Active trans-synaptic capture of membrane fragments by natural killer cells.

Prior to delivery of a lethal hit, NK cells form an immunological synapse to scan the target cells and engage their activatory and inhibitory receptors. Using freshly isolated NK cells, IL-2-activated polyclonal NK bulk or the NKL cell line, we report here that early during this recognition process, human NK cells actively capture target cell membrane fragments. This novel NK cell function occurs via the immunological synapse, is controlled by Src kinase, ATP, Ca(2+) and PKC and involves rearrangements of the actin cytoskeleton. Furthermore, this process is down-regulated by signals emanating from inhibitory NK receptors recognizing protective MHC class I alleles.