, in tissues where disease processes are ongoing.</p>