Immunology and Allergies — MCQs

An 8-year-old boy presents with recurrent infections since infancy, hepatosplenomegaly, lymphadenopathy, and eczema-like dermatitis. Peripheral blood smear examination during a staphylococcal infection reveals impaired or absent neutrophil bactericidal capacity. What is the most likely cause of this child's illness?

Immunology and Allergies Indian Medical PG Practice Questions and MCQs

Question 11: Which antibody is seen in neonatal lupus with congenital heart block?

A. Anti-ribosomal
B. Anti-Ro (SS-A) (Correct Answer)
C. Anti-neuronal
D. Anti-histone

Explanation: **Explanation:** Neonatal Lupus Erythematosus (NLE) is a rare acquired autoimmune disorder caused by the transplacental passage of maternal IgG autoantibodies. **Why Anti-Ro (SS-A) is correct:** The pathogenesis of neonatal lupus, specifically **congenital heart block (CHB)**, is strongly associated with **Anti-Ro (SS-A)** and **Anti-La (SS-B)** antibodies. These antibodies cross the placenta and bind to fetal cardiac tissue, leading to inflammation (myocarditis) and subsequent fibrosis of the AV node. This damage is permanent and results in a third-degree heart block, which is the most serious complication of NLE. **Analysis of Incorrect Options:** * **A. Anti-ribosomal:** These antibodies are highly specific for Systemic Lupus Erythematosus (SLE) but are primarily associated with **neuropsychiatric manifestations** (lupus psychosis) in adults, not neonatal heart block. * **C. Anti-neuronal:** These are associated with paraneoplastic syndromes or neuropsychiatric SLE, but they do not play a role in the cardiac conduction defects of a neonate. * **D. Anti-histone:** This is the hallmark antibody for **Drug-Induced Lupus**. While it is a type of ANA, it is not implicated in the transplacental injury seen in NLE. **High-Yield Clinical Pearls for NEET-PG:** * **Most common manifestation of NLE:** Cutaneous lesions (erythematous, annular "raccoon-eye" rash), which are transient and disappear as maternal antibodies wane (approx. 6 months). * **Most serious manifestation:** Congenital Heart Block (permanent; often requires a pacemaker). * **Maternal status:** Many mothers are asymptomatic at the time of delivery but may later develop SLE or Sjögren’s syndrome. * **Recurrence risk:** If a mother has one child with NLE, the risk for subsequent pregnancies increases to approximately 15-20%.

Question 12: Which chromosome is defective in De-George syndrome?

A. 7
B. 15
C. 17
D. 22 (Correct Answer)

Explanation: **Explanation:** **DiGeorge Syndrome** (also known as 22q11.2 deletion syndrome) is caused by a microdeletion on the **long arm (q) of chromosome 22**. This genetic defect results in the failure of the **3rd and 4th pharyngeal pouches** to develop properly during embryogenesis. This leads to thymic hypoplasia (causing T-cell deficiency) and parathyroid hypoplasia (causing hypocalcemia). **Analysis of Options:** * **Option D (22): Correct.** The specific locus is 22q11.2. It is the most common microdeletion syndrome in humans. * **Option A (7): Incorrect.** Deletions on chromosome 7 (specifically 7q11.23) are associated with **Williams Syndrome** (characterized by elfin facies, hypercalcemia, and supravalvular aortic stenosis). * **Option B (15): Incorrect.** Chromosome 15 defects are linked to **Prader-Willi Syndrome** (paternal deletion) or **Angelman Syndrome** (maternal deletion) at the 15q11-q13 locus. * **Option C (17): Incorrect.** Chromosome 17 mutations are associated with **Neurofibromatosis Type 1** (17q11.2) and Miller-Dieker syndrome. **High-Yield Clinical Pearls (CATCH-22):** To remember the clinical features of DiGeorge Syndrome, use the mnemonic **CATCH-22**: * **C:** **C**ardiac defects (especially Conotruncal anomalies like Tetralogy of Fallot, Truncus Arteriosus). * **A:** **A**bnormal facies (low-set ears, hypertelorism). * **T:** **T**hymic aplasia/hypoplasia (leads to recurrent viral/fungal infections due to T-cell deficiency). * **C:** **C**left palate. * **H:** **H**ypocalcemia (due to parathyroid hypoplasia, often presenting as neonatal tetany/seizures). * **22:** Chromosome **22**q11 deletion.

Question 13: An 'en coup de sabre' lesion is characteristic of which condition?

