When T cells, B cells, and natural killer (NK) cells of the immune system interact with target cells, plasma membrane signaling molecules accumulate at the cell-cell interaction site: the immunological synapse. It seems that proteins, as well as signals, are transferred between the interacting cells at such contacts. NK cells receive inhibitory signals from cells that express self major histocompatibility complex (MHC) molecules on their surface, and the NK cells can actually acquire MHC class I proteins during these interactions with target cells. Now Vanherberghen et al. show that the exchange goes both ways and that NK receptors are transferred only to target cells that express MHC class I ligands. The NK cell receptor Ly49A was transferred only to target cells that expressed the cognate MHC class I ligand. It is not yet clear what function the transferred receptor might serve, but it is possible that the NK receptor might mark a target cell that has already been scanned by a NK cell. This, in turn, might allow more efficient surveillance by NK cells if they could recognize the marker and avoid rescanning the same cell. -- LBR
Proc. Natl. Acad. Sci. U.S.A. 101, 16873 (2004).
