Immunology Practice Questions

Q: Which of the following statements is true about MHC class II?

Not involved in innate immunity. ***Not involved in innate immunity*** - **MHC class II molecules** are primarily involved in the **adaptive immune response**, presenting processed exogenous antigens to **helper T cells (CD4+)**. - Their function is to initiate a **specific and memory-driven immune response**, which is a hallmark of adaptive immunity, not innate immunity. *Cytotoxic T cells are involved* - **Cytotoxic T cells (CD8+)** recognize antigens presented by **MHC class I molecules**, which display endogenous peptides. - MHC class II molecules present antigens to **helper T cells (CD4+)**, which then coordinate the immune response. *Present only in B cells* - While **B cells** are important antigen-presenting cells that express MHC class II, they are not the only cells to do so. - **Macrophages** and **dendritic cells** are also professional antigen-presenting cells (APCs) that constitutively express MHC class II molecules. *Present in all nucleated cells* - **MHC class I molecules** are found on nearly all nucleated cells, presenting endogenous peptides to CD8+ T cells. - **MHC class II molecules** are restricted to professional antigen-presenting cells (APCs) like **dendritic cells, macrophages, and B cells**.

Q: Tuberculin test screens for

Cell mediated immunity. ***Cell mediated immunity*** - The tuberculin test, or **Mantoux test**, assesses cell-mediated immunity by introducing **tuberculin purified protein derivative (PPD)** into the skin. - A positive reaction indicates a **delayed-type hypersensitivity (Type IV) reaction**, mediated by **T-lymphocytes** that have previously been sensitized to *Mycobacterium tuberculosis* antigens. *Complement function* - Complement function is assessed by tests like **CH50** or **AH50**, which measure the overall activity of the classical or alternative complement pathways, respectively. - These tests evaluate the ability of complement proteins to lyse target cells, not T-cell responses. *Humoral immunity* - Humoral immunity involves **B lymphocytes** and **antibodies**, which are assessed by measuring immunoglobulin levels (e.g., IgG, IgM, IgA) or specific antibody titers. - The tuberculin test does not directly measure antibody production or B-cell function. *Phagocyte dysfunction* - Phagocyte dysfunction is evaluated by tests such as the **nitroblue tetrazolium (NBT) test** or **dihydrorhodamine (DHR) test**, which assess the respiratory burst activity of neutrophils. - These tests are used to diagnose conditions like **chronic granulomatous disease** and do not involve delayed-type hypersensitivity reactions.

Q: Which of the following is not true about innate immunity

Memory is seen. ***Memory is seen*** - Innate immunity is characterized by a **lack of immunological memory**, meaning it does not \"remember\" previous encounters with pathogens to mount a stronger, faster response. - This feature is a hallmark of **adaptive (acquired) immunity**, which develops memory cells after initial exposure. *It is relatively non specific* - Innate immune responses are **non-specific** and target broad categories of pathogens, rather than specific antigens. - It recognizes conserved structures on pathogens, known as **Pathogen-Associated Molecular Patterns (PAMPs)**, shared by many different microbes. *It is first line of defence* - Innate immunity serves as the **body's immediate and primary defense** against invading pathogens. - It provides rapid protection through physical barriers, cellular components, and soluble factors, often preventing infection before it takes hold. *It is present prior to antigenic exposure* - The components of innate immunity are **pre-existing and fully functional** before any exposure to pathogens or antigens. - This readiness allows for an **instantaneous response** upon microbial invasion, without requiring prior sensitization.

Q: Tuberculin test positivity indicates -

Good cell-mediated immunity. ***Good cell-mediated immunity*** - A positive tuberculin test (Mantoux test) indicates the presence of **functional cell-mediated immunity** with **memory T cells** that recognize tuberculous antigens - This demonstrates a **delayed-type hypersensitivity (Type IV) reaction** mediated by **sensitized T lymphocytes** - The test confirms that the individual has a functioning **cell-mediated immune system** capable of mounting an immune response to mycobacterial antigens - **Important note**: A positive test shows the *presence* of CMI response to prior exposure, though it doesn't quantify the overall strength of immunity *Infection with Mycobacterium* - While a positive tuberculin test indicates **prior exposure or infection** with *Mycobacterium tuberculosis*, BCG vaccination, or non-tuberculous mycobacteria, the test specifically *measures* the **cell-mediated immune response** to this exposure - The test does not distinguish between **latent infection, active disease, or past exposure** - The question asks what the test "indicates" in immunological terms, which is the **presence of cell-mediated immunity**, rather than just infection status *Good humoral immunity* - The tuberculin test evaluates **cell-mediated immunity (Type IV hypersensitivity)**, not humoral immunity (antibody-mediated) - Humoral immunity involves **B cells and antibodies**, while the Mantoux test depends on **T cell-mediated responses** - Protection against *Mycobacterium tuberculosis* primarily requires cell-mediated immunity *None of the options* - This is incorrect because the tuberculin test directly demonstrates the **integrity and functionality of cell-mediated immunity** - The test's fundamental principle is detection of **memory T cells** that have been sensitized to mycobacterial antigens

