Immunology Practice Questions

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: What is required for precipitation in comparison to agglutination?

Soluble antigen. ***Soluble antigen*** - **Precipitation reactions** involve the interaction of antibodies with **soluble antigens** to form a detectable precipitate. - Unlike **agglutination**, which involves particulate antigens (e.g., cells), precipitation requires the antigen to be dissolved in a solution. *Increased temperature* - Most immunologic reactions, including precipitation and agglutination, are typically performed at **physiological temperatures** (e.g., 37°C) or room temperature. - An **increased temperature** is not a specific requirement that differentiates precipitation from agglutination. *Specific cofactor* - While some complex immunologic reactions might require **cofactors**, neither precipitation nor agglutination inherently requires a specific cofactor to occur. - The primary components are **antigen** and **antibody**. *Lower pH* - Both precipitation and agglutination reactions are sensitive to pH and typically occur within a **narrow pH range** close to neutral (e.g., pH 7.0-7.4). - A **lower pH** (acidic environment) could lead to antibody denaturation or non-specific aggregation, ultimately hindering the reaction rather than being a requirement.

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: Which of the following does not stimulate active immunity?

Transplacental antibody transfer in newborn. ***Transplacental antibody transfer in newborn*** - This is a form of **passive immunity**, where pre-formed **antibodies from the mother** are transferred to the newborn, providing immediate but temporary protection. - It does not involve the newborn's own immune system generating an immune response or creating **memory cells**. *Subclinical infection* - Even without overt symptoms, a **natural infection** exposes the immune system to pathogens, triggering an active immune response and generating **memory cells**. - This leads to **long-term immunity** against future exposures to the same pathogen. *Clinical infection* - A **symptomatic natural infection** involves the immune system actively responding to the pathogen, producing antibodies and **memory cells**. - This process is the basis of **naturally acquired active immunity** and provides durable protection. *Vaccination* - Vaccines contain weakened or inactive forms of pathogens, or their components, which stimulate the immune system to produce **antibodies** and **memory cells** without causing disease. - This is an example of **artificially acquired active immunity**, providing long-lasting protection.

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: 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: Which human IgG subclass has the highest serum concentration?

IgG1. ***IgG1*** - **IgG1** constitutes approximately **60-70%** of the total IgG in human serum, making it the most abundant subclass. - Its high concentration reflects its crucial role in **neutralizing toxins**, agglutinating viruses, and opsonizing bacteria for phagocytosis. *IgG2* - **IgG2** makes up about **20-30%** of total IgG and is primarily important in protecting against **polysaccharide-encapsulated bacteria**. - While significant, its serum concentration is notably lower than that of IgG1. *IgG3* - **IgG3** is the least abundant IgG subclass, accounting for only **5-8%** of total IgG, and is characterized by a shorter half-life. - Despite its low concentration, it is highly efficient in activating the **complement system** due to its flexible hinge region. *IgG4* - **IgG4** comprises approximately **3-6%** of total IgG and is unique for its ability to undergo **Fab arm exchange**, leading to bispecific antibodies. - It does not activate complement and is often associated with allergy and protection against parasitic infections, but its concentration is significantly less than IgG1.

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.

Q: In the context of immune response, which of the following cell types does not express MHC class II molecules?

NK cells. ***NK cells*** - **Natural Killer (NK) cells)** are innate lymphocytes that do **NOT express MHC class II molecules** under any circumstances. - NK cells use alternative recognition mechanisms (KIRs, activating receptors) to detect target cells, primarily recognizing the **absence of MHC class I** or stress-induced ligands. - They function in innate immunity without antigen presentation capability. - **This is the best answer** as NK cells never express MHC class II, making them distinctly different from professional APCs. *Cortical macrophages* - **Cortical macrophages** in lymphoid organs are professional **antigen-presenting cells (APCs)** that constitutively express **MHC class II molecules**. - They present processed antigens to CD4+ T helper cells, playing a crucial role in initiating adaptive immune responses. *Medullary macrophages* - **Medullary macrophages** are also professional APCs that constitutively express **MHC class II molecules**. - They participate in antigen presentation and immune surveillance within the medullary regions of lymphoid tissues. *Neutrophils* - Neutrophils are granulocytes that **typically do not constitutively express MHC class II molecules** in their resting state. - However, under certain inflammatory conditions with prolonged stimulation (IFN-γ, GM-CSF), neutrophils can be induced to express low levels of MHC class II. - While neutrophils generally lack MHC class II, **NK cells are the more definitive answer** as they never express MHC class II under any physiological or pathological conditions.

Question 1

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 2

What is required for precipitation in comparison to agglutination?

Accepted Answer

Soluble antigen

Answer

Increased temperature

Answer

Specific cofactor

Answer

Lower pH

Question 3

Phagocytosis of mycobacterium tuberculosis by macrophages is mainly mediated by:

Accepted Answer

Interferon Gamma

Answer

Interleukin 6

Answer

Interleukin 3

Answer

Interleukin 12

Question 4

CD3 is a marker for which type of cells?

Accepted Answer

T - cells

Answer

B - cells

Answer

NK - cells

Answer

Monocytes

Question 5

Which of the following does not stimulate active immunity?

Accepted Answer

Transplacental antibody transfer in newborn

Answer

Clinical infection

Answer

Vaccination

Answer

Subclinical infection

Question 6

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 7

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

Accepted Answer

Nagler reaction

Answer

VDRL

Answer

Widal test

Answer

Kahn test

Question 8

Which human IgG subclass has the highest serum concentration?

Accepted Answer

IgG1

Answer

IgG2

Answer

IgG3

Answer

IgG4

Question 9

Interleukin 2 is produced by

Accepted Answer

T helper cells 1

Answer

T helper cells 2

Answer

Natural killer cells

Answer

Basophils

Question 10

In the context of immune response, which of the following cell types does not express MHC class II molecules?

Accepted Answer

NK cells

Answer

Cortical macrophages

Answer

Neutrophils

Answer

Medullary macrophages

Immunology — MCQs

Immunology — MCQs

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