EROS (Essential for Reactive Oxygen Species) regulates the protein expression of gp91phox in macrophages and neutrophils. gp91phox is an essential membrane-bound component of the phagocyte NADPH oxidase. If EROS or gp91phox are absent, the primary immunodeficiency Chronic Granulomatous Disease (CGD) develops. CGD in EROS deficient patients has additional autoimmune features compared to gp91phox deficient patients, suggesting further functions of EROS besides gp91phox regulation. EROS also regulates the expression of the ATP-gated purinergic receptor P2X7. gp91phox and P2X7 are both involved in various signalling processes in CD4+ T cells, therefore I hypothesised that EROS may too have an effect on CD4+ T cell biology.
This thesis demonstrates that EROS is expressed in CD4+ T cells, and regulates gp91phox and P2X7 expression in these cells. Losing EROS reduces the ATP-driven shedding of CD27, CD62L and IL-6R from the cell surface, and the induction of cell death in CD4+ T cells. EROS deficiency drives Th2 skewing of CD4+ T cells, highlighted by 4-10x fold excess secretion of IL-4, IL-5 and IL-13, and upregulated Rbpj, Plexin d1 and Gata3 expression. P2X7 deficiency or inhibition recapitulates EROS deficiency, but gp91phox deficiency does not, demonstrating that the Th2 phenotype is a P2X7-dependent process. There are more T resident memory (TRM) and Type 2 Innate Lymphoid Cells (ILC2) in EROS deficient mice, however this does not contribute to a more effective Th2-orchestrated immune response. Less IgG1 is secreted in EROS deficient mice, dampening any Th2-driven protection against Helminth parasitic infections. CRISPR-mediated deletion of EROS in human CD4+ T cells demonstrates conservation of function, with decreased P2X7 levels, augmented IL-4 production and impaired surface marker shedding.
Overall, this thesis shows that EROS negatively regulates Th2 immune responses in mouse and human CD4+ T cells by upregulating the expression of P2X7.