Immunology Practice Questions

Q: Which of the following is an example of a neutralization reaction?

Nagler reaction. ***Nagler reaction*** - The Nagler reaction is a **neutralization test** used to detect α-toxin (lecithinase) produced by *Clostridium perfringens*. - A positive result occurs when Lecithinase activity is **neutralized by antitoxin**, preventing hydrolysis of lecithin in egg yolk agar. *VDRL* - The **Venereal Disease Research Laboratory (VDRL) test** is a flocculation test used for screening syphilis, detecting cardiolipin antibodies. - It involves the clumping of **antigen-antibody complexes**, not the neutralization of a toxin. *Widal test* - The **Widal test** is an agglutination test for the diagnosis of enteric fever (typhoid), detecting antibodies against *Salmonella* O and H antigens. - It identifies bacterial agglutination, which is the **clumping of bacterial cells** in the presence of specific antibodies. *Kahn test* - The **Kahn test** is another flocculation test, similar to VDRL, historically used for syphilis screening. - It involves the precipitation of a lipid antigen by syphilitic antibodies, which is an **agglutination phenomenon**, not neutralization.

Q: Phagocytosis of mycobacterium tuberculosis by macrophages is mainly mediated by:

Interferon Gamma. ***Interferon Gamma*** - **Interferon gamma (IFN-γ)** is the most critical cytokine for **macrophage activation** in tuberculosis, enabling effective phagocytosis and intracellular killing of **Mycobacterium tuberculosis**. - IFN-γ (produced by **Th1 cells** and **NK cells**) primes macrophages by: - Enhancing **phagosome-lysosome fusion** - Increasing expression of **Fc receptors** and **complement receptors** for better opsonization - Stimulating production of **reactive oxygen species (ROS)** and **nitric oxide (NO)** - Upregulating **MHC class II** for improved antigen presentation - Without IFN-γ, macrophages cannot effectively control intracellular mycobacterial growth (as seen in **IFN-γ or IL-12 receptor deficiencies** leading to disseminated mycobacterial infections). *Interleukin 6* - **IL-6** is a pro-inflammatory cytokine involved in **acute-phase responses**, fever induction, and B-cell differentiation. - While it contributes to systemic inflammatory responses in TB, it does not directly activate macrophages for mycobacterial phagocytosis and killing. *Interleukin 3* - **IL-3** is a **hematopoietic growth factor** that promotes proliferation and differentiation of myeloid and lymphoid progenitor cells in bone marrow. - It plays no direct role in the effector functions of mature macrophages against *M. tuberculosis*. *Interleukin 12* - **IL-12** (produced by macrophages and dendritic cells) is essential for initiating **Th1 immunity** by promoting differentiation of naive CD4+ T cells into **Th1 cells** that produce IFN-γ. - IL-12 acts **upstream** of IFN-γ in the immune cascade but does not directly mediate macrophage phagocytic function. - The **IL-12/IFN-γ axis** is critical for TB immunity, but IFN-γ is the direct macrophage activator.

Q: CD3 is a marker for which type of cells?

T - cells. ***T - cells*** - **CD3** is a complex of proteins that is universally expressed on the surface of all **T lymphocytes** (T cells). - It plays a crucial role in **T cell activation** by transducing signals from the T cell receptor (TCR) to the cell's interior. *B - cells* - **B cells** are characterized by the expression of unique surface markers like **CD19**, **CD20**, and surface **immunoglobulins**, not CD3. - Their primary function is to produce **antibodies** and present antigens. *NK - cells* - **Natural Killer (NK) cells** are a type of lymphocyte that lacks both CD3 and a T cell receptor (TCR), differentiating them from T cells. - They express markers such as **CD16** and **CD56** and are involved in innate immunity, particularly against viral infections and tumor cells. *Monocytes* - **Monocytes** are myeloid cells, not lymphocytes, and are characterized by markers such as **CD14** and **CD68**. - They differentiate into macrophages and dendritic cells, playing a significant role in phagocytosis and antigen presentation.

Q: What is the Oakley-Fulthorpe procedure primarily used for?

Detection of specific antibodies in serum. ***Detection of specific antibodies in serum*** - The **Oakley-Fulthorpe procedure** is an **immunodiffusion technique** used to detect and identify **precipitating antibodies** in serum. - It is a modification of the **Ouchterlony double diffusion method**, performed in **agar gel** where antigen and antibody solutions diffuse toward each other. - When specific antibody-antigen complexes form, they create visible **precipitin lines** in the gel, allowing for identification and comparison of antibodies. - This technique is particularly useful for detecting **antibodies in serum** against specific antigens. *Determining blood type* - Blood typing is performed using **agglutination assays** (e.g., forward and reverse typing) to identify ABO and Rh antigens on red blood cells. - This involves direct mixing of blood with antisera, not immunodiffusion techniques. *Measuring hormone levels* - Hormone levels are measured using **immunoassays** such as ELISA (Enzyme-Linked Immunosorbent Assay), radioimmunoassays (RIA), or chemiluminescence assays. - These methods quantify hormone concentrations directly, not through diffusion-based precipitin reactions. *Identifying bacterial infections* - Bacterial infections are diagnosed through **culture and sensitivity testing**, microscopy, molecular methods (PCR), or rapid antigen tests. - While immunodiffusion can detect antibodies against bacterial antigens, it is not the primary method for diagnosing active bacterial infections in clinical practice.

