Interactions between PSGL-1 and L-selectin depend on the tyrosine sulfate motif. (A) COS cells were cotransfected with cDNA encoding PSGL-1, FucT-VII, and C2GnT. COS cells were preincubated with either KPL1 or control antibody for 15 minutes. After extensive washing, 300.19/P or 300.19/L cells were added to the COS cells and the assay was performed as described in Materials and Methods. Adhesion of both cell types was completely inhibited by preincubation of transfected COS cells with KPL1, but not control MoAb (not shown). (B) COS cells were cotransfected with cDNA encoding FucT-VII, C2GnT, and either PSGL-1 or FFFE/PSGL-1. Binding of 300.19/L or 300.19/P cells to the FFFE mutant was undetectable. Values are mean ±SD; one of three experiments.