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  • Title: IL-4-secreting secondary T follicular helper (Tfh) cells arise from memory T cells, not persisting Tfh cells, through a B cell-dependent mechanism.
    Author: Fairfax KC, Everts B, Amiel E, Smith AM, Schramm G, Haas H, Randolph GJ, Taylor JJ, Pearce EJ.
    Journal: J Immunol; 2015 Apr 01; 194(7):2999-3010. PubMed ID: 25712216.
    Abstract:
    Humoral immunity requires cross-talk between T follicular helper (Tfh) cells and B cells. Nevertheless, a detailed understanding of this intercellular interaction during secondary immune responses is lacking. We examined this by focusing on the response to a soluble, unadjuvanted, pathogen-derived Ag (soluble extract of Schistosoma mansoni egg [SEA]) that induces type 2 immunity. We found that activated Tfh cells persisted for long periods within germinal centers following primary immunization. However, the magnitude of the secondary response did not appear to depend on pre-existing Tfh cells. Instead, Tfh cell populations expanded through a process that was dependent on memory T cells recruited into the reactive LN, as well as the participation of B cells. We found that, during the secondary response, IL-4 was critical for the expansion of a population of plasmablasts that correlated with increased SEA-specific IgG1 titers. Additionally, following immunization with SEA (but not with an Ag that induced type 1 immunity), IL-4 and IL-21 were coproduced by individual Tfh cells, revealing a potential mechanism through which appropriate class-switching can be coupled to plasmablast proliferation to enforce type 2 immunity. Our findings demonstrate a pivotal role for IL-4 in the interplay between T and B cells during a secondary Th2 response and have significant implications for vaccine design.
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