GM-CSF/IL-3–deficient mice develop insulitis. (A) Wild-type mouse with normal islets, original magnification × 100. (B) Insulitis and peri-insulitis in GM-CSF/IL-3–deficient mouse, original magnification × 200. (C) B220⁺ B cells in the islets of GM-CSF/IL-3–deficient mouse, original magnification × 400. (D) CD3⁺ T cells in the islets of GM-CSF/IL-3–deficient mouse, original magnification × 400. (E) Insulin-producing β cells in wild-type mouse, original magnification × 200. (F) Decreased insulin-producing β cells in GM-CSF/IL-3–deficient mouse, original magnification × 200. (G) Insulitis with β-cell destruction in GM-CSF/IL-3–deficient mouse, original magnification × 400.