Immunology Practice Questions

Q: The nitroblue tetrazolium (NBT) reduction assay is used to determine what?

Polymorphonuclear leucocytes' ability to produce superoxide. **Explanation:** The **Nitroblue Tetrazolium (NBT) reduction assay** is a classic screening test used to evaluate the metabolic activity of phagocytes, specifically their ability to undergo a "respiratory burst." **Why Option C is Correct:** During phagocytosis, polymorphonuclear leukocytes (neutrophils) activate the **NADPH oxidase enzyme complex** to produce **superoxide radicals**. In the NBT test, the colorless, water-soluble NBT dye is added to the patient's neutrophils. If the cells are functioning correctly and producing superoxide, the NBT is reduced into an insoluble, dark blue-black substance called **formazan**. A positive result (blue color) indicates intact oxidative killing power. **Why Other Options are Incorrect:** * **Option A:** While it technically tests a "function" of granulocytes, "Granulocyte function" is too broad. It could refer to chemotaxis or adhesion; the NBT test specifically measures the **oxidative burst**. * **Option B:** T-cell function is typically assessed via delayed-type hypersensitivity (DTH) skin tests or flow cytometry (CD3/CD4/CD8 counts), not oxidative assays. * **Option D:** B-lymphocyte staining involves identifying surface markers like CD19/CD20 or surface immunoglobulins, unrelated to superoxide production. **High-Yield Clinical Pearls for NEET-PG:** * **Chronic Granulomatous Disease (CGD):** This is the primary condition diagnosed using the NBT test. In CGD, there is a genetic defect in NADPH oxidase; therefore, neutrophils **fail to reduce NBT**, and the dye remains colorless. * **Modern Alternative:** The **Dihydrorhodamine (DHR) flow cytometry assay** is now the preferred gold standard over NBT due to higher sensitivity and quantitative results. * **Catalase-positive organisms:** Patients with CGD are specifically susceptible to infections by *Staphylococcus aureus*, *Aspergillus*, and *Serratia marcescens*.

Q: What is the type of antigen-antibody reaction seen in VDRL?

Flocculation. ### Explanation **Correct Answer: B. Flocculation** **Why it is correct:** The VDRL (Venereal Disease Research Laboratory) test is a non-specific screening test for Syphilis. It utilizes a **flocculation** reaction, which is a specific type of precipitation. In this reaction, the soluble antigen (Cardiolipin) reacts with the antibody (Reagin) in the patient's serum. Instead of forming a sediment at the bottom (as in standard precipitation), the antigen-antibody complexes remain suspended as visible **flakes or clumps** (floccules) due to the lipids involved. This is typically visualized under a light microscope. **Why the other options are incorrect:** * **A. Agglutination:** This involves the clumping of **particulate** antigens (like whole bacteria or RBCs). In VDRL, the antigen is soluble cardiolipin, not a particle. * **C. Passive Agglutination:** This occurs when a soluble antigen is artificially coated onto a carrier particle (like latex or charcoal) to convert a precipitation reaction into an agglutination reaction. An example is the **RPR (Rapid Plasma Reagin)** test, which uses charcoal particles. * **D. Gel Precipitation:** This involves the diffusion of antigens and antibodies through an agar gel (e.g., Elek’s test). VDRL is performed in a liquid medium (on a slide). **High-Yield Clinical Pearls for NEET-PG:** * **Antigen used in VDRL:** Cardiolipin (derived from beef heart), cholesterol, and lecithin. * **RPR vs. VDRL:** RPR is a modified flocculation test that uses charcoal particles, allowing the results to be read with the naked eye (Passive Agglutination). VDRL requires a microscope. * **Prozone Phenomenon:** A false-negative VDRL result can occur due to very high antibody titers (seen in secondary syphilis). * **Biological False Positives (BFP):** VDRL can be positive in non-syphilitic conditions like SLE, Leprosy, Malaria, and Pregnancy.

Q: A 10-year-old male presented to the pediatric OPD with colicky pain, nausea, and vomiting. An erect abdominal X-ray shows multiple air-fluid levels. Stool examination shows a specific type of egg. Which of the following interleukin is secreted in this scenario?

