Immunology Practice Questions

Q: DNA is detected by:

Southern blot. **Explanation:** The detection of specific biological molecules is a fundamental concept in molecular biology and immunology, often tested in NEET-PG via the "Blotting Techniques" mnemonic. **1. Why Southern Blot is Correct:** The **Southern blot** is the gold standard technique used to detect specific **DNA** sequences in a sample. It involves the enzymatic digestion of DNA into fragments, separation by gel electrophoresis, transfer (blotting) to a membrane, and hybridization with a labeled DNA probe. It was named after its inventor, **Edwin Southern**. **2. Why Other Options are Incorrect:** * **Northern Blot:** This technique is used to detect **RNA** (specifically mRNA) to study gene expression. * **Western Blot:** This is used to detect specific **Proteins**. In clinical practice, it is famously used as a confirmatory test for **HIV** (detecting antibodies against p24, gp41, and gp120/160). * **Eastern Blot:** This is a specialized technique used to detect **post-translational modifications** of proteins (such as carbohydrates or lipids). **3. High-Yield Clinical Pearls for NEET-PG:** To remember these easily, use the **"SNOW DROP"** mnemonic: * **S**outhern = **D**NA * **N**orthern = **R**NA * **O** = **O** (No match) * **W**estern = **P**rotein * **Southwestern Blot:** A hybrid technique used to detect **DNA-binding proteins** (e.g., transcription factors like c-Jun or c-Fos). * **Polymerase Chain Reaction (PCR):** While blotting detects DNA, PCR is used to **amplify** DNA. * **ELISA:** Primarily used for protein/antigen/antibody detection; it is the screening test for HIV, whereas Western Blot is the confirmatory test.

Q: MHC class III genes encode which of the following?

Tumor necrosis factor. **Explanation:** The Major Histocompatibility Complex (MHC) is a cluster of genes located on the short arm of **Chromosome 6**. While MHC Class I and II are primarily involved in antigen presentation, **MHC Class III** genes are unique because they do not encode cell-surface receptors. Instead, they encode various secreted proteins involved in the immune and inflammatory response. **Why Option B is correct:** MHC Class III genes encode several critical inflammatory mediators, most notably **Tumor Necrosis Factor (TNF-α and TNF-β)**. Additionally, they encode heat shock proteins (HSP) and specific components of the complement system. **Analysis of Incorrect Options:** * **Option A (C3):** While MHC Class III encodes complement components **C2, C4, and Factor B**, it does **not** encode C3. This is a common trap in NEET-PG; remember that C3 is the most abundant complement protein but is not linked to the MHC locus. * **Option C (Interleukin 2):** IL-2 is a T-cell growth factor encoded on Chromosome 4, not Chromosome 6. * **Option D (Beta 2 microglobulin):** This is the light chain of the MHC Class I molecule. Crucially, while the heavy chain of MHC I is encoded on Chromosome 6, $\beta_2$-microglobulin is encoded on **Chromosome 15**. **High-Yield Clinical Pearls for NEET-PG:** * **MHC Class I:** HLA-A, B, C (Present endogenous antigens to CD8+ T cells). * **MHC Class II:** HLA-DP, DQ, DR (Present exogenous antigens to CD4+ T cells). * **MHC Class III:** Includes Complement (C2, C4), TNF, and Heat Shock Proteins. * **MHC Restriction:** CD8+ cells are MHC I restricted; CD4+ cells are MHC II restricted. * **Non-classical MHC:** HLA-G (expressed on cytotrophoblasts) protects the fetus from maternal NK cell attack.

Q: Interleukins and growth factors are considered examples of which of the following?

