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The effect of endogenously generated reactive oxygen metabolites on the interaction of human blood monocytes with tumour necrosis factor-alpha (TNF-α) was investigated. Pre-exposure of unactivated human blood monocytes to dimethylthiourea, a scavenger of hydroxyl radical (OH.), or to desferrioxamine (DFX), an iron chelator preventing the synthesis of OH., enhanced the specific binding of 125I-TNF-α to its receptors. Scavengers of superoxide anion or hydrogen peroxide were without effect. DFX-induced up-regulation of 125I-TNF-α binding depended on the concentration of the drug (1-5 mM) and on the duration of the treatment (1-18 h). It was not due to a reduction of receptor occupancy by endogenously generated TNF-α. Scatchard analysis of binding data revealed that DFX caused an approximately two-fold increase in the number of type II TNF-α receptors, with no change in their affinity. This up-regulation, that did not require synthesis of new proteins, was associated with a decrease in the internalization rate of TNF-α receptors, the half-life of which was doubled. Conversely, these findings suggest that OH. generation by monocytes may have a physiological role in reducing the activity of membrane-associated TNF-α receptors. [ABSTRACT FROM AUTHOR]

Blood monocytes from tuberculosis patients release high amounts of tumour necrosis factor-alpha (TNF-α). Because the biological efficiency of TNF-α would depend on the expression of TNF-α receptors on target cells, we thought to analyse the capacity of blood monocytes from a group of patients with pulmonary tuberculosis to binding 125I-TNF-α. We report a slight but not significant enhancement in specific binding of 125I -TNF-α on monocytes of 15 consecutively studied patients compared with 10 controls. Percent cell surface bound and internalized 125I -TNF-α was identical in the two groups. To evaluate the receptor occupancy by endogenously generated TNF-α, similar experiments were performed after cell exposure to low-pH glycine buffer. Under these conditions, specific binding of 125I-TNF-α was significantly higher on tuberculosis monocytes compared with control monocytes. Moreover, the occupancy of TNF-α receptors by endogenously generated TNF-α that was found to be significantly higher on tuberculosis monocytes than on control monocytes, was directly related to the enhanced capacity or mononuclear cells to generate TNF-α in vitro. It normalized after 3 months of antituberculous therapy, Scatchard analysis of the binding data revealed that tuberculosis infection caused a significant increase in high affinity 125I-TNF-α binding to monocytes without any significant change in the dissociation constant. Collectively, these results indicate an up-regulation of TNF-α generation and binding to blood monocytes in patients with pulmonary tuberculosis. They provide support to the hypothesis that TNF-α is of critical importance in the pathogenesis of this infection. [ABSTRACT FROM AUTHOR]