Cleavage of the synthetic peptide overlapping the CD11b cleavage region by the 3 serprocidins and the specific inhibition of PMN transmigration by the CD11b-derived peptide. (A) A 20-amino-acid peptide (20-mer) with a random sequence (CTL-P1) or a sequence matching the cleavage region of CD11b (CD11b-P1) was synthesized. (B) Mass spectrometry analysis of CD11b-P1 cleavage by NE, NPR-3, and NCG, respectively. The synthetic peptides were incubated with each serprocidin for 30 minutes under appropriate conditions. (C) Reverse-phase HPLC analysis of the kinetics of CD11b-P1 cleaved by NE. Note that the peak of the intact peptide (indicated by the arrow) rapidly disappeared and shifted to that of the smaller peptide with a running time of 8.0-9.0. (D-E) The effects of synthetic peptides on fMLP-induced migration of human PMNs across collagen-coated Transwell filters. (F) No effect of synthetic peptides on FBG-CD11b/CD18 binding. Data represent the mean ± SD of 3 independent experiments, each performed in triplicate. *P < .05; **P < .01.