Abstract
In Dictyostelium discoideum, AprA is a secreted protein that inhibits proliferation and causes chemorepulsion of Dictyostelium cells, yet AprA has little sequence similarity to any human proteins. We found that a predicted structure of AprA has similarity to human dipeptidyl peptidase IV (DPPIV). DPPIV is a serine protease present in extracellular fluids that cleaves peptides with a proline or alanine in the second position. In Insall chambers, DPPIV gradients below, similar to, and above the human serum DPPIV concentration cause movement of human neutrophils away from the higher concentration of DPPIV. A 1% DPPIV concentration difference between the front and back of the cell is sufficient to cause chemorepulsion. Neutrophil speed and viability are unaffected by DPPIV. DPPIV inhibitors block DPPIV-mediated chemorepulsion. In a murine model of acute respiratory distress syndrome, aspirated bleomycin induces a significant increase in the number of neutrophils in the lungs after 3 d. Oropharyngeal aspiration of DPPIV inhibits the bleomycin-induced accumulation of mouse neutrophils. These results indicate that DPPIV functions as a chemorepellent of human and mouse neutrophils, and they suggest new mechanisms to inhibit neutrophil accumulation in acute respiratory distress syndrome.