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How does the complement system help antibodies destroy invading microbes?
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antibody
The four-chain structure of an antibody, or immunoglobulin, molecule. The basic unit is composed of two identical light (L) chains and two identical heavy (H) chains, which are held together by disulfide bonds to form a flexible Y shape. Each chain is composed of a variable (V) region and a constant (C) region.
The complement system assists antibodies in destroying microbes primarily through the classical pathway. This process begins when antibodies bind to antigens on the surface of an invading microorganism. Once bound, the tail of the antibody interacts with the complement protein C1, triggering a chemical chain reaction.12
This cascade leads to the activation of the pivotal protein C3, which is cleaved into fragments, including C3b. C3b facilitates the destruction of the microbe in two primary ways:
- Membrane Attack Complex: C3b activates subsequent complement proteins to form a ringlike structure that inserts itself into the microbe's membrane. This creates holes that cause the cell contents to leak out, resulting in lysis (bursting).12
- Opsonization: C3b molecules coat the surface of the pathogen. This process, known as opsonization, makes the microbe more attractive to phagocytic cells like macrophages and neutrophils, which recognize and ingest the pathogen.12
Additionally, small fragments released during this activation promote inflammation, further aiding the immune response.12