Immunology and Allergies Practice Questions

Q: A 5-month-old boy presented with spontaneous nosebleeds and bloody diarrhea. He also has a history of recurrent chest and ear infections requiring frequent hospitalizations. On examination, the child had atopic dermatitis and petechiae all over the body. Laboratory findings suggested an abnormally low platelet count along with eosinophilia. Which of the following statements is NOT true about this condition?

Low IgM and IgG levels.. ### **Explanation** The clinical presentation of **thrombocytopenia** (petechiae, nosebleeds), **eczema** (atopic dermatitis), and **recurrent infections** in a male infant is the classic triad of **Wiskott-Aldrich Syndrome (WAS)**. This is an X-linked recessive disorder caused by a mutation in the *WASP* gene, which affects the actin cytoskeleton in hematopoietic cells. #### **Why Option B is the Correct Answer (The "NOT True" Statement)** In Wiskott-Aldrich Syndrome, the characteristic immunoglobulin pattern is: * **Low IgM** * **Normal to Low IgG** * **High IgA and High IgE** Option B states that both IgM and IgG are low; however, the hallmark of WAS is specifically a **low IgM** level. #### **Analysis of Other Options** * **Option A:** True. WAS involves a combined immunodeficiency. There is a progressive depletion of T-cells in the peripheral blood and paracortical areas of lymph nodes, leading to impaired cellular immunity. * **Option C:** True. Serum IgA and IgE levels are typically elevated in these patients. Eosinophilia (mentioned in the stem) is also a common finding. * **Option D:** True. Patients with WAS have a significantly increased risk of developing autoimmune diseases and malignancies, particularly **B-cell lymphomas** (often EBV-associated). #### **NEET-PG High-Yield Pearls** * **Mnemonic (TIE):** **T**hrombocytopenia, **I**mmunodeficiency, **E**czema. * **Platelet Morphology:** WAS is unique because it features **microthrombocytes** (abnormally small platelets). This is a high-yield diagnostic clue. * **Genetics:** X-linked recessive; *WASP* gene (Xp11.22). * **Defect:** Failure of actin polymerization, affecting leukocyte migration and immune synapse formation. * **Treatment:** Hematopoietic stem cell transplant (HSCT) is the definitive cure.

Q: Delayed separation of the umbilical cord stump is a characteristic feature of which condition?

Leukocyte adhesion deficiency. **Explanation:** **Leukocyte Adhesion Deficiency (LAD) Type 1** is the correct answer. This condition is caused by a defect in the **CD18 subunit of β2-integrins**, which are essential for the firm adhesion of neutrophils to the vascular endothelium. Because neutrophils cannot migrate from the bloodstream into the tissues (extravasation), they cannot reach the site of the umbilical cord to facilitate its separation through normal inflammatory processes. * **Why LAD is correct:** The hallmark clinical triad of LAD-1 includes **delayed separation of the umbilical cord** (typically >3 weeks), recurrent skin and mucosal infections without pus formation (cold abscesses), and persistent peripheral blood **leukocytosis** (neutrophilia). * **Why Option A is incorrect:** **Chediak-Higashi syndrome** is a defect in lysosomal trafficking (LYST gene). It presents with partial oculocutaneous albinism, giant granules in neutrophils, and peripheral neuropathy, but cord separation is usually normal. * **Why Option B is incorrect:** **Chronic Granulomatous Disease (CGD)** is a defect in the NADPH oxidase enzyme, leading to an inability to generate a respiratory burst. While it causes recurrent infections with catalase-positive organisms, it does not affect neutrophil migration or cord separation. **High-Yield Clinical Pearls for NEET-PG:** * **Normal cord separation:** Usually occurs within 7–14 days. * **LAD Diagnosis:** Flow cytometry showing **decreased CD11b/CD18** expression. * **Key finding:** Absence of pus at infection sites despite high WBC counts in the blood. * **LAD Type 2:** Similar presentation but includes growth retardation and the **Bombay blood group** phenotype.

