Anti-NK1.1 monoclonal antibody (mAb) triggered activation of natural killer (NK) cells

NK1.1, the most specific murine serologic marker on the surface of NK cells, is an isoform of NKR-P1. In the rat NKR-P1 can trigger killing and induce a cascade of biochemical events that characterize NK cell activation. In mice, the anti-NK1.1 mAb PK136 can specifically trigger NK cells to lyse otherwise insensitive targets. We sought to determine if mAb PK136 was also capable of stimulating C57BL/6-derived splenic NK cells to perform other events. MAb PK136 induced NK cell proliferation as defined by ³H-thymidine incorporation. This response was dependent on low doses of IL-2 and immobilization of the mAb to the plastic tissue culture wells. This implied an apparent necessity for crosslinking of NK1.1. An isotype matched control mAb AF68853 (anti-K^b) that binds NK cells at equivalent levels did not stimulate proliferation. These data demonstrate that the response is specific for NK1.1 and not secondary to Fc receptor binding. Flow cytometric analysis 4 days after stimulation revealed that the stimulated cells uniformly expressed NK1.1, CD69, and FcγRII/III molecules, but were essentially CD3-, confirming that responding cells were NK cells and not T cells. In ⁵¹Cr release assays, these cells also lysed the NK sensitive target YAC-1. These studies demonstrate that activation through NK1.1 leads to a series of other NK cell functions, in addition to cytotoxicity.