This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Immune Response – Clonal Selection Theory”.
1. According to the “instructive model” the antigen instructs lymphocytes to produce antibodies.
Explanation: Against every antigen and associated disease, an array of antibodies is generated. According to an earlier model – the “instructive model” the antigen instructs the lymphocytes to produce antibodies against itself.
2. Who proposed the clonal selection theory?
a) James Watson
b) Niels Jerne
c) Francis Crick
d) Frank MacFarlane Burnet
Explanation: Frank MacFarlane Burnet was an Australian immunologist who in 1957 proposed the clonal selection theory – a model that dictates how the production of a single type of antibody is produced in excess.
3. B-cells arise from ______________________
a) progenitor cells
d) natural killer cells
Explanation: B-cells arise from undifferentiated and uncommitted progenitor cells. As the B-cells become mature they become committed towards producing a single type of antibody.
4. Antigens that do not require the involvement of T-cells for the activation of B-cells are _____________________
c) intracellular pathogens
d) facultative anaerobes
Explanation: T-cells are usually involved in the process of activation of B-cells and subsequent production of a single type of antibody. Few antigens such as polysaccharides of bacterial cell walls do not require the involvement of T-cells and therefore termed thymus-independent antigens.
5. Some of the activated B-cells lead to the formation of short-lived ______________________
a) plasma cells
b) evanescent waves
c) memory cells
d) thymus cells
Explanation: The antibody-producing B-cells are activated after encounter with antigen. A proportion of these antibody producing cells are differentiated into short-lived plasma cells that secrete large amounts of antibodies.
6. Plasma cells possess extensive smooth endoplasmic reticulum.
Explanation: Plasma cells are differentiated from the B-cells (precursors) and contain an extensive network of rough endoplasmic reticulum to provide for the excessive protein synthesis involved in antibody production.
7. B-lymphocytes that do not differentiate into plasma cells are called _______________________
b) Helper T-cells
c) Memory B cells
d) Memory T-cells
Explanation: Not all activated B-cells are differentiated into plasma cells; some are also retained in the lymphoid tissue. These memory B-cells can reappear and respond rapidly to the invading antigen if a second encounter happens.
8. In case of acquired immune system, a secondary immune response is generated by the ______________
a) memory B-cells
b) germ cells
c) lymphoid tissues
Explanation: A few activated B-cells remain in the lymphoid tissue as memory B-cells. These cells generate a secondary immune response by differentiating into plasma cells upon a second encounter with the same antigen.
9. For the body to develop immunologic tolerance, production of ____________________ must be prevented.
Explanation: For the body to develop immunologic tolerance, the production of autoantibodies must be prevented. Autoantibodies can react with the body’s own tissues and cause organ destruction.
10. Who discovered the vaccination against smallpox?
a) Louis Pasteur
b) Francis Crick
c) Barbara McClintock
d) Edward Jenner
Explanation: In 1796, Edward Jenner discovered the vaccine against smallpox by deliberately infecting an eight-year-old boy with cowpox and then injecting the pus of smallpox lesion under his skin. He then found out that the boy showed immunity against the latter.
11. A harmless version of tetanus toxin is called _________________
Explanation: Tetanus is caused by an anaerobic soil bacterium known as Clostridium tetani. For immunity against tetanus, infants are inoculated with a harmless version of the tetanus neurotoxin – toxoid.
12. Which of the following serves as antigen receptors?
d) necrosis factors
Explanation: Antibodies are proteins produced by the B lymphocytes and their descendants (plasma cells) that are incorporated in the plasma membranes of the former. The antibodies act as antigen receptors on the surface of B cells.
13. The heavy and light chains of the antibodies are linked to one another by ____________________
a) covalent bonds
b) disulfide bonds
c) ionic bonds
d) hydrogen bonds
Explanation: The antibodies are globular proteins that contain heavy chains (molecular mass of 50,000 to 70,000 daltons) and light chains (23,000 daltons). The heavy and light chains are joined together by disulfide bonds.
14. Which is the first antibody secreted by B cells following stimulation by an antigen?
Explanation: B cells produce five different types of Immunoglobulins (antibodies) – IgG, IgM, IgA, IgD, IgE. The first antibody to be secreted by the B cells following stimulation by an antigen is IgM.
15. Which antibody is produced at high levels in response to parasitic functions?
Explanation: IgE is produced at high levels in response to parasitic infections and these immunoglobulins also bind to the surface of mast cells with high affinity, triggering histamine release, which causes allergy and inflammation.
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