Converting enzyme-independent release of tumor necrosis factor a and IL-1b from a stimulated human monocytic cell line in the presence of activated neutrophils or purified proteinase 3 (neutrophil elastaseycytokine processingyproteinase inhibitors)

Two important cytokines mediating inf lam- mation are tumor necrosis factor a (TNFa) and IL-1b, both of which require conversion to soluble forms by converting enzymes. The importance of TNFa-converting enzyme and IL-1b-converting enzyme in the production of circulating TNFa and IL-1b in response to systemic challenges has been demonstrated by the use of specific converting enzyme inhib- itors. Many inf lammatory responses, however, are not sys- temic but instead are localized. In these situations release andyor activation of cytokines may be different from that seen in response to a systemic stimulus, particularly because associations of various cell populations in these foci allows for the exposure of procytokines to the proteolytic enzymes produced by activated neutrophils, neutrophil elastase (NE), proteinase 3 (PR3), and cathepsin G (Cat G). To investigate the possibility of alternative processing of TNFa andyor IL-1b by neutrophil-derived proteinases, immunoreactive TNFa and IL-1b release from lipopolysaccharide-stimulated THP-1 cells was measured in the presence of activated human neu- trophils. Under these conditions, TNFa and IL-1b release was augmented 2- to 5-fold. In the presence of a specific inhibitor of NE and PR3, enhanced release of both cytokines was largely abolished; however, in the presence of a NE and Cat G selective inhibitor, secretory leucocyte proteinase inhibitor, reduction of the enhanced release was minimal. This finding suggested that the augmented release was attributable to PR3 but not NE nor Cat G. Use of purified enzymes confirmed this conclusion. These results indicate that there may be alterna- tive pathways for the production of these two proinf lamma- tory cytokines, particularly in the context of local inf lamma-