Islet Autoimmunity Is Highly Prevalent and Associated With Diminished β-Cell Function in Patients With Type 2 Diabetes in the GRADE Study

Islet autoimmunity may contribute to β-cell dysfunction in type 2 diabetes (T2D). Its prevalence and clinical significance have not been rigorously determined. In this ancillary study to the Glycemia Reduction Approaches in Diabetes: A Comparative Effectiveness Study (GRADE), we investigated the prevalence of cellular and humoral islet autoimmunity in patients with T2D duration of 4.0 ± 3.0 years (HbA_1c 7.5 ± 0.5% on metformin alone). We measured T-cell autoreactivity against islet proteins, islet autoantibodies against 65-kDa GAD antigen, IA-2, and zinc transporter-8, and β-cell function. Cellular islet autoimmunity was present in 41.3%, humoral islet autoimmunity in 13.5%, and both in 5.3%. β-Cell function calculated as incremental area under the curve of glucose from 0–120 min (iAUC-CG) and ΔC-peptide(0–30)/Δglucose(0–30) from an oral glucose tolerance test was lower among T-cell–positive (T⁺) than T-cell–negative (T⁻) individuals using two different adjustments for insulin sensitivity (iAUC-CG: 13.2% [95% CI 0.3, 24.4] or 11.4% [95% CI 0.4, 21.2] lower; ΔC-peptide[0–30]/Δglucose[0–30]: 19% [95% CI 3.1, 32.3] or 17.7% [95% CI 2.6, 30.5%] lower). T⁺ patients had 17% higher HbA_1c (95% CI 0.07, 0.28) and 7.7 mg/dL higher fasting plasma glucose levels (95% CI 0.2, 15.3) than T⁻ patients. We conclude that islet autoimmunity is much more prevalent in patients with T2D than previously reported. T-cell–mediated autoimmunity is associated with diminished β-cell function and worse glycemic control.