MCQ in Immunology (71-85): Basic Concepts Answers with Explanation

This is the collection of some multiple-choice questions to check your understanding of immunology;  definitions, terms, concepts, etc. At the end of these Immunology MCQs, I also posted the answers. I expect persons with good exposure to immunology must give correct answers to at least 14 questions; if you fail to do so, please revise immunology once again.

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71. Naturally acquired active immunity would be most likely acquired through which of the following processes?

a. Vaccination

b. Drinking colostrum

c. Natural birth

d. Infection with disease-causing organism followed by recovery

72. Which of the following conveys the longest-lasting immunity to an infectious agent?

a. Naturally acquired passive immunity

b. Artificially acquired passive immunity

c. Naturally acquired active immunity

d. All of these

e. None of these

73. Which substances will not stimulate an immune response unless they are bound to a larger molecule?

a. Antigen

b. Virus

c. Hapten

d. Miligen

e. Antibody

74. B and T cells are produced by stem cells that are formed in:

a. Bone marrow

b. The liver

c. The circulatory system

d. The spleen

e. The lymph nodes

75. B cells mature in the __ while T cells mature in the __

a. Thymus / bone marrow and gut-associated lymphoid tissue (GALT)

b. Spleen / bone marrow and GALT

c. Bone marrow and GALT / thymus

d. Liver / kidneys

76. Which of the following immune cells/molecules are most effective at destroying intracellular pathogens?

a. T helper cells

b. B cells

c. Antibodies

d. Complement

e. T cytolytic cells

77. A living microbe with reduced virulence that is used for vaccination is considered:

a. A toxoid

b. Dormant

c. Virulent

d. Attenuated

e. Denatured

78. B cells that produce and release large amounts of antibodies are called:

a. Memory cells

b. Basophils

c. Plasma cells

d. Killer cells

e. Neutrophils

79. The specificity of an antibody is due to:

a. Its valence

b. The heavy chains

c. The Fc portion of the molecule

d. The variable portion of the heavy and light chains

80. In agglutination reactions, the antigen is a __ and in precipitation reactions, the antigen is a __

a. Whole-cell / soluble molecule

b. Soluble molecule / whole-cell

c. Bacterium / virus

d. Protein / carbohydrates

e. Protein / antibody

81. B Cells are activated by:

a. Complement

b. Antibody

c. Interferon

d. Memory cells

e. Antigen

82. Fusion between a plasma cell and a tumor cell creates a:

a. Myeloma

b. Natural killer cell

c. Lymphoblast

d. Lymphoma

e. Hybridoma

83. Monoclonal antibodies recognize a single:

a. Antigen

b. Bacterium

c. Epitope

d. B cell

e. Virus

84. Cell-mediated immunity is carried out by __ while humoral immunity is mainly carried out by __

a. B cells / T cells

b. Epitopes / antigens

c. T cells / B cells

d. Antibodies / antigens

e. Antibodies / phagocytes

85. The ability of the immune system to recognize self-antigens versus non-self antigens is an example of:

a. Specific immunity

b. Self-tolerance or immunological tolerance

c. Cell-mediated immunity

d. Antigenic immunity

e. Humoral immunity

Answers of MCQ Immunology:Basic Concepts (71-85)

Here is the explanation guide, formatted cleanly with clear headings, bolded answers, and proper layout so it is easy to read and review.

Immunology MCQs: Answer Key & Explanations

**71. Correct Answer: d (Infection with disease-causing organism followed by recovery)**

• Explanation: This is a fundamental definition in immunology. Naturally acquired active immunity is produced when a person is naturally exposed to a live pathogen, develops the disease, and subsequently recovers, leaving behind memory cells.

**72. Correct Answer: c (Naturally acquired active immunity)**

• Explanation: Active immunity typically lasts significantly longer than passive immunity because the host's own immune system produces the antibodies and memory cells. Among the choices, naturally acquired active immunity (like recovering from chickenpox) provides the most robust, long-lasting protection.

