FSME activated pDCs are potent killer pDCs. NK cells were stimulated with IL-2 and human pDCs were activated overnight with various stimuli as indicated and cocultured with PKH-labeled K562 cells. After 18 hours or 3 days of coculture specific lysis was determined by studying the expression of annexin V and propidium iodide (A) and the absolute number (B) of K562 cells. Data shown are mean values ± SEM of at least 3 independent experiments performed with different donors (*P < .05, **P < .01). (C) FSME activated pDCs were cocultured with PKH67-labeled K562 target cells at an E/T ratio of 20:1 in the presence of either anti-CD56, anti-TRAIL blocking mAb, or the granule exocytosis inhibitor concanamycin A. Parallel experiments were performed using TRAIL isotype-matched control mAbs. Furthermore, K562 cells were cultured in the presence of supernatant derived FSME-pDC cultures or in a transwell assay. (D) PDCs were activated overnight with FSME and cocultured with PKH-labeled K562, Jurkat, MEL624, Daudi, and Glioma cells. (C-D) Specific lysis of target cells was determined after 18 hours of incubation. Data shown are mean values ± SEM of at 3 independent experiments performed with different donors at least in duplo.