CEACAM1-mediated inhibition of decidual NK cytotoxicity. Decidual NK clones were stained for CEACAM1 expression. (a) CEACAM1 staining of decidual NK clone 17 using the anti-CEACAM1 mAb 5F4 (bold line). The thin line shows the control staining. (b) Killing and inhibition of NK clone 17 by .221 cells and by .221 cells transfected with CEACAM1 (.221/CEACAM1). Blocking experiments were performed using 40 μl/ml of anti-CEACAM antibodies. Average of three independent experiments is shown. Similar results were obtained when other CEACAM1+ NK clones were used.