Antigen-independent, fibroblast-mediated Ttek activation drives acinar dysfunction in Sjögren’s Disease before lymphocytic infiltration

The mechanism of salivary gland (SG) dysfunction in Sjögren’s disease (SjD) is unknown, but is unrelated to SG lymphocytic infiltration. Acinar cells are responsible for saliva manufacture. When we probed the acinar transcriptome in the parotid SG of SjD patients without lymphocytic infiltration (patients with a focus score of 0, “FS0”), we observed acinar gene dysregulation, interferon signature presence and fewer but larger mitochondria than controls. Cell-cell communication analysis suggested that fibroblasts expressing CXCL12 and/or extracellular matrix (ECM) proteins (collagens, laminin, fibronectin) communicate with tissue resident CD8+ T cells (Trm) and/or CD8+ granzyme K+ T cells (“Tteks”), in FS0 SjD SGs. Podoplanin+ and vimentin+ fibroblasts were localized close to CD8+granzyme K+ Tteks in FS0 SjD SGs, amongst acinar cells. CD8+CD27- T cells exposed to CXCL12 and the ECM component collagen increased granzyme K+ expression, without concurrent T cell receptor stimulation. Healthy acinar cells in our organoid culture system exposed to Ttek effector molecules granzyme K and perforin showed both acinar cell gene dysregulation and interferon signature expression. A-Amylase activity assay. We suggest that SG dysfunction in SjD is triggered prior to lymphocytic infiltration by activated fibroblasts, whose expression of CXCL12 and ECM proteins stimulates resident Ttek activation in an antigen-independent fashion. Subsequent granzyme K production by Tteks mediates destruction of acinar cell function and initiation of an interferon signature in acinar cells, setting the stage for development of the later phases of SG pathology in SjD.