Specific engagement of the CD94/NKG2-A killer inhibitory receptor by the HLA-E class Ib molecule induces SHP-1 phosphatase recruitment to tyrosine-phosphorylated NKG2-A: evidence for receptor function in heterologous transfectants

Abstract

It has been recently demonstrated that the CD94/NKG2‐A killer inhibitory receptor (KIR) specifically recognizes the HLA‐E class Ib molecule. Moreover, the apparent CD94‐mediated specific recognition of different HLA class Ia allotypes, transfected into the HLA‐defective cell line 721.221, indeed depends on their selective ability to concomitantly stabilize the surface expression of endogenous HLA‐E molecules, which confer protection against CD94/NKG2‐A⁺ effector cells. In the present study, we show that a selective engagement of the CD94/NKG2‐A inhibitory receptor with a specific monoclonal antibody (mAb) (Z199) was sufficient to induce tyrosine phosphorylation of the NKG2‐A subunit and SHP‐1 recruitment. These early biochemical events, commonly related to negative signaling pathways, were also detected upon the specific interaction of NK cells with an HLA‐E⁺ 721.221 transfectant (.221‐AEH), and were prevented by pre‐incubation of .221‐AEH with an anti‐HLA class I mAb. Furthermore, mAb cross‐linking of the CD94/NKG2‐A receptor, segregated from other NK‐associated molecules by transfection into a rat basophilic leukemia cell line (RBL‐2H3), promoted tyrosine phosphorylation of NKG2‐A and co‐precipitation of SHP‐1, together with an inhibition of secretory events triggered via FcϵRI. Remarkably, interaction of CD94/NKG2‐A⁺ RBL cells with the HLA‐E⁺ .221‐AEH transfectant specifically induced a detectable association of SHP‐1 with NKG2‐A, constituting a more formal evidence for the receptor‐HLA class I interaction.