Immunology Questions and Answers – Cell and Antibody-Mediated Immunity

This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Cell and Antibody-Mediated Immunity”.

1. Which of the following is known as a key component/factor of the immune system?
a) Antigen
b) Antibody
c) Phagocytes
d) B and T cells
View Answer

Answer: b 
Explanation: Antibodies are known to be the key component of the immune system as they provide long-term protective immunity against many pathogens and help in regulating immune responses. Antibodies consist of two domains with distinct functions. The variable Fab domain (it mediates antigen specificity and binds its respective antigen) and the Fc domain (it mediates diverse effector functions via recruitment of effector molecules such as complement and Fc receptors (FcRs)).

2. Which of the following statement is correct about the structure of antibody?
a) Antibody consists of two light and two heavy chains and is linked together by diphosphate bonds
b) Antibody consists of one light and two heavy chains and is linked together by disulfide bonds
c) Antibody consists of two light and one heavy chain and is linked together by dinitride bonds
d) Antibody consists of two light and two heavy chains and is linked together by disulfide bonds
View Answer

Answer: d
Explanation: Antibody is a Y-shaped structure consisting of two light and two heavy chains. These chains are basically polypeptides bonded with one another by disulfide bonds. A disulfide bond is a covalent bond between two sulfur atoms (S-S) which is formed by the coupling of two thiol (-SH) group. Antibody is also termed as immunoglobulin. These two terms are interchangeable. There are five types of antibodies found in serum which differ in their structural and functional properties. They are – IgG, IgM, IgA, IgD and IgE.

3. Which of the following antibody isotype functions as the most important glycosylation site?
a) IgA
b) IgG
c) IgE
d) IgD
View Answer

Answer: b
Explanation: IgG is one of the most important antibody isotypes which plays an important role in glycosylation mechanisms. IgG consists of asparagine at 297th position which is the point of site for glycosylation. It provides nutrition and support to glycans which take part in glycosylation. This causes the glycan to make variable combinations with mannose, glucose or sialic acid.  

4. ADCC (antibody-dependent cell-mediated cytotoxicity) is known to be the most important component against which of the following virus?
a) HIV
b) Viral hepatitis
c) Pneumonia
d) Shingles
View Answer

Answer: a
Explanation: In the field of tumor immunology, ADCC has been recognized as an important mechanism of action for therapeutic monoclonal antibodies (mAbs) that target tumor cells. ADCC has been shown to form a critical component of effective immunity against HIV and influenza virus. ADCC-inducing HIV-specific antibodies were identified as a key to correlate protection in the RV144 HIV vaccine trial. 

5. Antibody recognizes and binds to which part of the antigen?
a) Epitope
b) Paratope
c) Immunogenic site
d) Antigenic site
View Answer

Answer: a
Explanation: Epitope is the specific determinant of the antigen. Antibody recognizes the epitope on antigen in order to regulate the immune system. It is the specific region on antigen and is made up of 5-8 amino acid long chains. Epitope is also termed as antigenic determinant. On the other hand, paratope is the antigen-binding site present on the antibody. It is made up of around 5-10 amino acid long chains. 

6. What is the antibody that binds to toxins called?
a) Complement antibody
b) Antoxin
c) Antitoxin
d) Toxoid antibody
View Answer

Answer: c
Explanation: The binding of antibody to toxin is called as Antitoxin. Antibodies attack the antigens by binding to them. Similarly, antibodies attack the toxins by binding to them. This bond kills and inhibits the activity of toxins. Toxins are poisonous in humans and is produced by living cells. They damage enzymes and inhibit production of haemoglobin in the blood by lowering the body’s capacity to prevent the free-radical damage that causes aging. 

7. Antibodies produced in membrane bound as well as in secreted forms is stimulated by which type of cells?
a) T cells
b) B cells
c) Cytotoxic T cells
d) Memory T cells
View Answer

Answer: b
Explanation: Antibodies produced in membrane bound and secreted forms is stimulated by B cells. They are specifically produced by B lymphocytes and plasma cells in lymphoid organs and bone marrow. However, they perform their effector functions away from their site of production. In humoral immunity, antibodies bind to antigen in both recognition and effector phase. This binding is also carried out by antigen-stimulated B cells. 

