Complement System Test 2

Welcome to your Complement System Test 2

1. Which component is the central convergence point of all complement activation pathways?

A) C1q

B) C2

C) C3

D) C5

2. Which pathway is specifically activated by antigen-antibody complexes?

A) Alternative pathway

B) Lectin pathway

C) Classical pathway

D) Terminal pathway

3. Which immunoglobulin is the most potent activator of the classical pathway?

A) IgA

B) IgE

C) IgG

D) IgM

4. Among IgG subclasses, which one does NOT effectively activate the classical complement pathway?

A) IgG1

B) IgG2

C) IgG3

D) IgG4

5. What is the primary function of C3b?

A) Neutrophil chemotaxis

B) Opsonization

C) Mast cell degranulation

D) Pore formation

7. What is the most powerful complement-derived chemotactic factor for neutrophils?

A) C3a

B) C4a

C) C5a

D) Leukotriene B4

8. Which of the following is the only known positive regulator of the complement system?

A) Factor H

B) Decay-accelerating factor (DAF)

C) Properdin (Factor P)

D) C1 inhibitor (C1INH)

6. Which complement fragments are classified as anaphylatoxins?

A) C2a and C4a

B) C3b and C4b

C) C3a and C5a

D) C5b and C6

9. The Membrane Attack Complex (MAC) is formed by the sequential assembly of which components? Correct Answer: C) C5b, C6, C7, C8, C9 Explanation: The MAC (C5b-9) is the terminal lytic complex. C5b initiates the non-enzymatic, sequential assembly of C6, C7, C8, and multiple C9 molecules to form a pore in the target membrane.

A) C1, C4, C2, C3

B) C3a, C3b, C5a

C) C5b, C6, C7, C8, C9

D) Factor B, Factor D, Properdin

10. Which membrane protein is crucial for protecting host cells from bystander lysis by the MAC?

A) Factor I

B) CD59 (Protectin)

C) Membrane Cofactor Protein (MCP)

D) Properdin

11. A patient with a history of severe, recurrent pyogenic infections is most likely deficient in which complement component?

A) C1

B) C2

C) C3

D) C9

12. The spontaneous, low-level hydrolysis of C3 in plasma, which continuously primes the alternative pathway, is known as:

A) Opsonization

B) Chemotaxis

C) Tickover

D) Amplification

13. Which of the following cleaves C3 into C3a and C3b in the Lectin Pathway?

A) C1s

B) MASP-2

C) Factor D

D) C3 Convertase

14. Which molecule serves as the "C3 convertase" of the Alternative Pathway?

A) C3bBb

B) C4b2a

C) C3(H2O)

D) C5b6789

15. The binding of C3b to which receptor on B-cells significantly lowers the threshold for B-cell activation?

A) CR1 (CD35)

B) CR2 (CD21)

C) CR3 (CD11b/CD18)

D) C5aR1

16. Which ion is essential for maintaining the structural integrity of the C1 complex (C1q-C1r2-C1s2)?

A) Magnesium (Mg²⁺)

B) Iron (Fe²⁺)

C) Calcium (Ca²⁺)

D) Zinc (Zn²⁺)

17. A patient presents with hereditary angioedema. This is most directly caused by a deficiency in which complement regulator?

A) Factor H

B) CD59

C) C1 Inhibitor (C1INH)

D) Decay-Accelerating Factor (DAF)

18. Which of the following is the correct sequence for the formation of the Alternative Pathway C5 convertase?

A) C3b binds C5, then binds Factor B

B) C3b binds Factor B, which is cleaved by Factor D to form C3bBb

C) C3b binds Factor B, cleaved by Factor D to form C3bBb, and a second C3b molecule binds to this complex

D) C5 is cleaved directly by Factor D

20. Which statement best describes the role of complement in clearance of apoptotic cells?

A) MAC lyses apoptotic cells to release intracellular antigens.

B) C5a attracts macrophages to phagocytose apoptotic cells.

C) C1q and other collectins bind to surface markers on apoptotic cells, facilitating non-inflammatory phagocytosis.

D) Apoptotic cells are highly resistant to complement activation.

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