Immunology Practice Questions

Q: When is the prozone phenomenon seen?

Antibody excess to antigen. ***Antibody excess to antigen*** - The **prozone phenomenon** occurs when there is a significant **excess of antibodies** relative to the antigen, leading to inhibition of lattice formation. - In this state, too many antibodies bind to individual antigen sites, preventing cross-linking and thus inhibiting visible **agglutination** or **precipitation**. *Same concentration of antibody and antigen* - This scenario typically represents the **zone of equivalence**, where optimal lattice formation and visible reaction (agglutination or precipitation) occur. - It is where the concentrations of antibody and antigen are balanced, leading to maximum complex formation. *In antigen excess to antibody* - This situation is known as the **postzone phenomenon**, where an excess of antigen prevents the formation of stable antibody-antigen complexes. - The antigen saturates the limited antibody sites, resulting in no or minimal visible reaction. *Hyperimmune reaction* - A hyperimmune reaction refers to an **exaggerated immune response**, often resulting from repeated exposure to an antigen. - While it involves high antibody levels, it is a clinical state rather than a specific phenomenon describing antibody-antigen ratios in *in vitro* tests.

Q: Which immunoglobulin is known as the pentameric immunoglobulin?

IgM. ***IgM*** - **IgM** is found as a **pentamer** in its secreted form, meaning it is composed of five immunoglobulin monomer units joined together. - This pentameric structure gives IgM a high valency, making it very effective at **binding multiple antigens** simultaneously and activating the **complement system**. *IgA* - **IgA** primarily exists as a **monomer** in serum and as a **dimer** in secretions like mucus, tears, and saliva. - Its main function is to provide **mucosal immunity**, protecting epithelial surfaces from pathogens. *IgG* - **IgG** is the most abundant immunoglobulin in serum and exists as a **monomer**. - It crosses the **placenta** to provide passive immunity to the fetus and is crucial for **opsonization** and neutralizing toxins and viruses. *IgE* - **IgE** is present in very low concentrations in serum and exists as a **monomer**. - It plays a critical role in **allergic reactions** and defense against **parasites** by binding to mast cells and basophils.

Q: Which of the following statements about interferons is true?

Interferons inhibit viral replication in host cells.. **Interferons inhibit viral replication in host cells.** - Interferons are a crucial part of the **innate immune response** against viral infections. - They work by inducing an **antiviral state** in neighboring uninfected cells, preventing viral replication. - Interferons are **non-specific** antiviral cytokines with broad-spectrum activity. *Interferons are specific for particular viruses.* - This is incorrect. Interferons are **virus-non-specific** in their antiviral action. - While their production is triggered by viral infection, they can inhibit replication of various different viruses. - This broad-spectrum activity is a key feature distinguishing them from antibodies (which are specific). *Interferons have no effect on viral infections.* - This is false. Interferons are potent **antiviral cytokines** essential for host defense against viruses. - They activate immune cells (NK cells, macrophages) and induce expression of genes that inhibit viral processes. *Interferons are synthetic antiviral agents.* - This is incorrect. Interferons are **naturally produced proteins** by the body's cells (leukocytes, fibroblasts, dendritic cells) in response to viral infections. - While recombinant interferons are used therapeutically, interferons are biological molecules, not synthetic drugs.

Q: Which component is considered the central part of the complement pathway?

C3 (complement component 3). ***C3*** - **C3** is considered the central component because all three major pathways of complement activation (classical, alternative, and lectin) converge at the point of **C3 activation**. - Its cleavage product, **C3b**, is crucial for opsonization, formation of the C5 convertase, and initiating the assembly of the **membrane attack complex (MAC)**. *C1 (complement component 1)* - **C1** is the initial component of the **classical complement pathway** but does not play a direct role in the alternative or lectin pathways. - Its primary function is to bind to **antibody-antigen complexes** or directly to pathogens to activate C4 and C2. *C2 (complement component 2)* - **C2** is a component of the **classical** and **lectin pathways**, acting as a substrate for C1s and MASP to form the C3 convertase. - It is not involved in the initial activation of the **alternative pathway**. *C5 (complement component 5)* - **C5** is activated downstream of C3 and is a key component in the formation of the **membrane attack complex (MAC)**. - While critical for pathogen lysis, its activation is dependent on the prior cleavage of **C3** into C3b.

Q: Which antibody is elevated in parasitic infections?

