Original Article

Astragaloside II triggers T cell activation through regulation of CD45 protein tyrosine phosphatase activity

Chun-ping Wan, Li-xin Gao, Li-fei Hou, Xiao-qian Yang, Pei-lan He, Yi-fu Yang, Wei Tang, Jian-min Yue, Jia Li, Jian-ping Zuo
DOI: 10.1038/aps.2012.208


Chun-ping WAN1, 3, Li-xin GAO2, Li-fei HOU2, Xiao-qian YANG2, Pei-lan HE2, Yi-fu YANG1, Wei TANG2, Jian-min YUE2, *, Jia LI2, *, Jian-ping ZUO1, 2, *
1Laboratory of Immunology and Virology, Shanghai University of Traditional Chinese Medicine, Shanghai 201203, China; 2State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China; 3Central Laboratory, No 1 Hospital Affiliated Yunnan University of Traditional Chinese Medicine, Kunming 650021, China

Aim: To investigate the immunomodulating activity of astragalosides, the active compounds from a traditional tonic herb Astragalus membranaceus Bge, and to explore the molecular mechanisms underlying the actions, focusing on CD45 protein tyrosine phosphatase (CD45 PTPase), which plays a critical role in T lymphocyte activation.
Methods: Primary splenocytes and T cells were prepared from mice. CD45 PTPase activity was assessed using a colorimetric assay. Cell proliferation was measured using a [3H]-thymidine incorporation assay. Cytokine proteins and mRNAs were examined with ELISA and RT-PCR, respectively. Activation markers, including CD25 and CD69, were analyzed using flow cytometry. Activation of LCK (Tyr505) was detected using Western blot analysis. Mice were injected with the immunosuppressant cyclophosphamide (CTX, 80 mg/kg), and administered astragaloside II (50 mg/kg).

Results: Astragaloside I, II, III, and IV concentration-dependently increased the CD45-mediated of pNPP/OMFP hydrolysis with the EC50 values ranged from 3.33 to 10.42 µg/mL. Astragaloside II (10 and 30 µg/mL) significantly enhanced the proliferation of primary splenocytes induced by ConA, alloantigen or anti-CD3. Astragaloside II (30 µg/mL) significantly increased IL-2 and IFN-γ secretion, upregulated the mRNA levels of IFN-γ and T-bet in primary splenocytes, and promoted CD25 and CD69 expression on primary CD4+ T cells upon TCR stimulation. Furthermore, astragaloside II (100 ng/mL) promoted CD45-mediated dephosphorylation of LCK (Tyr505) in primary T cells, which could be blocked by a specific CD45 PTPase inhibitor. In CTX-induced immunosuppressed mice, oral administration of astragaloside II restored the proliferation of splenic T cells and the production of IFN-γ and IL-2. However, astragaloside II had no apparent effects on B cell proliferation.

Conclusion: Astragaloside II enhances T cell activation by regulating the activity of CD45 PTPase, which may explain why Astragalus membranaceus Bge is used as a tonic herb in treating immunosuppressive diseases.

Keywords: immunomodulating agent; Astragalus membranaceus Bge; astragaloside II; CD45 PTPase; LCK; T cell; splenocyte; Src-family kinase; IFN-γ; IL-2; cyclophosphamide

This work was supported by grants from the National Natural Science Foundation of China (81072652 and 81273524), and National Science & Technology Major Project “New Drug Creation and Manufacturing Program” China (2012ZX09102-101-006).
* To whom correspondence should be addressed.
E-mail jpzuo@mail.shcnc.ac.cn (Jian-ping ZUO); jli@mail.shcnc.ac.cn (Jia LI);
myue@mail.shcnc.ac.cn (Jian-ming YUE)
Received 2012-10-23 Accepted 2012-12-26

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