一种蛋白，由免疫系统的细胞产生，参与破坏杀死引发疾病的病原体。人体可以产生超过一万亿个不同的抗体。从结构上讲，每个抗体由两个相同的重链和两个相同的轻链组成，构成Y形。Y形的头部可以识别并结合细菌、病毒等病原体的蛋白区。这一结合是引起免疫系统破坏并清除病原体的一系列反应的第一步。抗体具有非常特异性，每种抗体只识别和结合一种蛋白质区域。这种特异性和结合能力是免疫系统对外来蛋白作出反应的重要机制，也是使抗体用于研究和治疗成为可能的重要属性。抗体可以用来在诊断中检测蛋白，从混合物中分离蛋白或用于治疗疾病，如专门针对肿瘤。单克隆抗体可以在治疗或诊断用靶子引导下大量产生。

A protein, produced by cells of the immune system, that is involved in the destruction of disease-causing pathogens. The human body is capable of generating over a trillion different antibodies. Structurally, each antibody is formed by the interaction of two identical “heavy” chains and two identical light chains, all of which combine to form a Y shape (the heavy chains span the entire Y, and the light chains the two arms only). The tips of the Y recognize and bind to areas of protein in disease-causing agents such as bacteria and virus. This binding is the first step in a series of responses that lead to destruction or disposal of the pathogens by the immune system. Antibodies are very specific in that each antibody will recognize and bind to one protein region only. This specificity and binding ability is an important mechanism by which the immune response targets foreign proteins, but is also an important property allowing the use of antibodies for research and therapeutic purposes. Antibodies can be used to detect proteins for diagnostic purposes, to isolate a protein from a mixture, or for therapeutic purposes such as specifically targeting tumors. Identical antibodies called monoclonal antibodies can be generated in large amounts against a therapeutic or diagnostic target.