complement binding

Definition

Target type: molecularfunction

Binding to a component or product of the complement cascade. [GOC:add, ISBN:0781735149]

Complement binding is a crucial process in the innate immune system, involving the recognition and attachment of complement proteins to target surfaces. These targets can include pathogens like bacteria, viruses, and parasites, as well as damaged or apoptotic cells. This binding initiates a cascade of events known as the complement cascade, leading to the elimination of the target.

The molecular function of complement binding can be summarized as follows:

1. Recognition: Complement proteins, specifically the C1q component of the classical pathway, have globular heads that can bind to specific structures on the target surface. These structures can include:
- Antibodies bound to antigens (classical pathway activation)
- Microbial surface components like lipopolysaccharide (LPS) or mannose (lectin pathway activation)
- Damaged or apoptotic cells (alternative pathway activation)

2. Activation: Once C1q binds to the target, it activates the complement cascade, a series of proteolytic reactions that amplify the immune response. This activation involves the sequential cleavage of complement proteins, generating active enzymes and forming a complex on the target surface.

3. Effector functions: The complement cascade leads to various effector functions, including:
- Opsonization: Complement proteins like C3b bind to the target surface, enhancing phagocytosis by immune cells like macrophages and neutrophils.
- Membrane attack complex (MAC) formation: The terminal components of the complement cascade assemble into a pore-forming complex, disrupting the target cell membrane and leading to cell lysis.
- Recruitment of immune cells: Complement proteins act as chemoattractants, drawing immune cells like neutrophils, macrophages, and lymphocytes to the site of infection.

In summary, complement binding is a key step in the innate immune system, triggering a cascade of events that ultimately eliminate pathogens and damaged cells. It involves specific recognition, activation, and various effector functions, contributing to the overall immune defense of the host.'
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Proteins (1)

Compounds (1)