Specificity of KPL1 for PSGL-1 by flow cytometry and Western blotting. (A) Untransfected 300.19 cells or 300.19 cells transfected with human PSGL-1 cDNA were stained with a negative control (top) or KPL1 (bottom) as described in Materials and Methods. KPL1 does not stain untransfected 300.19 cells, whereas it stains 300.19/PSGL-1 transfectants. (B) Western blotting of whole cell lysates made from HL60 cells (lane 1), 300.19 cells (lane 2), 300.19 cells transfected with human PSGL-1 cDNA (lane 3), COS cells transfected with a control plasmid (lane 4), or COS cells transfected with human PSGL-1 cDNA (lane 5) with the KPL1 antibody. Bands of the appropriate molecular weight (∼120 and ∼240 KD) were seen only in lysates from cells expressing PSGL-1 endogenously (HL60 cells in lane 1) or transfected with human PSGL-1 cDNA (lanes 3 and 5).