Rat NKp46 activates natural killer cell cytotoxicity and is

Abstract: NKp46 has been identified in the hu-man, rat, mouse, monkey, and cattle. We have generated a monoclonal antibody, WEN23, against rat NKp46. By flow cytometry, NKp46 is ex-pressed by all natural killer (NK) cells but not by T cells, B cells, granulocytes, monocytes, dendritic cells, or macrophages. Thus, NKp46/WEN23 is the first NK cell-specific marker in the rat. In a redirected lysis assay, preincubation of the effector cells with WEN23 augmented lysis of the Fc recep-tor (FcR) murine tumor target cells, indicating that NKp46 is an activating NK cell receptor. Moreover, preincubation of the effector cells with WEN23 F(ab)2 fragments reduced killing of target cells, confirming the activating function of NKp46 and indicating that the mouse tumor target cells express a ligand for rat NKp46. Lysis of FcR– mouse and human tumor target cells was reduced after incubation of effector cells with WEN23, sug-gesting that rat NKp46 recognizes a ligand that is conserved between primates and rodents. By West-ern blot and immunoprecipitation using WEN23, NKp46 is expressed as a monomer of 47 kDa in interleukin-2-activated NK cells. The immunore-ceptor tyrosine-based activation motif bearing adaptor proteins CD3 and FcR for immunoglob-ulin -I coprecipitates with NKp46 from lysates of NK cells, indicating that rat NKp46 activates NK cell cytotoxicity by similar pathways as CD16