Enhancement of production of superoxide anion by human monocytes exposed to products of HT 29 human colonic adenocarcinoma cell line.

The generation of superoxide anion (O2-) by human blood monocytes in response to stimulation by either phorbol myristate acetate (PMA) or opsonized Zymosan was greatly enhanced (range: 100-200% according to donor) by prior exposure of the peripheral blood mononuclear cells (PBM) to human colonic adenocarcinoma cells (HT 29 line) or their conditioned culture medium (DMEM-HT 29). This priming effect was observed after 5 hr and persisted for up to 15 hr of contact between PBM and endotoxin-free DMEM-HT 29. Beyond this time, primed monocytes gradually lost this ability. However, they maintained a higher capacity (about 100%) to produce O2- when compared to controls. DMEM-HT 29-induced monocyte priming requires that the tumor-active substance(s) act(s) on 2 target cells: first, on non adherent mononuclear cells (NA-PBM) to induce cytokine production and, second, on the monocyte itself. Priming activity was also found in conditioned medium from FR3T3 embryonic fibroblasts but not in conditioned medium from HT 29 repolarized cells (by culture in glucose-free medium) or from non-tumorous human colonic mucosa explants.