Interleukin-2-secreting T helper cells promote extra-follicular B cell maturation via intrinsic regulation of a B cell mTOR-AKT-Blimp-1 axis.

During antigen-driven responses, B cells can differentiate at extra-follicular (EF) sites or initiate germinal centers (GCs) in processes that involve interactions with T cells. Here, we examined the roles of interleukin (IL)-2 secreted by T helper (Th) cells during cognate interactions with activated B cells. IL-2 boosted the expansion of EF plasma cells and the secretion of low-mutated immunoglobulin G (IgG). Conversely, genetically disrupting IL-2 expression by CD4 ⁺ T cells, or IL-2 receptor (CD25) expression by B cells, promoted B cell entry into the GC and high-affinity antibody secretion. Mechanistically, IL-2 induced early mTOR activity, expression of the transcriptional regulator IRF4, and metabolic changes in B cells required to form Blimp-1-expressing plasma cells. Thus, T cell help via IL-2 regulates an mTOR-AKT-Blimp-1 axis in activated B cells, providing insight into the mechanisms that determine EF versus GC fates and positioning IL-2 as an early switch controlling plasma cell versus GC B cell commitment.
Competing Interests: Declaration of interests S.C. has consulted for GSK, JP Morgan, Citi, Morgan Stanley, Avalia NZ, Nutcracker Therapeutics, University of California, California State Universities, United Airlines, Adagio, Sanofi, and Roche. W.R.S. is inventor on patent applications related to immunogens in this manuscript filed by Scripps and IAVI. W.R.S. is an employee of Moderna, Inc. S.B. is a current employee of VIR Biotechnology and may possess shares of VIR Biotechnology.
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