Immunology Practice Questions

Q: In chronic allergy, which Ig is more persistent in the body?

Ig E. ***Ig E*** - **IgE** is the primary antibody involved in **allergic reactions**, binding to receptors on **mast cells** and **basophils** to trigger histamine release. - In chronic allergy, sustained exposure to allergens leads to continuous production of IgE, making it a **persistent** and dominant immunoglobulin in the allergic response. *Ig A* - **IgA** is mainly found in **mucosal secretions**, such as tears, saliva, and gut, protecting against pathogens at these sites. - While important for immunity, IgA does not play a direct role in the **immediate hypersensitivity reactions** characteristic of chronic allergies. *Ig G* - **IgG** is the most abundant antibody in serum, providing **long-term immunity** against pathogens through neutralization, opsonization, and complement activation. - Though present, IgG is not the **primary mediator** of the **allergic response** in chronic allergy, instead often associated with protective immunity or certain non-IgE mediated hypersensitivities. *Ig M* - **IgM** is the first antibody produced during a **primary immune response** and is effective at activating the complement system. - It is predominantly found in the bloodstream and functions as a **short-term defender**, but it is not directly involved in the pathogenesis or persistence of chronic allergies.

Q: Which immune response is primarily responsible for controlling herpes simplex virus (HSV) infection during latency?

Cell-mediated immunity. ***Cell-mediated immunity*** - **T lymphocytes**, particularly **CD8+ cytotoxic T cells**, are crucial for controlling HSV during latency by recognizing and eliminating reactivating infected cells. - This response prevents the virus from replicating and causing overt symptoms, maintaining the **latent state** in neuronal ganglia. *Humoral immunity* - While **antibodies** (humoral immunity) can prevent initial infection and reduce viral spread during active outbreaks, they are less effective at clearing already established latent infections within host cells. - Antibodies primarily target **extracellular virus particles** and are not as effective against virus hidden inside cells during latency. *Complement activation* - The **complement system** is an important part of innate immunity that helps clear pathogens and damaged cells. - However, HSV has evolved mechanisms to evade complement, and complement activation itself is not the primary mechanism for maintaining viral latency. *Natural killer cell activity* - **Natural killer (NK) cells** are innate immune cells that can kill virus-infected cells, especially early in infection before adaptive immunity is fully active. - While NK cells contribute to initial containment, **adaptive cell-mediated immunity** (T cells) plays the dominant role in controlling latent HSV.

Q: A patient's serum sample shows the presence of antibodies that cause agglutination of red blood cells in the presence of a specific antigen. What type of antigen-antibody reaction is this, and what is its clinical relevance?

Agglutination; useful in blood typing and crossmatching. ***Agglutination; useful in blood typing and crossmatching*** - This describes **agglutination**, where antibodies bind to **particulate antigens** such as those on red blood cells, causing them to clump together. - Its clinical relevance lies primarily in **blood typing** (ABO/Rh systems) and **crossmatching** to ensure compatibility before transfusions, preventing severe hemolytic reactions [1]. *Precipitation; useful in detecting soluble antigens* - **Precipitation** reactions involve antibodies binding to **soluble antigens** to form an insoluble complex that settles out of solution. - While useful for detecting soluble antigens (e.g., in immunodiffusion), it does not involve the clumping of particulate cells like red blood cells. *Neutralization; used in viral serology* - **Neutralization** reactions involve antibodies binding to toxins or viruses, thereby **blocking their biological activity** or infectivity. - It is crucial in **viral serology** and toxin detection but does not result in the agglutination of cells. *Complement fixation; indicative of complement activation* - **Complement fixation** tests detect the presence of antibodies or antigens by observing whether the **complement system** is activated and consumed in the process. - This process involves a complex cascade and does not directly manifest as the visible clumping of red blood cells. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 627-628.

Q: Which component of the complement system acts as an opsonin?

C3b. ***C3b*** - **C3b** is a crucial component of the complement system that acts as an **opsonin**, binding to microbial surfaces and C3b receptors on phagocytes. - Opsonization by C3b enhances **phagocytosis** by coating pathogens, making them more easily recognized and engulfed by immune cells. *C3a* - **C3a** is an **anaphylatoxin** that promotes inflammation by inducing mast cell degranulation and vasodilation. - It does not directly opsonize pathogens but plays a role in attracting immune cells to the site of infection. *C5a* - **C5a** is a potent **anaphylatoxin** and **chemoattractant** for neutrophils and monocytes, promoting inflammation. - While it contributes to the immune response, **C5a** itself does not act as an opsonin. *C6* - **C6** is a component of the **Membrane Attack Complex (MAC)**, which forms pores in the membrane of target cells, leading to lysis. - It is involved in pathogen killing but does not have opsonin activity.

