Immunology: MCQ on Complement Pathway

Multiple Choice Questions on Complement Pathway and Immune Response 

1) Complements are the proteins that are involved in the clearance of antigens/bacteria. 
Which of the following pathway is involved in the adaptive immune response?
a) Alternative Pathway
b) Classical Pathway
c) Lectin Binding Pathway
d) All of the above

2) In the classical pathway, the antibody activated the C1 complex consisting of the C1q, C1r & C1s subunits. 
Which of the following subunit binds to the antibody?
a) C1q
b) C1r
c) C1s
d) All of the above

3) Which of the following isotype antibody is a potent activator of the classical complement pathway?
a) IgM
b) IgA
c) IgE
d) IgG

4) Which of the following C1 subunit has the catalytic activity that cleaves C4 and C2 complement proteins?
a) C1q
b) C1r
c) C1s
d) None of the above

5) In the classical pathway, which of the following complement complex serve as C3 convertase
a) C4aC2a
b) C4bC2b
c) C4bC2a
d) C4aC2b

6) In the classical pathway, after the proteolysis of the C3 complement pathway.
Which component is cleaved by C4bC2aC3b and initiates the formation of membrane attack complex?
a) C5
b) C6
c) C7
d) C8

7) The alternative pathway is activated in response to antigens but does not require antibody interaction. The following proteins are the component of the alternative pathway, except?
a) C3
b) Factor B
c) Factor D
d) Properdin

8) C3 undergo spontaneous hydrolysis to form C3a and C3b, but they have a short half before encountering the carbohydrate bacterial antigens only. 
Which of the following carbohydrate moieties are present in the mammalian cells to inactivate C3b?
a) Mannose-6-phosphate
b) Sialic acid
c) Sphingosine
d) None of the above

9) Which of the following process is required for the formation of a C3 convertase that amplifies complement activation?
a) C3b must bind to foreign antigens
b) Factor B must bind to C3b for its proteolysis by Factor D
c) Properdin must bind to the C3bBb complex for stabilization
d) All of the above

10) Certain microorganisms such as Salmonella, Listeria, Neisseria, and Cryptococcus consist of specific carbohydrate moieties on the surface antigen that activate
a) Alternative Pathway
b) Classical Pathway
c) Lectin Binding Pathway
d) All of the above

11) The membrane attack complex consists of five different complement proteins C5, C6, C7, C8, and C9. 
Which of the following subunits bind to the surface and provide a binding site for a subsequent component?
a) C5a
b) C5b
c) C6a
d) None of the above

12) Which of the following complement protein polymerizes to form a perforin-like structure that stabilizes membrane attack complex?
a) C6
b) C7
c) C8
d) C9

13) Which of the following component of complement proteins enhances inflammation (anaphylatoxin)?
a) C3a
b) C5a
c) Both of the above
d) None of the above

14) Which of the following complement component facilitate opsonization and phagocytosis?
a) C3a
b) C3b
c) C5a
4) C5b

15) Which of the complement receptor activate phagocytosis by binding to C3b & C4b coated particles
a) CR1
b) CR2
c) CR3
d) CR4

16) Which of the following complement receptor activate a humoral response by promoting the trapping of an antigen-antibody complex?
a) CR1
b) CR2
c) CR3
d) CR4

17) The deficiency of the complement proteins (C1q, C1q, C1s) or the complement receptors leads to the accumulation of immune complexes resulting in SLE or vasculitis. 
The deficiency affects which of the following complement pathway?
a) Alternative pathway
b) Lectin binding pathway
c) Classical pathway
d) None of the above

18) The deficiency of the complement component factor D and properdin leads to recurrent bacterial infection. 
Which of the following pathway is affected in this condition?
a) Alternative pathway
b) Classical pathway
c) Lectin binding pathway
d) None of the above

19) Erythrocytes express the complement receptor help that transport and clear the immune complex from circulation. 
Which of the following complement receptor is expressed in the erythrocytes?
a) CR4
b) CR2
c) CR3
d) CR1

20) Paroxysmal Nocturnal Hemoglobinuria is the condition that manifests as increased fragility of erythrocytes, leading to chronic hemolytic anemia, pancytopenia, and venous thrombosis. 
Which of the following option is associated with PNH?
a) Deficiency of complement protein C9
b) Deficiency of Factor D
c) Deficiency of DAF
d) Deficiency of complement receptor

Multiple Choice Answer:
1- b) Classical Pathway
2- a) C1q
3- a) IgM
4- c)C1s
5- b)C4bC2b
6- a)C5
7- a)C3
8- b)Sialic acid
9- d)All of the above
10- c)Lectin Binding Pathway
11- b)C5b
12- d)C9
13- c)Both of the above
14- b)C3b
15- a)CR1
16- b)CR2
17- c)Classical pathway
18- a)Alternative pathway
19- d)CR1
20- c)Deficiency of DAF


  1. hi
    thank you for the mcqs they are very helpful. A couple of them though are answered incorrectly.
    the right answers should be: 2-a, 5-c, 6-a, 11-a.

  2. Thank you for your complements and suggestion. As for Question 5, it seemed confusing, as C4bC2a was referenced in some study materials. And the correct answer is C4bC2b.

  3. hi. thank you so much for the quiz. i agree with C4bC2a being the answer for question 5. As for question 11, i think you should check on the answer again because i believe that the correct answer should be C5b which is B.

  4. Thank you for the suggestion, yeah I agree that 11- should be 11b

  5. thanks ,, the mcqs are usefull,, but regarding 5th question.. c2 is exception as for all others b part is heavy but for c2 it should be a part heavy ,, so c4bC2a should be c3 convertase


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