Peptides corresponding to the MHC class II and the putative CD1 regions binding to CD4 affect effector responses and TCR engagement of CD4 ⁺ iNKT cells. (A) iNKT cell clones CD4 ⁺ 20.49 (closed symbols) and DN 20.22 (open symbols) were pre-incubated with grading doses of DR or CD1 peptides for 1 hour at 37°C, washed, and subsequently cocultured with HeLa CD1d cells pre-loaded with α-GalCer (10⁻¹ μg/mL). After 20 hours, IL-4 (triangles) and IFN-γ (squares) released in the supernatants were titrated by enzyme-linked immunosorbent assay. Data represent the average value of duplicate samples ± SD and are representative of at least 3 independent experiments. (B) α-GalCer–loaded CD1d tetramer binding to iNKT cell clones 20.22 and 20.49 in the absence (filled histograms) or presence of DR (shaded histograms) and CD1 peptides (open histograms). One representative experiment (of 3) is shown.