Classical pathway

Definition

The classical pathway is a mechanism of the complement system that is activated by antibodies bound to antigens, leading to a cascade of immune responses. It plays a crucial role in both innate and adaptive immunity.

5 Must Know Facts For Your Next Test

1. The classical pathway is initiated when C1 complex binds to antigen-antibody complexes.
2. Activation of the classical pathway leads to the formation of the membrane attack complex (MAC), which can lyse pathogens.
3. It involves sequential activation of complement proteins C1, C4, C2, and C3.
4. Complement component C3b acts as an opsonin, marking pathogens for phagocytosis.
5. Deficiencies in components of the classical pathway can result in increased susceptibility to infections.

Review Questions

• What triggers the activation of the classical pathway?
• Name the complement proteins involved in the early stages of the classical pathway.
• How does the formation of C3b contribute to pathogen elimination?

Related terms

Alternative Pathway:

A complement activation pathway triggered by pathogen surfaces without antibodies.

Lectin Pathway:

A complement activation route initiated by binding mannose-binding lectin to microbial surfaces.

Membrane Attack Complex (MAC): A structure formed by terminal complement components that can lyse target cells.