Q: Antigen presented along with HLA-II stimulates

CD4 cells. ***CD4 cells*** - Antigen presented with **MHC class II molecules** (formerly HLA-II) on antigen-presenting cells (APCs) is recognized by the **T-cell receptor (TCR)** on **CD4+ T helper cells**. - This interaction is crucial for the activation and differentiation of CD4+ T cells, leading to cytokine production and the coordination of the adaptive immune response. *CD2 cells* - **CD2** is a surface molecule found predominantly on T cells and NK cells, involved in cell adhesion and co-stimulation but not directly in the primary antigen recognition with MHC class II. - While CD2 plays a role in T cell activation, it does not directly recognize antigen presented via MHC class II. *CD8 cells* - **CD8+ T cells** (cytotoxic T lymphocytes) primarily recognize antigens presented by **MHC class I molecules**, which display intracellular (endogenous) antigens. - MHC class I presentation signals to CD8 cells to induce apoptosis in infected or cancerous cells. *CD19 cells* - **CD19** is a cell surface marker found on **B lymphocytes** and is involved in B cell activation and signaling. - B cells can act as APCs and present antigen, but their primary recognition of antigen is typically through their B-cell receptor (BCR), and they are not themselves stimulated by MHC class II in the same manner as T cells.

Q: Rose-Waaler test is?

Passive agglutination for rheumatoid arthritis. ***Passive agglutination for rheumatoid arthritis*** - The **Rose-Waaler test** detects **rheumatoid factor (RF)**, a type of autoantibody, using **sheep red blood cells** coated with rabbit IgG. - It is a **passive agglutination** method, meaning that the antigen (rabbit IgG) is adsorbed onto an inert particle (sheep red blood cells). *Active agglutination for rheumatoid arthritis* - This description is incorrect because the Rose-Waaler test uses **antigen-coated particles** (passive), rather than directly agglutinating the rheumatoid factor for detection (active). - **Active agglutination** (e.g., direct bacterial agglutination) involves antibodies directly binding to and clumping antigens that are naturally present on or within cells. *Active agglutination for rheumatic fever* - Rheumatic fever is diagnosed based on **clinical criteria** (Jones criteria) and evidence of recent **Streptococcus pyogenes infection**, not directly by an agglutination test for rheumatic fever itself. - The **Rose-Waaler test** is specifically for **rheumatoid factor**, associated with rheumatoid arthritis, not rheumatic fever [1]. *Passive agglutination for rheumatic fever* - Although it's a **passive agglutination** test, the **Rose-Waaler test** is designed to detect **rheumatoid factor** (RF) in serum, which is a hallmark of **rheumatoid arthritis** [1]. - Rheumatic fever diagnosis involves tests like **ASO titer** or anti-DNase B, which are also antibody detection tests but against streptococcal antigens, not rheumatoid factor, and may not be classified as passive agglutination in the same manner. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1212-1214.

Q: Which of the following is a function of MHC class I and II?

Antigen presentation to T cell. ***Antigen presentation to T cell*** - **MHC class I** molecules present **endogenous antigens** to **CD8+ cytotoxic T cells**, leading to the destruction of infected or cancerous cells. - **MHC class II** molecules present **exogenous antigens** to **CD4+ helper T cells**, which then coordinate the immune response. *Antibody class switching* - This process is primarily influenced by **cytokines** secreted by helper T cells, rather than direct MHC function. - While T cells interact with B cells to facilitate class switching, the direct role is not performed by the MHC molecules themselves. *Signal transduction in T cell* - **T cell receptor (TCR)** and associated co-receptors (like **CD3 complex**) are responsible for signal transduction upon antigen recognition. - MHC molecules present the antigen, but they do not directly mediate the intracellular signaling cascades within the T cell. *Increase the secretion of cytokine* - Cytokine secretion is a downstream effect of T cell activation, which occurs after successful antigen presentation by MHC molecules. - MHC molecules' direct function is presentation, not the direct increase in cytokine secretion.

