The opioid peptide methionine-enkephalin (MENK) has significant immunomodul
atory ability in addition to its neurotransmitter function. Since neutral e
ndopeptidase (NEP, CD10, enkephalinase EC 3.4.24.11) cleaves opioid peptide
s, the presence and activity of NEP in neutrophils from different persons m
ight be responsible for the diverse, neuropeptide-induced, responses of neu
trophils from different donors [Ann. N. Y. Acad. Sci. 650 (1992) 146]. The
results obtained showed statistically significant differences in NEP activi
ty among donors (high, medium and low). A 10-fold higher NEP activity in ne
utrophils (160-280 nmol/10(6) cells/h) and in their corresponding membrane
preparations (550 nmol/mg protein/min) in our study, as compared to literat
ure data, was a result of high specificity and affinity of Suc-Ala-Ala-Phe-
pNA as substrate. In control nontreated neutrophils. the number of CD10 pos
itive cells were not correlated with NEP activity. However, in neutrophils
treated with a physiological (10(-10) M) concentration of MENK, two main ev
ents occurred: not only did the number of CD10 positive cells correlate wit
h NEP activity, but contrary to control samples, MENK upregulated the expre
ssion of CD10 marker as demonstrated by an increase of mean florescence int
ensity (F-mean) in donors with low NEP activity. Taken together, these data
add some clarity to the diverse activity of enkephalins in association wit
h enzyme cleavage of those molecules. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.