Final answer:
The cascade of serum proteins that attack bacterial invaders is called the activation of complement, which includes various pathways such as the classical, alternate, and lectin pathways for initiating a sequence of immune responses leading to pathogen destruction.
Step-by-step explanation:
The cascade of 20 serum proteins that attack bacterial invaders is known as the activation of complement. The complement system includes multiple proteins that work in tandem to eliminate pathogens. This sophisticated system is continuously synthesized mainly by liver cells and macrophages and plays a critical role in the innate immune response. It can be activated through various pathways, one of which is the classical pathway, where antibodies such as IgG or IgM bind to the surface of a pathogen cell, triggering the sequence of events in the complement cascade.
There are also other pathways like the alternate pathway and the lectin pathway, which can activate the complement system without the need for antibodies. Once activated, complement proteins sequentially bind and cover the pathogen, which results in opsonization, promoting phagocytosis, and can lead to the destruction of the pathogen through the formation of the membrane attack complex (MAC).