Immunology Practice Questions

Q: Which of the following statements regarding Cytotoxic T lymphocytes (CTLs) is correct?

Are important in the control of viral infections. **Explanation:** **Cytotoxic T Lymphocytes (CTLs)**, which are CD8+ T cells, play a pivotal role in cell-mediated immunity by identifying and eliminating cells infected with intracellular pathogens, particularly **viruses**, as well as tumor cells. 1. **Why Option C is Correct:** CTLs recognize viral peptides presented by **MHC Class I** molecules on the surface of any nucleated cell. Once activated, they induce apoptosis of the infected cell via the **Perforin-Granzyme pathway** or **Fas-Fas ligand interaction**, effectively halting viral replication and spread. 2. **Why Other Options are Incorrect:** * **Option A:** CTLs (CD8+) recognize antigens presented on **MHC Class I**, whereas CD4+ T cells recognize antigens on **MHC Class II**. They do not recognize the same antigen-MHC complex. * **Option B:** This is the function of **Helper T cells (CD4+)**, specifically the Th2 subset, which secretes IL-4 and IL-5 to stimulate B cell differentiation into plasma cells. * **Option D:** This describes the **Exogenous Pathway** of antigen processing (MHC II), typical for CD4+ T cells. CTLs recognize antigens processed via the **Endogenous Pathway**, where proteins synthesized within the cytosol (like viral proteins) are degraded by proteasomes. **High-Yield Clinical Pearls for NEET-PG:** * **MHC Restriction:** CD8+ = MHC I (Rule of 8: 8 × 1 = 8); CD4+ = MHC II (4 × 2 = 8). * **Markers:** CTLs express CD8, CD3, and the T-cell receptor (TCR). * **Granzymes:** Serine proteases that enter the target cell to activate caspases, leading to programmed cell death.

Q: A patient is genetically unable to synthesize J chains. Which immunoglobulins would be affected?

IgM and IgA. **Explanation:** The **J chain (Joining chain)** is a small glycoprotein (approx. 15 kDa) required for the polymerization of specific immunoglobulins. It is synthesized by plasma cells and is essential for stabilizing the multimeric structures of **IgM** and **IgA**. * **IgM:** Typically exists as a **pentamer** in serum. The J chain is required to link the five monomeric units together. * **IgA:** While it exists as a monomer in serum, it forms **dimers** in secretions (Secretory IgA). The J chain is vital for dimerization and facilitates the binding of IgA to the secretory component for transport across mucosal surfaces. Therefore, a genetic inability to synthesize J chains would prevent the formation of pentameric IgM and dimeric IgA, severely compromising mucosal immunity and the primary immune response. **Analysis of Incorrect Options:** * **IgG, IgE, and IgD:** These immunoglobulins always function as **monomers**. They do not possess or require a J chain for their structure or function. * **Options A, B, and D:** These are incorrect because they include IgG or IgE, which are unaffected by J chain deficiency. **NEET-PG High-Yield Pearls:** * **Structure:** IgM is a pentamer (contains J chain); IgA is a dimer (contains J chain) or monomer. * **Valency:** Pentameric IgM has a theoretical valency of 10, but an effective valency of 5 due to steric hindrance. * **Mucosal Immunity:** IgA is the most produced antibody in the body, primarily found at mucosal surfaces (tears, saliva, colostrum, GI tract). * **Complement Activation:** IgM is the most potent activator of the classical complement pathway due to its multimeric structure.

Q: Memory T cells can be identified by using which of the following markers?

CD 45 RO. **Explanation:** The identification of T cell subsets relies on the expression of different isoforms of the **CD45 molecule** (Leukocyte Common Antigen). CD45 is a tyrosine phosphatase essential for T-cell receptor signaling. **Why CD45RO is correct:** Memory T cells (both CD4+ and CD8+) are characterized by the expression of **CD45RO**. When a "naive" T cell encounters an antigen, it undergoes alternative splicing of the CD45 gene, removing the A, B, and C exons. This results in the shortest isoform, CD45RO. This marker indicates that the cell has been previously activated and has transitioned into a long-lived memory state, allowing for a rapid immune response upon re-exposure to the same pathogen. **Analysis of Incorrect Options:** * **CD45RA:** This is the marker for **Naive T cells** (cells that have not yet encountered their specific antigen). It is the longest isoform containing the 'A' peptide. * **CD45RB and CD45RC:** These isoforms are expressed on various subsets of B cells, naive T cells, and NK cells, but they are not specific markers used to identify the memory T cell population in clinical immunology. **High-Yield Facts for NEET-PG:** * **Naive T cells:** CD45RA+ (Think 'A' for "At rest" or "Antigen-inexperienced"). * **Memory T cells:** CD45RO+ (Think 'O' for "Old" or "Once-activated"). * **CD45** is known as the **Leukocyte Common Antigen (LCA)** and is used in immunohistochemistry to differentiate lymphomas from carcinomas. * **Central Memory T cells (Tcm)** also express **CCR7 and L-selectin (CD62L)**, allowing them to home to lymph nodes, whereas **Effector Memory T cells (Tem)** lack these and circulate in peripheral tissues.

