Rhaphidophora korthalsii (Araceae) is a root-climber plant which has been previously
identified as splenocyte immunostimulator. The purpose of this study was to examine
the in vitro and in vivo immunomodulatory effect of R. korthalsii methanol extract on
immune cell proliferation, cytokine expression and cytotoxicity. More specifically,
immunomodulatory effects of R. korthalsii methanol extract on the stimulation of NK
cells activity and cytotoxicity against HepG2 monolayer and spheroid culture were
determined. Immune cells [peripheral blood mononuclear cells (PBMC) and mice
splenocytes] treated with this extract resulted in stimulation of cell proliferation,
cytokine expression and cytotoxicity in dose and time dependent manner. For the in
vivo immunostimulatory effect study, unlike rIL-2 which degraded rapidly, the
stimulatory effect from the extract managed to last until day 15. In order to
understand the activation of NK cells by R. korthalsii methanol extract, NK cells were
treated directly or indirectly. Both direct and indirect stimulated NK cells showed
high-level expression of cell surface FasL, NKG2D, 16B4 and extra-cellular IFN-γ
and TNF-α. These activations contributed to the killing of NK cells against HepG2 monolayer cells through Granzyme B mitochondria caspases dependent secretory
apoptosis pathway where DNA fragmentation, phosphatidylserine (PS)
externalisation, caspase 3, caspase 8, caspase 9 up-regulation and XIAP, Bid downregulation
were observed. Apart from that, extract stimulated NK cells which caused
cell death on the HepG2 spheroid and inhibited the HepG2 cell invasion, suggesting
that R. korthalsii methanol extract was a potential agent to inhibit liver tumour
metastasis. Our findings indicated a potential IL-2 free immunotherapy through direct
and indirect R. korthalsii activation on NK cells which can further induce apoptosis
on the HepG2 monolayer and spheroid culture