NKR-P1A IS A TARGET-SPECIFIC RECEPTOR THAT ACTIVATES NATURAL-KILLER-CELL CYTOTOXICITY

NKR-P1A is a lectinlike surface molecule expressed on rat natural kill er (NK) cells. NKR-P1A has structural and functional features of an ac tivating NK cell receptor, but a requirement for NKR-P1A in target cel l lysis has not been determined. To define the role of NKR-P1A in natu ral killing, we have generated a mutant of the rat NK cell line, RNK-1 6, lacking expression of all members of the NKR-P1 receptor family. Al though these NKR-P1-deficient NK cells were able to kill many standard tumor targets, including YAC-1, they were selectively deficient in th e lysis of IC-21 macrophage, B-16 melanoma, and C1498 lymphoma targets . Reexpression of a single member of the NKR-P1 family, NKR-P1A, on mu tant cells restored lysis of IC-21, and killing of IC-21 targets throu gh rat NKR-P1A was completely blocked by F(ab')(2) anti-NKR-P1A. Reexp ression of NKR-P1A also restored transmembrane signaling to IC-21, as assessed by the generation of inositol-1,4,5-trisphosphate. The genera tion of inositol-1,4,5-trisphosphate was also restored in response to B-16 targets, but both B-16 and C1498 cells remained resistant to lysi s, indicating that other NK cell molecules, perhaps within the NKR-P1 family, are required for the efficient killing of these tumors. These results are the first to demonstrate that NKR-P1A is a target-specific receptor that activates natural killing.