Astragalus membranaceus Root Extract Improves T Cell Immunity in CTX-Immunosuppressed Mice and Is Associated with Hypermethylation of the Cpt1a Locus.

Astragalus membranaceus (AM) has been reported to support immune function, but its epigenetic mechanism on immune restoration of cyclophosphamide (CTX)-induced immunosuppression remains unclear. To evaluate the recovery of immune function, we assessed the injury of splenic pathology, cytokines levels in serum, proportional changes in CD4+ and CD8+ T cells, and the recall response of Hspx-specific T cell. In addition, to define the underlying epigenetic regulatory mechanism, we measured the expression levels of DNA methyltransferases (Dnmt1, Dnmt3a and Dnmt3b) and the methylation status of the Carnitine palmitoyltransferase 1A (Cpt1a) gene. The results showed that the crude extract of AM repaired the immunosuppression induced by CTX. This is reflected in the alleviation of splenic pathological injury, the elevated proportions of CD4+ and CD8+ T cells, and the increased levels of serum IL-2 and IFN-γ. The crude extract of AM also enhanced the recall response of Hspx-specific CD8+ T cells; that is, the frequencies of the resulting IL-2+ and IFN-γ+ cells were significantly higher than those in the CTX + Vaccine group. All these results indicate that the adaptive immune response induced by the crude extract of AM is significantly enhanced. On the other hand, AM crude extract reversed the CTX-induced downregulation of Dnmt3a mRNA and restored CpG methylation of Cpt1a gene to a level comparable to the vaccine group at molecular level. Consistent with the elevated CpG methylation, CTX-induced upregulation of Cpt1a mRNA was also reduced. These findings reveal that AM extract enhances the antigen-specific functional recall responses of CD8+ T cells in immunosuppressed mice were associated with Cpt1a gene methylation, thereby establishing a translational link between traditional herbal medicine and modern epigenetics.