To determine whether the differentiation of IL-4–expressing cells from Foxp3RFP+CD25high T reg cells occurred in lympho-complete environments, we generated a fate-reporter system by crossing Foxp3YFP/Cre (Rubtsov et al., 2008) and R26RFP635 (Coomes et al., 2015) mice on an Il4GFP background (Mohrs et al., 2001) to generate Il4GFPFoxp3YFP/CreR26RFP635 mice, allowing us to identify whether Il4GFP+ Th2 cells originated from Foxp3YFP+ cells (Il4GFP+Foxp3FATE+) during Hp 1° and Hp 2° infection (Fig. 4, A and B, left). Here, HP is linked to infection.