T Follicular Helper Cell-Derived IL-4 Is Required for IgE Production during Intestinal Helminth Infection.

IgE production plays a crucial role in protective as well as pathogenic type 2 immune responses. Although the cytokine IL-4 is required for the development of IgE-producing plasma cells, the source of IL-4 and cellular requirements for optimal IgE responses remain unclear. Recent evidence suggests that T follicular helper (Tfh) cells are the primary producer of IL-4 in the reactive lymph node during type 2 immune responses. As Tfh cells are also required for the development of plasmablasts derived from germinal center and extrafollicular sources, we hypothesized that this cell subset is essential for the IgE plasmablast response. In this study, we show that during intestinal helminth infection, IL-4 derived from Tfh cells is required for IgE class switching and plasmablast formation. Notably, early IgE class switching did not require germinal center formation. Additionally, Tfh cell-derived IL-4 was required to maintain the Th2 response in the mesenteric lymph nodes of infected mice. Collectively, our results indicate that IL-4-producing Tfh cells are central orchestrators of the type 2 immune response in the reactive lymph nodes during parasitic helminth infection.