The influence of toll-like receptor (TLR-) agonists on lysozyme activity, TNF-alpha secretion and intercellular adhesion in THP-1 cells

Monocytes play a major role in modulating inflammation and can be found as circulating blood cells or, after extravasation, as differentiated tissue specific macrophages. The activation of TLRs (Toll-like receptors) modulates their action and contributes considerably to the eradication of pathogens. Aim of this study was to investigate the influence of TLR-agonists on TNF-alpha secretion and lysozyme activity in a comparative assay. To explore the importance of differentiation the monocytic cell line THP-1 was pre-treated with PMA and IFNy. Stimulation of undifferentiated cells with various bacterial antigens had almost no effect on TNF-alpha secretion and lysozyme activity but influenced adhesion molecule expression clearly. Differentiated THP-1 cells were much more sensitive to further stimulation with TLR-agonists yet revealed an opposing effect on lysozyme activity and TNF-alpha secretion. The results suggest a coordinated activation of inter-cellular adhesion molecule expression and cytokine secretion in the differentiation process from monocytes to macrophages.