Dysregulated NK cell PLCγ2 signaling and activity in juvenile dermatomyositis

Juvenile dermatomyositis (JDM) is a debilitating pediatric autoimmune disease manifesting with characteristic rash and muscle weakness. To delineate signaling abnormalities in JDM, mass cytometry was performed with PBMCs from treatment-naive JDM patients and controls. NK cell percentages were lower while frequencies of naive B cells and naive CD4(+) T cells were higher in JDM patients than in controls. These cell frequency differences were attenuated with cessation of active disease. A large number of signaling differences were identified in treatment-naive JDM patients compared with controls. Classification models incorporating feature selection demonstrated that differences in phospholipase C gamma 2 (PLC gamma 2) phosphorylation comprised 10 of 12 features (i.e., phosphoprotein in a specific immune cell subset) distinguishing the 2 groups. Because NK cells represented 5 of these 12 features, further studies focused on the PLC gamma 2 pathway in NK cells, which is responsible for stimulating calcium flux and cytotoxic granule movement. No differences were detected in upstream signaling or total PLC gamma 2 protein levels. Hypophosphorylation of PLC gamma 2 and downstream mitogen-activated protein kinase-activated protein kinase 2 were partially attenuated with cessation of active disease. PLC gamma 2 hypophosphorylation in treatment-naive JDM patients resulted in decreased calcium flux. The identification of dysregulation of PLC gamma 2 phosphorylation and decreased calcium flux in NK cells provides potential mechanistic insight into JDM pathogenesis.