Cytokines. **Explanation:** **Why Cytokines is the correct answer:** Cytokines are low-molecular-weight, soluble proteins or glycoproteins secreted by cells of both the innate and adaptive immune systems. They act as chemical messengers that regulate the intensity and duration of the immune response by stimulating or inhibiting the activation, proliferation, and differentiation of various cells. **Interleukins (ILs)** are a subset of cytokines originally thought to act only between leukocytes, while **Growth Factors** (like TGF-β) are cytokines that primarily regulate cell survival and proliferation. They function through autocrine, paracrine, or endocrine pathways. **Why other options are incorrect:** * **Neurotransmitters:** These are chemical messengers (e.g., Acetylcholine, Dopamine) released by neurons at synapses to transmit signals to other neurons, muscle cells, or glands. * **Metalloproteinases (MMPs):** These are calcium-dependent, zinc-containing enzymes that degrade extracellular matrix components (e.g., collagenase). They are involved in tissue remodeling, not primary cell signaling. * **Phosphoproteinases (Phosphatases):** These are enzymes that remove phosphate groups from proteins (dephosphorylation), acting as regulatory switches within intracellular signaling pathways rather than extracellular messengers. **High-Yield Clinical Pearls for NEET-PG:** * **Pleiotropy:** One cytokine having multiple different effects on different cell types (e.g., IL-4 acting on B-cells, T-cells, and mast cells). * **Redundancy:** Multiple cytokines exerting the same effect (e.g., IL-2, IL-4, and IL-5 all trigger B-cell proliferation). * **Pro-inflammatory Cytokines:** IL-1, IL-6, and TNF-α (Key mediators of the acute phase response). * **Anti-inflammatory Cytokines:** IL-10 and TGF-β. * **IL-8:** The primary chemotactic factor for neutrophils ("Clean up on aisle 8").

Q: Lack of reaction to our own HLA (human leukocyte antigen) is known as?

Tolerance. ### Explanation **Correct Answer: C. Tolerance** **Understanding the Concept:** **Immunological tolerance** is the state of unresponsiveness of the immune system to substances or tissues that have the potential to induce an immune response. Specifically, **self-tolerance** is the body's ability to recognize and not attack its own antigens, such as HLA (Human Leukocyte Antigens). This is achieved through two primary mechanisms: 1. **Central Tolerance:** Occurs during lymphocyte development in the thymus (T-cells) and bone marrow (B-cells) via negative selection (deletion of self-reactive clones). 2. **Peripheral Tolerance:** Occurs in the secondary lymphoid organs through mechanisms like anergy (functional inactivation), suppression by T-regulatory cells, or apoptosis. **Why Incorrect Options are Wrong:** * **A. Autoimmunity:** This is the exact opposite of tolerance. It is a clinical state where the immune system fails to recognize "self" and mounts an attack against the body's own HLA or tissues. * **B. Clonal Selection:** This is the process by which a specific antigen activates and expands only those lymphocytes that have receptors specific for that antigen. It explains how we respond to foreign pathogens, not why we ignore self-antigens. * **C. Complement System:** This is a part of the innate immune system consisting of plasma proteins that enhance (complement) the ability of antibodies and phagocytic cells to clear pathogens. It does not dictate self-recognition. **High-Yield Clinical Pearls for NEET-PG:** * **HLA (MHC) Restriction:** T-cells only recognize antigens when presented on self-MHC molecules. * **AIRE Gene:** The Autoimmune Regulator (AIRE) gene is crucial for central tolerance; mutations lead to **APECED** (Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy). * **Anergy:** Occurs when a T-cell recognizes an antigen without the necessary co-stimulatory signal (e.g., CD28-B7 interaction).

Q: Which of the following laboratory assays can be used to detect the number and types of immune cells in the peripheral blood?

Flow cytometry. **Explanation:** **Flow cytometry** is the gold standard for identifying and quantifying specific cell populations in a fluid suspension. It works by passing cells in a single-file stream through a laser beam. Cells are pre-labeled with fluorescent-tagged monoclonal antibodies that bind to specific surface markers (Clusters of Differentiation or **CD markers**). As each cell passes the laser, it scatters light and emits fluorescence, allowing the machine to measure the cell's size (Forward Scatter), granularity (Side Scatter), and specific type (Fluorescence). This makes it the ideal tool for "immunophenotyping"—calculating the absolute number and percentage of T-cells (CD3), B-cells (CD19/20), and NK cells. **Why the other options are incorrect:** * **Immunofixation electrophoresis:** Used to identify specific types of monoclonal antibodies (M-protein) in conditions like Multiple Myeloma. It detects proteins, not whole cells. * **Immunoblot (Western Blot):** Used to detect specific proteins (antigens or antibodies) in a sample (e.g., confirmatory test for HIV). It involves protein separation by molecular weight. * **Enzyme immunoassay (EIA/ELISA):** Used to detect and quantify soluble antigens or antibodies in serum (e.g., screening for Hepatitis B or HIV). It cannot count or differentiate cell populations. **High-Yield Clinical Pearls for NEET-PG:** * **CD4/CD8 Ratio:** Flow cytometry is the primary method used to monitor the CD4 count in HIV/AIDS patients. * **Leukemia/Lymphoma:** It is essential for the "lineage" determination of malignant cells (e.g., distinguishing AML from ALL). * **PNH (Paroxysmal Nocturnal Hemoglobinuria):** Flow cytometry is the most sensitive test to detect the absence of CD55 and CD59 on RBCs/WBCs.

