抗體，也叫免疫球蛋白（Ig），是一種能特異性結合抗原的糖蛋白，而抗原是在易感染動物體內引發抗體產生的物質。在體內，抗體是由于外源性分子的侵襲而產生的。抗體以一個或者多個Y字形單體存在，每個Y字形單體由4條多肽鏈組成，包含兩條相同的重鏈和兩條相同的輕鏈。輕鏈和重鏈是根據它們的分子量大小來命名的。Y字形結構的頂端是可變區，為抗原結合部位。任何一個抗體的輕鏈都可以分為κ或λ型（基于小分子多肽結構上的差異），每一個抗體的重鏈則決定了它的類或型。
The protein encoded by this gene is the 80-kilodalton subunit of the Ku heterodimer protein which is also known as ATP-dependant DNA helicase II or DNA repair protein XRCC5. Ku is the DNA-binding component of the DNA-dependent protein kinase, and it functions together with the DNA ligase IV-XRCC4 complex in the repair of DNA double-strand break by non-homologous end joining and the completion of V(D)J recombination events. This gene functionally complements Chinese hamster xrs-6, a mutant defective in DNA double-strand break repair and in ability to undergo V(D)J recombination. A rare microsatellite polymorphism in this gene is associated with cancer in patients of varying radiosensitivity. [provided by RefSeq, Jul 2008]
備注：圖片僅供參考。僅供科研，不可用于臨床。
