In the four type 1 diabetes samples exhibiting compartmentalisation of T cells and B cells in association with insulin-positive (from donors no. 6362, no. E308 and no. E124B) and insulin-negative islets (from donor no. SC115) (Table 3 and ESM Fig. 4), the T cell compartment contained a dense RF network visualised by collagen VI staining and the B cell zone showed less-dense RFs and the presence of CD21+ FDCs (Fig. 7a and ESM Fig. 4), similarly to inflamed islets from NOD mice (Fig. 7b). Here, INS is linked to type 1 diabetes mellitus.