C1 complex

Definition

The C1 complex is a key component of the classical pathway of the complement system, which is part of the immune response. It consists of three subcomponents: C1q, C1r, and C1s.

5 Must Know Facts For Your Next Test

1. The C1 complex initiates the classical pathway by binding to antibodies that are attached to pathogens.
2. C1q binds to the Fc region of IgM or IgG antibodies, triggering a conformational change.
3. This conformational change activates C1r, which then activates C1s by proteolytic cleavage.
4. Activated C1s cleaves the next components in the cascade, specifically C4 and C2.
5. Deficiencies in any components of the C1 complex can lead to increased susceptibility to infections and autoimmune diseases.

Review Questions

• What are the three subcomponents of the C1 complex?
• How does the activation of the C1 complex begin?
• What roles do activated C1r and C1s play in the complement cascade?

Related terms

Complement System: A group of proteins that enhance immune responses through opsonization, chemotaxis, and cell lysis.

Classical Pathway: One of three pathways that activate the complement system; it is initiated by antigen-antibody complexes.

Antibody: A protein produced by B cells that binds specifically to antigens and targets them for destruction.