Q: An 8-month-old boy with a history of recurrent pneumonia is found to have almost no circulating IgG. Cellular immunity is normal. His brother had this same disease and died of echovirus encephalitis. His parents and sisters have normal serum levels of IgG. What is the appropriate diagnosis?

X-linked agammaglobulinemia of Bruton. ### Explanation **Correct Option: D. X-linked agammaglobulinemia (XLA) of Bruton** **Why it is correct:** XLA is caused by a mutation in the **Bruton Tyrosine Kinase (BTK) gene**, which is essential for B-cell maturation. Without BTK, pre-B cells cannot develop into mature B cells, leading to a near-total absence of all immunoglobulin classes (IgG, IgA, IgM). * **Clinical Presentation:** Symptoms typically appear after 6 months of age (as maternal IgG wanes) with recurrent sinopulmonary infections caused by encapsulated bacteria (*S. pneumoniae, H. influenzae*). * **Key Clue:** Susceptibility to **Enteroviruses** (like Echovirus and Poliovirus) is a classic hallmark of XLA, often leading to fatal encephalitis or chronic meningitis. * **Inheritance:** It is X-linked recessive, explaining why only male siblings are affected while parents and sisters are healthy. **Why other options are incorrect:** * **A. DiGeorge Syndrome:** This is a defect in **T-cell (cellular) immunity** due to thymic hypoplasia. The question states cellular immunity is normal. * **B. Isolated IgA Deficiency:** This is the most common primary immunodeficiency. While patients have low IgA, their **IgG levels are normal**, and they do not typically present with severe agammaglobulinemia or fatal echovirus infections. * **C. Wiskott-Aldrich Syndrome:** Characterized by the triad of **Eczema, Thrombocytopenia (small platelets), and Immunodeficiency**. It involves both B and T cell dysfunction, not isolated IgG absence. **NEET-PG High-Yield Pearls:** * **Flow Cytometry:** Shows absent or <2% CD19+ and CD20+ B cells. * **Physical Exam:** Characterized by **absent or hypoplastic tonsils** and lymph nodes (due to lack of germinal centers). * **Treatment:** Lifelong Intravenous Immunoglobulin (IVIG) replacement. Live vaccines (like OPV) are strictly contraindicated.

Q: A 4-year-old child presents with recurrent pyogenic infections caused by organisms with polysaccharide capsules. Which of the following immunoglobulin deficiencies should be investigated?

IgG 2. **Explanation:** The correct answer is **C. IgG 2**. **Medical Concept:** IgG is divided into four subclasses (IgG1, IgG2, IgG3, and IgG4). Each subclass has a specific affinity for different types of antigens. **IgG2** is the primary subclass responsible for the immune response against **polysaccharide antigens**, which are found in the capsules of bacteria such as *Streptococcus pneumoniae*, *Haemophilus influenzae* type b, and *Neisseria meningitidis*. In children, the ability to produce IgG2 matures slowly (reaching adult levels around age 10), making them more susceptible to these encapsulated organisms. A selective deficiency in IgG2 leads to recurrent sinopulmonary infections despite normal total IgG levels. **Analysis of Options:** * **IgA (Option A):** While IgA deficiency is the most common primary immunodeficiency, it typically presents with mucosal infections or is asymptomatic. It is not specifically linked to the failure of polysaccharide-encapsulated bacterial clearance. * **IgG1 (Option B):** IgG1 is the most abundant subclass and primarily responds to **protein antigens** (e.g., toxins like tetanus/diphtheria). * **IgA + IgG2 (Option D):** While IgG2 deficiency often coexists with IgA deficiency, the question specifically asks which deficiency is responsible for the failure to handle **polysaccharide capsules**. IgG2 is the specific mediator for this response. **NEET-PG High-Yield Pearls:** * **IgG1 & IgG3:** Respond to protein antigens (viral proteins). * **IgG2 & IgG4:** Respond to carbohydrate/polysaccharide antigens. * **Clinical Hint:** If a child has recurrent pneumonia/otitis but a normal total IgG level, always check **IgG subclasses**. * **Wiskott-Aldrich Syndrome:** Often associated with low levels of antibodies to polysaccharide antigens.

