B. Mytar et al., Induction of reactive oxygen intermediates in human monocytes by tumour cells and their role in spontaneous monocyte cytotoxicity, BR J CANC, 79(5-6), 1999, pp. 737-743
The present study examined the ability of human monocytes to produce reacti
ve oxygen intermediates after a contact with tumour cells. Monocytes genera
ted oxygen radicals, as measured by luminol-enhanced chemiluminescence and
superoxide anion production, after stimulation with the tumour, but not wit
h untransformed, cells. The use of specific oxygen radical scavengers and i
nhibitors, superoxide dismutase, catalase, dimethyl sulphoxide and deferoxa
mine as well as the myeloperoxidase inhibitor 4-aminobenzoic acid hydrazide
, indicated that chemiluminescence was dependent on the production of super
oxide anion and hydroxyl radical and the presence of myeloperoxidase. The t
umour cell-induced chemiluminescent response of monocytes showed different
kinetics from that seen after activation of monocytes with phorbol ester. T
hese results indicate that human monocytes can be directly stimulated by tu
mour cells for reactive oxygen intermediate production. Spontaneous monocyt
e-mediated cytotoxicity towards cancer cells was inhibited by superoxide di
smutase, catalase, deferoxamine and hydrazide, implicating the role of supe
roxide anion, hydrogen peroxide, hydroxyl radical and hypohalite, We wish t
o suggest that so-called 'spontaneous' tumoricidal capacity of freshly isol
ated human monocytes may in fact be an inducible event associated with gene
ration of reactive oxygen intermediates and perhaps other toxic mediators,
resulting from a contact of monocytes with tumour cells.