c-kit expression on WT andPU.1^−/− E16.5 FL cells. c-kitexpression by WT and PU.1^−/− E16.5 FL cells was examined by flow cytometry using a c-kit–specific MoAb. Representative data for staining by isotype-match control or an anti–c-kit MoAb for individual WT orPU.1^−/− E16.5 FL cells are shown.