35. 免疫系统是人体最复杂的系统之一，由几种细胞（淋巴细胞和辅助细胞）组成，这些细胞在全身形成战略性的分布，完全能够识别抗原（非自身或外来物质和细胞），并对之进行中和或将其摧毁，从而保护身体免遭感染和患上癌症。有两种不同但相互关联的免疫形式：先天免疫和获得性免疫。先天免疫在任何外来物质进入身体之前即已在充分运作，因此能够提供迅速保护。获得性免疫是在病原体进入身体之后发展起来的，对以前的接触存有记忆，因此在后来遇到同一抗原时能够作出更强烈的反应。获得性免疫反应主要由 B 淋巴细胞（体液反应）和 T 淋巴细胞（细胞媒介反应）产生。
35. The immune system, one of the most complex systems of the human body, is composed of cells of several types (lymphocytes and accessory cells) strategically spread throughout the body, perfectly positioned to recognize antigens (non-self or foreign substances and cells) and to neutralize or destroy them; this protects against infections and cancer. There are two different but interrelated forms of immunity: innate and acquired immunity. Innate immunity is fully functional before any foreign agent enters the body and thereby provides a rapid defence. Acquired immunity develops after a pathogen has entered the body and maintains memory of previous exposures, yielding a stronger response following subsequent exposure to the same antigen. Acquired immune responses are mainly executed by B-lymphocytes (humoral responses) and T-lymphocytes (cell-mediated responses).