Postnatal neutralizing IL-4 treatment prevents fasting hyperglycemia and loss of β-cell mass in adulthood. Glucose homeostasis and β-cell mass was measured in 6–10-month-old adult animals: (A) fasting blood glucose (n = 8 animals/treatment group); (B) fasting C-peptide levels (picomolar; n = 8 animals/treatment group; (C) islet mass (mg per total pancreas; n = 4 animals/treatment group). Values are ± SEM. *, significant difference at P < 0.05 versus CV; †, significant difference at P < 0.05 versus IV; white circles, CV; black circles, IV; white squares, CIL4; black squares, IIL4; white bars, CV; gray bars, IV; white bars with hatch marks, CIL4; gray bars with hatch marks, IIL4.