Q: Eye involvement is seen in which of the following subtypes of Juvenile Rheumatoid Arthritis?

Seronegative pauciarticular JRA, early onset. ### Explanation The correct answer is **D. Seronegative pauciarticular JRA, early onset.** **1. Why the Correct Answer is Right:** Juvenile Idiopathic Arthritis (JIA), formerly known as JRA, is classified based on the number of joints involved and the presence of biomarkers. **Pauciarticular (Oligoarticular) JIA** involves $\le$ 4 joints. The **early-onset subtype** (typically girls < 5 years old) is strongly associated with **positive Antinuclear Antibody (ANA)** and a high risk of **chronic asymptomatic iridocyclitis (anterior uveitis)**. Because the eye involvement is often "silent" (painless and non-red), regular slit-lamp examinations are mandatory to prevent blindness. **2. Why the Other Options are Wrong:** * **A & B (Late-onset Pauciarticular):** This subtype typically affects older boys (> 8 years) and is often associated with **HLA-B27**. It frequently involves the lower limbs and may progress to Ankylosing Spondylitis. While eye involvement (acute uveitis) can occur, it is symptomatic (painful, red eye), unlike the classic "silent" involvement of the early-onset type. * **C (Polyarticular JRA):** This involves $\ge$ 5 joints. While uveitis can occur in the seronegative polyarticular form, the risk is significantly lower (approx. 5%) compared to the early-onset pauciarticular group (approx. 20-30%). **3. NEET-PG High-Yield Pearls:** * **ANA Positivity:** The single best predictor for the development of uveitis in JIA. * **Systemic JIA (Still’s Disease):** Characterized by evanescent salmon-pink rashes and quotidian fever; notably, it is **least likely** to have uveitis. * **Screening:** Children with ANA+ oligoarticular JIA require slit-lamp exams every 3 months. * **RF Positivity:** Seropositive polyarticular JIA (RF+) mimics adult Rheumatoid Arthritis and has a poorer joint prognosis but lower risk of uveitis.

Q: DiGeorge syndrome is associated with all of the following except?

Hypocalcemia. **Explanation:** DiGeorge Syndrome (DGS) is a primary immunodeficiency caused by the **maldevelopment of the 3rd and 4th pharyngeal pouches**. This results in a classic triad of thymic hypoplasia (T-cell deficiency), parathyroid hypoplasia, and conotruncal cardiac defects. **Why Option A is the correct answer (The "Except"):** DiGeorge syndrome is associated with **Hypocalcemia**, not Hyperthyroidism. The failure of the 3rd and 4th pharyngeal pouches leads to **hypoplasia of the parathyroid glands**, resulting in low Parathyroid Hormone (PTH) levels and subsequent hypocalcemic tetany or seizures, typically presenting in the neonatal period. **Analysis of Incorrect Options:** * **Option B (Small jaws):** Micrognathia (small jaw) is a classic dysmorphic facial feature of DGS, along with low-set ears, hypertelorism, and a short philtrum. * **Option C (22q11 deletion):** This is the underlying genetic cause in >90% of cases. It is often detected via FISH (Fluorescence In Situ Hybridization). * **Option D (Hypocalcemia):** As explained above, this is a hallmark clinical finding due to parathyroid aplasia/hypoplasia. **High-Yield Clinical Pearls for NEET-PG:** * **CATCH-22 Mnemonic:** **C**ardiac defects (Truncus arteriosus/TOF), **A**bnormal facies, **T**hymic hypoplasia, **C**left palate, **H**ypocalcemia, **22**q11 deletion. * **Chest X-ray:** Characteristically shows an **absent thymic shadow**. * **Immunology:** Low T-cell count but normal B-cell count (though antibody production may be impaired). * **Velocardiofacial Syndrome:** A related spectrum disorder also involving 22q11 deletion but with more prominent cleft palate and facial dysmorphism.