IL-5. ### Explanation **Clinical Correlation:** The clinical presentation of colicky pain, vomiting, and air-fluid levels on X-ray indicates **intestinal obstruction**. In a pediatric patient, a common parasitic cause of obstruction is *Ascaris lumbricoides* (roundworm). The mention of "specific eggs" in the stool confirms a **Helminthic infection**. **Why IL-5 is Correct:** Helminthic infections trigger a **Type 2 Helper T-cell (Th2) response**. Th2 cells secrete a specific cytokine profile (IL-4, IL-5, and IL-13) to combat extracellular parasites: * **IL-5** is the primary cytokine responsible for the **recruitment, activation, and survival of eosinophils**. Eosinophils release major basic protein (MBP) to damage the parasite's tegument. * **IL-4 and IL-13** stimulate B-cell class switching to **IgE**, which coats the parasite and facilitates antibody-dependent cellular cytotoxicity (ADCC). **Why Other Options are Incorrect:** * **IL-1:** A pro-inflammatory cytokine produced by macrophages. It mediates the acute phase response and fever; it is not specific to the Th2 anti-parasitic response. * **IL-2:** Produced by Th1 cells; it acts as a T-cell growth factor and is essential for the proliferation of CD4+ and CD8+ T-cells. * **IL-3:** A multilineage colony-stimulating factor that supports the growth of hematopoietic stem cells in the bone marrow. While it can support mast cell growth, it is not the primary mediator for eosinophilia in helminthiasis. **NEET-PG High-Yield Pearls:** * **Th1 Response:** Secretes IFN-γ, IL-2, and TNF-β (targets intracellular pathogens like *M. tuberculosis*). * **Th2 Response:** Secretes IL-4, IL-5, IL-10, and IL-13 (targets extracellular parasites/allergens). * **Eosinophilia + IgE elevation** is the classic laboratory hallmark of helminthic infestations. * *Ascaris lumbricoides* is the most common cause of parasitic intestinal obstruction worldwide.

Q: Which cell type lacks HLA antigens?

Red blood cell. **Explanation:** The Human Leukocyte Antigen (HLA) system is the human version of the **Major Histocompatibility Complex (MHC)**. HLA Class I antigens (HLA-A, B, and C) are expressed on the surface of almost all **nucleated cells** in the body. **1. Why Red Blood Cells (RBCs) are the correct answer:** Mature Red Blood Cells are **non-nucleated** cells. Because they lack a nucleus and the necessary protein-synthesizing machinery, they do not express HLA Class I or Class II antigens on their surface. Instead, RBCs express blood group antigens (ABO and Rh systems). This is why HLA matching is not required for simple blood transfusions, whereas it is critical for organ and bone marrow transplants. **2. Why the other options are incorrect:** * **Monocytes (A) & Neutrophils (C):** These are nucleated white blood cells. As nucleated cells, they express high levels of HLA Class I antigens. Monocytes, being professional antigen-presenting cells (APCs), also express HLA Class II antigens. * **Thrombocytes/Platelets (B):** Although platelets are anucleated fragments of megakaryocytes, they are a notable **exception** to the "nucleated cell" rule. Platelets **do express HLA Class I antigens** on their surface (inherited from the megakaryocyte). This is clinically significant as patients can develop "HLA alloimmunization" after multiple platelet transfusions. **High-Yield NEET-PG Pearls:** * **HLA Class I:** Found on all nucleated cells + Platelets. (Mnemonic: 1 x 8 = 8; interacts with CD8+ T cells). * **HLA Class II:** Found only on professional Antigen Presenting Cells (B-cells, Macrophages, Dendritic cells, and Thymic epithelial cells). (Mnemonic: 2 x 4 = 8; interacts with CD4+ T cells). * **Trophoblasts:** These are another important cell type that lacks classical HLA-A and HLA-B to avoid maternal immune rejection.

Q: Which of the following is NOT an example of delayed type hypersensitivity?

