P-selectin/PSGL-1 and CD44/HA are separate pathways in vitro. (A) Preincubation of Th1 cells with a blocking Ab to PSGL-1 does not inhibit interactions of Th1 cells with HA-coated coverslips. (B) Preincubation of Th1 cells with a blocking Ab to CD44 does not inhibit interactions with P-selectin–coated coverslips. Data are expressed as the arithmetic means ± SEM of 4 separate experiments.