Methionine-enkephalin primes human neutrophils for enhanced superoxide anion production.

Methionine-enkephalin (MENK) is not an effective stimulus for inducing the superoxide (O2-) generation of human neutrophils, but it enhanced the O2- generation stimulated by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) or human recombinant interferon gamma (hrIFN gamma) when the cells had been preincubated with MENK for 30 min at 37 degrees C. The priming effect of MENK was not observed with stimulus such as lipopolysaccharide (LPS) or phorbol-12-myristate-13-acetate (PMA). The enhancing effect of MENK was abrogated if cells were treated with protein kinase C (PKC) inhibitor H7 (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine) before fMLP or IFN gamma. This finding indicates that MENK is a potent modulator of human neutrophils and can contribute to inflammatory process.