HCLL activity is independent of PSGL-1.

(A) Flow cytometric analysis of PSGL-1 levels on KG1a cells and HL60 cells. Data shown are results obtained using P-selectin–Ig to stain cells, and therefore are reflective of PSGL-1 functional levels. Note that PSGL-1 expression is characteristic of both HL60 and KG1a cells. (B) L-selectin–mediated adherence of lymphocytes occurs on KG1a cells but not HL60 cells. Representative result of lymphocyte adherence assay performed on cytospin mixture of KG1a cells and HL60 cells. Immunohistochemical staining for CD34 antigen (pink stain) identifies KG1a cells. As demonstrated by arrows, note that lymphocytes (solid blue dots) adhere only to pink (KG1a) cells (background stain is methyl green-thionin, 250 × magnification).