Adjuvant potentials of AcF1, an immunostimulant fraction of Alchornea cordifolia extract

As a result of strong experimental data supporting effectiveness and safety, herb-based immunomodulators are paving way as alternative sources of potent adjuvants for vaccines. In this study, the immunostimulatory and adjuvant properties of AcF1, a flavonoid-rich fraction of Alchornea cordifolia extract, were evaluated. AcF1 was shown to activate total splenocytes, CD4+ T cells, and B cells; inducing remarkable increases in CD69 expression, proliferation, cytokine (IL-4 and IFN-γ) expression by naïve splenic cells in a concentration-dependent manner. Lympho-activation and proliferation induced by AcF1 was partly inhibited by U0126, a selective mitogen activated protein kinase kinase (MKK) inhibitor. Additionally, AcF1 was shown to induce structural and functional maturation of bone-marrow derived dendritic cells (BM-DCs) and also increased their specific-antigen presentation functions in vitro. When employed as an adjuvant in a homologous prime-boost OVA immunisation in C57BL/6 mice, AcF1 significantly (P<0.05) increased the level of OVA-specific IgG1 and IgG2a titres in the sera of immunised mice, compared to the control group immunised with OVA alone. The antigen-specific CTL responses, measured by intracellular staining for CD8+/IFN-γ+, did not show any significant difference. The improvement in antibody responses and strong immune cells activating properties observed in the study show that AcF1 could be employed as a potential vaccine adjuvant and requires further study in combination with other vaccine antigens capable of eliciting strong CTL responses.

Acknowledgements: The Alexander von Humboldt Foundation is gratefully acknowledged for postdoctoral fellowship award to Dr C.S Nworu

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