"A close examination of the IL-2–IL-2Rα binding interface reveals a putative “pH Switch” consisting of the interaction between Arg38 in IL-2 and His120 in IL-2Rα (Fig. 2F). We hypothesized that, at the low pH in the TME, His120 would become protonated, resulting in release of IL-2 from IL-2Rα and therefore lack of signaling."