Q: Reactive cold agglutinins suggest which of the following diseases?

Primary atypical pneumonia. **Explanation:** **Primary atypical pneumonia**, most commonly caused by *Mycoplasma pneumoniae*, is classically associated with the production of **cold agglutinins**. These are autoantibodies (typically IgM) directed against the **I-antigen** on the surface of human red blood cells. At low temperatures (0–4°C), these antibodies cause RBCs to clump together (agglutinate). While not specific to *Mycoplasma*, a titer of ≥1:64 is a high-yield diagnostic clue in a patient presenting with an insidious onset of non-productive cough, headache, and "patchy" infiltrates on X-ray. **Analysis of Incorrect Options:** * **Chronic infectious mononucleosis:** While EBV can cause cold agglutinins (specifically anti-i antibodies), it is more famously associated with **Heterophile antibodies** (detected by the Paul-Bunnell/Monospot test). * **Primary syphilis:** This is caused by *Treponema pallidum* and is diagnosed via dark-field microscopy or serology (VDRL/RPR). It does not trigger cold agglutinin production. * **Scarlet fever:** Caused by *Streptococcus pyogenes* (Group A Strep) erythrogenic toxin; it presents with a "sandpaper" rash and "strawberry tongue." Diagnosis is via ASLO titers or throat culture. **High-Yield Clinical Pearls for NEET-PG:** * **Target Antigen:** Cold agglutinins in *Mycoplasma* are **Anti-I**, whereas in Infectious Mononucleosis, they are **Anti-i**. * **Complication:** These antibodies can lead to **Autoimmune Hemolytic Anemia (AIHA)** of the "cold" variety. * **Treatment:** *Mycoplasma* lacks a cell wall; therefore, Beta-lactams are ineffective. **Macrolides** (Azithromycin) or Doxycycline are the drugs of choice.

Q: Which of the following affects cellular immunity?

Cytokines. **Explanation:** Immunity is broadly divided into **Humoral Immunity** (mediated by B-cells and antibodies) and **Cellular Immunity** (mediated by T-cells and their products). **Why Cytokines is the correct answer:** Cellular immunity (Cell-Mediated Immunity or CMI) relies on the activation of T-lymphocytes, macrophages, and NK cells. **Cytokines** (such as Interferon-gamma, IL-2, and TNF) are the primary signaling molecules that coordinate this response. They act as chemical messengers that regulate the growth, differentiation, and activation of effector cells involved in CMI. For example, Th1 cells secrete IFN-γ to activate macrophages to destroy intracellular pathogens. **Analysis of Incorrect Options:** * **B & C. Immunoglobulins / Gamma-globulins:** These are synonymous in this context. Immunoglobulins (Antibodies) are the mediators of **Humoral Immunity**. They are produced by plasma cells (derived from B-cells) and act against extracellular pathogens. They do not directly mediate cellular immunity. * **D. Prostaglandins:** These are lipid compounds derived from arachidonic acid that act as local mediators of inflammation, fever, and pain. While they can modulate immune responses, they are not the primary effectors or regulators of cellular immunity. **High-Yield NEET-PG Pearls:** * **Key CMI Cells:** CD4+ T-helper cells and CD8+ Cytotoxic T-cells. * **Tests for CMI:** Skin tests (e.g., Mantoux/Tuberculin test), Lymphocyte transformation test, and Migration inhibition factor (MIF) test. * **Intracellular Pathogens:** CMI is the primary defense against viruses, fungi, and intracellular bacteria like *M. tuberculosis* and *L. leprae*. * **Cytokine Profile:** Th1 cells produce IL-2 and IFN-γ (promoting CMI), while Th2 cells produce IL-4, IL-5, and IL-10 (promoting Humoral immunity).