**73. Correct Answer: c (Hapten)**

• Explanation: A hapten is a small, non-immunogenic molecule. It possesses reactivity but lacks inherent immunogenicity; it cannot stimulate an immune response on its own unless it covalently binds to a larger carrier protein molecule.

**74. Correct Answer: a (Bone marrow)**

• Explanation: This question tracks the lineage of adaptive immune cells. While early stem cell development begins in primitive embryonic tissues and shifts to the fetal liver, the final and definitive site where hematopoietic stem cells form both B and T cell precursors is the bone marrow.

**75. Correct Answer: c (Bone marrow and GALT/thymus)**

• Explanation: An easy way to remember this is that T cells are thymus-derived (maturing in the thymus). Conversely, B cells undergo differentiation and maturation in the bone marrow and are functionally localized in gut-associated lymphoid tissue (GALT).

**76. Correct Answer: e (T cytolytic cells)**

• Explanation: Intracellular pathogens (like viruses or certain bacteria replicating inside host cells) are shielded from circulating antibodies. T cytolytic cells ($T_C$ or CD8+ T cells) and Natural Killer (NK) cells are specialized to recognize and destroy these compromised host cells.

**77. Correct Answer: d (Attenuated)**

• Explanation: Attenuated literally means weakened. Live attenuated vaccines use a live microorganism that has been treated or cultured to lose its pathogenicity (virulence) while fully retaining its immunogenicity (the ability to stimulate a protective immune response).

**78. Correct Answer: c (Plasma cells)**

• Explanation: This is a direct definition question. When a naive B cell encounters its specific antigen and receives helper T cell signals, it differentiates into a plasma cell, which functions as a molecular factory capable of secreting thousands of antibody molecules per second.

**79. Correct Answer: d (The variable portion of the heavy and light chains)**

• Explanation: The highly diverse variable regions ($V_H$ and $V_L$) at the amino-terminal ends of both the heavy and light chains form the antigen-binding site (paratope). The massive genetic recombination of these segments allows the immune system to generate millions of unique antibody specificities.

**80. Correct Answer: a (Whole-cell/soluble molecule)**

• Explanation: * Agglutination reactions involve particulate antigens (like intact bacteria or red blood cells) clumping together.

• Precipitation reactions involve soluble antigens that cross-link with antibodies to form an insoluble lattice that precipitates out of solution.

**81. Correct Answer: e (Antigen)**

• Explanation: Naive B cells require a specific signal to initiate activation. This occurs when a specific antigen binds directly to the membrane-bound immunoglobulin molecules that function as the B-cell receptor (BCR), triggering the downstream intracellular signaling cascade.

**82. Correct Answer: e (Hybridoma)**

• Explanation: In monoclonal antibody production, a hybridoma cell line is created by fusing a short-lived, antibody-producing plasma B cell with an immortal, cancerous plasma cell (myeloma cell). This yields a cell line that produces a single antibody type indefinitely.

**83. Correct Answer: c (Epitope)**

• Explanation: Monoclonal antibodies are highly specific clones that recognize and bind to a single, specific epitope (also known as the antigenic determinant), which is the precise chemical structure on an antigen that an antibody locks onto.

**84. Correct Answer: c (T cells/B cells)**

• Explanation: The adaptive immune system is divided into two arms:

• Cell-mediated immunity is driven primarily by T lymphocytes.

• Humoral immunity (antibody-mediated) is driven by B lymphocytes, which secrete antibodies into bodily fluids (humors).

**85. Correct Answer: b (Self-tolerance or immunological tolerance)**

• Explanation: Self-tolerance is the essential quality of a healthy immune system that allows it to remain unresponsive to the body's own native molecules (self-antigens) while aggressively attacking foreign agents (non-self antigens). A breakdown in this system leads to autoimmune disease.