Specific pre-plasma cell states and local proliferation at the dark zone – medulla interface characterize germinal center-derived plasma cell differentiation in lymph node (Figure 4 and Figure 5)

High affinity antibody-producing plasma cell (PC) production in germinal centers (GC) is crucial for antibody-mediated immune protection after vaccination or infection. The selection of high affinity B cells in the GC light zone instructs PC differentiation in a subset of cells, but the phenotype, differentiation trajectory and spatial localization of those prePC intermediates remain to be characterized. Here, we have used a mouse model to track GC-derived B cells with integrative single-cell and spatial analyses in draining lymph node after immunization. We first identified putative prePC in scRNA-seq datasets, then enriched those cells through their specific surface phenotype for further analysis of their gene expression trajectories and BCR repertoire. We found a continuum of actively proliferating transitional states bridging selected LZ GC B cells and recently exported PCs, with gradually increasing levels of endoplasmic reticulum stress-associated genes and immunoglobulin transcripts. Spatial analyses revealed that recently differentiated PC continued their maturation and proliferation at the interface between the DZ and extensions of the lymph node medulla. Our results provide insights into the intermediate stages and microenvironmental factors involved in the differentiation of GC B cells into PC, with implications for vaccine development and understanding antibody responses. C57BL/6 mice were immunized with NP-KLH in Sigma Adjuvant System, and we investigated cells 4 days after tamoxifen gavage, at day 15 of the primary response.