Sandwich ELISA measurements of rhIL-2 concentrations formulated in (A) 680mM ChCl pH7.4, (B) 680mM NaCl pH7.4, (C) 680mM NaDHP pH7.4, and (D) 680mM CDHP pH 7.4 versus no CDHP control (white bars), and heated at temperatures ranging from 45°C to 85°C. Data are expressed as mean relative rhIL-2 concentrations ±SEM, normalized to the initial amount (T0) of protein. n=9; *: p<0.05; **: P<0.01.