Dynamic polarization of the microtubule cytoskeleton during CTL-mediated killing.

Efficient unidirectional killing by cytotoxic T lymphocytes (CTL) requires translocation of the microtubule organizing center (MTOC) to the target cell contact site. Here we utilize modulated polarization microscopy and computerized 3D reconstruction of tubulin and LFA-1 immunofluorescence images to investigate how this is accomplished. The results show that the MTOC is drawn vectorially to the contact site by a microtubule sliding mechanism. Once the MTOC arrives at the contact site, it oscillates laterally. Microtubules loop through and anchor to a ring-shaped zone (pSMAC) defined by the dense clustering of LFA-1 at the target contact site. Microtubules that run straight between the MTOC and pSMAC and then turn sharply may indicate the action of a microtubule motor such as dynein.