Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disease (AID) that presents similar characteristics to systemic lupus erythematosus. These characteristics include pathophysiology and genetic factors. Our team and other groups have highlighted an interferon (IFN) signature in salivary glands and PBMCs from patients with Sjögren syndrome. This signature demonstrates new pathways in pSS and lupus, focusing research on innate immunity and in the IFN pathway.We have confirmed the implication of 2 genes in the pSS, and these genes are involved in the IFN pathway. The first gene is IRF5 which is in the type I IFN pathway and the second is STAT4 which is in the type II IFN pathway. We have shown a functional consequence of IRF5 at-risk allele. Regarding STAT4, the associated SNP did not altered STAT4 mRNA expression but was highly correlated with type I IFN genes expression.The epigenetic deregulation could play a triggering role in autoimmune diseases, particularly through DNA methylation which is highly implicated in the suppression of gene expression. We studied the methylation of IRF5 promoter and found no methylation. Our team is currently undertaking a global approach with methylome analysis. This methylome study will assess specific gene methylation patterns and will allow a better understanding of the role of these genes in autoimmune diseases.We further demonstrated that IL-12 specifically induces a type I IFN signature through a CD4+ T cells and pDCs crosstalk. These results could explain the implication of STAT4 polymorphism not only in type II IFN-dependent AIDs but also in type I IFN-dependent AIDs. Our data confirm that type I IFN- and type II IFN-mediated AIDs do not have to be opposed. They are only the yin and the yang of a common STAT4 activation which may induce secretion of both cytokines.
