膜攻击复合物（MAC），系一通常生成于致病细菌表面的结构。人体补体系统的替代补体途径、经典补体途径、凝集素途径均可产生这种复合物。该复合物是免疫系统的效应蛋白之一，它可以在靶细胞的细胞膜上形成能破坏后者磷脂双分子层的穿膜通路，从而使得靶细胞裂解死亡。

有多种蛋白质参与膜攻击复合物的组装。具有高活性的C5b会与C6连接形成C5b-6复合体，随后，C5b还会与C7连接形成C5b-6-7复合体。C5b-6-7复合物又会与由α、β、γ三条炼构成的C8结合，形成C5b-6-7-8配合体。后者又会与C9结合，并作为C9聚合的催化剂。

The membrane attack complex (MAC) or terminal complement complex (TCC) is a structure typically formed on the surface of pathogenic bacterial cells as a result of the activation of the host's alternative pathway, classical pathway, or lectin pathway of the complement system, and it is one of the effector proteins of the immune system. The membrane-attack complex (MAC) forms transmembrane channels. These channels disrupt the cell membrane of target cells, leading to cell lysis and death.