STI1 co-registers with PrPC in islets. (a, e, i) PrPC is expressed in non-diabetic, type 1 diabetic INS(+) and type 1 diabetic INS(−) islets. (b, f, j) STI1 is highly expressed in the pancreatic islets of non-diabetic, type 1 diabetic INS(+) and type 1 diabetic INS(−) islets. (d, h, l) We found that STI1 highly co-registers with PrPC in all three groups, as shown in z-stack 3D reconstruction images. (j, k, l) Even with no insulin expression in INS(−) islets, STI1 expression is still evident, with co-registration with glucagon-positive cells (ESM Fig. 6). Scale bars, 20 μm. (m) STIP1 total mRNA levels in type 1 diabetic donors is significantly increased compared with non-diabetic donors 13.42-fold (p ≤ 0.0001). (n) We also compared mRNA levels in AAb+ donors to non-diabetic donors and observed increased STIP1 expression of 2.09-fold (p = 0.0064) compared with non-diabetic donors (white diamond, single AAb+; black diamond, multiple AAb+). *p < 0.05. ND, non-diabetic; T1D, type 1 diabetic