CEACAM1-mediated inhibition of IFN-γ secretion from NKT cells. (a) CEACAM1 expression on isolated activated NKT clone. The bold line shows the staining with 5F4 mAb, and the thin line shows the control staining. (b) The amount of IFN-γ in culture supernatant of mAb-treated and untreated NKT clone cells measured by ELISA. The average of two independent experiments is shown. Cross-linking of surface CEACAM1 was performed without (c) or with (d) the Kat4c mAb, and intracellular staining for IFN-γ was performed. One representative experiment is shown out of two performed. Similar results were obtained when other NKT cell clones were used.