Sustained post-developmental T-bet expression is critical for the maintenance of type one innate lymphoid cells in vivo

Abstract

Innate lymphoid cells (ILC) play a significant role in the intestinal immune response and T-bet+ CD127+ group 1 cells (ILC1) have been linked to the pathogenesis of human inflammatory bowel disease (IBD). However, the functional importance of ILC1 in the context of an intact adaptive immune response has been controversial. In this report we demonstrate that induced depletion of T-bet using a Rosa26-Cre-ERT2 model resulted in the loss of intestinal ILC1, pointing to a post-developmental requirement of T-bet expression for these cells. Surprisingly, neither colonic intraepithelial ILC1, colonic lamina propria (cLP) ILC2 nor cLP ILC3 abundance were altered upon induced deletion of T-bet. Furthermore, Th1 polarization was not significantly altered upon induced T-bet deletion in vivo. Mechanistically, we report that STAT1 or STAT4 are not required for intestinal ILC1 development and maintenance. Mice with induced deletion of T-bet and subsequent loss of ILC1 were protected from the induction of severe colitis in vivo. Hence, this study provides support for the clinical development of an IBD treatment based on ILC1 depletion via targeting T-bet or its downstream transcriptional targets.

Transcription factor-driven regulation of ILC1 and ILC3

“…This balance appears to be mediated by the plasticity that has been documented whereby ILC1 differentiation can be achieved from an ILC3 precursor (ILC3-ILC1 plasticity) and vice versa [28,29]. This ILC1:ILC3 balance is well described in human and murine intestines [2,3]; indeed, a balance shift toward ILC1 differentiation was observed in patients with IBD and in mice developing colitis or CRC [8,19,28,29,68,69]. This highlights the importance of regulating the balance between pathogenic ILC1 and ILC3, which appear to have a predominantly protective role.…”

“…Transcriptional control of murine ILC1 and ILC3 maintenance and functionality ILC1 T-bet-dependent ILC1 SI LP ILC1 are absent in Tbx21 -/mice and Ncr1-Cre × Tbx21 fl/fl mice and, overall, their development depends on TF T-bet [10,36,[70][71][72][73] (Box 2 and Figure 1). Intestinal LP ILC1 are also almost absent in the colonic and SI LP if T-bet is temporally ablated in Tbx21 fl/fl × Cre-Ert2 mice [19]. Moreover, NKp46 (encoded by Ncr1) and NK1.1 expression in these ILC1 is diminished shortly after induced depletion of T-bet in these mice, indicating that T-bet promotes their expression [19].…”

“…ILC1 have a beneficial role during the early immune response in mice to Mouse Cytomegalovirus (MCMV) in the liver, to Toxoplasma gondii in the brain, and to epithelial infection with Cryptosporidium parvum, but can also be pathogenic in association with colitis in mouse models, and during IBD in humans [1, 19,28,29,47,48]. The detrimental effect of ILC1 appears to be mediated by the production of IFNγ and TNFα, both of which induce apoptosis of epithelial cells in vitro, which is likely to contribute to disruption of the intestinal barrier in vivo and to microbiota-driven inflammation [9,[49][50][51].…”

“…In terms of lineage markers, the use of CD3 and a B cell marker, such as CD19, is the minimal requirement for detecting ILCs in mouse and human, but it is recommended and practiced in most studies reviewed here to use additional lineage markers targeting macrophages, neutrophils, granulocytes, and platelets. Some studies also use CD5 in the lineage cocktail [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. However, the use of CD5 as a lineage marker is controversial because ILCs have been reported to express CD5, while CD5 + ILCs have also been shown to express αβTCR and have been related to nonfunctional T cells [2,24,25].…”

“…However, the use of CD5 as a lineage marker is controversial because ILCs have been reported to express CD5, while CD5 + ILCs have also been shown to express αβTCR and have been related to nonfunctional T cells [2,24,25]. Furthermore, CD127 is often used as a mouse and human ILC marker; however, CD127 expression in murine ILCs can be lost upon stimulation with IL7 [18][19][20][26][27][28][29][30][31][32][33][34][35]. Similarly, CD90 expression, in particular its high expression, has been used in a few studies to detect ILC3 [12,14,22,[36][37][38][39][40].…”