Question 1

A 5-month-old boy presented with spontaneous nosebleeds and bloody diarrhea. He also has a history of recurrent chest and ear infections requiring frequent hospitalizations. On examination, the child had atopic dermatitis and petechiae all over the body. Laboratory findings suggested an abnormally low platelet count along with eosinophilia. Which of the following statements is NOT true about this condition?

Accepted Answer

Low IgM and IgG levels.

Answer

There is progressive loss of T lymphocytes in the peripheral blood and in the T-cell zones (paracortical areas) of the lymph nodes.

Answer

High levels of IgA.

Answer

Patients are prone to developing B-cell lymphomas.

Question 2

Delayed separation of the umbilical cord stump is a characteristic feature of which condition?

Accepted Answer

Leukocyte adhesion deficiency

Answer

Chediak Higashi syndrome

Answer

Chronic granulomatous disease

Answer

All of the above

Question 3

Maternal antibodies do not provide protective immunity to the neonate against which of the following diseases?

Accepted Answer

Polio

Answer

Diphtheria

Answer

Pertussis

Answer

Tetanus

Question 4

An 8-month-old boy with a history of recurrent pneumonia is found to have almost no circulating IgG. Cellular immunity is normal. His brother had this same disease and died of echovirus encephalitis. His parents and sisters have normal serum levels of IgG. What is the appropriate diagnosis?

Accepted Answer

X-linked agammaglobulinemia of Bruton

Answer

DiGeorge syndrome

Answer

Isolated IgA deficiency

Answer

Wiskott Aldrich syndrome

Question 5

A four-year-old child presents with mild fever, malaise, purpura, arthritis, abdominal pain, and microscopic hematuria. What would be the most likely diagnosis?

Accepted Answer

Henoch-Schonlein purpura

Answer

Thrombasthenia

Answer

Idiopathic thrombocytopenic purpura

Answer

Systemic lupus erythematosus

Question 6

A 4-year-old child presents with recurrent pyogenic infections caused by organisms with polysaccharide capsules. Which of the following immunoglobulin deficiencies should be investigated?

Accepted Answer

IgG 2

Answer

IgA

Answer

IgG 1

Answer

IgA + IgG 2

Question 7

A 4-year-old boy presents with epistaxis. He has a history of recurrent respiratory tract infections and eczema. His uncle had similar problems. Physical examination reveals multiple petechial lesions on the skin and mucous membranes. Laboratory findings include increased serum IgE and decreased platelet count. Which of the following is the most likely diagnosis?

Accepted Answer

Wiskott-Aldrich syndrome

Answer

Acquired hypogammaglobulinemia

Answer

DiGeorge syndrome

Answer

Selective IgA deficiency

Question 8

Eye involvement is seen in which of the following subtypes of Juvenile Rheumatoid Arthritis?

Accepted Answer

Seronegative pauciarticular JRA, early onset

Answer

Seropositive pauciarticular JRA, late onset

Answer

Seronegative pauciarticular JRA, late onset

Answer

Seronegative polyarticular JRA, early onset

Question 9

DiGeorge syndrome is associated with all of the following except?

Accepted Answer

Hypocalcemia

Answer

Hyperthyroidism

Answer

Small jaws

Answer

22q11 deletion

Question 10

A 9-month-old girl with a history of recurrent pulmonary infections is found to have a congenital deficiency of adenosine deaminase, which is associated with a virtual absence of lymphocytes in her peripheral lymphoid organs. What is the appropriate diagnosis?

Accepted Answer

Severe combined immunodeficiency

Answer

Bruton X-linked agammaglobulinemia

Answer

DiGeorge syndrome

Answer

Isolated IgA deficiency

Immunology and Allergies — MCQs

Immunology and Allergies — MCQs

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