Q: What is the Rose Waaler test used for?

Passive hemagglutination test. ***Passive hemagglutination test*** - The **Rose Waaler test** is a historical **rheumatoid factor (RF)** detection method based on **passive hemagglutination**. - It uses sheep red blood cells coated with a subagglutinating dose of rabbit anti-sheep red blood cell antibody to detect RF in patient serum. *Complement fixation test* - This assay detects the presence of **antibody** or **antigen** by observing whether **complement** is consumed in an antigen-antibody reaction. - The Rose Waaler test does not involve the measurement of complement consumption. *Precipitation in gel* - This technique, such as **immunodiffusion**, involves the formation of a visible **precipitate** when soluble antigens and antibodies diffuse through a gel matrix and meet at optimal concentrations. - The Rose Waaler test relies on agglutination of red blood cells, not precipitation in gel. *Ring precipitation* - A **ring precipitation test** involves layering an antigen solution over an antibody solution, creating an antigen-antibody complex visible as a **precipitate ring** at the interface of the two solutions. - This method is distinct from the Rose Waaler test which uses red blood cell agglutination.

Q: IgM appears in fetus at what gestational age -

20 weeks. ***20 weeks*** - The fetal immune system begins to develop around **20 weeks of gestation**, at which point the fetus starts producing its own **IgM antibodies**. - **IgM** is the first antibody isotype produced by the developing fetal **B lymphocytes** and is important for early immune responses. *10 weeks* - While some components of the immune system may start to differentiate earlier, **IgM production** at a functional level is not yet established at **10 weeks of gestation**. - At this early stage, the fetal immune system is still primarily in its **developmental phase**, with major organogenesis occurring. *30 weeks* - By **30 weeks**, the fetus has already been producing IgM for several weeks, and the immune system is more mature, capable of a more robust **antibody response**. - While **IgG** levels are significantly increasing due to maternal transfer at this stage, **IgM production** began earlier. *at birth* - At birth, a neonate has circulating **IgM antibodies**, which are indicative of prior fetal immune activation and are measurable in umbilical cord blood. - However, the initial production of **fetal IgM** occurs much earlier in gestation, not at the time of birth.

Q: What type of immunity is primarily associated with the administration of transfer factor?

Adoptive immunity. ***Adoptive immunity (Correct)*** - **Transfer factor** consists of small, dialyzable molecules extracted from immune T lymphocytes of an immune donor - Its administration transfers **cell-mediated immunity** from donor to recipient, which defines adoptive immunity - This represents transfer of **immune cells or their products** (not antibodies), providing antigen-specific cellular immunity - Also called **adoptive immunotherapy** or adoptive transfer *Artificial passive immunity (Incorrect)* - Involves the **transfer of pre-formed antibodies** (e.g., antitoxins, immunoglobulins, antiserum) from an immune individual or animal - Provides **immediate but temporary humoral protection** - Does NOT transfer cellular immunity - this is the key distinction from adoptive immunity - Examples: Anti-rabies immunoglobulin, anti-tetanus serum *Natural active immunity (Incorrect)* - Occurs when an individual is **naturally exposed to an antigen** (infection) and produces their own antibodies and immune cells - The host's own immune system **actively responds** to develop long-lasting immunity - Example: Immunity after recovering from measles or chickenpox *Artificial active immunity (Incorrect)* - Achieved through **vaccination** with attenuated, inactivated, or subunit antigens - The recipient's body is **actively stimulated** to produce protective immunity - Provides long-lasting protection through immunological memory

Q: Which of the following is a specific feature of acquired immunity?

Immunological memory. ***Immunological memory*** - A key characteristic of **acquired immunity** is the ability to "remember" previous encounters with specific pathogens. - This memory leads to a more rapid and robust immune response upon subsequent exposure to the same pathogen. - This is the **defining feature** that distinguishes acquired immunity from innate immunity. *Affected by genetic makeup* - While genetic makeup can influence the *efficiency* of the acquired immune system, it is not a **specific feature** that distinguishes it from innate immunity. - **Both innate and acquired immunity** are affected by genetic factors, determining baseline resistance and immune response capability. *No antigen exposure* - **Acquired immunity** is specifically characterized by its *dependence* on antigen exposure to develop specific responses. - The phrase "no antigen exposure" describes how the **innate immune system** functions, providing immediate, non-specific protection without prior contact with a pathogen. *Immediate response* - **Innate immunity** provides an immediate, non-specific response to pathogens. - **Acquired immunity** takes time to develop (days to weeks) after initial antigen exposure, but provides a faster response upon re-exposure due to immunological memory.

