The defensive function of defensive qi in Huangdi Neijing (The Yellow Emperor 's Inner Classic) includes the effect of immune system of human body against the pathogen invasion. According to the basic research, it is believed that the circulation of defensive qi in meridian is interpreted as the flow of interstitial fluid in the low hydraulic resistance channel that is overlapped with lymphatic vessels, transporting the antigen information from interstitium to lymph nodes and generating adaptive immune response. Enhancing meridian circulation and promoting the flow of interstitial fluid may improve the immunity, which demonstrating the thought of traditional Chinese meridian as "pathogens failing to invade the body when the anti-pathogenic qi is strong enough inside".
《黄帝内经》卫气的卫外功能包含了人体免疫系统抵御病原体侵犯的作用。根据基础研究，卫气在经络中的运行可解析为组织液在低流阻间质通道中的流动，其路径与淋巴管重合，可将抗原信息从间质输运至淋巴结，产生适应性免疫应答。疏通经络、促进组织液流动可提高免疫力，彰显“正气存内，邪不可干”的中医思想。.
Keywords: Huangdi Neijing (The Yellow Emperor's Inner Classic); defensive qi; immune system; interstitial fluid; meridian.