8. Which of the following IgG subclasses have high affinity to Fc gamma receptors?
a) IgG1 and IgG4
b) IgG2 and IgG5
c) IgG1 and IgG3
d) IgG1, IgG2 and IgG3
View Answer

Answer: c
Explanation: Fc gamma receptors majorly respond to IgG1 and IgG3. These two molecules are the subclasses of IgG antibody isotype. They activate the Fc gamma receptor. However, IgG3 has a shorter life span as compared to IgG1. As a result, during therapies, IgG1 subclass is always considered for activating Fc gamma receptors because this subclass remains intact throughout their activation processes.  

9. During the process of neutralization, antibodies block the binding of which molecules to cellular receptor?
a) Microbes and microbial toxins
b) Microbes and bacterial toxins
c) Microbes and viral toxins
d) Microbes and fungal toxins
View Answer

Answer: a
Explanation: Neutralization is one of the most important prosses and an effector function of antibodies. The antibodies are usually produced in response to microbes and microbial toxins and hence, they block the binding of microbes and their toxins to cellular receptors. This process inhibits the activity of these microbes and limits the injurious effects of the infection caused. The antibody specific to microbe binds with it in order to prevent infection of the cell whereas the antibody that binds to toxin prevents pathological effects.

10. Which of the following is NOT an Fc-mediated antibody effector function?
a) Antibody-dependent cell-mediated cytotoxicity
b) Antibody-dependent cellular phagocytosis
c) Complement-dependent cytotoxicity
d) Antibody-dependent complement cytotoxicity
View Answer

Answer: d
Explanation: Humoral immune response consists of an integral function which is termed as antibody effector functions which act as a mediating link between both types of immune systems, adaptive and innate immune system. The effector functions are mediated by various factors out of which Fc fragment of antibody reconciles the most accurate and useful functions. They help in interaction with complement proteins, induce phagocytosis as well as carry out the functions necessary for cytotoxicity. 

11. Which antibody isotype promotes phagocytosis of microbes?
a) IgA
b) IgD
c) IgE
d) IgG
View Answer

Answer: d
Explanation: Antibodies of IgG isotype promotes phagocytosis of microbes by binding to Fc receptor on phagocytes. The mononuclear phagocytes and neutrophils take in the microbe in order to promote intracellular killing and degradation. These phagocytes express variety of cell surface receptor that directly bind and ingest them. Binding to Fc receptor promotes phagocytosis by delivering signals in order to stimulate the activity of microbes. 

12. Which of the following is the Fc receptor of NK cells that promotes lysis of antibody-coated cells?
a) CD8
b) CD4
c) CD16
d) CD21
View Answer

Answer: c
Explanation: The Fc receptor of NK cells is CD16 which results in the lysis of antibody-coated cells. This lysis takes place by binding of CD16 to IgG antibody attached to the cells. This results in enhancement of cytotoxicity hence, also termed as Antibody-dependent cell-mediated cytotoxicity. CD16 is a low affinity molecule and as a result it only binds to clustered IgG molecules and not to circulating monomeric IgG. This Fc receptor of NK cells is also termed as FcγRIII. 

13. The role of ADCP (Antibody-Dependent Cellular Phagocytosis) in viral infection is clear and successful.
a) True
b) False
View Answer

Answer: b
Explanation: ADCP has been commonly described for its role in protection against bacteria, but its importance during viral infections is unclear. Some studies have been performed for influenza virus, showing that phagocytosis by (alveolar) macrophages may contribute to protection from infection in mice. It also plays a role in the recovery from severe infections in humans. However for some virus types like cytomegalovirus (CMV), it is shown that vaccine-induced antibodies play an important role in vaccine efficacy, independent of ADCC capacity. As a result, in absence of ADCC capacity, viral infections were to be cured because of the major roles played by ADCP which is potentially known to be the most important component against virus. 

14. Which of the following receptor connects the antibody mediated immune response to cellular effector functions?
a) BCR
b) TCR
c) FcR
d) APR
View Answer

Answer: c
Explanation: Antibody consists of two main fragments: Fc and Fab fragments. These two fragments have different roles based on their own receptors. Fc receptors (also denoted as FcRs) mediate several effector functions necessary for various activities like inducing cytotoxicity, carrying out interactions between complement proteins and-the-like. They help in controlling the humoral immune response and acts as a link between antibody mediated immune response and cellular effector functions. 