Q: The Group A carbohydrate antigen of Streptococcus pyogenes shares antigenic similarity with which human tissue component?

Cardiac valves. **Explanation:** The correct answer is **Cardiac valves**. This phenomenon is a classic example of **molecular mimicry**, where exogenous antigens share structural similarities with host self-antigens, leading to an autoimmune response. 1. **Why Cardiac Valves?** The cell wall of *Streptococcus pyogenes* (Group A Strep) contains a specific **Group A carbohydrate antigen** (N-acetylglucosamine). This antigen shares structural homology with **glycoproteins** found in human **cardiac valves**. Following a pharyngeal infection, the immune system produces antibodies against the bacterial carbohydrate; these antibodies cross-react with the valvular tissue, leading to the inflammatory damage seen in **Acute Rheumatic Fever (ARF)**. 2. **Analysis of Incorrect Options:** * **Myocardium:** While the myocardium is involved in Rheumatic Fever, it is the **M protein** of *S. pyogenes* that mimics myocardial **sarcolemma and myosin**, not the Group A carbohydrate. * **Synovial fluid:** Joint involvement (migratory polyarthritis) in ARF is due to immune complex deposition rather than direct molecular mimicry with the Group A carbohydrate. * **Vascular intima:** Though vasculitis can occur in various streptococcal sequelae, it is not the primary target of the Group A carbohydrate cross-reactivity. **High-Yield Clinical Pearls for NEET-PG:** * **M Protein:** The most important virulence factor of *S. pyogenes*; it mimics **myocardial sarcolemma**. * **Hyaluronic Acid Capsule:** Mimics human **synovial fluid/connective tissue** (making the bacteria non-immunogenic). * **Cytoplasmic Membrane:** Shares antigens with the **subthalamic and caudate nuclei**, leading to Sydenham’s Chorea. * **Jones Criteria:** Used for the diagnosis of ARF (Major: Joint, Carditis, Nodules, Erythema marginatum, Sydenham chorea).

Q: Which immunoglobulin has the highest molecular weight?

IgM. **Explanation:** The molecular weight of an immunoglobulin is primarily determined by its structural configuration (monomer vs. polymer) and the number of amino acids in its heavy chains. **Why IgM is correct:** IgM is the largest antibody, often referred to as the **"Millionaire Molecule"** due to its high molecular weight of approximately **900,000 Daltons (900 kDa)**. In its secreted form, IgM exists as a **pentamer** (five Y-shaped units) held together by disulfide bonds and a polypeptide called the **J-chain** (Joining chain). This pentameric structure gives it 10 antigen-binding sites, making it highly efficient in agglutination and complement activation. **Why the other options are incorrect:** * **IgG (150 kDa):** The most abundant antibody in serum. It exists as a monomer and has the lowest molecular weight among the options, allowing it to cross the placenta. * **IgE (190 kDa):** Exists as a monomer. While its heavy chain (epsilon) is slightly longer than IgG’s, it remains significantly smaller than the pentameric IgM. * **IgA (160–385 kDa):** Exists as a monomer in serum but as a **dimer** in secretions (tears, saliva, colostrum). Even as a dimer, its weight (~385 kDa) does not exceed that of IgM. **High-Yield NEET-PG Pearls:** * **IgM:** First antibody to appear in response to an antigen (acute infection) and the first to be synthesized by the fetus. * **Valency:** IgM has a theoretical valency of 10, but an effective valency of 5 due to steric hindrance. * **Sedimentation Coefficient:** IgM is 19S (the highest), while IgG is 7S. * **Intravascular Distribution:** Due to its large size, IgM is confined primarily to the intravascular compartment.

Q: Which cell type produces IL-I?