Q: The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Clonal selection. ***Clonal selection*** - **Clonal selection** is the fundamental process by which an antigen-specific B lymphocyte is **selected** when its B cell receptor (BCR) recognizes and binds to a matching antigen. - This binding triggers the B cell to become **activated**, **proliferate** (undergo clonal expansion), and **differentiate** into plasma cells that produce antibodies specific to that antigen. - This process is the cornerstone of **adaptive immunity**, ensuring that only B cells with receptors matching the encountered antigen are stimulated to respond. *Class switching* - **Class switching** (isotype switching) occurs AFTER clonal selection and activation. - It allows already-activated B cells to change the **antibody class** they produce (from IgM to IgG, IgA, or IgE) while maintaining the **same antigen specificity**. - This process modifies effector functions but does NOT involve the initial selection and activation of antigen-specific B cells. *Group switching* - This is not a recognized term in immunology. - It does not describe any standard process of B cell activation or antibody production. *Hybridisation* - **Hybridization** refers to the formation of double-stranded nucleic acids from complementary strands or the creation of hybrid cells (e.g., hybridomas for monoclonal antibody production). - It is not the physiological process by which B lymphocytes are selected and activated in response to antigen exposure.

Q: Interleukin 2 is produced by

T helper cells 1. ***T helper cells 1*** - **T helper 1 (Th1) cells** are a primary source of **interleukin-2 (IL-2)**, which is crucial for the proliferation and survival of T cells. - IL-2 acts as a **T-cell growth factor**, promoting the expansion of activated T cells, including cytotoxic T lymphocytes. *T helper cells 2* - **T helper 2 (Th2) cells** primarily produce cytokines like **IL-4, IL-5, IL-6, IL-10, and IL-13**, which are involved in humoral immunity and allergic responses. - While Th2 cells are important for immune responses, they are not major producers of IL-2. *Natural killer cells* - **Natural killer (NK) cells** are part of the innate immune system and produce cytokines such as **interferon-gamma (IFN-$\gamma$)** and **tumor necrosis factor-alpha (TNF-$\alpha$)**. - They are not a significant source of IL-2, which is primarily a T-cell derived growth factor. *Basophils* - **Basophils** are granulocytes involved in allergic reactions and anti-parasitic immunity, producing mediators like **histamine** and cytokines such as **IL-4** and **IL-13**. - Basophils do not produce IL-2; their role is distinct in the immune response compared to T cells.

Question 1

Which of the following is an example of a neutralization reaction?

Accepted Answer

Nagler reaction

Answer

VDRL

Answer

Widal test

Answer

Kahn test

Question 2

Phagocytosis of mycobacterium tuberculosis by macrophages is mainly mediated by:

Accepted Answer

Interferon Gamma

Answer

Interleukin 6

Answer

Interleukin 3

Answer

Interleukin 12

Question 3

CD3 is a marker for which type of cells?

Accepted Answer

T - cells

Answer

B - cells

Answer

NK - cells

Answer

Monocytes

Question 4

What is the Oakley-Fulthorpe procedure primarily used for?

Accepted Answer

Detection of specific antibodies in serum

Answer

Determining blood type

Answer

Measuring hormone levels

Answer

Identifying bacterial infections

Question 5

What is the Rose Waaler test used for?

Accepted Answer

Passive hemagglutination test

Answer

Ring precipitation

Answer

Precipitation in gel

Answer

Complement fixation test

Question 6

IgM appears in fetus at what gestational age -

Accepted Answer

20 weeks

Answer

10 weeks

Answer

30 weeks

Answer

at birth

Question 7

What type of immunity is primarily associated with the administration of transfer factor?

Accepted Answer

Adoptive immunity

Answer

Natural active immunity

Answer

Artificial active immunity

Answer

Artificial passive immunity

Question 8

Which of the following is a specific feature of acquired immunity?

Accepted Answer

Immunological memory

Answer

Affected by genetic makeup

Answer

No antigen exposure

Answer

Immediate response

Question 9

The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Accepted Answer

Clonal selection

Answer

Class switching

Answer

Group switching

Answer

Hybridisation

Question 10

Interleukin 2 is produced by

Accepted Answer

T helper cells 1

Answer

T helper cells 2

Answer

Natural killer cells

Answer

Basophils

Immunology — MCQs

Immunology — MCQs

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