Peripheral blood samples were collected once from 8 individuals including 6 children with JIA and 2 young adult female healthy controls (Table 1, for participant attributes). For each participant, separate 1-mL cultures of peripheral blood were incubated with or without TNF activation for 24 h at 37 °C, after which an aliquot was used for single cell RNA sequencing on the 10X Genomics Chromium platform. Here, TNF is linked to juvenile idiopathic arthritis.