Confirmation of peptide-specificity of isolated CD4⁺ T-cell clones. Clonal CD4⁺ T cells were cocultured for 36 hours with 50 000 peptide-pulsed B lymphoblasts and assayed for IFNγ secretion with the ELISPOT assay technique. HPA-1a–derived peptide L33, but not peptide Lol P1, induced IFNγ secretion. Duplicate assays are shown. Two hundred T cells were assayed per well of clones D7T1 and D7T4, and the number of D7T5, D7T8, and D7T9 was not determined. Wells marked “APC only” contained peptide-pulsed B lymphoblasts and no T cells. APC indicates antigen-presenting cell.