Group 2 innate lymphoid cells (ILC2) are innate lymphocytes that confer protective type 2 immunity during helminth infection and are also involved in allergic airway inflammation. innate lymphoid cells. RESULTS ILC2 Express T Lineage Genes During early T cell development, bone marrow lymphoid progenitors home to the thymus, Rosiglitazone gradually lose alternative lineage potentials and express T cell genes (Love and Bhandoola, 2011). Once progenitors enter the thymus, T cell-fate specification and commitment are initiated by intrathymic Notch signals that upregulate expression of transcription factors such as TCF-1 and GATA-3 (Rothenberg, 2012). Interestingly, many phenotypic and gene expression similarities between ILC2 and T cells have been noted (Moro et al., 2010; Spits and Cupedo, 2012; Wong et al., 2012). For example, ILC2 from mesenteric fat-associated lymphoid clusters (FALC) express genes characteristic of T cells and T cell progenitors such as and (Moro et al., 2010). Also, ILC2 generated in vitro with OP9-DL1 coculture express (the gene for TCF-1) and (Wong et al., 2012). Therefore, we compared the amount of key T lineage transcription factors and also T cell structural genes in ILC2, DN3 cells, and bone marrow multipotent progenitors. For these experiments, we used ILC2 obtained from the lungs of by ILC2 (see Figure S1 available online). We found that Rosiglitazone lung ILC2 also expressed many other genes that are highly expressed by T-lineage-committed DN3 progenitors. These molecules included the Notch target genes and and the TCR signaling molecule (Figure S1). ILC2 and DN3 cells also expressed comparable amounts of several cytokine receptors, including (Moro et al., 2010; Neill et al., 2010; Price et al., 2010). Therefore, we examined the responses of infection. infection induced the expansion of ILC2 in multiple sites including the BAL, lungs, and mesenteric lymph nodes of WT mice at 10 days postinfection (Figures 3A and 3B). infection, whereas infected was elevated approximately 4.5-fold in and and expression in ILC2. WT and and (Hebenstreit et al., 2008; Hosoya et al., 2009; Zhu et al., 2004). Indeed, and (Figure S3), and the amounts remained lower than those of WT cells in responses to papain challenge (Figure S2). Hence, the few ILC2 that develop in the absence of TCF-1 are functionally compromised. Notch Promotes ILC2 Development We investigated the upstream signals that elicit TCF-1 expression during ILC2 development. Notch signals directly upregulate Rosiglitazone TCF-1 expression during early T cell development (Germar et al., 2011; Weber et al., 2011). Notch also promotes the generation of ILC2 in vitro (Wong et al., 2012); however, a role for Notch in ILC2 development in vivo remains to be established. By using retroviral dominant-negative Mastermind like-1 (dnMAML), a pan-Notch inhibitor (Maillard et al., 2006), we confirmed that Notch signaling is required for ILC2 generation in vivo. DnMAML-expressing multipotent bone marrow progenitors (Lin?Sca-1+Kit+ or LSK cells) failed to efficiently give rise to ILC2 in vivo (Figures 4A and 4B). Cotransduction of retrovirus partially restored the generation of ILC2 from dnMAML-expressing LSK cells (Figures 4A and 4B). To determine whether the ILC2 generated from and dnMAML cotransduced progenitors were functional, we cultured them with the cytokines IL-2, IL-7, and IL-33, which were reported to induce the production of type-2 cytokines by ILC2 (Moro et al., 2010). These cells produced IL-5 and IL-13 (Figure 4C) and expressed (Figure 4D), suggesting they were functional ILC2. Together, these data indicate that TCF-1 acts downstream of Notch signaling during ILC2 development. Figure 4 Notch Promotes ILC2 Development Like is another direct Notch target that is critically involved in early T cell development (Tomita et al., 1999). The expression of during early T cell development does not require TCF-1 (Weber et al., 2011). Because is expressed by ILC2 (Figure S1), we examined whether HES-1 is involved in ILC2 development in vivo. (Goux et al., 2005); however, ectopic expression of BclXL or Bcl2 does not rescue the early T cell development defects in (Figure 5A). These cytokine receptors were previously reported to Rosiglitazone promote the generation or function of ILC2 (Moro et al., 2010; Neill et al., 2010; Wilhelm et al., 2011). GATA-3 is similarly essential for the generation and maintenance of ILC2 (Hoyler et al., 2012; Liang et al., 2012; Mj?sberg et al., 2012). These data indicate that TCF-1 may direct ILC2 development by IL17RC antibody upregulating and important ILC2 cytokine receptor genes. Figure 5 TCF-1 Directly Regulates Expression of in vivo. To further understand the mechanisms by which TCF-1 promotes ILC2 development, we examined whether GATA-3 is required for.