[Immunoelectron microscopic studies on the process of tumor cytolysis mediated by lymphokine activated NK cells]

The second fraction (F2) cells isolated from PBL by discontinuous Percoll density gradient centrifugation were used as the enriched natural killer (NK) cells. After being incubated with rIL2, the activated F2 cells (F2 LAK) acquired the cytolytic ability upon NK resistant tumor cell lines. In F2 LAK, about 45% of the cells were CD16+, therefore F2 LAK were used as the enriched CD16+LAK cells (or lymphokine activated NK cells). The cytolysis process of lung adenocarcinoma LTEPa-2 or K562 tumor cells mediated by CD16+LAK cells were investigated with colloidal gold labelled Ab via scanning and transmission immunoelectron microscopy. The results showed that the CD16+LAK cells extended their protrusions deep into the target cells. Crypts of various diameter and depth were observed on the surface of the target cells with membrane injury at the bottom of the crypts. It was found that the cytoplasmic granules and vacuoles of CD16+LAK cells were concentrated in the area close to the E-T conjugated side, and sometimes the granules were found within the LAK protrusions. The attacked target cells died by apoptosis and necrosis. This study provided direct evidence that lymphokine activated NK cells are effectors of LAK cells.