Complement System Overview

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Questions and Answers

What can cause biologic effects of complement activation?

Nutritional deficiencies

Persistent infection or autoantibodies (correct)

Environmental toxins

Genetic mutations only

What effect does complement activation have on disease pathology?

It has no significant effects

It may contribute to inflammation and lysis (correct)

It exclusively promotes healing

It inhibits the inflammatory response

What is a common result of elevated complement levels?

Specific diagnosis of infections

Improved tissue regeneration

Decreased immune response

Association with inflammatory conditions (correct)

Which of the following best explains decreased complement levels?

Complement is currently being consumed Signup and view all the answers

What role does the C1 inhibitor (C1INH) play in the complement system?

Blocks activities of C1 Signup and view all the answers

Which component is targeted by MAC inhibitors?

C5b-7 complex Signup and view all the answers

Deficiencies in complement are linked to which of the following?

Primary immunodeficiencies Signup and view all the answers

What is the function of complement receptor type I (CRI or CD35)?

Inactivate C4b and C3b Signup and view all the answers

What is the primary function of the complement system in relation to pathogens?

Facilitates direct phagocytosis of pathogens Signup and view all the answers

Which of the following correctly describes the activation of complement components?

Activation requires cleavage by proteolytic enzymes Signup and view all the answers

Which component of the complement system is synthesized mainly by hepatocytes?

C1 Signup and view all the answers

What are the three main physiological activities of the complement system?

Host defense, interaction with adaptive immunity, waste disposal Signup and view all the answers

Which complement pathway is independent of mannose?

Properidin pathway Signup and view all the answers

What happens to complement components once they are activated?

They catalyze the next step in the pathway Signup and view all the answers

Which statement about the complement system is false?

It functions mainly through signaling pathways Signup and view all the answers

Which of the following groups of components is specifically involved in the classical pathway of complement activation?

C1q, C1r, C1s Signup and view all the answers

What is the function of C3 convertase?

It converts C3 into C3a and C3b. Signup and view all the answers

Which factor is involved in the formation of the C5 convertase?

C4b2b Signup and view all the answers

What role does properidin play in the complement system?

It stabilizes the C3b-Bb complex. Signup and view all the answers

What is the result of C3 and C5 complement activation in the immune response?

Stimulates mast cells and basophils. Signup and view all the answers

In the presence of pathogen components like LPS, what happens to Factor H?

It is inhibited, affecting C3 convertase function. Signup and view all the answers

What three main physiological activities are associated with the complement system?

Cell lysis, opsonization, and anaphylatoxin release. Signup and view all the answers

What stimulates mast cells and basophils during complement activation?

C3a, C4a, and C5a Signup and view all the answers

Which of the following is NOT a component of the classical pathway of complement activation?

C5 convertase Signup and view all the answers

What happens if complement complexes accumulate in tissues?

They might lead to tissue damage. Signup and view all the answers

Study Notes

Complement Proteins

Over 20 serum glycoproteins
Synthesized by hepatocytes (except C1)
Important for killing pathogens, recruiting inflammatory cells, opsonizing pathogens, and clearing immune complexes
Many circulate as proenzymes (inactive enzymes) that require proteolytic cleavage for activation.
Once activated, components catalyze the next step of the pathway.
Activated components remain active for a short time.

Functions of the Complement System

Three main functions
- Host defense against infection
- Interface between innate and adaptive immunity
- Disposal of waste

Complement System Activation Pathways

Three main pathways
- Classical
- Alternative
- Mannose-binding lectin

Classical Pathway

Initiated by antigen-antibody complexes or certain pathogen components
C1q binds antigen-antibody complexes or pathogen surface
C1r and C1s are activated.
C1s cleaves C4, generating C4a and C4b
C2 binds C4b and is cleaved by C1s, generating C2a and C2b
C4b2a complex forms the classical pathway C3 convertase.
C3 convertase cleaves C3 to C3a and C3b.
C4b2a3b complex forms the classical pathway C5 convertase.
C5 convertase cleaves C5 resulting in C5a and C5b.

C1q

Binds to antigen-antibody complexes and pathogen surfaces.

C1r & C1s

Cleave C4 and activate complement by triggering the classical cascade.

C4

Cleaved by C1s.

C2

Cleaved by C1s after binding to C4b

Properidin

Stabilizes the alternative pathway C3 convertase (C3bBb).

Results of Complement Activation

C3a, C4a, C5a activate mast cells and basophils.
C5a activates neutrophils and monocytes.
C5b-9 forms the membrane attack complex (MAC), which can lyse cells.

Complement Activation and Disease

Elevated complement levels can be associated with inflammatory conditions, trauma, and acute illness.
Decreased complement levels can be associated with excessive complement activation, complement consumption, or genetic deficiencies in specific complement components.

Complement Regulation

Control mechanisms ensure complement system activation is regulated and does not cause excessive damage:
- C1 inhibitor (C1INH): blocks C1 activity
- Anaphylatoxin inactivator: inactivates C4a, C3a, and C5a.
- MAC inhibitors: inactivate C5b-7.
- Complement receptor type I (CRI or CD35): inactivates C4b and C3b.

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Description

Explore the essential components and functions of the complement system in this quiz. Understand how it plays a crucial role in host defense, immune response, and waste disposal through various activation pathways. Dive into the details of classical, alternative, and mannose-binding lectin pathways.