Immunology — MCQs

Immunology Indian Medical PG Practice Questions and MCQs

Question 1031: All of the following are pattern recognition receptors for extracellular or ingested microbes, except:

A. Toll-like receptors (TLRs) - Detect pathogen-associated molecular patterns (PAMPs).
B. NOD-like receptors (NLRs) - Intracellular sensors for microbial components.
C. Killer-cell immunoglobulin receptors (KIRs) - Recognize MHC class I molecules on host cells. (Correct Answer)
D. C-type lectin receptors (CLRs) - Recognize carbohydrate structures on microbes.

Explanation: ***Killer-cell immunoglobulin receptors (KIRs)*** - KIRs are primarily involved in regulating **natural killer (NK) cells**, not in recognizing microbes [1]. - They primarily interact with **MHC class I molecules** and play a role in **immune surveillance**, rather than pattern recognition of pathogens [1]. *NOD-like receptors (NLRs)* - NLRs detect **intracellular pathogens** and damaged cells, playing a crucial role in **innate immunity** [2]. - They initiate responses to **bacterial peptidoglycans** and work in the recognition of microbial patterns [2]. *Toll-like receptors (TLRs)* - TLRs are well-known for recognizing **extracellular microbes** and activate the immune response upon pathogen detection [3]. - They are critical in detecting **lipopolysaccharides (LPS)** and **viral nucleic acids** to elicit immune responses. *C-type lectin receptors (CLRs)* - CLRs specifically recognize **carbohydrate structures** on pathogens, playing a key role in **innate immune responses** [3]. - They are important in identifying **fungi** and **bacteria**, enhancing phagocytosis and cytokine production. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 200-201. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 196. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 200.

Question 1032: In utero infection leads to which immunoglobulin?

A. IgG
B. IgA
C. IgM (Correct Answer)
D. IgD

Explanation: ***IgM*** - **IgM** is the first antibody produced by the fetus in response to an in utero infection, as it cannot cross the placenta. - Its presence in a newborn's blood indicates an **active fetal immune response** to an infection acquired before birth. *IgG* - **IgG** antibodies from the mother cross the placenta and provide passive immunity to the fetus, but their presence does not necessarily indicate an active fetal infection. - High IgG levels in a neonate are typically maternal and do not reflect the infant's own immune response to an in utero infection. *IgA* - **IgA** is primarily found in mucosal secretions and is not typically produced by the fetus in significant amounts in response to in utero infection. - Its presence in a neonate's blood might suggest contamination or specific unusual circumstances, rather than routine in utero infection. *IgD* - The function of **IgD** is not fully understood, but it is primarily found on the surface of B lymphocytes and is not a major effector antibody in the primary immune response to infection. - It does not play a significant role in diagnosing in utero infections.

Question 1033: Which type of hypersensitivity is associated with cell-mediated immunity?

A. Type 2
B. Type 3
C. Type 4 (Correct Answer)
D. Type 1

Explanation: ***Type 4*** - Cell-mediated immunity primarily involves **T-lymphocytes** [1], essential for targeting and eliminating **intracellular pathogens** like viruses. - It plays a crucial role in **delayed-type hypersensitivity reactions** [2], making it vital for the adaptive immune response. *Type 3* - Type 3 immune responses are primarily associated with **immune complex-mediated** diseases and not directly with cell-mediated immunity. - This type involves primarily **B-cells** and antibodies in the response against antigens. *Type 2* - Type 2 immunity mainly concerns the activation of **B-lymphocytes** and antibody production against **extracellular pathogens** like bacteria. - It is characterized by **IgE-mediated responses** [3], particularly in allergic reactions, rather than cell-mediated actions. *Type 1* - Type 1 responses are associated with **Th1 cells** [2] and are more specifically linked to **autoimmunity and cell-mediated pathways**, but represent only a part of the broader cell-mediated immunity. - This type mainly focuses on clearance of **intracellular pathogens** but is not synonymous with the entire process of cell-mediated immunity. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 216-218. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 208-210.

Question 1034: Which of the following is not a component of innate immunity?