Arthus phenomenon. ### Explanation **1. Why Arthus Phenomenon is the Correct Answer:** The **Arthus phenomenon** is a localized **Type III Hypersensitivity** reaction (Immune-complex mediated). It occurs when an antigen is injected into the skin of an individual with high levels of pre-existing circulating IgG antibodies. This leads to the formation of antigen-antibody complexes that deposit in small blood vessel walls, activating the complement system and causing inflammatory vasculitis and tissue necrosis. Unlike delayed-type reactions, it is mediated by antibodies, not T-cells. **2. Analysis of Incorrect Options (Type IV Hypersensitivity):** * **Contact Dermatitis (Option B):** A classic example of Type IV hypersensitivity. It is mediated by CD4+ and CD8+ T-cells reacting to haptens (like nickel or poison ivy) upon re-exposure. * **Tuberculin Test (Option C):** The prototype of Delayed-Type Hypersensitivity (DTH). It involves the recruitment of macrophages by Th1 cells in response to PPD (Purified Protein Derivative), peaking at 48–72 hours. * **Graft versus Host Reaction (Option D):** This involves donor T-cells recognizing and attacking the recipient’s (host) tissues. It is a cell-mediated immune response, falling under the spectrum of Type IV reactions. **3. High-Yield Clinical Pearls for NEET-PG:** * **Coombs and Gell Classification:** * **Type I:** Immediate (IgE) * **Type II:** Cytotoxic (IgG/IgM) * **Type III:** Immune Complex (Arthus, Serum Sickness) * **Type IV:** Delayed/Cell-mediated (T-cells) * **Memory Aid:** **"ACID"** (Anaphylactic, Cytotoxic, Immune-complex, Delayed). * **Arthus vs. Serum Sickness:** Arthus is **localized** (e.g., post-vaccination swelling), while Serum Sickness is **systemic** (e.g., fever, rash, arthralgia after antitoxin administration). Both are Type III.

Q: CD4 cells are involved in all of the following processes, EXCEPT:

Processing and presenting antigens. ### Explanation The correct answer is **B. Processing and presenting antigens.** **1. Why Option B is correct:** CD4+ T cells (Helper T cells) are the **recipients** of antigen presentation, not the presenters. Antigen processing and presentation is the function of **Antigen-Presenting Cells (APCs)** such as Dendritic cells, Macrophages, and B cells. These APCs process exogenous antigens and present them via **MHC Class II** molecules to the T-cell receptor (TCR) on CD4 cells. CD4 cells then become activated to coordinate the immune response. **2. Why the other options are incorrect:** * **Option A:** CD4 cells (specifically Th2 subset) provide "help" to B cells by releasing cytokines (like IL-4, IL-5) and through CD40-CD40L interaction, which is essential for B cell activation, isotype switching, and memory cell formation. * **Option C:** Upon activation, CD4 cells (specifically Th1 subset) produce **Interleukin-2 (IL-2)**, which acts as an autocrine growth factor to stimulate T-cell proliferation (clonal expansion). * **Option D:** Activated Th1 cells produce **Interferon-gamma (IFN-γ)**, which is the primary cytokine responsible for activating macrophages and enhancing their microbicidal activity. **3. High-Yield Clinical Pearls for NEET-PG:** * **MHC Restriction:** CD4 cells recognize antigens only in association with **MHC Class II** (Rule of 8: 4 × 2 = 8), while CD8 cells recognize **MHC Class I** (8 × 1 = 8). * **Th1 vs. Th2:** Th1 cells primarily mediate **Cell-Mediated Immunity** (IFN-γ, IL-2, TNF-β), while Th2 cells mediate **Humoral Immunity** (IL-4, IL-5, IL-10, IL-13). * **HIV Pathogenesis:** HIV selectively infects and depletes CD4+ T cells by binding to the CD4 molecule and CCR5/CXCR4 co-receptors, leading to profound immunodeficiency.

Q: Which are the gene components of HLA class I?

