The mechanism of T-cell mediated cytotoxicity. VII. Lysis of isolated cytoplasts and karyoplasts.

Isolated P815 karyoplasts are up to four times more susceptible to lysis by T cells than intact cells, suggesting that the target cells nucleus or a nuclear associated structure may be particularly sensitive to cell-mediated cytotoxicity. Cytoplasts showed variable susceptibility. The morphological changes seen by time-lapse cinematography show that the first change seen with intact cells is a burst of zeiosis (membrane blebbing), whereas neither cytoplasts nor karyoplasts exhibit zeiosis. These observations suggest that zeiosis results from changes in the cytoskeletal system. This is discussed in relation to the possibility that T cells kill target cells by causing physical damage to a critical organelle inside the cell rather than to the membrane itself.