Q: Post zone phenomenon is due to

Antigen excess. ***Antigen excess*** - The **postzone phenomenon** occurs when there is **excess antigen** relative to antibody in the reaction mixture - This leads to formation of **small, soluble antigen-antibody complexes** that remain in solution and do not precipitate effectively - Results in a **false-negative** or weak reaction despite the presence of both antigen and antibody - Seen in the **descending limb** of the precipitin curve *Antibody excess* - This causes the **prozone phenomenon**, not postzone - Occurs when excess antibody prevents optimal lattice formation - Results in false-negative reactions but due to **antibody excess** rather than antigen excess *Haptens* - Haptens are small molecules that can bind antibodies but are **not immunogenic alone** - Require carrier proteins to elicit immune responses - Not directly related to zone phenomena in precipitation reactions *Balanced Antigen and Antibody Levels* - Represents the **zone of equivalence** - Produces **optimal precipitation** with formation of large, insoluble immune complexes - This is the ideal condition for maximal precipitation, opposite of postzone phenomenon

Q: IL-2 is secreted by?

Helper T-cells. ***Helper T-cells*** - **Helper T-cells** (CD4+ T-cells) are the **primary source of IL-2** upon activation by antigen presentation. - **IL-2** acts as a **T-cell growth factor**, essential for the clonal expansion of antigen-specific T-cells and immune response amplification. - Activated **CD8+ cytotoxic T-cells** also produce IL-2, though in smaller amounts. *Neutrophils* - **Neutrophils** are phagocytic cells primarily involved in acute inflammation and bacterial killing. - They mainly produce **chemokines** and **pro-inflammatory cytokines** like IL-8 and IL-1β, but do not secrete significant amounts of IL-2. *NK cells* - **Natural Killer (NK) cells** are part of the innate immune system and are crucial for targeting virus-infected and tumor cells. - While activated NK cells can produce small amounts of IL-2, they are primarily **IL-2 responders** rather than major producers. - NK cells predominantly secrete **IFN-gamma** and **TNF-alpha** upon activation. *Macrophages* - **Macrophages** are antigen-presenting cells that phagocytose pathogens and cellular debris. - They predominantly secrete **pro-inflammatory cytokines** such as TNF-alpha, IL-1, IL-6, and IL-12, rather than IL-2.

Q: MHC II is associated with:-

Antigen presenting cells. ***Antigen presenting cells*** - **MHC II (Major Histocompatibility Complex class II)** molecules are primarily expressed on the surface of professional **antigen-presenting cells (APCs)**. - APCs, such as **macrophages**, **dendritic cells**, and **B lymphocytes**, use MHC II to present **extracellularly derived antigens** to **CD4+ T helper cells**. *Red blood cells* - **Red blood cells (RBCs)** are anucleated and lack MHC molecules entirely. - Their primary function is **oxygen transport**, not immune cell communication. *Platelets* - **Platelets** are cell fragments involved in **hemostasis** (blood clotting). - They do not express MHC class II molecules as they are not involved in antigen presentation. *Epithelial cells* - Most **epithelial cells** primarily express **MHC class I** molecules to present **intracellular antigens** to **CD8+ cytotoxic T cells**. - They do not typically express MHC class II unless under specific inflammatory conditions, and even then, not as their primary function.

Question 1

Which of the following statements is true about MHC class II?

Accepted Answer

Not involved in innate immunity

Answer

Cytotoxic T cells are involved

Answer

Present only in B cells

Answer

Present in all nucleated cells

Question 2

Tuberculin test screens for

Accepted Answer

Cell mediated immunity

Answer

Complement function

Answer

Humoral immunity

Answer

Phagocyte dysfunction

Question 3

Which of the following is not true about innate immunity

Accepted Answer

Memory is seen

Answer

It is relatively non specific

Answer

It is first line of defence

Answer

It is present prior to antigenic exposure

Question 4

Tuberculin test positivity indicates -

Accepted Answer

Good cell-mediated immunity

Answer

Infection with Mycobacterium

Answer

Good humoral immunity

Answer

None of the options

Question 5

Antigen presented along with HLA-II stimulates

Accepted Answer

CD4 cells

Answer

CD2 cells

Answer

CD8 cells

Answer

CD19 cells

Question 6

Rose-Waaler test is?

Accepted Answer

Passive agglutination for rheumatoid arthritis

Answer

Active agglutination for rheumatoid arthritis

Answer

Active agglutination for rheumatic fever

Answer

Passive agglutination for rheumatic fever

Question 7

Which of the following is a function of MHC class I and II?

Accepted Answer

Antigen presentation to T cell

Answer

Antibody class switching

Answer

Signal transduction in T cell

Answer

Increase the secretion of cytokine

Question 8

Post zone phenomenon is due to

Accepted Answer

Antigen excess

Answer

Antibody excess

Answer

Haptens

Answer

Balanced Antigen and Antibody Levels

Question 9

IL-2 is secreted by?

Accepted Answer

Helper T-cells

Answer

Neutrophils

Answer

NK cells

Answer

Macrophages

Question 10

MHC II is associated with:-

Accepted Answer

Antigen presenting cells

Answer

Red blood cells

Answer

Platelets

Answer

Epithelial cells

Immunology — MCQs

Immunology — MCQs

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