A. Epithelial barriers
B. NK cells
C. Dendritic cells
D. Helper T lymphocytes (Correct Answer)

Explanation: ***Helper T lymphocyte*** - Helper T lymphocytes are a crucial part of **adaptive immunity** [4], facilitating responses against pathogens. - They specifically activate B cells and cytotoxic T cells [2], unlike components of innate immunity, which respond nonspecifically. *NK cells* - Natural Killer (NK) cells are integral to **innate immunity** [1], targeting infected or tumor cells without prior sensitization. - They play a role in the initial response to viral infections and can produce **cytokines** [2]. *Epithelial barriers* - Epithelial barriers act as the first line of defense in **innate immunity** [1], preventing pathogen entry. - They include physical and chemical barriers like skin and mucous membranes [3]. *Dendritic cells* - Dendritic cells are key antigen-presenting cells involved in **innate immunity** [1] and link to adaptive immunity. - They capture and present antigens [2], activating T cells to mount an immune response. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 194-196. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 152-153. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 196-198.

Question 1035: What is the primary mechanism by which cytotoxic T lymphocytes (CTLs) recognize target cells in the immune response?

A. Are important in the control of viral infections
B. Recognize antigens presented by MHC class I molecules (Correct Answer)
C. Secrete cytokines that stimulate the differentiation and proliferation of T cells
D. Most often recognize antigens presented by MHC class II molecules

Explanation: ***Recognize antigens presented by MHC class I molecules*** - **Cytotoxic T lymphocytes (CTLs)**, or CD8+ T cells, specifically recognize antigens presented by **MHC class I molecules** on the surface of target cells. - This recognition is crucial for identifying and eliminating **virally infected** or **cancerous cells**. *Secrete cytokines that stimulate the differentiation and proliferation of T cells* - While CTLs do secrete some cytokines, their primary role is direct cytotoxicity rather than broadly stimulating T cell differentiation and proliferation. - **Helper T cells (CD4+ T cells)** are primarily responsible for secreting cytokines that orchestrate the immune response and stimulate other immune cells. *Are important in the control of viral infections* - This statement is true, but it describes a *consequence* of CTL function, not their fundamental *role* in antigen recognition. - CTLs eliminate virally infected cells, thereby controlling viral spread, but their initial role is antigen recognition via MHC class I. *Most often recognize antigens presented by MHC class II molecules* - **MHC class II molecules** are primarily recognized by **helper T cells (CD4+ T cells)**, which respond to extracellular antigens processed by professional antigen-presenting cells. - CTLs (CD8+ T cells) are specific for antigens presented by **MHC class I molecules**.

Question 1036: What is the primary cellular target of Human immunodeficiency virus (HIV)?

A. Erythrocytes
B. Connective tissue cells
C. CD4+ T cells (Correct Answer)
D. Allergy-mediating cells

Explanation: ***CD4+ T cells*** - HIV primarily targets and replicates within **CD4+ T lymphocytes**, which are crucial for the body's immune response. - The progressive destruction of these cells leads to **immunodeficiency**, making the body susceptible to opportunistic infections. *Erythrocytes* - **Red blood cells** (erythrocytes) are not directly targeted or infected by HIV. - HIV infection can indirectly lead to **anemia**, but this is not due to direct viral replication within erythrocytes. *Connective tissue cells* - While HIV can have effects on various organs, it does not primarily infect or replicate within **connective tissue cells**. - Its main cellular target is specific immune cells. *Allergy-mediating cells* - **Mast cells** and **basophils** are allergy-mediating cells that are not the primary targets of HIV. - HIV does not directly infect these cells to establish its life cycle.

Question 1037: TNF and IL-1 are produced by

A. Neutrophils
B. Monocytes
C. Activated Macrophages (Correct Answer)
D. Lymphocytes

Explanation: ***Activated Macrophages*** - Activated macrophages are the primary source of **TNF** and **IL-1**, which are key cytokines in inflammatory responses [1]. - They play a crucial role in **immune modulation** and act as important mediators of the inflammatory process [1]. *Lymphocytes* - Lymphocytes primarily produce **antibodies** and other cytokines like **IL-2**, but they are not the main producers of TNF and IL-1. - Their role is more prominent in the adaptive immune response rather than in the innate response where TNF and IL-1 are more directly involved. *Neutrophils* - Neutrophils are involved in acute **inflammation** and primarily release **proteolytic enzymes** and reactive oxygen species, but not TNF and IL-1. - They are crucial for initial defense against infections but do not have a significant role in producing these cytokines. *Monocytes* - Monocytes can differentiate into macrophages and play a role in inflammation, but they do not produce **TNF** and **IL-1** to the same extent as activated macrophages. - Their primary function is as precursors to macrophages and dendritic cells, contributing indirectly to cytokine production. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 105-106.

