Permissive selection followed by affinity-based proliferation of GC light zone B cells dictates cell fate and ensures clonal breadth

• Published in: Proceedings of the National Academy of Sciences - PNAS 2021-01, Vol.118 (2), p.1-12
• Main Authors: Nakagawa, Rinako, Toboso-Navasa, Amparo, Schips, Marta, Young, George, Bhaw-Rosun, Leena, Llorian-Sopena, Miriam, Chakravarty, Probir, Sesay, Abdul Karim, Kassiotis, George, Meyer-Hermann, Michael, Calado, Dinis Pedro
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; B-Lymphocytes - metabolism; Biological Sciences; Cell Differentiation; Cell Proliferation; Cells, Cultured; Clonal Selection, Antigen-Mediated; Female; Germinal Center - immunology; Humans; Lymph Nodes; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Plasma Cells; Receptors, Antigen, B-Cell - genetics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2016425118

Affinity maturation depends on how efficiently germinal centers (GCs) positively select B cells in the light zone (LZ). Positively selected GC B cells recirculate between LZs and dark zones (DZs) and ultimately differentiate into plasmablasts (PBs) and memory B cells (MBCs). Current understanding of the GC reaction presumes that cMyc-dependent positive selection of LZ B cells is a competitive affinity-dependent process; however, this cannot explain the production of GC-derived lower-affinity MBCs or retention of GC B cells with varied affinities. Here, by combining single-cell/bulk RNA sequencing and flow cytometry, we identified and characterized temporally and functionally distinct positively selected cMyc⁺ GC B cell subpopulations. cMyc⁺ LZ B cell subpopulations enriched with either higher- or lower-affinity cells diverged soon after permissive positive selection. The former subpopulation contained PB precursors, whereas the latter comprised less proliferative MBC precursors and future DZ entrants. The overall affinity of future DZ entrants was enhanced in the LZ through preferential proliferation of higher-affinity cells. Concurrently, lower-affinity cells were retained in GCs and protected from apoptosis. These findings redefine positive selection as a dynamic process generating three distinct B cell fates and elucidate how positive selection ensures clonal diversity for broad protection.