Blocking CD4 inhibits antigen-specific activation of CD4 ⁺ iNKT cell clones. The CD4⁺ iNKT cell clones LP16DC1 and LP16DC7 were cultured in duplicate wells at 2:1 ratio with C1R-CD1d transfectants, pulsed with α-GalCer. Cultures received nothing (nil), isotype-matched control IgG (IgG), or the anti-CD4 mAb S3.5 (anti-CD4). After 48 hours, supernatants were collected and tested by enzyme-linked immunosorbent assay for the content of IFN-γ or IL-4. One representative experiment of 3 is shown. Similar data were obtained by using the anti-CD4 6D10 blocking mAb.