Oleuropein, a secoiridoid glycoside, is a potential antioxidant and antimicrobial agent. The aim of the present study was to investigate the in vitro effects of oleuropein and Olea europaea extracts on unstimulated lymphocytes. Oleuropein did not produce any significant cytotoxic effects on lymphocytes. On the contrary, it had a stimulatory effect, and was capable of inducing and maintaining high proliferation rates in lymphocytes. The stimulatory effects of oleuropein and extracts were concentration-dependent with a range of median stimulatory concentration 1 mM at 48 h. The cytotoxicity effect of oleuropein and extracts increased with time resulting in a greater cytotoxic effect on already-stimulated lymphocytes at 96 h even though dose dependence was not demonstrated. Morphological observations showed that oleuropein and extracts induced blastogenesis similar to that of phytohaemagglutinin (PHA). In fact, from lymphocyte activation studies, oleuropein exhibited a high degree of lymphocyte aggregation, which is an indicator of cell activation and proliferation.
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