Immunology Practice Questions

Q: Identify the antibody shown in the diagram which has a joining chain and is mainly found in mucosal areas.

IgA. ***IgA*** - The diagram shows a **dimeric** antibody structure, which consists of two monomer units linked by a **J chain** (joining chain) and a **secretory component**, a classic representation of secretory IgA (sIgA). - IgA is the predominant immunoglobulin found in **mucosal secretions** such as saliva, tears, breast milk, and gastrointestinal fluids, where it provides the first line of defense against pathogens. ***IgG*** - IgG is a **monomer**, meaning it exists as a single Y-shaped unit, and it does not have a J chain or form polymeric structures. - It is the most abundant antibody in the **blood** and tissue fluids, plays a key role in the secondary immune response, and is the only immunoglobulin that can cross the **placenta**. ***IgM*** - IgM exists as a **pentamer** in its secreted form, consisting of five monomer units linked by a J chain, which is much larger than the dimer shown in the image. - It is the first antibody class produced during a **primary immune response** and is highly effective at activating the complement system. ***IgE*** - IgE is a **monomer** and does not contain a J chain or form polymers. - It is present in very low concentrations in the serum and is primarily involved in **allergic reactions** (type I hypersensitivity) and defense against **parasitic worms**.

Q: A patient presents with recurrent infections with Neisseria gonorrhoeae. Which of the following investigations is most appropriate to evaluate the underlying immunodeficiency?

Terminal complement (C5-C9) assay. ***Terminal complement (C5-C9) assay*** - Recurrent infections with *Neisseria* species (gonorrhoeae or meningitidis) are the classic presentation of a deficiency in the **Terminal Complement Components (C5-C9)**. - These components assemble the **Membrane Attack Complex (MAC)**, which is crucial for the lysis and killing of the thin cell walls of Neisserial organisms. *C1 esterase inhibitor assay* - This assay is used to diagnose **Hereditary Angioedema (HAE)**, which presents with recurrent episodes of swelling, not recurrent bacterial infections like *N. gonorrhoeae*. - HAE involves uncontrolled activation of the complement and kinin pathways, not failure to eliminate bacteria. *Quantitative immunoglobulin levels* - Measuring **IgG, IgA, and IgM** levels evaluates humoral immunity, typically diagnosing conditions like **Common Variable Immunodeficiency (CVID)**. - Antibody deficiencies usually lead to recurrent sinopulmonary infections with encapsulated bacteria (*Strep pneumoniae*, *H flu*), not specifically *Neisseria*. *Nitroblue tetrazolium test* - This test, or the modern DHR assay, screens for **Chronic Granulomatous Disease (CGD)**, a defect in phagocyte function (NADPH oxidase). - CGD patients suffer from severe, deep-seated infections and abscesses caused by **catalase-positive organisms** (e.g., *Staph aureus*, *Aspergillus*), not complement-dependent issues like recurrent *Neisseria*.

Q: The following image shows effect of repeated antigenic stimulus on antibody production. What does phase 3 represent?

Negative response. ***Negative response*** - Phase 3 shows a **decrease in antibody levels** after the second antigenic stimulus, indicated by the downward trend in the curve. - This decline means that the antibody production rate is lower than the degradation rate or the antigen might be cleared, resulting in a **negative net effect** on circulating antibody concentration. *Primary immune response* - The **primary immune response** typically refers to the antibody production pattern after the **first exposure** to an antigen, which is slower and produces lower antibody titers. - Phase 1 in the diagram likely represents this initial response, with a gradual increase followed by a plateau or decline, not the dip seen in phase 3. *Secondary immune response* - The **secondary immune response** (anamnestic response) occurs upon **re-exposure** to an antigen, characterized by a **faster, stronger**, and more prolonged antibody production. - An increase in antibody levels is observed during phase 2 and 4, following subsequent antigenic stimuli. *Lag phase* - The **lag phase** is the initial period after antigen exposure during which **no detectable antibodies** are produced, while B cells are recognizing the antigen and differentiating. - This phase would be represented by the flat baseline before the first rise in antibody, not the dip that occurs after a response has already been initiated.

Q: All are correct about the **X** mark in antibody structure except: (Recent NEET Pattern 2016-17)

Each of these chains has three domains in constant region. ***Each of these chains has three domains in constant region*** - This statement is incorrect. The "X" mark in the image points to a **light chain** of an antibody. Light chains are composed of **one variable domain** and **one constant domain**, not three constant domains. *Composed up of kappa and lambda chains* - This statement is correct. Light chains (**marked X**) can be either **kappa (κ)** or **lambda (λ)**, determining the isotype of the light chain. - While an individual antibody molecule will only have one type of light chain (either two kappa or two lambda), the overall antibody pool in a human body contains both types. *Has molecular weight of 25,000* - This statement is correct. The **light chain** (marked X) has an approximate **molecular weight of 25 kDa**. - This molecular weight is characteristic for both kappa and lambda light chains. *Kappa:lambda occur in ratio of 2:1* - This statement is correct. In humans, **kappa light chains** are generally found in about **twice the abundance as lambda light chains** in serum antibodies. - This ratio is important for assessing clonality in lymphoproliferative disorders.

