Immunomodulatory Effect of Rhaphidophora korthalsii on Natural Killer Cell Cytotoxicity

Abstract

The in vivo immunomodulatory effect of ethanolic extracts from leaves of Rhaphidophora korthalsii was determined via immune cell proliferation, T/NK cell phenotyping, and splenocyte cytotoxicity of BALB/c mice after 5 consecutive days of i.p. administration at various concentrations. Splenocyte proliferation index, cytotoxicity, peripheral blood T/NK cell population, and plasma cytokine (IL-2 and IFN-γ) in mice were assessed on day 5 and day 15. High concentration of extract (350 μg/mice/day for 5 consecutive days) was able to stimulate immune cell proliferation, peripheral blood NK cell population, IL-2, and IFN- γ cytokines, as well as splenocyte cytotoxicity against Yac-1 cell line. Unlike rIL-2 which degraded rapidly, the stimulatory effect from the extract managed to last until day 15. These results suggested the potential of this extract as an alternative immunostimulator, and they encourage further study on guided fractionation and purification to identify the active ingredients that contribute to this in vitro and in vivo immunomodulatory activity.

Figure 1

The general time course of the in vivo studies. The time of repletion and immune response assays varied somewhat among experiments. Animals were injected with extract, mouse rIL-2, or normal saline (for control group) for 5 days. Half of the animals (total of 30 mice) were sacrificed on days 6 and the remaining animals (the remaining 30 mice) were sacrificed on day 16.

Figure 2

NK cell immunophenotyping on mice blood after being treated with various concentration of R. korthalsii methanol extract or mice rIL-2 for day 6 and day 16 in vivo. Each value represents the means ± SEM for three assays in duplicate each. The differences between the control group and treated group were determined by one-way ANOVA (*P ≤ 0.05).

Figure 3

Effects of R. korthalsii methanol extract on cytokine production in vivo. The serum concentrations of IL-2 and IFN-γ were tested by ELISA assay. (a) Concentration of IL-2 in vivo. (b) Concentration of IFN-γin vivo. Each value represents the means ± SEM for three assays in duplicate each. The differences between the control group and treated group were determined by one-way ANOVA (*P ≤ 0.05).

Figure 4

Viability of Yac-1 after being treated with different ratio of R. korthalsii extract or mouse rhIL-2-activated splenocytes in vivo (a) after day 5 of treatment and (b) after day 15 of treatment. Each value represents the means ± SEM for three assays in triplicate each. The differences between the control group and treated group were determined by one-way ANOVA (*P ≤ 0.05).