NEGATIVE SIGNALING PATHWAYS OF THE KILLER-CELL INHIBITORY RECEPTOR AND FC-GAMMA-RIIB1 REQUIRE DISTINCT PHOSPHATASES

Inhibition of natural killer (NK) cells by the killer cell inhibitory receptor (KIR) involves recruitment of the tyrosine phosphatase SHP-1 by KIR and is prevented by expression of a dominant negative SHP-1 mut ant. Another inhibitory receptor, the low affinity Fc receptor for imm unoglobulin G (IgG) (Fc gamma RIIb1), has been shown to bind SHP-1 whe n cocross-linked with the antigen receptor on B cells (BCR). However, coligation of Fc gamma RIIb1 with BCR and with Fc epsilon RI on mast c ells leads to recruitment of the inositol 5' phosphatase SHIP and to i nhibition of mast cells from SHP-1-deficient mice. In this study, we e valuated the ability of these two inhibitory receptors to block target cell lysis by NK cells, and the contribution of SHP-1 and SHIP to inh ibition. Recombinant vaccinia viruses encoding chimeric receptors and dominant negative mutants of SHP-1 and SHIP were used for expression i n mouse and human NK cells. When the KIR cytoplasmic tail was replaced by that of Fc gamma RIIb1, recognition of HLA class I on target cells by the extracellular domain resulted in inhibition. A dominant negati ve mutant of SHP-1 reverted the inhibition mediated by the KIR cytopla smic tail but not that mediated by Fc gamma RIIb1. In contrast, a domi nant negative mutant of SHIP reverted only the inhibition mediated by the Fc gamma RIIb1 tail, providing functional evidence that SHIP plays a role in the Fc gamma RIIb1-mediated negative signal. These data dem onstrate that inhibition of NK cells by KIR involves primarily the tyr osine phosphatase SHP-1, whereas inhibition mediated by Fc gamma RIIb1 requires the inositol phosphatase SHIP.