TGF-β activity produced by monocytes is decreased by NAC and DTT. Human monocytes (5 × 106/condition) were incubated in media alone or with M-CSF (100 ng/ml), GM-CSF (100 ng/ml) or LPS (100 ng/ml) for 18 hours. (A) Cell-free supernatants were harvested and analyzed by TMLC assay for active TGF-β (Grey bars) and compared against total TGF-β produced (Black bars). M-CSF, GM-CSF and LPS induce more active TGF-β from monocytes than that induced by incubation with media alone, p = 0.06 for M-CSF, p < 0.05 for GM-CSF and p < 0.01 for LPS. These data are composite of six independent studies. These same conditions are shown titrated against increasing concentrations of NAC and DTT, non stimulated (B) or incubated with M-CSF (C), GM-CSF (D) or LPS (E). After incubation, cell-free supernatants were evaluated for TGF-β by TMLC assay and were expressed as percent control of samples treated without NAC and DTT. NAC (20 mM) and DTT (both 1 and 10 mM) reduced TGF-β activation and production by all the stimulating agents and from cells left not stimulated (p < 0.01 versus samples not treated with NAC or DTT). The data shown are representative of four measurements each from six independent studies.