免疫力(immunity)
抵抗入侵微生物或较大寄生虫攻击或克服感染的能力。以身体的免疫系统的正常运作为基础，在自然免疫或天生免疫中，出生时就有的免疫机制对众多不同的微生物发生作用，不管先前是否遭遇过。後天的免疫反应（适应後对特定微生物或其产物发生作用）受到先前该种微生物出现的刺激。先前受到特定病原体感染或接种疫苗时，会产生这类的免疫。天生免疫的机制包括物理障碍（如皮肤）和化学障碍（例如唾液中出现的杀菌）。穿透身体自然障碍的微生物会遭遇到抑制其生长与繁殖的物质（例如干扰素）。噬细胞（吞噬粒子的细胞）包围并摧毁入侵的微生物，而自然杀手细胞会刺穿微生物的细胞膜。天生免疫并不赋予身体永久的抵抗力或免疫力。後天免疫以B细胞和T细胞对於抗原的辨识为基础，在天生机制不足以遏止抗体进一步入侵时活跃起来。杀手T细胞或毒害T细胞摧毁受感染的细胞和外来的细胞。助手T细胞把受抗体出现而遭到刺激并增殖的B细胞变为分泌抗体的细胞，也就是浆细胞。浆细胞所产生的抗体附着於产生抗体的细胞，标示毁灭的记号。後天免疫仰赖致敏记忆B细胞和T细胞的长期存活，它们能在同一病原体再度感染时快速繁殖。亦请参阅immunodeficiency、immunology、leukocyte、reticuloendothelial system。
English version：
immunity
Ability to resist attack or overcome infection by invading microbes or larger parasites. Immunity is based on the proper functioning of the body's immune system. In natural or innate immunity, immune mechanisms present at birth work against a wide variety of microbes whether or not they have been encountered before. Acquired immune responses, tailored to act against a specific microbe or its products, are stimulated by the prior presence of that microbe. Previous infection with a particular pathogen, as well as vaccines, produce this type of immunity. The mechanisms of innate immunity include physical barriers (including the skin) and chemical barriers (such as bactericidal enzymes present in saliva). Microbes that penetrate the body's natural barriers encounter substances (such as interferon) that inhibit their growth or reproduction. Phagocytes (particle-engulfing cells), surround and destroy invading microbes, and natural killer cells pierce the microbe's outer membrane. Innate immunity does not confer lasting resistance, or immunity, to the body. Acquired immunity is based on the recognition of antigen by B and T cells and is activated when innate mechanisms are insufficient to stem further invasion by pathogens. Killer or cytotoxic T cells destroy infected and foreign cells. Helper T cells induce B cells stimulated by the presence of antigen to proliferate into antibody-secreting cells, or plasma cells. Antibodies produced by plasma cells bind to antigen-bearing cells, marking them for destruction. Acquired immunity relies on the long-term survival of sensitized T and B memory cells, which can proliferate quickly upon reinfection by the same pathogen. See also immunodeficiency, immunology, leukocyte, reticuloendothelial system.