In vitro modulation of the innate immune response and phagocytosis by three Hypoxis spp. and their phytosterols

• Three Hypoxis spp. extracts increased ROS and NO production in U937 cells.
• H. stellipilis had the greatest effect on ROS and NO production.
• Phytosterols increased SOD activity.
• Three Hypoxis spp. extracts and β-sitosterol increased phagocytosis.

Hypoxis forms an important part of South African traditional medicine. Crude Hypoxis extracts and hypoxoside have extensively been investigated for its biological activities. This study investigated the in vitro biological activities of Hypoxis extracts and its phytosterols on the innate immune system. Reactive oxygen species (ROS) and nitric oxide (NO) production in undifferentiated and/or differentiated human promonocytic U937 leukemia cells were investigated using the fluorescent dyes, 2,7-dichlorofluorescein diacetate and 5,6-diaminofluorescein diacetate, respectively. The phagocytic ability of U937 cells was investigated using pHrodo™ E. coli Bioparticle® Conjugate. Superoxide dismutase activation in Chang liver cells were measured following (phyto)sterol treatment. Hypoxis stellipilis extract has shown the highest ROS and NO production. Hypoxis extracts and β-sitosterol significantly increased phagocytic activity of pretreated differentiated U937 cells. For superoxide dismutase activation, only the (phyto)sterols had an effect. Phytosterols, in combination with other compounds found in Hypoxis extracts, might be responsible for increased ROS and NO production and phagocytosis seen in U937 cells, ultimately influencing the innate immune system response.