Question 1038: The complement components responsible for bacterial lysis are:

A. C3a
B. C3b
C. C5-9 (Correct Answer)
D. C5a

Explanation: ***C5-9*** - The **C5-9 complement complex**, also known as the **membrane attack complex (MAC)**, is directly responsible for the lysis of bacterial cells [1][2]. - This complex forms pores in the **bacterial membrane**, leading to cell death [2]. *C5a* - While C5a is an important **anaphylatoxin** that enhances inflammation, it does not directly cause lysis [2][3]. - C5a primarily functions in **chemotaxis** and activation of immune cells rather than in bacterial membrane disruption [3]. *C3a* - C3a is another **anaphylatoxin** that promotes inflammation and recruitment of immune cells but does not participate in the lytic action against bacteria [2][3]. - Its role is primarily in **modulating the immune response**, not in direct bacterial lysis. *C3b* - C3b plays a key role in **opsonization**, marking bacteria for phagocytosis but it does not directly lyse bacterial cells [2]. - It facilitates the binding of pathogens to immune cells, enhancing **clearance** but does not form the lytic complex like C5-9. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 99. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 99-100. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 163-164.

Question 1039: Which type of lymphocyte is characterized by the following markers: CD3-, CD16+, CD56+, and responds to IL-12?

A. B lymphocytes
B. Cytotoxic T lymphocytes
C. Natural killer cells (Correct Answer)
D. T helper 1 subset

Explanation: ***Natural killer cells*** - **Natural killer (NK) cells** are characterized by the absence of **CD3** (signifying they are not T cells) and the presence of **CD16** and **CD56**. - They respond to **IL-12**, which promotes their cytotoxicity and interferon-gamma production, crucial for innate immune responses against viruses and tumor cells. *B lymphocytes* - **B lymphocytes** express **CD19**, **CD20**, and **surface immunoglobulin**, but not **CD3**, **CD16**, or **CD56**. - Their primary role is **antibody production**, not direct cytotoxicity, and they respond to different cytokine profiles. *Cytotoxic T lymphocytes* - **Cytotoxic T lymphocytes (CTLs)** are defined by expressing **CD3** and **CD8**, enabling them to recognize and kill target cells in an MHC class I-restricted manner. - They typically do not express **CD16** or **CD56** and are activated by T-cell receptor engagement. *T helper 1 subset* - **T helper 1 (Th1) cells** are a subset of **CD4+ T cells**, meaning they express **CD3** and **CD4**. - They are primarily involved in orchestrating cell-mediated immunity through cytokines like **IFN-γ** and **IL-2**, not direct cytotoxicity via **CD16** or **CD56**.

Question 1040: What is the primary use of the lepromin test in leprosy?

A. Diagnosis of leprosy
B. Assessment of cell-mediated immunity (Correct Answer)
C. Epidemiological studies
D. Determining treatment efficacy

Explanation: ***Assessment of cell-mediated immunity*** - The lepromin test primarily measures the host's **cell-mediated immune response** to *Mycobacterium leprae* antigens. - A positive reaction indicates a strong CMI, typically seen in **tuberculoid leprosy**, while a negative reaction suggests absent or suppressed CMI, as in **lepromatous leprosy**. *Diagnosis of leprosy* - The lepromin test is **not used for diagnosing active leprosy**, as it does not distinguish between current infection, past exposure, or vaccination. - Diagnosis relies on clinical signs, **acid-fast bacilli** in smears, and histopathology. *Epidemiological studies* - While it can provide insights into population immune profiles, it's **not the primary tool for epidemiological surveillance** or prevalence estimation, which often uses clinical examination. - Its utility in epidemiology is limited by its inability to identify active cases or recent infections. *Determining treatment efficacy* - The lepromin test remains positive for a long time after effective treatment and thus **cannot be used to monitor treatment response** or cure. - Treatment efficacy is assessed by clinical improvement and reduction in bacterial load.

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Cells and Organs of Immune System

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Innate Immunity

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Adaptive Immunity

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Antigens and Antibodies

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Major Histocompatibility Complex

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Complement System

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Cytokines and Chemokines

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Hypersensitivity Reactions

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Autoimmunity and Autoimmune Diseases

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Immunodeficiency Disorders

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Transplantation Immunology

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Tumor Immunology

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Immunology — MCQs

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