Immunomodulatory effects of glycyrrhizin and glucomannan on cytokine gene expression in human PBMCs: implications for vaccine adjuvant development.

BACKGROUND

Vaccine adjuvants enhance immune responses to weak antigens. Natural compounds such as glycyrrhizin and glucomannan show immunomodulatory potential, but their combined effects on human cytokine expression as an adjuvant remain unclear.

OBJECTIVE

To evaluate the immunomodulatory effects of glucomannan (GA) from Amorphophallus konjac and glycyrrhizin (GL) from Glycyrrhiza glabra on cytokine gene expression in human peripheral blood mononuclear cells (PBMCs), assessing their potential to promote Th1 polarization as candidate vaccine adjuvants.

METHODS

PBMCs isolated from ten healthy donors were treated with GA and GL at 25 and 50 µg/mL, either individually or in combination. Cell viability was assessed using the MTT assay. Gene expression levels of pro-inflammatory cytokines (IL-6, TNF-α), the Th1 cytokine (IFN-γ), and Th2/regulatory cytokines (IL-10, TGF-β) were quantified using RT-qPCR.

RESULTS

GA and GL significantly increased IL-6, TNF-α, and IFN-γ expression in a dose-dependent manner (p < 0.05 to p < 0.001), while significantly reducing IL-10 and TGF-β expression compared with the control group (p < 0.05 to p < 0.001). The combined treatment produced the strongest immunomodulatory response, characterized by enhanced expression of pro-inflammatory and Th1-associated cytokines and greater suppression of Th2/regulatory cytokines relative to individual treatments (p < 0.001). The MTT assay identified 25 and 50 µg/mL as safe and effective GA concentrations for subsequent experiments, based on cell proliferation and cytotoxicity assessments.

CONCLUSION

In human PBMCs, GA and GL promote a Th1-biased cytokine response at the mRNA expression level under in vitro conditions, suggesting their implications for vaccine adjuvant development. However, these results are limited to in vitro gene expression data and have not been validated at the protein level, a gap that warrants further investigation.