Q: Allergic rhinitis is which type of hypersensitivity reaction?

Type-1. **Explanation:** **Allergic rhinitis** is a classic example of **Type-1 (Immediate) Hypersensitivity**. This reaction is mediated by **IgE antibodies** and occurs within minutes of exposure to an allergen (like pollen or dust). Upon first exposure, the individual is sensitized, leading to IgE production which binds to the surface of **mast cells and basophils**. On re-exposure, the allergen cross-links these IgE molecules, triggering **degranulation** and the release of primary mediators like **histamine**, which causes sneezing, rhinorrhea, and nasal congestion. **Why other options are incorrect:** * **Type-2 (Cytotoxic):** Mediated by IgG or IgM against antigens on specific cell surfaces or tissues. Examples include ABO incompatibility, Rh incompatibility, and Myasthenia Gravis. * **Type-3 (Immune-Complex):** Caused by the deposition of antigen-antibody complexes in tissues, leading to complement activation. Examples include SLE, Post-streptococcal glomerulonephritis (PSGN), and Arthus reaction. * **Type-4 (Delayed-type):** A cell-mediated response involving T-lymphocytes (Th1/Th17) rather than antibodies. It typically takes 48–72 hours to manifest. Examples include the Mantoux test, Contact dermatitis, and Lepromin test. **High-Yield Clinical Pearls for NEET-PG:** * **Coombs and Gell Classification:** The standard system used to classify these four types. * **Type-1 Mnemonic:** **"A"** for **A**naphylaxis, **A**topy, and **A**sthma. * **Key Cells:** Mast cells are the central effector cells in Type-1 reactions. * **Late-phase reaction:** Occurs 2–8 hours after the initial Type-1 response, primarily mediated by **eosinophils**.

Question 1

DNA is detected by:

Accepted Answer

Southern blot

Answer

Northern blot

Answer

Western blot

Answer

Eastern blot

Question 2

MHC class III genes encode which of the following?

Accepted Answer

Tumor necrosis factor

Answer

Complement component C3

Answer

Interleukin 2

Answer

Beta 2 microglobulin

Question 3

Interleukins and growth factors are considered examples of which of the following?

Accepted Answer

Cytokines

Answer

Neurotransmitters

Answer

Metalloproteinases

Answer

Phosphoproteinases

Question 4

Lack of reaction to our own HLA (human leukocyte antigen) is known as?

Accepted Answer

Tolerance

Answer

Autoimmunity

Answer

Clonal selection

Answer

Complement system

Question 5

The variable region of an antibody molecule is located where?

Accepted Answer

N-terminal

Answer

C-terminal

Answer

Intermediate region

Answer

Carbohydrate moiety

Question 6

Which of the following laboratory assays can be used to detect the number and types of immune cells in the peripheral blood?

Accepted Answer

Flow cytometry

Answer

Immunofixation electrophoresis

Answer

Immunoblot

Answer

Enzyme immunoassay (EIA)

Question 7

Reactive cold agglutinins suggest which of the following diseases?

Accepted Answer

Primary atypical pneumonia

Answer

Chronic infectious mononucleosis

Answer

Primary syphilis

Answer

Scarlet fever

Question 8

Which of the following affects cellular immunity?

Accepted Answer

Cytokines

Answer

Immunoglobulins

Answer

Gamma-globulins

Answer

Prostaglandins

Question 9

A 15-year-old male presents with fever (103°F), severe headache, stiff neck, and a petechial rash. A lumbar puncture reveals Gram-negative diplococci (Neisseria meningitidis). Which of the following tests, combining features of gel diffusion and immunoelectrophoresis, is applicable to negatively charged antigens for confirming the causative agent?

Accepted Answer

Counter immunoelectrophoresis (CIE)

Answer

Coagglutination (COA)

Answer

Enzyme-linked immunosorbent assay (ELISA)

Answer

Latex agglutination (LA)

Question 10

Allergic rhinitis is which type of hypersensitivity reaction?

Accepted Answer

Type-1

Answer

Type-2

Answer

Type-3

Answer

Type-4

Immunology — MCQs

Immunology — MCQs

On this page

Practice by Chapter

Want unlimited practice?