Arabinogalactan G1-4A isolated from Tinospora cordifolia induces PKC/mTOR mediated direct activation of natural killer cells and through dendritic cell cross-talk.

Background: Tinospora cordifolia polysaccharide G1-4A activates antigen-presenting cells, but its effect on natural killer (NK) cells is not known. The objective of this study is to assess the effect of G1-4A on NK cells; direct effects as well as through dendritic cell (DC) cross-talk.

Methods: NK cell phenotype and function were assessed in spleen cells treated in vitro with G1-4A or isolated from mice administered with G1-4A. Following treatment with G1-4A in vitro or in cells isolated from G1-4A treated mice (in vivo), activated NK cell phenotype was characterized as CD3NKp46CD69 cells by flow cytometry; NK cell function was evaluated by IFN-γ secretion (ELISA) and cytotoxicity assay (calcein release by target cells in effector: target cells co-culture assay).

Results: Both in vitro as well as in vivoG1-4A treatment increased phenotypic and functional activation of NK cells. So, we wanted to determine if this was through NK-DC crosstalk or direct activation of NK cells. There was increased NK cell activation following co-culture with bone marrow derived DC matured withG1-4A in vitro or splenic DC isolated from G1-4A administered mice indicating crosstalk. G1-4A also increased activation of NK cells in (a) CD11c depleted splenic cells that was contact dependent and (b) purified NKp46 cells that was abrogated by PKC/mTOR inhibitors indicating direct effects on NK cells.

Conclusion: In summary, treatment with G1-4A results in phenotypic and functional activation of NK cells directly as well as through NK-DC cross talk and has the potential to be used as an immunotherapeutic agent.