A. Neonatal lupus
B. Systemic juvenile idiopathic arthritis
C. Juvenile dermatomyositis
D. Juvenile scleroderma (Correct Answer)

Explanation: **Explanation** **Correct Answer: D. Juvenile scleroderma** **Underlying Medical Concept:** 'En coup de sabre' (French for "strike of the sword") is a classic clinical subtype of **Linear Morphea**, which falls under the umbrella of **Juvenile Localized Scleroderma (JLS)**. It presents as a linear, depressed, atrophic band of skin and subcutaneous tissue, typically occurring on the forehead or scalp. It may extend into the muscle or bone, occasionally leading to facial hemiatrophy (Parry-Romberg syndrome) or neurological complications like seizures. **Analysis of Incorrect Options:** * **A. Neonatal Lupus:** Characteristically presents with a "raccoon-eye" or annular erythematous rash. It is associated with congenital heart block and maternal anti-Ro/SSA or anti-La/SSB antibodies. * **B. Systemic Juvenile Idiopathic Arthritis (sJIA):** Presents with a classic "salmon-pink," evanescent (fleeting) maculopapular rash that typically coincides with fever spikes. * **C. Juvenile Dermatomyositis:** Features pathognomonic skin findings such as **Gottron papules** (over knuckles) and a **Heliotrope rash** (violaceous discoloration of the eyelids), along with proximal muscle weakness. **High-Yield Clinical Pearls for NEET-PG:** * **Localized Scleroderma (Morphea)** does *not* typically progress to systemic sclerosis (involvement of internal organs). * **CREST Syndrome** (Calcinosis, Raynaud’s, Esophageal dysmotility, Sclerodactyly, Telangiectasia) is associated with **Anti-centromere antibodies**. * **Systemic Sclerosis (Diffuse)** is associated with **Anti-Scl-70 (anti-topoisomerase I) antibodies**. * The most common form of localized scleroderma in children is the **Linear** type.

Question 14: A 24-year-old male presents with abdominal pain, rashes, palpable purpura, and arthritis. What is the most probable diagnosis?

A. Henoch-Schönlein Purpura (HSP) (Correct Answer)
B. Sweet syndrome
C. Meningococcemia
D. Hemochromatosis/Kawasaki Disease

Explanation: ### Explanation **Correct Answer: A. Henoch-Schönlein Purpura (HSP)** **Clinical Reasoning:** Henoch-Schönlein Purpura (now commonly termed **IgA Vasculitis**) is a small-vessel leukocytoclastic vasculitis characterized by the deposition of **IgA-dominant immune complexes**. The classic clinical tetrad presented in this case is pathognomonic: 1. **Palpable Purpura:** Non-thrombocytopenic, typically found on gravity-dependent areas (lower limbs/buttocks). 2. **Arthritis/Arthralgia:** Usually migratory and affecting large joints (knees/ankles). 3. **Abdominal Pain:** Due to bowel wall edema or intussusception. 4. **Renal Involvement:** Ranging from hematuria to glomerulonephritis. **Why other options are incorrect:** * **Sweet Syndrome:** An acute febrile neutrophilic dermatosis characterized by painful, erythematous plaques/nodules and fever, usually associated with malignancy or infections, rather than the IgA-mediated systemic tetrad. * **Meningococcemia:** Presents with a rapidly progressing petechial/purpuric rash and high-grade fever. Patients appear acutely toxic/septic with signs of meningitis or DIC, which is absent here. * **Kawasaki Disease:** Primarily affects children <5 years. Key features include prolonged fever, conjunctivitis, strawberry tongue, and coronary artery aneurysms, not the purpura-arthritis-abdominal pain triad. **High-Yield Pearls for NEET-PG:** * **Most common** systemic vasculitis in childhood (though it can occur in adults). * **Trigger:** Often follows an Upper Respiratory Tract Infection (URTI). * **Biopsy:** Shows leukocytoclastic vasculitis with **IgA and C3 deposition** on immunofluorescence. * **Complication:** Intussusception in HSP is typically **ileo-ileal** (unlike the common idiopathic ileo-colic type). * **Prognosis:** Generally excellent; long-term morbidity is determined by the severity of **renal involvement**.

Question 15: What laboratory evaluation is most likely to be abnormal in a 10-year-old patient with discrete facial erythema?

