Immunoprecipitation of CPN from human plasma reduces SDF-1α and SDF-1α C-terminal peptide cleavage activity. Plasma or serum was either mock immunoprecipitated (no antibody added) or immunoprecipitated with control rabbit serum or with rabbit anti-CPN antibodies. After removal of the immunoprecipitate with protein-G, supernatant was tested for enzymatic activity. (A) SDF-1 carboxypeptidase activity in serum or plasma following immunoprecipitation. Peptidase activity was calculated for untreated 10% plasma or serum (Mock IP); 10% plasma or serum immunoprecipitated with control rabbit serum; and 10% plasma or serum immunoprecipitated with rabbit anti-CPN antibodies. Peptide cleavage was evaluated by RP-HPLC. Shown is the mean plus or minus the standard deviation from 3 independent experiments. (B) SDF-1α cleavage evaluated by immunoblotting. SDF-1α incubated for 10 minutes at room temperature with 10% of the following: lane 1: PBS alone; lane 2: plasma (10%); lane 3: 10% plasma, mock immunoprecipitated; lane 4: 10% plasma immunoprecipitated with control rabbit IgG; lane 5: 10% plasma immunoprecipitated with rabbit anti-CPN antibodies.