Anti-Inflammatory Mechanism of Astragaloside IV in the Recurrence of Asthma: Critical Role of Memory T Cells and OX40/OX40L Signaling Pathway

Abstract

The recurrence of asthma is partly mediated by central memory CD4(+) T cells(TCM) that promote lung inflammation through the production of effector T cells. Targeting the expansion of pathogenic TCM(central memory CD4(+) T cells) is a promising therapeutic strategy to block production of effector T cells. The study aimed to evaluate the regulatory effects of Astragaloside IV (AS-IV) on TCMs and try to explore the anti-inflammatory mechanism of AS-IV in asthmatic mice. We developed a murine model of asthma by ovalbumin(OVA) challenge. Flow cytometry was used to determine the counts of CD4(+) memory T cells subgroups. Pulmonary tests, inflammatory cytokines in blood and inflammatory cells in bronchoalveolar lavage fluid,were measured to evaluate the inflammatory response level before and after AS-IV treatment. To further determine the role of TCM in the recurrence of inflammation, TCM were isolated by Magnetic-activated cell sorting (MACS) from spleens of asthma, control, AS-IV and dexamethasone treatment mice. The isolated cells were adoptive transferred into nude mice via tail intravenous injection, respectively, and the inflammatory response level of the lung was measured after OVA challenge. The effects of AS-IV on TCM viability, the number of the frequency (in percent) of CD44highCD62Lhigh cells, and the expression of OX40 and OX40L were measured before and after AS-IV treatment. In circulation blood, we demonstrated increased percentages of CCR7highCD62LlowCD4+ effector memory T cells(TEM) and decreased CCR7highCD62LhighCD4(+) TCM in asthma mice. On the contrary, the TEM subgroup percentage were decreased and the TCM phenotypes were increased in asthmatic spleen. AS-IV treatment significantly decreased CD4(+) T effector phenotypes in blood and inhibited the lung inflammatory response. Additionally, the inflammation of nude mice that adoptive transferred TCM from AS-IV treatment asthmatic mice had relieved inflammation compared with asthmatic group. In vitro, we successfully used spleen T lymphoid cells stimulated with IL-7 and OVA to induce a central memory T cell model. TCM co-cultured with DC cells had a significantly increased expression of OX40/OX40L. AS-IV pretreatment partially inhibited the expression of OX40 signal pathway. This study indicates that AS-IV can ameliorate asthma inflammation by inhibiting the production of TEM form TCM. The treatment mechanism maybe involved in the OX40/OX40L pathway.