Browsing by Author "Dell'Aringa, Mark"

Over 1.5 billion individuals are infected with intestinal helminths worldwide, with a majority of those infected living in developing nations. In developed nations intestinal helminth infections are very rare, while incidences of allergy and asthma are common. The incidence of allergic afflictions is growing rapidly every year. Both clearance of helminth infections and propagation of allergic disease are mediated by type 2 immune responses. The cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13) play major roles in the propagation of type 2 immune responses. IL-4 and IL-13 are produced by a number of immune cells, within both the innate and adaptive arms of immunity, that are important in driving allergic responses.

CD4+ T follicular helper (Tfh) cells reside in the B-cell follicle and specialize in aiding the maturation of germinal center (GC) B cells. IL-4 produced by Tfh cells is required for GC B cell Immunoglobulin (Ig) class switching to type-2 isotypes, IgE and IgG1. IgE serves as a critical mediator of type-2 immune responses. CD4+ T helper 2 (Th2) cells localize to the periphery at sites of infection and damage. Th2 cells make both IL-4 and IL-13 cytokines. Th2 cells, along with multiple innate cell types, are critical for driving the peripheral hallmarks of type-2 immune responses, including mucus production and smooth muscle contractility.

Elucidating the pathways that regulate the differentiation, function, and maintenance of Tfh and Th2 cells is critically important for discovering potential therapies for allergic disease and helminth infections. Notch signaling is capable of driving Th2 IL-4 production and differentiation in vitro. However, the in vivo role for Notch signaling in Th2 populations remains unclear. The mechanisms controlling Tfh IL-4 production are largely unknown. Given that Notch signaling is required for the differentiation of Tfh cells and is known to influence cytokine production in T cells, we hypothesized that Notch signaling also plays an important role in regulating the function of Tfh cells. Nippostrongylus brasiliensis infection drives a robust type-2 immune response and allows for analysis of both Tfh and Th2 cells. Here, infection with N. brasiliensis was used to characterize whether Notch signaling is required for Th2 and Tfh differentiation and function in vivo.

Deletion of Notch receptors on T cells of infected mice results in reduced IL-4 producing Tfh, but not Th2 cells. As a result, we saw impairments in overall Tfh functionality while peripheral Th2 immunity remained intact. Notch deficient T cells had major impairments in Tfh, but not Th2, cell differentiation. Overexpression of Notch signaling in CD4+ T cells leads to increased IL-4 production by Tfh cells, but not Th2 cells. Furthermore, we identified that conventional dendritic cells (cDCs) do play a role as sources for Notch ligand early during the immune response. However, neither cDCs or follicular dendritic cells (FDCs) are essential sources of Notch ligand to drive Tfh cell differentiation.

While Notch signaling is critical for Tfh differentiation, it is not known if Notch signaling plays a continued role beyond Tfh differentiation. We used pharmacologic inhibition of Notch signaling to assess a role for Notch in Tfh maintenance. Here, we show that inhibition of Notch signaling after Tfh differentiation results in altered expression and activity of important trafficking receptors. This change was accompanied by aberrant localization of IL-4 expressing T cells in the lymph node. Additionally, late Notch inhibition resulted in an altered transcriptional program in Tfh cells. These findings suggest that Notch signaling plays a critical role in Tfh, but not Th2 driven immunity. In total, the data shown here demonstrate that Notch signaling is not only important for Tfh differentiation, but also for regulating Tfh cell fate, function, and maintenance.