Macrophage. **Explanation:** **Interleukin-1 (IL-1)** is a key pro-inflammatory cytokine that serves as a primary mediator of the innate immune response. 1. **Why Macrophages are correct:** Macrophages (and monocytes) are the **primary cellular source** of IL-1. Upon activation by pathogen-associated molecular patterns (PAMPs) like Endotoxin (LPS), macrophages secrete IL-1. Its chief functions include inducing fever (by acting on the hypothalamus), stimulating the liver to produce acute-phase reactants (CRP, Fibrinogen), and activating T-cells and vascular endothelium. 2. **Why other options are incorrect:** * **Helper T lymphocytes (CD4+):** These cells primarily produce **IL-2, IL-4, IL-5, and IFN-gamma**. While they are the targets of IL-1 (which acts as a co-stimulator for T-cell activation), they do not produce it. * **B cells:** Their primary role is antigen presentation and antibody production. While they can produce some cytokines (like IL-6 or IL-10), they are not a major source of IL-1. * **Cytotoxic T-cells (CD8+):** These cells are involved in direct cell killing via perforins and granzymes and produce cytokines like **IFN-gamma**, but not IL-1. **High-Yield Clinical Pearls for NEET-PG:** * **Endogenous Pyrogen:** IL-1 is known as the "Endogenous Pyrogen" because it stimulates PGE2 synthesis in the anterior hypothalamus to raise the body's temperature set-point. * **IL-1 Family:** It exists in two forms, **IL-1α** (cell-bound) and **IL-1β** (secreted). * **Inflammasome:** The maturation of IL-1β requires the activation of the **Caspase-1** enzyme within a protein complex called the Inflammasome. * **Synergy:** IL-1 often works synergistically with **TNF-α** and **IL-6** to mediate systemic inflammatory response syndrome (SIRS).

Question 1

A 25-year-old man is exposed to Ascaris but does not develop clinical signs of infection. Which of the following mechanisms is likely to be responsible for his resistance to infection?

Accepted Answer

IgE-mediated type I hypersensitivity disrupting worm attachment

Answer

Antibody-mediated destruction of worm-infected host cells

Answer

Cytotoxic T-lymphocyte (CTL) induced apoptosis of worm-infected host cells

Answer

Complement-mediated lysis of worms attached to host tissues

Question 2

Which of the following statements regarding Cytotoxic T lymphocytes (CTLs) is correct?

Accepted Answer

Are important in the control of viral infections

Answer

Recognize the same antigens as CD4 T cells

Answer

Secrete cytokines that stimulate the differentiation and proliferation of B cells

Answer

Most often recognize antigens that have been phagocytosed, degraded, and presented on the surface of an APC

Question 3

A patient is genetically unable to synthesize J chains. Which immunoglobulins would be affected?

Accepted Answer

IgM and IgA

Answer

IgG and IgA

Answer

IgM and IgE

Answer

IgG and IgM

Question 4

Memory T cells can be identified by using which of the following markers?

Accepted Answer

CD 45 RO

Answer

CD 45 RA

Answer

CD 45 RB

Answer

CD 45 RC

Question 5

The Group A carbohydrate antigen of Streptococcus pyogenes shares antigenic similarity with which human tissue component?

Accepted Answer

Cardiac valves

Answer

Synovial fluid

Answer

Myocardium

Answer

Vascular intima

Question 6

Which immunoglobulin has the highest molecular weight?

Accepted Answer

IgM

Answer

IgG

Answer

IgE

Answer

IgA

Question 7

Which of the following statements is true about isotypic variation?

Accepted Answer

Changes in the heavy and light chains in the constant region are responsible for the class and subclass of immunoglobulins.

Answer

These result due to subtle amino acid changes resulting from allelic differences.

Answer

These result due to changes in amino acids in the heavy and light chains at the variable region.

Answer

These are areas in an antigen that bind specifically to an antibody.

Question 8

Which cell type produces IL-I?

Accepted Answer

Macrophage

Answer

Helper T lymphocytes

Answer

B cells

Answer

Cytotoxic T-cells

Question 9

Which of the following statements best describes a key feature of innate immunity?

Accepted Answer

It includes interaction between pattern recognition receptors on phagocytes and pathogen-associated molecular patterns

Answer

It improves with repeated exposure to a given antigen

Answer

It requires antigen processing for activation

Answer

It is not associated with primary immune deficiency

Question 10

Which type of hypersensitivity reaction can occur when a single dose of antigen acts as both the sensitizing and shocking dose?

Accepted Answer

Serum sickness

Answer

Anaphylaxis

Answer

Arthus reaction

Answer

Contact dermatitis

Immunology — MCQs

Immunology — MCQs

On this page

Practice by Chapter

Want unlimited practice?