Lung disease is a severe and often fatal complication of systemic JIA. Despite this, little is known about how the immune cells are different in children who develop lung disease compared to those who do not. We have received immune cell samples from 35 children with SJIA-LD in the CARRA Registry. We propose this CARRA Data Analysis Support grant to complete analysis of this data and rapidly move to publication. Aim 1 will use multiple approaches to find differing immune cell populations in children with SJIA-LD. Aim 2 will examine how these populations compare to lung disease activity. This grant will provide essential support to complete the project. This will help aid in early detection of SJIA-LD, and to understanding the cause of this complication. These outcomes will impact the lives of children and families with SJIA-LD, and help screen for lung disease in all SJIA patients.