Abstract GATA3 is an important transcription factor for the development of CD4 T cells and innate lymphoid cells (ILCs); it is also essential for the differentiation and function of Th2 cells and ILC2s. To understand the physiological role of GATA3 in these cells particularly in vivo, we have generated a novel GATA3 reporter mouse strain by inserting the ZsGreen-T2A cassette in front of the translation initiation site of the Gata3 allele already carrying two loxp sites which allow inducible Gata3 deletion when it is crossed to the CreERT2 transgenic mouse strain. Our initial experiments with this mouse line showed that the reporter expression faithfully reflects the GATA3 protein expression in both in vitro differentiated Th subsets and in vivo isolated T cells and ILCs. Furthermore, the reporter expression was still observed even when the Gata3 exon 4 (encoding zinc fingers) was deleted by tamoxifen treatment. Thus, this novel mouse model will allow us to separate GATA3-deficient “Th2” cells and “ILC2s” during in vivo immune responses. We are now using this reporter system to explore the role of GATA3 in various cells types generated in vivo by comparing GATA3-sufficient and GATA3-deficient reporter positive cells.