Gene expression profiles of peripheral blood mononuclear cells (PBMC) from children with active idiopathic nephrotic syndrome (INS) and healthy controls (HC) [RTXrel_vs_RTXrem]
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. Here, we performed single-cell RNA-sequencing (scRNAseq) on B cells isolated from peripheral blood mononuclear cells (PBMC) collected from four children with INS during the B cell recovery phase of a previous RTX treamtent while in remission or relapse (paired relapse-remisison samples). We show that the post-RTX B cell landscape is overwhelmingly antigen-inexperienced with minimal transcriptomic differences between relapse and remission. However, post-RTX relapses were associated with an early resurgence of an extrafollicular B cell population expressing genes associated with marginal zone B cells (MZB1, CD24, IGHM, CD1C, TNFRSF13B, GPR183). Together, 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 with INS during the B cell recovery phase of previous RTX treatments during relapse and remission. Live B cells were sorted by fluorescence-activated cell sorting (FACS) and analyzed by single-cell RNA-sequencing (scRNAseq).