15. Which receptor is engaged with Fc domain when ADCC (antibody-dependent cell-mediated cytotoxicity) is induced?
a) Fc-gamma-Receptors
b) Fc-alpha-Receptor
c) Fc-beta-Receptor
d) Fc-delta-Receptor
View Answer

Answer: a
Explanation: Fc gamma receptors generate antibody mediated effector functions in order to induce cytotoxicity, phagocytosis and related immune responses. To maintain and carry forward this cytotoxicity, the Fc receptor gets engaged with the Fc domain of antibodies that are bound to viral proteins on the surface of cell which is eventually infected by virus. This gives rise to a specialised function mediated by antibody called Antibody-Dependent Cell Mediated Cytotoxicity (ADCC). This mechanism further helps in releasing cytotoxic granules which kill the infected cells. 

16. What is another term used for Antibody-Dependent Cellular Phagocytosis (ADCP)?
a) Opsonophagocyte
b) Cellulophagocytosis
c) Opsonophagocytosis
d) Anti-opsonophagocytosis
View Answer

Answer: b
Explanation: ADCP is also known as Opsonophagocytosis. It is defined as the uptake of virus-antibody complexes or antibody-coated virus-infected cells by phagocytic cells. Phagocytic cells, including monocytes, macrophages, neutrophils, eosinophils and dendritic cells (DCs), express FcγRI, FcγRII, and FcαRI, which can all mediate immune complex uptake. The exact phagocytic capacity of effector leukocytes is dependent upon the cell type, differentiation stage, and level of FcγR expression.

17. Which of the following immunopathological effect is NOT caused due to activation of phagocytes which is led by RSV (respiratory syncytial virus)-antibody complexes?
a) Tissue damage
b) Cell damage
c) Platelet aggregation
d) Bronchoconstriction 
View Answer

Answer: b
Explanation: Tissue damage, platelet recombination and bronchoconstriction are some of the major immunopathological effects caused in patients suffering from respiratory syncytial virus (commonly denoted as RSV). RSV is a disorder of the lungs and nasal passage and the patient suffering from it might have common cold-like symptoms at early stages. However, it can get serious in patients having breathing difficulties. In such a case, the patient’s immune system begins the mechanisms of immunomodulation with the help of antibodies. This gives rise to formation of RSV-antibody complexes. These complexes force the phagocytes to get activated due to which tissues majorly get damage. Along with it, platelets get aggregated. 

18. What does ADE stand for?
a) Antibody-dependent enhancement 
b) Antibody-determined enthalpy
c) Antibody-determined enhancement
d) Antigen-dependent enhancement 
View Answer

Answer: a
Explanation: ADE (Antibody-Dependent Enhancement) refers to a phenomenon in which virus-specific antibodies promote, rather than inhibit, infection or disease. In ADE of infection (also known as extrinsic ADE), the number of virus-infected cells is increased in the presence of natural or monoclonal antibodies that are non-neutralizing or present in sub-neutralizing concentrations. ADE of infection requires the presence of FcγRs on target cells and is an efficient in vitro tool to assess Fc-FcγR interactions.

19. In humans, how many subclasses of IgG are known and which of the following are they?
a) 4 subclasses – IgG1, IgG2, IgG3, IgG5
b) 5 subclasses – IgG1, IgG2, IgG3, IgG4, IgG5
c) 1 subclass – IgG2
d) 4 subclasses – IgG1, IgG2, IgG3, IgG4
View Answer

Answer: d
Explanation: In humans, four different IgG subclasses are known. They are IgG1, IgG2, IgG3 and IgG4. These subclasses differ in amino acid sequence, which influences their capacity to interact with certain classes of FcγRs and complement components. The serum abundance of the four subclasses (from IgG1 to IgG4) is 60%, 32%, 4% and 4% respectively. 

20. Upon antigen encounter what do the antibodies form?
a) Immune complexes
b) Antigen-antibody complexes
c) Antibody complexes
d) Antigen complexes
View Answer

Answer: a
Explanation: Fc-gamma-Receptors are expressed by most hematopoietic cells and they represent the main effector molecules recruited by IgG. This theory was modulated by Nimmerjahn and Ravetch in 2008. Furthermore, Kalergis and Ravetch in 2002 found out a different type of complex as and when there was an antigen encounter. This complex was formed by antibodies which encountered the antigen and hence they named this complex as immune complexes (which is also designated as ICs). They further found out that antibodies forming these ICs with their cognate antigen bind to Fc-gamma-Receptors. The uptake of ICs by activating Fc-gamma-Receptors on dendritic cells (DCs) has shown to result in cell maturation and efficient presentation of antigen on MHC-I and MHC-II molecule. This was framed as an evidence to support their observation. 

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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