RBC adhesion to laminin at 0.4 dyne/cm² and Lu/BCAM phosphorylation (P) after blood fractionation. (A) Adhesion of UT RBCs from whole blood (W), the reticulocyte-rich low-density fraction (LDF), and the pellet containing the mature RBC-rich fraction (PF). Horizontal lines are medians. More LDF cells adhered than those from W (P < .01) or the PF (P < .05; Friedman test). (B) Typical results (1 of 5 experiments) showing the phosphorylation of the Lu-gp long isoform in W, LDF, and PF of an UT patient. The percentage of reticulocytes was determined by flow cytometry for each sample. Total immunoprecipitated Lu/BCAM proteins were quantified by WB. P/WB ratio estimates the proportion of phosphorylated proteins. (C) Linear regression between phosphorylation and reticulocyte percentage in UT patients (r² = 0.985, P < .001, n = 5 patients, 3 samples for each patient: W, LDF, and PF). (D) Lu/BCAM phosphorylation as a function of the reticulocyte percentage in 8 HU-treated patients (r² = 0.03, P = .66, n = 8).