Murine natural killer cells express the Ly24 (Pgp-1) marker on their surface

The Ly24 (Pgp-1) marker is expressed on some, but not all, mature T lymphocytes. It has recently become apparent that the development of Ly24- T lymphocytes is dependent on the presence of an intact thymus and that virgin Ly24- T cells rapidly acquire this marker upon antigenic or mitogenic stimulation. Although natural killer (NK) cells can develop and function in the absence of an intact thymus, some NK cell subsets express certain markers normally associated with T lymphocytes. The experiments in this report were undertaken to determine if NK cells express Ly24 and whether such an expression could be used to delineate distinct NK cell subsets. We found that mature functional NK cells expressed the Ly24 marker as defined by the monoclonal antibody 9F3. Double-color fluorescence analysis using C57BL/6 splenocytes (whose NK cells express the NK1.1 marker) showed all the NK1.1+ cells to be Ly24+ as well. For C3H/HeN (an NK1.1- strain), double-color fluorescence analysis utilizing asialo GM1 and Ly24 revealed a distinct subset positive for both markers and containing most of the functional NK cell activity. Whereas the Ly24 marker did not illuminate an NK cell subset, these findings demonstrate that this determinant can be useful for the further characterization and isolation of NK cells.