Gene expression profiles of peripheral blood mononuclear cells (PBMC) from children with active idiopathic nephrotic syndrome (INS) and healthy controls (HC) [HC_vs_INS]
An autoimmune B cell origin for childhood idiopathic nephrotic syndrome (INS) is predicted based on the efficacy of rituximab (RTX) at maintaining long-term remission from proteinuria. Knowledge regarding the nature of the culprit B cell response is very limited. In particular, no transcriptomics work has been performed to evaluate the B cell response in INS. Using single-cell RNA-sequencing (scRNAseq) on peripheral blood mononuclear cells (PBMC) isolated from four affected children with active INS and four age/sex-matched health controls (HC), we demonstrate that a B cell transcriptional program poised for effector functions represents the major immune perturbation in the blood of children with active INS. We show that this nephrotic B cell signature is conferred by the engagement of memory B cells through an extrafollicular developmental route defined by expression of the interfollicular-homing gene GPR183 and the expansion of atypical B cells and marginal zone-like B cells. Moreover, we show that genes involved in APRIL signaling, which promotes extrafollicular antibody-secreting cell development, were substantially upregulated in B cells, monocytes, and dendritic cells from INS children. Collectively, our study provides evidence for an extrafollicular origin for humoral immunity in active INS. Overall design: PBMC were isolated from the blood of four children at either first onset or relapse of INS and four healthy age-matched controls. Live lymphocytes and monocytes were sorted by fluorescence-activated cell sorting (FACS) and analyzed by single-cell RNA-sequencing (scRNAseq).