gms | German Medical Science

Background: Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disorder with dysregulation of both the innate and the adaptive immune system. Toll-like receptors (TLR) play a key role in SLE pathogenesis. TLRs recognize structures that are broadly shared between pathogens and different from host-derived molecules. Nucleic acids are recognized by endosomal TLRs. This triggers type I interferon signaling and phosphorylation of interferon regulatory factors (IRF) to promote antiviral responses. We report two siblings from a consanguineous family suffering from SLE accompanied by thrombocytopenia, severe anemia and hepatosplenomegaly. The aim of this study was to investigate the pathogenetic mechanism in the patients.

Methods: Exome analysis was carried out in both children and their parents. Blood samples and fibroblasts from patients and healthy donors were collected. Concentrations of proinflammatory cytokines in plasma and supernatants of lymphoblastoid cells were determined by bead-based immunoassay. Activation of transcription factors IRF3 and IRF7 in fibroblasts were analyzed by Western blot. Expression of interferon-stimulated genes (ISGs) was measured by qRT-PCR. TLR signaling in patient cells was assessed by stimulation with specific TLR ligands.

Results: Both children demonstrated a high type I interferon signature. We identified a homozygous mutation in a gene known to regulate TLR-function. To further characterize TLR signaling in the family, we analyzed proinflammatory cytokines in plasma of both patients and healthy age-matched controls. The concentrations of IL-6, IL-8, IL-10 and IL-18 were significantly increased indicating an inflammatory response. Lymphoblastoid cells of both patients exhibited increased amounts of IL-6 under basal conditions. After specific stimulation with TLR7, TLR8 and TLR9 ligands, IL-6 production was markedly enhanced in patient cells compared to control cells. In addition, patient fibroblasts showed a constitutive activation of IRF7 that was further amplified after stimulation with TLR7, TLR8 and TLR9 ligands.

Conclusion: Constitutive activation of type I IFN signaling in fibroblasts and enhanced IL-6 production in lymphoblastoid cells in response to TLR7, TLR8 and TLR9 ligands suggest a role of a TLR-dependent cell-intrinsic mechanism as cause of autoimmunity in both children. This data may form the basis for a targeted treatment (against IFNα/β or IL6) in both siblings.