IgE. **Correct: IgE** - **IgE** is centrally involved in the immune response to **parasitic infections**, particularly helminths. - This antibody promotes the release of inflammatory mediators from **mast cells** and **basophils**, leading to the expulsion of parasites. - Elevated IgE is a **characteristic finding** in helminthic infections and is used diagnostically. *Incorrect: IgA* - **IgA** is primarily found in **mucosal secretions** and plays a key role in protecting against pathogens at mucosal surfaces. - While it has a role in general immunity, it is **not the primary antibody** involved in the systemic response to parasitic infections. *Incorrect: IgG* - **IgG** is the most abundant antibody in serum and provides **long-term immunity** against many pathogens. - While IgG levels may rise in response to chronic parasitic infections, it is **not the characteristic or primary antibody** elevated in active or initial parasitic responses. *Incorrect: IgM* - **IgM** is the first antibody produced during a **primary immune response** and is important for activating the complement system. - While it indicates an early infection, it is **less specific** for parasitic infections compared to IgE.

Q: Which of the following is the most potent stimulator of Naive T-cells?

Mature dendritic cells. ***Mature dendritic cells*** - **Mature dendritic cells** are the most potent professional antigen-presenting cells (APCs) for activating **naive T cells** due to their efficient antigen processing, presentation abilities, and high expression of costimulatory molecules (e.g., CD80, CD86) and MHC-peptide complexes. - Activated by pathogens or inflammatory signals, they migrate to secondary lymphoid organs where they initiate primary immune responses by presenting antigens to and activating naive T cells. *Follicular dendritic cells* - **Follicular dendritic cells** primarily present intact antigens to **B cells** in germinal centers of secondary lymphoid organs, playing a crucial role in B cell maturation, selection, and antibody production. - They lack MHC class II molecules and thus cannot directly present antigens to naive T cells. *Macrophages* - While **macrophages** are professional APCs, they are generally less efficient than mature dendritic cells at activating **naive T cells**, especially in the initiation of primary immune responses. - They are more involved in presenting antigens to already activated T cells and clearing pathogens, often acting as secondary APCs. *B-cell* - **B cells** can act as APCs, but they are generally less efficient than **dendritic cells** in activating **naive T cells**, especially for the primary immune response. - Their primary role in antigen presentation is to present processed antigens to **helper T cells** to receive costimulation for their own activation and differentiation into plasma cells, often after being activated themselves.

Q: NK cells' activity is enhanced by?

IL-2. ***IL-2*** - **Interleukin-2** is a crucial cytokine that stimulates the proliferation and differentiation of T cells and **NK cells**, thus enhancing their cytotoxic activity. - It plays a vital role in both **adaptive and innate immune responses** by promoting NK cell maturation and increasing their ability to recognize and kill infected or cancerous cells. *IL-1* - **Interleukin-1** primarily functions as a **pro-inflammatory cytokine**, mediating systemic inflammatory responses and activating macrophages and endothelial cells. - While it modulates immune responses, its direct effect on **enhancing NK cell cytotoxicity** is not as prominent as that of IL-2. *TNF* - **Tumor Necrosis Factor (TNF)** is a cytokine involved in **systemic inflammation** and acute phase responses, also inducing apoptosis in tumor cells. - Though TNF can influence various immune cells, it is not primarily known for directly stimulating and **enhancing NK cells' activity** in the same manner as IL-2. *TGF-β* - **Transforming Growth Factor-beta (TGF-β)** is a cytokine with predominantly **immunosuppressive functions**, inhibiting the proliferation and differentiation of many immune cells, including NK cells. - It generally **downregulates immune responses** and promotes tolerance rather than enhancing NK cell activity.

Q: In utero infection leads to which immunoglobulin?

IgM. ***IgM*** - **IgM** is the first antibody produced by the fetus in response to an in utero infection, as it cannot cross the placenta. - Its presence in a newborn's blood indicates an **active fetal immune response** to an infection acquired before birth. *IgG* - **IgG** antibodies from the mother cross the placenta and provide passive immunity to the fetus, but their presence does not necessarily indicate an active fetal infection. - High IgG levels in a neonate are typically maternal and do not reflect the infant's own immune response to an in utero infection. *IgA* - **IgA** is primarily found in mucosal secretions and is not typically produced by the fetus in significant amounts in response to in utero infection. - Its presence in a neonate's blood might suggest contamination or specific unusual circumstances, rather than routine in utero infection. *IgD* - The function of **IgD** is not fully understood, but it is primarily found on the surface of B lymphocytes and is not a major effector antibody in the primary immune response to infection. - It does not play a significant role in diagnosing in utero infections.

