Characterization of SDF-1α cleavage by serum evaluated by mass spectrometry. (A) Fresh human serum was preincubated for 15 minutes at 37°C with or without the CD26/dipeptidyl peptidase inhibitor AB192 (50 μM), added (10% final dilution) to recombinant SDF-1α, and then incubated at room temperature for 20 hours. (B) Fresh human serum was heated at 56°C for 30 minutes or left at 4°C for 30 minutes, added (10% final dilution) to recombinant SDF-1α, and then incubated at room temperature for 20 hours. (C) Fresh human serum was preincubated at room temperature for 15 minutes with or without 20 mM EDTA, added (10% final dilution) to recombinant SDF-1α, and then incubated at room temperature for 10 minutes.