Extended Data Fig. 4: Analysis of the immunogenic segment in InsC peptides.

a, ELISPOT assay showing IFN-γ and IL-2 production by CD4⁺ T cells from 8-week old male NOD mice immunized with two Ins1C peptides lacking the complete C-terminus upon recalling with indicated relevant peptides. Responses to either Ins1C:41-55 (left) or Ins1C:37-56 (right) were indistinguishable from background (no antigen); the positive control (ConA) generated strong responses. Data (mean ± s.e.m.) summarize results from n = 3 independent experiments from n = 6 mice. b, The mass spectrometry spectrum of the synthetic citrullinated Ins1C:53-61 peptide (TLALEVArQ; the lowercase r indicates the presence of citrulline). This spectrum was distinct from the deamidated Ins1C:53-61E peptide found in the islet MHCII peptidome, confirming that the biologically induced PTM was deamidation but not citrullination.