一種蛋白，由免疫系統的細胞產生，參與破壞殺死引發疾病的病原體。人體可以產生超過一萬億個不同的抗體。從結構上講，每個抗體由兩個相同的重鏈和兩個相同的輕鏈組成，構成Y形。Y形的頭部可以識別并結合細菌、病毒等病原體的蛋白區。這一結合是引起免疫系統破壞并清除病原體的一系列反應的第一步。抗體具有非常特異性，每種抗體只識別和結合一種蛋白質區域。這種特異性和結合能力是免疫系統對外來蛋白作出反應的重要機制，也是使抗體用于研究和治療成為可能的重要屬性。抗體可以用來在診斷中檢測蛋白，從混合物中分離蛋白或用于治療疾病，如專門針對腫瘤。單克隆抗體可以在治療或診斷用靶子引導下大量產生。

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.