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The interaction of type 1 and 2 IFNs with neutrophils in JSLE Sophie Lindsay Irwin Introduction: Juvenile-onset Systemic Lupus Erythematosus (JSLE) is a multisystem autoimmune disease characterised by an increase in nuclear autoantigens and subsequent increased production in autoantibodies. Neutrophil function and apoptosis is dysregulated in JSLE, and thus neutrophils are thought to be an important factor in JSLE pathogenesis. Type 1 and 2 interferons (IFNs) have been shown to be increased in SLE and JSLE serum, and an IFN and granulocyte genetic signature within JSLE patients has indicated a potential interaction of IFNs and neutrophils within JSLE. However, specific mechanisms of IFNs on neutrophil apoptosis and function within JSLE is yet to be elucidated. Aim: To investigate the interaction of IFNs with neutrophil function, apoptosis and signalling pathways, with specific focus on how these interactions may change in an inflammatory disease such as JSLE. Methods: Neutrophils were isolated from whole blood from healthy adult volunteers and children with and without JSLE. Neutrophils were left na��ve or primed with TNF�� or IFNs, and subsequently stimulated with IFNs and other stimulants. Phagocytosis, apoptosis, activation states and receptor expression were analysed using flow cytometry. Intracellular signalling proteins were analysed using Western blotting. Chemotaxis was analysed using a transwell assay in the presence or absence of chemokines. NETosis was analysed using confocal microscopy and DNA quantification. Results: An in vitro model was developed to investigate the role of IFNs on a range of key neutrophil functions. IFNs were shown to have little effect on specific aspects of chemotaxis, phagocytosis and NETosis of healthy volunteer neutrophils. IFNs were shown to be anti-apoptotic towards na��ve neutrophils from healthy adult volunteers but could either lose this ability or induce apoptosis when neutrophils were primed with TNF��. The anti-apoptotic effect observed was via reduced cleavage of caspase 3 but not through the stability of MCL1. Patient serum (including paediatric control) activated neutrophils from healthy adult volunteers, but this had no significant effect on neutrophil apoptosis downstream. Priming with TNF�� reduced IFNAR1 expression on neutrophils from healthy adult volunteers but did not change the expression of other IFN receptor chains. There was no difference in IFN receptor chain expression on neutrophils from JSLE patients compared to paediatric controls. Following priming with TNF��, there was a reduction of STAT3 phosphorylation and an increase in STAT1 phosphorylation in neutrophils from healthy adult volunteers. Conclusion: IFNs have an important influence on neutrophil apoptosis. In primed neutrophils, lower concentrations of IFNs lose their anti-apoptotic ability and can induce apoptosis at high concentrations. This may reflect what is happening at sites of inflammation in active patients. Drug treatment may help to reduce this potentially IFN-related increase in neutrophil apoptosis in JSLE patients. Patients with inactive JSLE disease, likely due to their medication, had similar rates of apoptosis to matched controls. Activation of healthy adult neutrophils reduced the expression of IFNAR1 alone, which may contribute to the differential IFN induced phosphorylation of anti-apoptotic STAT3 and pro-apoptotic STAT1. This manipulation of the IFN signalling pathway through TNF�� priming (and therefore through activation of neutrophils in inflammatory diseases) may contribute to the dual IFN effect on apoptosis, with STAT1 possibly involved in increased neutrophil apoptosis in JSLE. Inhibition of STAT1 may therefore be therapeutically beneficial in JSLE. |
