Immunology Questions and Answers – Immune Complex-Mediated (Type III) Hypersensitivity

This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Immune Complex-Mediated (Type III) Hypersensitivity”.

1. In type III hypersensitivity, overproduction of which two antibody isotypes can lead to formation of excess amounts of immune complexes?
a) IgM &IgG
b) IgA & IgD
c) IgM & IgD
d) IgG & IgE
View Answer

Answer: a
Explanation: In type III hypersensitivity, overproduction of antibody isotypes like IgG and IgM can lead to formation of excessive amounts of immune complexes. These over produced antibody isotypes come in contact with foreign or self-antigen which leads to deposition of large amounts of immune complexes. These complexes are insoluble and, in most cases, appear in clumped form due to which it becomes difficult to remove from various tissues by phagocytosis. 

2. Which of the following is referred to as Type III Hypersensitivity reaction?
a) Immediate hypersensitivity
b) Cytotoxic reaction
c) Immune complex reaction
d) Cell mediated hypersensitivity 
View Answer

Answer: c
Explanation: Hypersensitivity denotes a condition in which an exaggerated immune response of a host results in inappropriate reactions that lead to destruction of host tissue. There are mainly 4 types of hypersensitivity reactions – Type I, II, III, IV. Type III hypersensitivity is also referred to as immune complex hypersensitivity which involves destruction of cells mediated by antigen-antibody complex. Like type II hypersensitivity reaction, type III hypersensitivity reaction is also mediated by IgG and IgM antibody isotypes. 

3. What is the local immune complex reaction caused due to type III hypersensitivity reaction called?
a) Antigen-antibody Reaction
b) Lupus Reaction
c) Plasma reaction
d) Arthus Reaction
View Answer

Answer: d
Explanation: Arthus reaction is a local immune complex reaction which is caused due to type III hypersensitivity reaction. This reaction is a resultant of deposited antigen-antibody complexes in blood vessel walls, serous membrane and in globular structures of fibres, neurons, etc. This reaction was first discovered by Nicolas Maurice Arthus in 1903. 

4. Which of the following disorder is NOT caused by type III hypersensitivity reaction?
a) Lupus nephritis
b) Serum sickness
c) Membranous nephropathy
d) Dermatitis
View Answer

Answer: d
Explanation: Type III hypersensitivity reaction is mediated by immune complexes which causes various disorders such as Lupus nephritis, serum sickness and membranous nephropathy. Dermatitis is a disorder caused due to type IV hypersensitivity reaction which takes place due to inflammation of skin. Type IV hypersensitivity reaction is mediated by cells and therefore, skin is always its first priority to be destructed. 

5. Which type of antigens cause immune-complex mediated injuries?
a) Exogenous antigens
b) Endogenous antigens
c) Both Exogenous and Endogenous antigens
d) Self-antigens
View Answer

Answer: c
Explanation: Immune-complex mediated injuries are caused by endogenous as well as exogenous antigen types. These antigens bind with antibodies to form antigen-antibody complexes which deposit at the targeted sites. This gives rise to inflammation at the deposited sites which further result in tissue damage. Few examples of exogeneous antigens are foreign proteins, bacteria or virus while that of endogenous antigens are those antigens that can produce antibodies against self-components such as nucleoproteins. 

6. Which complement component is released during mechanism of tissue injury which is activated by immune complexes?
a) C3a
b) C3b
c) C3c
d) C3d
View Answer

Answer: a
Explanation: Immune complexes trigger the inflammatory processes which cause tissue damage. These complexes activate the complement component C3a which stimulate degradation of basophiles and mast cells. This degradation further causes release of histamine which eventually regulates and helps deposition of immune complexes. 

7. Reactive arthritis is caused due to binding of which type of antigen?
a) Viral antigen
b) Bacterial antigen
c) Cell surface antigen
d) Protein mediated antigen
View Answer

Answer: b
Explanation: Reactive arthritis is a very rare disorder caused due to reactions of type III hypersensitivity. This results in joint pain and swelling which is triggered by infection in other parts of the body. Bacterial antigens bind to antibody to form antigen-antibody complex in targeted part of the body. This complex trigger infection to be caused in that particular targeted body part. Most common bacterial antigens that cause reactive arthritis are yersinia, salmonella and chlamydia. 

8. Immune complex mediated diseases are which of the following two types?
a) Systemic and General
b) Systemic and Localised 
c) Localised and Innate
d) Localised and Adaptive
View Answer

Answer: b
Explanation: Immune complex-mediated diseases can be of two major types: Generalised (systemic) and Localised.  Systemic immune complex disease is caused as they initiate acute inflammatory reactions after a very long duration when antigen-antibody complexes are formed. For example: In acute serum sickness, once complexes are deposited in tissues. Inflammatory reactions are seen nearly 10 days after the formation and deposition of the complexes. Most common symptoms of serum sickness are fever, urticaria, lymph node enlargement. On the other hand, Localised immune complex disease is a type in which there is a formation of localised area of tissues and it results in necrosis. The tissues remain clumped in various targeted sites. Inflammatory reactions are initiated few hours after the formation and deposition of antigen-antibody complexes. For example: Arthus reaction.

9. Which of the following factor is the most important which influences formation and deposition of antigen-antibody complexes?
a) Valency of antigen
b) The affinity of the antigen to various tissue components
c) Strength of antibody
d) Size of the complex
View Answer

Answer: d
Explanation: One of the most important factors that influence the formation and deposition of antigen-antibody complexes is its size. It plays an important role in tissue deposition of immune complexes. If large complexes are formed, they are rapidly removed from circulation by phagocytes, and hence are relatively harmless. On the other hand, valency of antigen, its affinity to the targeted tissues as well as the overall strength of antibody to bind to antigen are some of the secondary factors which play equally important role in deposition of complexes. 

10. Which type of fragments are formed in classical complement pathway during complement activation drops down on the surface of antigens?
a) C3b
b) C3a
c) Antigen-binding site
d) RBC receptors
View Answer

Answer: a
Explanation: The binding of antigen and antibody activates the classical complement pathway. The C3b fragments are formed during this pathway where activation falls on surface of antigens. At this point, C3b needs particular receptors so as to enhance further movement. RBC membrane provides receptor for C3b to bind. RBC membrane shows presence of C3b receptors which work as binding site for C3b molecules present on surface of antigens. Once the binding is done, RBC moves through liver and spleen and then further bind to Fc region on macrophage membrane.

Sanfoundry Global Education & Learning Series – Immunology.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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