Extended Data Fig. 5: The mITGB1 epitope is presented on I-A^b.

a, T3 CD4⁺ T cell hybridomas were stimulated with 2 μg ml⁻¹ mITGB1(710Y) or wild-type ITGB1(710N) peptide-pulsed splenocytes. Activation was measured by CTLL assay. Representative data from three independent hybridoma lines are shown as average of technical replicate wells. b, Mapping of the mITGB1 MHC-II binding core was performed using the CD4⁺ T cell hybridoma line 41 stimulated with naive splenocytes pulsed with 2 μg ml⁻¹ of overlapping peptides covering mITGB1_697–724. Red denotes the T3-specific mutant amino acid at position p1 of the minimal epitope; underlining denotes the validated binding core. Green amino acids represent random residue substitutions used to specifically define valines at residues 715 and 718 as the p6 and p9 MHC-II binding positions and the complete MHC-II binding core. Representative data from two independent experiments are shown as the average of technical triplicate wells. c, MHC-II I-A^b staining of parental T3 cells, IFNγ-stimulated T3 cells and T3 cells transduced with a vector encoding CIITA (T3.CIITA). Representative data from one of three independent experiments are shown. d, Mirror plot showing match between MS/MS spectra of the 14-mer peptide sequence encompassing the N710Y site of mITGB1 eluted from T3.CIITA cells (positive axis) and a corresponding synthetic peptide (negative axis). Labelled m/z values reflect those experimentally observed for the endogenous peptide, with peaks representing b ions highlighted in blue and y ions in red.

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