Ligand binding to inhibitory killer cell Ig-like receptors induce colocalization with Src homology domain 2-containing protein tyrosine phosphatase 1 and interruption of ongoing activation signals.

Interaction of NK cells with target cells leads to formation of an immunological synapse (IS) at the contact site. NK cells form two distinctly different IS, the inhibitory NK cell IS (NKIS) and the cytolytic NKIS. Cognate ligand binding is sufficient to induce clustering of inhibitory killer cell Ig-like receptors (KIR) and phosphorylation of both the receptor and the phosphatase Src homology domain 2-containing protein tyrosine phosphatase 1 (SHP-1). Recruitment and activation of SHP-1 by a signaling competent inhibitory receptor are essential early events for NK cell inhibition. We have in the present study used three-dimensional immunofluorescence microscopy to analyze distribution of inhibitory KIR, SHP-1, LFA-1, and lipid rafts within the NKIS during cytolytic and noncytolytic interactions. NK clones retrovirally transduced with the inhibitory KIR2DL3 gene fused to GFP demonstrate colocalization of KIR2DL3 with SHP-1 in the center of early inhibitory NKIS. Ligand binding translocates the receptor to the center of the IS where activation signals are accumulating and provides a docking site for SHP-1. SHP-1 and rafts cluster in the center of early inhibitory NKIS and late cytolytic NKIS, and whereas rafts continue to increase in size in cytolytic conjugates, they are rapidly dissolved in inhibitory conjugates. Furthermore, rafts are essential only for cytolytic, not for inhibitory, outcome. These results indicate that the outcome of NK cell-target cell interactions is dictated by early quantitative differences in cumulative activating and inhibitory signals.