344 R. Helal and M. F. Melzig: Influence of longer treatment periods up to 72 hours on the expression of active lysozyme of epithelial cells was investigated using glycyrrhizinic acid. As a result, no significant effects of the saponin were found after long exposure to cells up to 72 hours regardless of the used non-toxic doses of the saponin. Conclusion Lysozyme has and still receives attention as a model protein for structural, physicochemical, crystallographic, enzymatic, immunological and evolutionary studies. It is well-known as one of the most important factors of innate immunity, since the principal function attributed to lysozyme in most animals is host defense [19]. There has been interest in lysozyme as a "natural" antibiotic [20]. Lysozyme is unique enzybiotic in that it exerts not only antibacterial activity, but also antiviral, anti- inflammatory, anticancer and immunomodulatory activities [21]. Lysozyme activity levels in the culture fluids of THP-1 monocytes and HT-29 epithelial cells were measured after exposure to selected saponins for various treatment periods using highly sensitive fluorescence-based lysozyme activity assay. An important point to be considered is that lysozyme secretion and production of human cell cultures could not be easily induced upon treatment with various synthetic, natural or bacterial products as proved by our experiments (Data not shown). In addition, most published reports that concerned lysozyme up- or down-regulation after treatment of the cell cultures with synthetic or natural compounds presented mostly conflicting results. These might be due to the characterization of the used cell lines, or the use of different assay methods that measure lysozyme as a protein, such as ELISA, or as an active enzyme, such as the turbidimetric and the fluorometric assay. Because the level of active lysozyme may be more relevant for elucidating a defensive role for this protein as an important component of the immune system, a sensitive assay method that can determine the active lysozyme in cell culture supernatants, such as the EnzChek® fluorometric assay used in our present investigation, would provide more meaningful results. Majority of the saponins examined in the present study were demonstrated to stimulate significantly the release of lysozyme activity of monocytes and epithelial cells after one hour treatment with cells at non-toxic concentrations. The results suggested positive contribution of some saponins to lysozyme release of monocytes and epithelial cells upon short exposure. Furthermore, demonstrated ability of saponins to enhance the release of lysozyme activity can present a new mechanism that contributes to explaining important biological characteristics of saponins, including the antibacterial, antiviral, anti-inflammatory or immune-stimulating properties. The surface-active characteristics of saponins could partly suggest a mechanism of action for the positive contribution of specific saponins to lysozyme secretion of saponin-treated Sci Pharm. 2011; 79: 337–349