FIG. 4.

ACP T-cells respond to PI-1(49–61), and full-length C-peptide presented by fixed APCs and the peptide-MHC (pMHC) complexes disassociate rapidly. A: The ACP1.28 T-cell responds well to PI-1(49–61):GDLQTLALEVARQ; however, reactivity was abolished with the loss of the P51Leu or the P61Gln. The ACP2.1 T-cell, in contrast, appeared to tolerate truncations of the flanks and recognized PI-1(49–60):GDLQTLALEVAR rather well and responded weakly to both PI-1(52–61):QTLALEVARQ and PI-1(49–59):GDLQTLALEVA. B: Both ACP1.28 and ACP2.1 responded strongly to fixed APCs pulsed with peptide, indicating that further processing of the peptide was not required. This was true for the PI-1(47–64) and PI-1(49–61) epitopes and the full-length C-peptide-1 molecule (peptide concentration 30 μmol/l; experiments performed in triplicate). C: The stability of the pMHC complexes formed from PI-1(47–64) or C-peptide-1 was examined by adding T-cells to antigen-pulsed and washed APCs over an 8-h time course. The percent maximal response was determined by dividing the T-cell response at T₄ or T₈, in counts per minute by the value achieved when the T-cells were added at T₀. APCs pulsed with either PI-1(47–64) or C-peptide-1 lost 50% of their ability to maximally stimulate T-cells in 3 h, indicating that the pMHC complexes disassociated rapidly on the surface of the APCs.