Q: The technique shown in the picture is used for: (AIIMS Nov 2018)

Synthesis of monoclonal antibodies. ***Synthesis of monoclonal antibodies*** - The image depicts the process of creating **hybridomas** by fusing antibody-producing spleen cells from an immunized mouse with myeloma cells. - These hybridomas are then cultured in **HAT medium** to select for stable cell lines that continuously produce a single type of antibody, known as **monoclonal antibodies**. *Preparing cell lines for viral culture* - While cell cultures are used for viral studies, the specific methodology shown involving immunization, spleen cell extraction, and fusion with myeloma cells is not for preparing routine **viral cultures**. - Viral culture typically involves growing target cells that are susceptible to a virus and then inoculating them with the virus for replication and study. *Synthesis of vaccine* - **Vaccine synthesis** involves producing antigens (e.g., inactivated viruses, attenuated microbes, or recombinant proteins) to stimulate an immune response, not the production of antibodies themselves. - The process shown aims to generate antibodies, which could *potentially* be used therapeutically, but not primarily for vaccine production. *Process of genetic engineering* - **Genetic engineering** involves manipulating an organism's genes, such as introducing foreign DNA or modifying existing genes. - While molecular biology techniques are involved in antibody production, the core process of fusing cells to create hybridomas specifically for large-scale antibody production is distinct from typical genetic engineering methods like gene cloning or gene editing.

Q: Which one of the following statements about Human Immunoglobulins is not correct?

IgG and IgM can both cross the placenta. ***IgG and IgM can both cross the placenta*** - This statement is incorrect because only **IgG** can actively cross the placenta, providing **passive immunity** to the fetus. - **IgM** is too large to cross the placental barrier, so its presence in a newborn suggests **congenital infection**. *The half life of IgM is about 10 days* - The approximate **half-life of IgM** is indeed around **5-10 days**, making this statement largely correct in general contexts. - This relatively short half-life means that IgM levels can change quickly in response to acute infections. *IgG comprises about 75-80% of the total serum immunoglobulins* - **IgG** is the most abundant immunoglobulin in serum, typically accounting for **75-80%** of the total immunoglobulins. - Its high concentration and long half-life contribute to its critical role in **secondary immune responses** and **long-term immunity**. *IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions* - **IgA** accounts for about **10-15%** of the total serum immunoglobulins, with a significant proportion found in secretions. - It plays a crucial role in **mucosal immunity**, protecting surfaces like the gastrointestinal, respiratory, and genitourinary tracts.

Q: During the EARLY phase of a primary immune response, which of the following best describes the relationship between peak IgM and IgG antibody levels?

100 times more. ***100 times more*** - In the **early phase of a primary immune response**, **IgM** is the first antibody produced and reaches peak levels when **IgG** levels are still very low. - During this early period (approximately days 5-10), the **IgM concentration** can be significantly higher than IgG, with some references citing ratios up to 100-fold. - **Important note:** As the primary response matures, **IgG levels rise and eventually exceed IgM levels** through class switching. This question specifically addresses the early peak comparison. *50 times more* - While IgM does predominate early in the primary response, the 50-fold ratio underestimates the typical difference during the **early peak phase** when IgG production has just begun. - The most commonly cited ratio for early primary response is closer to 100-fold. *25 times more* - This ratio **underestimates** the relative abundance of **IgM** compared to **IgG** during the early peak of a primary immune response. - **IgG** levels are typically very low or just beginning to rise in the early stages, while IgM has reached peak levels. *10 times more* - This significantly **underestimates** the difference in antibody levels during the early primary immune response. - The rapid and robust initial production of **IgM** with delayed IgG production creates a much larger differential in the early phase. **Clinical Note:** In a **secondary immune response**, the pattern reverses dramatically—IgG is produced rapidly and in much higher quantities than IgM (often 100-1000 times more) due to memory B cell activation.

Q: Antigen presented on MHC class I molecules activates which of the following cells?