Q: Which of the following mechanisms primarily contributes to antibody diversity?

Gene rearrangement. ***Gene rearrangement*** - **V(D)J recombination** (Variable, Diversity, Joining segments) is the primary mechanism that shuffles and combines different gene segments to create unique antibody genes. - This process occurs in **B lymphocytes** during their development, generating a vast repertoire of immunoglobulin specificities. *Gene translocation* - Refers to the movement of chromosomal segments to new locations, which can lead to **oncogene activation** or fusion proteins, but does not primarily contribute to antibody diversity in the same way as V(D)J recombination. - While translocations can be involved in some B-cell malignancies, they are not a normal physiological mechanism for generating antibody diversity. *Antigenic variation* - This mechanism is primarily utilized by **pathogens** to evade host immune responses by altering their surface antigens. - It does not contribute to the initial generation of antibody diversity within the host immune system but rather describes how pathogens change to avoid existing antibodies. *a and c* - This option is incorrect because while **gene rearrangement** (a) is a primary mechanism for antibody diversity, **antigenic variation** (c) is a mechanism used by pathogens to evade immunity and does not contribute to the generation of antibody diversity within the host.

Q: Antibody specificity is due to ?

Amino acid sequence in the variable region of both chains. ***Amino acid sequence in the variable region of both chains*** - Antibody specificity is determined by the **variable (V) regions of both heavy and light chains** working together to form the antigen-binding site (paratope). - The antigen-binding site contains **6 complementarity-determining regions (CDRs)**: 3 from the heavy chain (H1, H2, H3) and 3 from the light chain (L1, L2, L3). - **Both chains contribute equally** to antigen recognition - the CDRs from both chains create the three-dimensional binding pocket that determines specificity. - This is the fundamental principle of antibody diversity and specificity in adaptive immunity. *Amino acid sequence in the variable region of the heavy chain* - While the heavy chain variable region is essential, it **cannot determine specificity alone** without the light chain contribution. - The heavy chain CDRs (especially CDR-H3, the most variable region) contribute significantly, but specificity requires **both chains**. - This option is incomplete as it ignores the critical contribution of light chain CDRs. *Amino acid at the carboxy terminal of the heavy chain* - The carboxy-terminal (C-terminal) is part of the **constant region (Fc region)** of the heavy chain. - This region determines the antibody **isotype** (IgG, IgM, IgA, IgD, IgE) and mediates **effector functions** (complement fixation, Fc receptor binding). - The constant region does **not** determine antigen specificity. *Amino acid sequence in the variable region of the light chain* - The light chain variable region is crucial for antigen binding, but it **cannot determine specificity alone** without the heavy chain contribution. - Light chain CDRs (L1, L2, L3) form part of the antigen-binding site but require the heavy chain CDRs to create the complete binding pocket. - This option is incomplete as it ignores the critical contribution of heavy chain CDRs.

Q: Which antibody is most effective in precipitating soluble antigens in immunological reactions?

IgM. ***IgM*** - **IgM** is a pentameric antibody with **10 antigen-binding sites**, making it the most effective immunoglobulin for precipitating soluble antigens. - Its **high valency** allows rapid and efficient cross-linking of soluble antigens to form large **antigen-antibody lattices** that precipitate out of solution. - IgM is the **first antibody produced** in immune responses and is highly efficient at forming immune complexes even at low concentrations. - Its multivalent structure enables it to create stable precipitates more effectively than bivalent antibodies. *IgG* - **IgG** is a monomeric antibody with only **2 antigen-binding sites**, making it less efficient than IgM at cross-linking soluble antigens. - While IgG can participate in precipitation reactions, it requires **higher concentrations** and more time to form precipitates compared to IgM. - IgG is the most abundant antibody in serum and plays important roles in opsonization, complement fixation, and antibody-dependent cellular cytotoxicity, but is not the most effective at precipitation. *IgA* - **IgA** primarily functions in **mucosal immunity** and exists as a monomer in serum and a dimer in secretions. - Its main role is to **prevent pathogen adherence** to mucosal surfaces rather than precipitating soluble antigens in systemic immunological reactions. *IgD* - **IgD** is found predominantly on the surface of **naive B lymphocytes** as an antigen receptor. - Present in very low concentrations in serum, it has **no significant role** in precipitating soluble antigens or forming immune complexes.

