Dynamic chromatin accessibility licenses STAT5- and STAT6-dependent innate-like function of TH9 cells to promote allergic inflammation

Allergic diseases are a major global health issue. Interleukin (IL)-9-producing helper T (TH9) cells promote allergic inflammation, yet TH9 cell effector functions are incompletely understood because their lineage instability makes them challenging to study. Here we found that resting TH9 cells produced IL-9 independently of T cell receptor (TCR) restimulation, due to STAT5- and STAT6-dependent bystander activation. This mechanism was seen in circulating cells from allergic patients and was restricted to recently activated cells. STAT5-dependent Il9/IL9 regulatory elements underwent remodeling over time, inactivating the locus. A broader 'allergic TH9' transcriptomic and epigenomic program was also unstable. In vivo, TH9 cells induced airway inflammation via TCR-independent, STAT-dependent mechanisms. In allergic patients, TH9 cell expansion was associated with responsiveness to JAK inhibitors. These findings suggest that TH9 cell instability is a negative checkpoint on bystander activation that breaks down in allergy and that JAK inhibitors should be considered for allergic patients with TH9 cell expansion.

Crosstalk between ILC2s and Th2 cells varies among mouse models

Type 2 T helper (Th2) cells and group 2 innate lymphoid cells (ILC2s) provide protection against helminth infection and are involved in allergic responses. However, their relative importance and crosstalk during type 2 immune responses are still controversial. By generating and utilizing mouse strains that are deficient in either ILC2s or Th2 cells, we report that interleukin (IL)-33-mediated ILC2 activation promotes the Th2 cell response to papain; however, the Th2 cell response to ovalbumin (OVA)/alum immunization is thymic stromal lymphopoietin (TSLP) dependent but independent of ILC2s. During helminth infection, ILC2s and Th2 cells collaborate at different phases of the immune responses. Th2 cells, mainly through IL-4 production, induce the expression of IL-25, IL-33, and TSLP, among which IL-25 and IL-33 redundantly promote ILC2 expansion. Thus, while Th2 cell differentiation can occur independently of ILC2s, activation of ILC2s may promote Th2 responses, and Th2 cells can expand ILC2s by inducing type 2 alarmins.

Gata3 ZsG and Gata3 ZsG-fl: Novel murine Gata3 reporter alleles for identifying and studying Th2 cells and ILC2s in vivo

T helper-2 (Th2) cells and type 2 innate lymphoid cells (ILC2s) play crucial roles during type 2 immune responses; the transcription factor GATA3 is essential for the differentiation and functions of these cell types. It has been demonstrated that GATA3 is critical for maintaining Th2 and ILC2 phenotype in vitro; GATA3 not only positively regulates type 2 lymphocyte-associated genes, it also negatively regulates many genes associated with other lineages. However, such functions cannot be easily verified in vivo because the expression of the markers for identifying Th2 and ILC2s depends on GATA3. Thus, whether Th2 cells and ILC2s disappear after Gata3 deletion or these Gata3-deleted "Th2 cells" or "ILC2s" acquire an alternative lineage fate is unknown. In this study, we generated novel GATA3 reporter mouse strains carrying the Gata3 ZsG or Gata3 ZsG-fl allele. This was achieved by inserting a ZsGreen-T2A cassette at the translation initiation site of either the wild type Gata3 allele or the modified Gata3 allele which carries two loxP sites flanking the exon 4. ZsGreen faithfully reflected the endogenous GATA3 protein expression in Th2 cells and ILC2s both in vitro and in vivo. These reporter mice also allowed us to visualize Th2 cells and ILC2s in vivo. An inducible Gata3 deletion system was created by crossing Gata3 ZsG-fl/fl mice with a tamoxifen-inducible Cre. Continuous expression of ZsGreen even after the Gata3 exon 4 deletion was noted, which allows us to isolate and monitor GATA3-deficient "Th2" cells and "ILC2s" during in vivo immune responses. Our results not only indicated that functional GATA3 is dispensable for regulating its own expression in mature type 2 lymphocytes, but also revealed that GATA3-deficient "ILC2s" might be much more stable in vivo than in vitro. Overall, the generation of these novel GATA3 reporters will provide valuable research tools to the scientific community in investigating type 2 immune responses in vivo.

Gata3 plays a supportive role for the development of Tbet-expressing Th17 cells in EAE

IFNg+IL-17A+(or Tbet+RORgt+) Th17 cells are known to be key players in the pathology of experimental autoimmune encephalomyelitis (EAE), however the dynamics and overall stability of Tbet+ Th17 cells is less clear. Recent data from our lab (Zhong, C. et.al. 2016) has demonstrated that Gata3 plays a role in deciding the balance between Tbet and RORgt expression in gut NKp46+ ILC3 cells. Here, we hypothesized that Gata3 might be expressed by Th17 cell subsets during EAE, and that Gata3 expression would affect the generation or functionality of Tbet-expressing Th17 cells. Surprisingly, we found that all differentiating polyclonal and 2D2 transgenic Th17 cells upregulate Gata3 and subsequently maintain low levels of Gata3 thereafter, both in vitro and in vivo. Additionally, the re-stimulation or re-polarization of Th17 cells does not further affect Gata3 expression, reaffirming that Gata3 is induced during de novo Th17 polarization. To examine how the loss of Gata3 might affect the generation of Th17 or Tbet+ Th17 cells in EAE, we utilized complimentary Gata3 conditional knockout models. In a tamoxifen-inducible Gata3 knockout system, Tamoxifen treated CreERT2 Gata3Fl/Flmice (d6 P.I.) were resistant to EAE, and failed to mount a robust Tbet+Th17 response in comparison to vehicle controls. Similarly, Tbet-dependent Gata3 knockout Tbx21CreGata3Fl/Flmice failed to mount a robust Tbet+ Th17 response in the dLN or CNS, and were resistant to EAE symptoms in active and passive EAE models. Together, these data suggest that while all Th17 cells induce and maintain Gata3 expression, Tbet+ Th17 cells require Gata3 for their generation and survival in EAE.

This research was supported by the Intramural Research Program of NIAID, NIH.