CD19 and juvenile dermatomyositis: To define possible mechanisms upstream of the strong IFN type 1 signature and identify a transcriptional signature associated with immune dysfunction in JDM, we performed gene expression profiling on isolated CD4+T cells, CD8+T cells, CD19+B cells and CD14+monocytes from PBMC collected from JDM patients naïve to treatment (pre-treatment), at ~12 months on-treatment and age-matched controls (For demographics see online supplemental table 4).