NKp44L is a cell-surface ligand for NKp44. (A) Cell-surface expression of NKp44L was assessed by flow cytometry. The indicated tumor cell lines or primary PBMC were stained either with anti-NKp44L mAb and the NKp44-Ig fusion protein (bold lines) or with the corresponding controls (gray histograms). Data are representative of at least 3 independent experiments. (B) Cell-surface expression of NKp44L on kidney (from 3 different patients: patients 1, 2, and 3) and bladder cell carcinoma from primary biopsies. Tumor single-cell suspensions were stained with anti-NKp44L (bold lines), or with control (gray histograms). (C) NKp44L expression on mouse EL4-transfected cells. EL4 cells were stably transfected with the full-length (FL) sequence, the C-terminal-deleted (Δ21spe) sequence of NKp44L, or a control vector (Ctl). Transfected cells were drug-selected and then tested by flow cytometry with anti-NKp44L mAb (bold lines), or control (gray histograms). Two independent cell populations (FL-A and FL-B) expressing the full-length sequence of NKp44L were tested. (D) Blocking experiment on WM1361 cells. (Left panel) Staining with the anti-NKp44L mAb (bold line) or its IgM isotype control (grey histogram). (Right panel) Staining with the NKp44-Ig fusion protein, alone or in the presence of anti-NKp44L mAb (bold lines). IgG isotype control staining (grey histogram), serves as control.