When T cells, B cells, and natural killer (NK) cells of the immune system interact with target cells, signaling molecules are accumulated in the plasma membrane at structures known as the immunological synapse. Evidence is accumulating 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. Earlier evidence had shown that NK cells can actually acquire MHC class I proteins during interactions with target cells. Now Vanherberghen et al. show that the exchange goes both ways and that NK receptors are transferred to cells that express MHC class I ligands. The authors monitored transfer of biotinylated killer Ig-like receptor (KIR) KIR2DL1 by immunoblotting or green fluorescent protein-tagged receptor by fluorescence-activated cell sorting or laser-scanning confocal microscopy and observed transfer of KIRs. The NK cell receptor Ly49A was only transferred to target cells that expressed the cognate MHC class I ligand. It is not known what function the transferred receptor might serve, but the authors make an appealing suggestion: The NK receptor might mark a target cell that has already been scanned by a NK cell, which might allow more efficient surveillance by NK cells if they could use such a marker to avoid rescanning of the same cell.
B. Vanherberghen, K. Andersson, L. M. Carlin, E. N. M. Nolte-`t Hoen, G. S. Williams, P. Höglund, D. M. Davis, Human and murine inhibitory natural killer cell receptors transfer from natural killer cells to target cells. Proc. Natl. Acad. Sci. U.S.A. 101, 16873-16878 (2004). [Abstract] [Full Text]