Q: What determines the specificity of an antibody?

Fab region. ***Fab region*** - The **Fab (Fragment antigen-binding) region** contains the **variable domains** of both the heavy and light chains, which form the antigen-binding site. - This region is responsible for recognizing and binding to specific **epitopes** on antigens, thus determining the antibody's specificity. *Fc portion* - The **Fc (Fragment crystallizable) portion** primarily mediates effector functions such as binding to **Fc receptors** on immune cells and activating complement. - It does not directly participate in antigen recognition and therefore does not determine the antibody's specificity. *Carboxy terminal* - The **carboxy terminal** refers to the end of the polypeptide chain, specifically on the heavy chain within the Fc region, or at the end of the light chain. - While part of the antibody structure, it does not specifically determine the unique antigen-binding characteristics. *None of the options* - This option is incorrect because the **Fab region** is indeed responsible for determining antibody specificity.

Q: Which immunoglobulin provides passive immunity through colostrum and breast milk?

Immunoglobulin A (IgA). ***Immunoglobulin A (IgA)*** - **IgA** is the primary antibody found in **secretions** such as colostrum, breast milk, tears, saliva, and mucus. - It plays a crucial role in providing **passive immunity** to infants by protecting their mucous membranes from pathogens. *Immunoglobulin G (IgG)* - **IgG** is the only antibody that can cross the **placenta**, providing passive immunity to the fetus *in utero*. - While present in breast milk, it is not the *primary* immunoglobulin responsible for passive immunity via colostrum. *Immunoglobulin E (IgE)* - **IgE** is primarily associated with **allergic reactions** and defense against parasites. - It does not play a significant role in providing passive immunity to infants through breast milk. *Immunoglobulin M (IgM)* - **IgM** is the first antibody produced during a primary immune response and is found mainly in the **blood and lymph fluid**. - It does not significantly contribute to passive immunity via colostrum or breast milk.

Question 1

In chronic allergy, which Ig is more persistent in the body?

Accepted Answer

Ig E

Answer

Ig A

Answer

Ig G

Answer

Ig M

Question 2

Which immune response is primarily responsible for controlling herpes simplex virus (HSV) infection during latency?

Accepted Answer

Cell-mediated immunity

Answer

Humoral immunity

Answer

Complement activation

Answer

Natural killer cell activity

Question 3

A patient's serum sample shows the presence of antibodies that cause agglutination of red blood cells in the presence of a specific antigen. What type of antigen-antibody reaction is this, and what is its clinical relevance?

Accepted Answer

Agglutination; useful in blood typing and crossmatching

Answer

Precipitation; useful in detecting soluble antigens

Answer

Neutralization; used in viral serology

Answer

Complement fixation; indicative of complement activation

Question 4

A patient with systemic lupus erythematosus presents with recurrent infections. Laboratory tests reveal a low total hemolytic complement (CH50) level. What does this indicate about the patient's immune function?

Accepted Answer

Deficiency in complement pathway

Answer

Impaired phagocytosis

Answer

Decreased production of antibodies

Answer

Decreased T cell activity

Question 5

Which component of the complement system acts as an opsonin?

Accepted Answer

C3b

Answer

C3a

Answer

C5a

Answer

C6

Question 6

Which of the following mechanisms primarily contributes to antibody diversity?

Accepted Answer

Gene rearrangement

Answer

Antigenic variation

Answer

Gene translocation

Answer

a and c

Question 7

Antibody specificity is due to ?

Accepted Answer

Amino acid sequence in the variable region of both chains

Answer

Amino acid sequence in the variable region of the light chain

Answer

Amino acid sequence in the variable region of the heavy chain

Answer

Amino acid at the carboxy terminal of the heavy chain

Question 8

Which antibody is most effective in precipitating soluble antigens in immunological reactions?

Accepted Answer

IgM

Answer

IgG

Answer

IgA

Answer

IgD

Question 9

What determines the specificity of an antibody?

Accepted Answer

Fab region

Answer

Fc portion

Answer

Carboxy terminal

Answer

None of the options

Question 10

Which immunoglobulin provides passive immunity through colostrum and breast milk?

Accepted Answer

Immunoglobulin A (IgA)

Answer

Immunoglobulin G (IgG)

Answer

Immunoglobulin M (IgM)

Answer

Immunoglobulin E (IgE)

Immunology — MCQs

Immunology — MCQs

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