A multi-omics resource of B cell activation reveals genetic mechanisms for immune-mediated diseases

Most genetic variants that confer risk of complex immune-mediated diseases (IMD) affect gene regulation in specific cell types. Their target genes and focus cell types are often unknown, partially because some effects are hidden in untested cell states. B cells play important roles in IMDs, including autoimmune, allergic, infectious, and cancerous diseases. However, despite this established importance, B cell activation states are underrepresented in functional genomics studies. In this study, we obtained B cells from 26 healthy female donors. We stimulated B cells in vitro with six activation conditions targeting key pathways: the B cell receptor (BCR), Toll-like receptor 7 (TLR7), TLR9, CD40, and a cocktail that promotes differentiation into double negative 2 (DN2) IgD ⁻ CD27 ⁻ CD11c ⁺ CD21 ⁻ B cells, a likely pathogenic B cell subset for autoimmunity that is also expanded in infectious diseases. We profiled up to 24 human B cell activation states and up to 5 control conditions using RNA-seq, single-cell RNA-seq coupled with surface protein markers (CITE-seq), and ATAC-seq. We provide an in-depth characterization of how IMD-associated genes responded to stimuli and group into modules with distinct functions. Using high-depth RNA-seq data, we found pervasive splicing effects during B cell activation. Using single-cell data, we describe stimulus-dependent B cell fates. Chromatin data reveal the transcription factors likely involved in stimulus-dependent B cell activation. These open chromatin regions capture a significant proportion of the genetic risk of IMDs and elucidate IMD genetic risk variants with previously unknown function. These data are shared via an interactive browser that can be used to query the dynamics of gene regulation and B cell differentiation during activation by different stimuli, enhancing further investigation of B cells and their role in IMDs.