Objective and design: Peptides derived from neutrophil inhibitory factor (NIF), a known antagonist of Mac-1, were evaluated as inhibitors of neutrophil adherence.
Material: In vitro assays of adherence employed: 1) human polymorphonuclear cells (PMN), 2) human umbilical vein endothelial cells (HUVEC), and 3) CHO cells expressing ICAM-1 (CHO-ICAM cells).
Treatment: Cells, pretreated with NIF-derived peptides (0.1-100 microM) for 10 minutes, were permitted to adhere for 20 min in the continued presence of peptide.
Methods: Cell-based assays: 1) PMN adherence to HUVEC, 2) PMN adhesion to immobilized human serum proteins, and 3) adherence of CHO-ICAM cells to immobilized Mac-1.
Results: A NIF-derived peptide of 29 amino acids blocked PMN adherence to HUVEC, but behaved somewhat differently than the parent NIF protein. NIF specifically antagonized Mac-1 dependent adherence, but the peptide blocked neutrophil adherence that was dependent upon both Mac-1 and LFA-1 integrins. CHO-ICAM adherence to Mac-1 was blocked by NIF, but not by the peptide. Binding studies with NIF and the peptide indicate that the molecules bind to different sites.
Conclusions: A peptide derived from NIF blocks PMN adherence but, unlike NIF, the mechanism of action is not mediated by direct antagonism Mac-1.