Shared and unique functions of ESL-1 during mature and immature leukocyte trafficking. Schematic representation of the ESLs preferentially used by immature (HPCs) and mature (neutrophils) hematopoietic cells to migrate. The elevated levels of ESL-1 in HPCs correlate with its predominant function for E-selectin binding and migration in these cells. In neutrophils, both functions rely predominantly on PSGL-1 despite similar expression of the glycoprotein in mature and immature leukocytes.