A, B, C. The Human Leukocyte Antigen (HLA) system is the Major Histocompatibility Complex (MHC) in humans, located on the short arm of **Chromosome 6**. It is divided into three classes based on structure and function. ### **Explanation of the Correct Answer** **Option A (A, B, C)** is correct because these genes encode the **HLA Class I** molecules. * **Structure:** Class I molecules consist of a heavy chain (encoded by HLA-A, B, or C genes) non-covalently linked to a **$\beta_2$-microglobulin** (encoded on Chromosome 15). * **Distribution:** They are expressed on almost all **nucleated cells** and platelets (but not on mature RBCs). * **Function:** They present endogenous antigens to **CD8+ Cytotoxic T-cells**. ### **Explanation of Incorrect Options** **Options B, C, and D (DR, DQ, DP)** are incorrect because these genes encode **HLA Class II** molecules. * **Distribution:** Unlike Class I, Class II molecules are restricted to **Antigen-Presenting Cells (APCs)** such as macrophages, B-cells, and dendritic cells. * **Function:** They present exogenous antigens to **CD4+ Helper T-cells**. ### **High-Yield Clinical Pearls for NEET-PG** * **MHC Restriction:** CD8+ cells recognize Class I (Rule of 8: 8 × 1 = 8), while CD4+ cells recognize Class II (4 × 2 = 8). * **HLA-B27:** Strongly associated with Seronegative Spondyloarthropathies (e.g., Ankylosing Spondylitis). * **HLA-DR3/DR4:** Associated with Type 1 Diabetes Mellitus. * **HLA-B*5701:** Screening is mandatory before starting Abacavir (HIV) to prevent hypersensitivity. * **Class III MHC:** Includes genes for Complement components (C2, C4) and TNF (Tumor Necrosis Factor).

Question 1

The nitroblue tetrazolium (NBT) reduction assay is used to determine what?

Accepted Answer

Polymorphonuclear leucocytes' ability to produce superoxide

Answer

Granulocyte function

Answer

T-cell function

Answer

B-lymphocyte staining

Question 2

What is the type of antigen-antibody reaction seen in VDRL?

Accepted Answer

Flocculation

Answer

Agglutination

Answer

Passive agglutination

Answer

Gel precipitation

Question 3

A 10-year-old male presented to the pediatric OPD with colicky pain, nausea, and vomiting. An erect abdominal X-ray shows multiple air-fluid levels. Stool examination shows a specific type of egg. Which of the following interleukin is secreted in this scenario?

Accepted Answer

IL-5

Answer

IL-1

Answer

IL-2

Answer

IL-3

Question 4

Which cell type lacks HLA antigens?

Accepted Answer

Red blood cell

Answer

Monocyte

Answer

Thrombocytes

Answer

Neutrophil

Question 5

Prozone phenomenon is a feature of which of the following diseases?

Accepted Answer

Brucellosis

Answer

Tularemia

Answer

Legionnaire's disease

Answer

Plague

Question 6

ASLO titres are used in the diagnosis of which condition?

Accepted Answer

Acute rheumatic fever

Answer

Acute rheumatoid arthritis

Answer

Ankylosing spondylitis

Answer

Osteoarthritis

Question 7

Which of the following is NOT an example of delayed type hypersensitivity?

Accepted Answer

Arthus phenomenon

Answer

Contact dermatitis

Answer

Tuberculin test

Answer

Graft versus host reaction

Question 8

An eight-year-old child presents with recurrent chest infections since early childhood. Serological examination reveals a deficiency in a certain immunoglobulin. Which of the following is the most common immunoglobulin deficiency observed in such cases?

Accepted Answer

IgA

Answer

IgE

Answer

IgG

Answer

IgD

Question 9

CD4 cells are involved in all of the following processes, EXCEPT:

Accepted Answer

Processing and presenting antigens

Answer

Acting as a helper function for B cells

Answer

Producing and releasing interleukin-2

Answer

Producing and releasing interferon-gamma

Question 10

Which are the gene components of HLA class I?

Accepted Answer

A, B, C

Answer

DR

Answer

DQ

Answer

DP

Immunology — MCQs

Immunology — MCQs

On this page

Practice by Chapter

Want unlimited practice?