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 TNFalpha 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 intercellular adhesion molecule expression and cytokine secretion in the differentiation process from monocytes to macrophages.