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

Abstract

BackgroundTinospora 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. MethodsNK 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 CD3−NKp46+CD69+ 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). ResultsBoth 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. ConclusionIn 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.