Immunology Quiz on Complement System Functions

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of C3b in the opsonization process?

It neutralizes toxins produced by pathogens.

It triggers the inflammation response.

It directly kills pathogens by lysis.

It enhances the binding of pathogens to phagocytes. (correct)

Which complement component is the most potent chemoattractant that attracts neutrophils to the site of infection?

C2b

C3a

C5a (correct)

C4a

What occurs during class switching of B cells?

B cells enhance opsonization ability.

B cells change from producing IgG to IgM.

B cells change the type of antibody produced to meet immune needs. (correct)

B cells stop producing antibodies.

How does the binding of C3a, C4a, and C5a to mast cells contribute to inflammation?

By causing mast cell degranulation and histamine release. Signup and view all the answers

What happens if excess immune complexes are not cleared from circulation?

They deposit in blood vessel walls and cause inflammation. Signup and view all the answers

What is the main role of the membrane attack complex (MAC)?

Mediate lysis of pathogens Signup and view all the answers

Which pathway does not require antibodies for activation?

Both B and C Signup and view all the answers

Which protein is involved in the lectin pathway that binds to mannose on the surface of pathogens?

MBL Signup and view all the answers

Which of the following is a biological effect of complement activation?

Opsonization of pathogen Signup and view all the answers

What components are unique to the classical pathway compared to the other pathways?

C4 and C2 Signup and view all the answers

What triggers the cleavage of MASP in the lectin pathway?

Binding of mannose to MBL Signup and view all the answers

Which factor is needed for the activation of the alternative pathway?

Both A and B Signup and view all the answers

Which component is not required for the lectin pathway to function?

C1 Signup and view all the answers

What is the primary function of complement proteins?

To act as a cascade of enzymes for lysis of antigens Signup and view all the answers

What are the main proteins in the classical complement pathway?

C1 to C9 Signup and view all the answers

What is unique about IgM in relation to complement fixation?

IgM can fix complement more efficiently than IgG due to its pentamer structure Signup and view all the answers

How is complement inactivated?

By incubating it at 56°C for 30 minutes Signup and view all the answers

What distinguishes the larger and smaller fragments of complement proteins after activation?

The smaller fragment typically diffuses into circulation Signup and view all the answers

Which of the following is NOT a characteristic of complement proteins?

Produced only in the spleen Signup and view all the answers

Which statement correctly describes the assembly of the complement pathway's C1 protein?

C1 consists of three proteins: C1q, C1r, and C1s Signup and view all the answers

Which ion is necessary for the activation of C1 subunits in the classic pathway?

Calcium Signup and view all the answers

Which microbe-associated molecular pattern (MAMP) is specifically NOT found in the host?

IgM antibodies Signup and view all the answers

What complex is formed by the cleavage of C4 and C2 in the classic pathway?

C3 convertase Signup and view all the answers

Which component stabilizes the C3 convertase in the alternative pathway?

Properdin Signup and view all the answers

What triggers the activation of the alternative pathway?

Presence of endotoxins Signup and view all the answers

What is the primary role of C5b in the classic pathway?

Activate membrane attack complex (MAC) Signup and view all the answers

Which of the following statements about C3b is correct?

C3b is involved in both classic and alternative pathways. Signup and view all the answers

What best describes the function of C5a in the context of inflammation?

Acts as an inflammation mediator Signup and view all the answers

Which factor cleaves B factor into Ba and Bb in the alternative pathway?

Factor D Signup and view all the answers

Study Notes

Complement System

The complement system is a series of serum proteins that act as an enzyme cascade, produced by the liver.
It's present in all body fluids except cerebrospinal fluid (CSF) and urine.
It exists in an inactive form, becoming active upon activation, then leading to lysis of antigens (Ag).
The complement system has more than 23 proteins, ranging from C1 to C9.
A high concentration of complement proteins is found in guinea pig serum, making it suitable for in vitro experiments related to complement activation.
Complement proteins are thermolabile, meaning they are inactivated at 56°C for 30 minutes or even fewer hours at room temperature.
Complement proteins are designated by capital letter C followed by Arabic numbers (e.g., C1, C2).
Each protein, after activation, has two subunits (a and b).
The smaller fragment is designated 'a'.
The larger fragment is designated 'b', except for C2a, which is larger than C2b.
Larger fragments bind to functional complexes while smaller fragments diffuse into the circulatory system.

Complement Pathways

Complement activation occurs through three pathways: the classical pathway, the lectin pathway, and the alternative pathway.
Classical pathway: Triggered by antigen-antibody complexes (IgM and IgG).
- C1 binds to the Fc portion of the antibody.
- C1 activates C1r and C1s (esterase activity).
- C1s cleaves C4 and C2.
- C4b and C2a form C3 convertase (C4b2a).
- C3 convertase cleaves C3 into C3a and C3b.
- C3b joins C4b2a to form C5 convertase (C4b2a3b).
- C5 convertase cleaves C5 into C5a and C5b.
- C5b initiates the formation of the membrane attack complex (MAC).
Alternative pathway: Activated by microbial components like lipopolysaccharide (LPS) and endotoxins, and is part of the innate immune system.
- No antibody (Ab) is required.
- C3 undergoes spontaneous hydrolysis to form C3(H2O).
- Factor B binds to C3(H2O).
- Factor D cleaves Factor B into Ba and Bb.
- C3b, Bb, and properdin (factor P) form C3 convertase (C3bBb).
- C3 convertase further cleaves C3 and forms C5 convertase (C3bBb3b) which cleaves C5 into C5a and C5b.
- C5b initiates the formation of the MAC.
Lectin pathway: Activated by mannose-binding lectin (MBL) binding to mannose residues on microbial surfaces.
- MBL binds to pathogen surfaces.
- MBL-associated serine proteases (MASPs) cleave C4 and C2.
- This forms the C3 convertase, similar to the classical pathway.

Complement Activity Regulation

Complement activation is tightly regulated by proteins.
- Proteins on cell surfaces, such as sialic acid, facilitate the inactivation of complement components.
- Control proteins such as CD59, inhibits MAC formation.
- Serum proteins like C1 inhibitor, Factor H, and Factor I regulate complement activation.

Consequences of Complement Activation

Lysis of pathogens: MAC formation causes lysis of cells by forming pores in their membranes.
Opsonization: C3b and C4b enhance phagocytosis by binding to pathogens.
Inflammation: C3a, C4a, and C5a act as chemoattractants, attracting neutrophils.
Neutralization of viruses and toxins: C3b contributes to this process.
Clearance of immune complexes: Immune complexes are removed from the circulation.
Enhancement of antibody production: C3b binds to complement receptors on B cells leading to B cell proliferation and class switching.

Complement Deficiencies

Deficiencies in complement components can lead to recurrent infections, immune complex diseases, and other issues.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the complement system, including the functions of various complement components and their roles in opsonization, inflammation, and B cell class switching. This quiz covers key processes and pathways within the immune response.