Diabetic mice exhibited severe insulitis and loss of immunoreactive insulin in β cells. Thirteen weeks after LCMV or saline injection, the pancreata of nondiabetic (A and B) and diabetic (C and D) mice were dissected, embedded, cross-sectioned, and stained with H&E (A and C). Immunoreactive insulin was detected by using a mouse monoclonal anti–insulin antibody in adjacent sections. This procedure results in a brown reaction product (B and D). The procedure was performed on 3–4 mice per group with similar results.