Cytotoxic T cells. ***Cytotoxic T cells*** - **MHC class I** molecules present **intracellular antigens** (e.g., viral or tumor antigens) to **CD8+ T cells** (cytotoxic T cells). - This binding activates the cytotoxic T cells, leading to the destruction of the **infected** or **abnormal host cell**. *NK cells* - **Natural Killer (NK) cells** recognize and kill target cells that have **reduced or absent MHC class I** expression, which often occurs in virally infected or tumor cells, not cells presenting antigens on MHC class I. - They are part of the **innate immune system** and do not require prior sensitization or MHC-peptide presentation for activation. *Helper cells* - **Helper T cells** (CD4+ T cells) recognize antigens presented on **MHC class II** molecules, typically expressed by **antigen-presenting cells** (APCs) like macrophages, B cells, and dendritic cells. - Their primary role is to **orchestrate immune responses** by releasing cytokines. *B cells* - **B cells** are primarily involved in **humoral immunity**, producing antibodies after recognizing specific antigens directly via their B cell receptors or with T cell help. - While they can present antigens on **MHC class II** to helper T cells, direct antigen binding to **MHC class I** does not activate B cells.

Q: Affinity maturation of antibodies is because of _____ .

Somatic hypermutation. ***Somatic hypermutation*** - **Somatic hypermutation** is a process that introduces point mutations in the **variable regions** of immunoglobulin genes, primarily in B cells. - These mutations lead to the production of B cells with slightly altered **antibody affinities**, allowing for selection of those with higher affinity for the antigen. *Gene rearrangements* - **Gene rearrangements**, specifically **V(D)J recombination**, are responsible for the initial diversity of antibody specificities in immature B cells. - This process determines the basic antigen-binding site but does not fine-tune the **affinity** after initial antigen exposure. *CD40* - **CD40** is a co-stimulatory molecule on B cells that binds to **CD40L** on T cells, crucial for B cell activation, **isotype switching**, and germinal center formation. - While essential for antibody responses and germinal center reactions where affinity maturation occurs, **CD40** itself does not directly cause the molecular changes that lead to affinity maturation. *Differential mRNA processing* - **Differential mRNA processing** (or alternative splicing) primarily controls the production of different protein isoforms from a single gene. - In the context of antibodies, it can determine whether a B cell produces **membrane-bound** or **secreted** forms of antibodies, but it does not enhance the antigen-binding affinity.

Question 1

Identify the antibody shown in the diagram which has a joining chain and is mainly found in mucosal areas.

Accepted Answer

IgA

Answer

IgM

Answer

IgG

Answer

IgE

Question 2

A patient presents with recurrent infections with Neisseria gonorrhoeae. Which of the following investigations is most appropriate to evaluate the underlying immunodeficiency?

Accepted Answer

Terminal complement (C5-C9) assay

Answer

Nitroblue tetrazolium test

Answer

Quantitative immunoglobulin levels

Answer

C1 esterase inhibitor assay

Question 3

The following image shows effect of repeated antigenic stimulus on antibody production. What does phase 3 represent?

Accepted Answer

Negative response

Answer

Primary immune response

Answer

Secondary immune response

Answer

Lag phase

Question 4

All are correct about the **X** mark in antibody structure except: (Recent NEET Pattern 2016-17)

Accepted Answer

Each of these chains has three domains in constant region

Answer

Composed up of kappa and lambda chains

Answer

Has molecular weight of 25,000

Answer

Kappa:lambda occur in ratio of 2:1

Question 5

Which of the following is correct about the picture shown?

Accepted Answer

A=Zone of antibody excess, B=Equivalence zone, C=Zone of antigen excess

Answer

A=Equivalence zone, B=Zone of antibody excess, C=Zone of antigen excess

Answer

A=Zone of antigen excess, B=Equivalence zone, C=Zone of antibody excess

Answer

A=Zone of antibody excess, B=Zone of antibody excess, C=Equivalence zone

Question 6

The technique shown in the picture is used for: (AIIMS Nov 2018)

Accepted Answer

Synthesis of monoclonal antibodies

Answer

Preparing cell lines for viral culture

Answer

Synthesis of vaccine

Answer

Process of genetic engineering

Question 7

Which one of the following statements about Human Immunoglobulins is not correct?

Accepted Answer

IgG and IgM can both cross the placenta

Answer

The half life of IgM is about 10 days

Answer

IgG comprises about 75-80% of the total serum immunoglobulins

Answer

IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions

Question 8

During the EARLY phase of a primary immune response, which of the following best describes the relationship between peak IgM and IgG antibody levels?

Accepted Answer

100 times more

Answer

50 times more

Answer

25 times more

Answer

10 times more

Question 9

Antigen presented on MHC class I molecules activates which of the following cells?

Accepted Answer

Cytotoxic T cells

Answer

NK cells

Answer

Helper cells

Answer

B cells

Question 10

Affinity maturation of antibodies is because of _____ .

Accepted Answer

Somatic hypermutation

Answer

Gene rearrangements

Answer

CD40

Answer

Differential mRNA processing

Immunology — MCQs

Immunology — MCQs

On this page

Practice by Chapter

Want unlimited practice?