a) Glycosulfopeptide PSGL-1 microarray probed with human P-selectin-Fc chimera (hP-selectin) (5 μg/mL) with (top) and without (bottom) calcium in the binding buffer. In the presence of calcium, hP-selectin exhibits binding to sulfated human and mouse PSGL-1 peptides carrying SLex (25), di-sialyl-Lex (26), and human 2 X SLex (27) peptide as well as the recombinant full length PSGL-1 protein (66). b) Human E-selectin (5 μg/mL) showed broader specificity binding to most human sulfated peptides, with SLex peptide (25) exhibiting highest binding. c) Like hP-selectin, mP-selectin (5 μg/mL) exhibited cross-species binding to sulfated PSGL-1 peptides. y-axis = relative fluorescent units (RFU), error bars = +/− 1 standard deviation. Color coding in graphs matches with Figure 2.