MELATONIN INCREASES THE INTENSITY OF RESPIRATORY BURST AND PREVENTS L-SELECTIN SHEDDING IN HUMAN NEUTROPHILS IN-VITRO

Effects of melatonin priming of neutrophils and subsequent increase of phorbol 12-miristate 13-acetate stimulated respiratory burst were inv estigated on the modulation of L-selectin shedding and MAC-1 upregulat ion. Respiratory burst related H2O2 production and adhesion molecule e xpression were quantified by how cytometry. Phorbol 12-miristate 13-ac etate dose dependence of intracellular oxidation and adhesion molecule expression showed no relationship between respiratory burst intensity and MAC-1 expression or L-selectin shedding. Treatment of cells with 12.5 nM phorbol 12-miristate 13-acetate resulted in less than 20% of t he respiratory burst response, however it induced 91.7% of total MAC-1 expression and 62.8% of L-selectin shedding. Melatonin priming experi ments showed also no connection between the extent of respiratory burs t and MAC-1 expression, however melatonin priming almost completely pr evented L-selectin down-regulation elicited by phorbol 12-miristate 13 -acetate, without affecting MAC-1 expression. It is suggested that mel atonin may inhibit metalloproteases responsible for L-selectin cleavag e. (C) 1998 Academic Press.