In vitro Effects of Saponins on Lysozyme Activity of Human Cells 345 cultures of human monocytes and epithelial cells. Nevertheless, this mechanism cannot adequately explain the stimulatory effects of these saponins, since there are other surface- active saponins examined in this report that have not been able to induce lysozyme secretion of human cells. On the other hand, the stimulatory effects of these saponins on lysozyme secretion of the examined human cells might be due to one or more components of these saponins that can affect specific cell receptors. Nevertheless, this hypothesis needs further investigations Further possible mechanisms responsible for the increased levels of secreted lysozyme in some saponin-treated cultures might be through either increased lysozyme synthesis or decreased lysozyme degradation. However, these two mechanisms should be excluded in the short-term treatment experiments, since one hour treatment period has not been sufficient to affect lysozyme transcription, translation or catabolism. The stimulatory effects of specific saponins on lysozyme release in human cells have to be further investigated through extensive studies on the molecular mechanisms. Furthermore, the results obtained in the present study can provide the basis for further studies in vivo involve investigating lysozyme levels in blood and biological fluids (saliva, gastric juice, duodenal contents) in course of the treatment with herbal drugs that contain these saponins. Elevated lysozyme levels in body fluids can suggest in vivo evidence for the immune-stimulatory activity of these natural products among many other biological activities of lysozyme. The stimulation of immunological system, through elevation of lysozyme activity levels, introduced the specific saponins examined in this report as potential immunostimulant agents from natural origin through lysozyme, the important defense molecule of the innate immune system which is able to control the growth of susceptible bacteria and to modulate host immunity against infections and depressions of immune responses. Experimental Materials Cell lines & culture medium Human leukemia cell line THP-1 and human colon epithelial cell line HT-29 were purchased from German collection of microorganisms and cell cultures (DSMZ) Braunschweig, Germany. Sterile RPMI-1640 medium without phenol red, PBS, L-Glutamine, and fetal bovine serum were obtained from Biochrom, Germany. Aprotinin from bovine lung, obtained from Sigma, was dissolved in phosphate buffer (pH 7) in a 10 mg/ml (7.3 mM) stock solution, and then diluted with the culture medium to a final concentration of 2 µg/ml (0.3 µM). Sci Pharm. 2011; 79: 337–349