Q: Which type of hypersensitivity is associated with cell-mediated immunity?

Type 4. ***Type 4*** - Cell-mediated immunity primarily involves **T-lymphocytes** [1], essential for targeting and eliminating **intracellular pathogens** like viruses. - It plays a crucial role in **delayed-type hypersensitivity reactions** [2], making it vital for the adaptive immune response. *Type 3* - Type 3 immune responses are primarily associated with **immune complex-mediated** diseases and not directly with cell-mediated immunity. - This type involves primarily **B-cells** and antibodies in the response against antigens. *Type 2* - Type 2 immunity mainly concerns the activation of **B-lymphocytes** and antibody production against **extracellular pathogens** like bacteria. - It is characterized by **IgE-mediated responses** [3], particularly in allergic reactions, rather than cell-mediated actions. *Type 1* - Type 1 responses are associated with **Th1 cells** [2] and are more specifically linked to **autoimmunity and cell-mediated pathways**, but represent only a part of the broader cell-mediated immunity. - This type mainly focuses on clearance of **intracellular pathogens** but is not synonymous with the entire process of cell-mediated immunity. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 216-218. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 208-210.

Q: Which of the following is not a component of innate immunity?

Helper T lymphocytes. ***Helper T lymphocyte*** - Helper T lymphocytes are a crucial part of **adaptive immunity** [4], facilitating responses against pathogens. - They specifically activate B cells and cytotoxic T cells [2], unlike components of innate immunity, which respond nonspecifically. *NK cells* - Natural Killer (NK) cells are integral to **innate immunity** [1], targeting infected or tumor cells without prior sensitization. - They play a role in the initial response to viral infections and can produce **cytokines** [2]. *Epithelial barriers* - Epithelial barriers act as the first line of defense in **innate immunity** [1], preventing pathogen entry. - They include physical and chemical barriers like skin and mucous membranes [3]. *Dendritic cells* - Dendritic cells are key antigen-presenting cells involved in **innate immunity** [1] and link to adaptive immunity. - They capture and present antigens [2], activating T cells to mount an immune response. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 194-196. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 152-153. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 196-198.

Question 1

When is the prozone phenomenon seen?

Accepted Answer

Antibody excess to antigen

Answer

Same concentration of antibody and antigen

Answer

Hyperimmune reaction

Answer

In antigen excess to antibody

Question 2

Which immunoglobulin is known as the pentameric immunoglobulin?

Accepted Answer

IgM

Answer

IgA

Answer

IgG

Answer

IgE

Question 3

Which of the following statements about interferons is true?

Accepted Answer

Interferons inhibit viral replication in host cells.

Answer

Interferons are specific for particular viruses.

Answer

Interferons have no effect on viral infections.

Answer

Interferons are synthetic antiviral agents.

Question 4

Which component is considered the central part of the complement pathway?

Accepted Answer

C3 (complement component 3)

Answer

C1 (complement component 1)

Answer

C2 (complement component 2)

Answer

C5 (complement component 5)

Question 5

Which antibody is elevated in parasitic infections?

Accepted Answer

IgE

Answer

IgA

Answer

IgG

Answer

IgM

Question 6

Which of the following is the most potent stimulator of Naive T-cells?

Accepted Answer

Mature dendritic cells

Answer

Macrophages

Answer

B-cell

Answer

Follicular dendritic cells

Question 7

NK cells' activity is enhanced by?

Accepted Answer

IL-2

Answer

IL-1

Answer

TNF

Answer

TGF-β

Question 8

In utero infection leads to which immunoglobulin?

Accepted Answer

IgM

Answer

IgG

Answer

IgA

Answer

IgD

Question 9

Which type of hypersensitivity is associated with cell-mediated immunity?

Accepted Answer

Type 4

Answer

Type 2

Answer

Type 3

Answer

Type 1

Question 10

Which of the following is not a component of innate immunity?

Accepted Answer

Helper T lymphocytes

Answer

Epithelial barriers

Answer

NK cells

Answer

Dendritic cells

Immunology — MCQs

Immunology — MCQs

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