Neutrophil-activating intercrine secreted by porcine platelets is active without proteolytic processing.

A new member of the cytokine intercrine alpha-subfamily, porcine neutrophil-activating peptide 2 (pNAP-2), was isolated to homogeneity. Amino acid sequencing analysis showed two species of pNAP-2, a long form (pNAP-2-L) and a short form (pNAP-2-S). pNAP-2-L had seven more amino acids at the NH2-terminus than pNAP-2-S. The remaining amino acid sequences of the two molecules were identical. pNAP-2-S shared 65% homology with human neutrophil-activating peptide 2 (hNAP-2) including four cysteines in identical positions. Moreover, the NH2-terminal sequence Glu-Leu-Arg (E-L-R) was conserved in both molecules. Both pNAP-2-L and pNAP-2-S induced mobilization of cytosolic calcium in neutrophils and caused release of granulocyte elastase in a dose-dependent manner, although pNAP-2-L was less active. A desensitization study suggested that both hNAP-2 and pNAP-2-S may act on the same receptor. Whereas human platelets release inactive precursors that can be converted to hNAP-2 by cathepsin G from activated neutrophils, porcine platelets, upon stimulation with thrombin, appear to secrete active forms of pNAP-2. The activated neutrophils are not involved in the generation of pNAP-2.