Differences in Innate immune cell production of IFNα and IFNβ to cell activation in the Autoinflammatory Diseases CANDLE (Chronic Atypical Neutrophilic Dermatosis with Lipodystrophy and Elevated temperature) and SAVI (STING Associated Vasculopathy with Onset in Infancy)

Abstract

Abstract The Type I IFN mediated autoinflammatory diseases SAVI and CANDLE are caused by gain-of-function mutations in Stimulator of Interferon Genes (STING) and loss-of-function mutations in proteasome components. We evaluated the innate immune cellular origin of IFN Type I in SAVI and CANDLE. We examined expression of IFN genes from FACS sorted T, B, NK and monocytes in SAVI (n=5) and CANDLE (n=3) normalized to healthy controls (HC). The Interquartile Range of Type I IFN expression was 78(4–151) and 481-fold(56-38,242) of IFNB1 and 60(3–116) and 0.4-fold(0.1–39) of IFNA7/IFNA17 in CANDLE and SAVI monocytes, respectively. Monocyte depletion reduced IFN message by 90% and FACS analysis confirmed that monocytes and not dendritic cells are the main source of IFNs. The overall mean ratio of IFNβ to IFNα was 989:1 in SAVI and 1.3:1 in CANDLE monocytes. Mean IFNα plasma levels measured by pan IFNα ELISA with 31pg/ml ±58 SEM in CANDLE and 230pg/ml ±112 SEM in SAVI. IP10 serum levels were 2215pg/ml ±702 SEM and 3632pg/ml ±860 SEM in CANDLE and SAVI, respectively. STING pathway activation with cGAMP in the presence of cycloheximide (CHX), a blocker of translational elongation, led to IFNB1 but not IFNA1, 2, 7, 17, 21 while CHX + epoxomicin, a proteasome inhibitor led to transcription of IFNAs and IFNB1 suggesting secondary upregulation of IFNAs in SAVI. Compared to healthy controls, CANDLE and SAVI had increased left-shifted immature CD13lo CD16+ neutrophils (9 and 4-fold, respectively), as well as higher expression of the activation marker CD36+ (6.9 and 6.9-fold, respectively) in total granulocytes. In conclusion, Type I IFN is mainly produced in monocytes and analyses of the IFN signaling in CANDLE and SAVI will allow us to develop improved targeted therapies.