A. CD4 count
B. Creatine kinase (Correct Answer)
C. Rheumatoid factor
D. Thyrotropin

Explanation: The clinical presentation of **discrete facial erythema** in a 10-year-old child is highly suggestive of the **Heliotrope rash** (violaceous erythema of the eyelids) or a malar-like rash associated with **Juvenile Dermatomyositis (JDM)**. ### Why Creatine Kinase (CK) is the Correct Answer: Juvenile Dermatomyositis is an autoimmune inflammatory myopathy. The hallmark of the disease is proximal muscle weakness and characteristic skin rashes. When muscle fibers are damaged due to inflammation (myositis), intracellular enzymes leak into the bloodstream. **Creatine Kinase (CK)** is the most sensitive laboratory marker for muscle destruction. Other elevated enzymes include LDH, AST, ALT, and Aldolase. ### Explanation of Incorrect Options: * **A. CD4 count:** This is used to monitor HIV/AIDS or certain primary immunodeficiencies (like SCID). While JDM involves T-cell dysregulation, the absolute CD4 count is not a diagnostic or characteristic marker for this condition. * **C. Rheumatoid factor (RF):** RF is typically associated with Juvenile Idiopathic Arthritis (JIA), specifically the polyarticular subtype. It is not a primary marker for Dermatomyositis. * **D. Thyrotropin (TSH):** While hypothyroidism can cause muscle weakness and skin changes (myxedema), it does not present with the discrete, inflammatory facial erythema characteristic of JDM. ### High-Yield Clinical Pearls for NEET-PG: * **Pathognomonic Signs:** Look for **Gottron papules** (erythematous scaly plaques over MCP/PIP joints) and **Heliotrope rash** (periorbital edema with purplish discoloration). * **Diagnosis:** Definitive diagnosis often involves elevated muscle enzymes, EMG findings, and **Muscle Biopsy** (showing perivascular atrophy). * **Complication:** **Calcinosis cutis** (calcium deposits in skin/muscle) is more common in the juvenile form than the adult form of dermatomyositis. * **First-line Treatment:** High-dose Corticosteroids and Methotrexate.

Question 16: A diagnosis of X-linked Agammaglobulinemia should be suspected if which of the following is present?

A. Female sex
B. Absent tonsils and no palpable lymph nodes on physical examination (Correct Answer)
C. High isohemagglutinin titers
D. Low CD3 count

Explanation: **Explanation:** **X-linked Agammaglobulinemia (XLA)**, also known as Bruton’s Agammaglobulinemia, is a primary immunodeficiency caused by a mutation in the **BTK (Bruton Tyrosine Kinase) gene**. This defect leads to a failure of pre-B cells to differentiate into mature B cells (CD19/CD20+). 1. **Why Option B is Correct:** Since B cells are the primary components of germinal centers in lymphoid tissue, their absence results in **hypoplastic or absent lymphoid tissue**. Clinically, this manifests as **absent tonsils** and non-palpable lymph nodes, even during active infections. This is a classic physical exam finding that distinguishes XLA from other immunodeficiencies. 2. **Why Other Options are Incorrect:** * **Option A:** XLA is an **X-linked recessive** disorder, meaning it almost exclusively affects **males**. * **Option C:** Isohemagglutinins are naturally occurring antibodies (IgM) against ABO blood group antigens. In XLA, there is a profound deficiency of all immunoglobulin classes (IgG, IgA, IgM); thus, titers would be **low or absent**, not high. * **Option D:** CD3 is a marker for **T cells**. In XLA, T-cell numbers and functions are typically **normal**. A low CD3 count would suggest a T-cell deficiency or SCID. **High-Yield Clinical Pearls for NEET-PG:** * **Presentation:** Recurrent sinopulmonary infections with encapsulated bacteria (*S. pneumoniae, H. influenzae*) starting after **6 months of age** (as maternal IgG wanes). * **Susceptibility:** Increased risk of chronic **Enteroviral** (Echovirus, Coxsackievirus) infections and *Giardia*. * **Diagnosis:** Flow cytometry showing **absent/low B cells (CD19/20)** with normal T cells. * **Treatment:** Lifelong Intravenous Immunoglobulin (IVIG) replacement; **live vaccines are contraindicated.**

Question 17: All of the following are features of Hyper-IgE syndrome, except?

A. X-linked recessive inheritance (Correct Answer)
B. Recurrent infections of skin and lung
C. Hyperextensibility of joints
D. Facial dysmorphy

Explanation: **Explanation:** **Hyper-IgE Syndrome (HIES)**, also known as **Job Syndrome**, is a primary immunodeficiency characterized by a triad of elevated serum IgE (>2000 IU/mL), recurrent "cold" staphylococcal abscesses, and pneumonia with pneumatocele formation. 1. **Why Option A is correct:** Hyper-IgE syndrome is primarily inherited in an **Autosomal Dominant (AD)** fashion due to a mutation in the **STAT3 gene** (most common type). There is also an Autosomal Recessive (AR) form caused by mutations in *DOCK8* or *TYK2*. It is **not** X-linked recessive. 2. **Why Options B, C, and D are incorrect:** These are classic clinical features of the AD-STAT3 form: * **Recurrent infections (B):** Patients suffer from "cold" abscesses (lacking typical signs of inflammation like warmth or redness) and recurrent pneumonia, often leading to permanent lung damage (pneumatoceles). * **Hyperextensibility and Skeletal features (C):** Non-immunological features are hallmark signs, including joint hypermobility, scoliosis, and osteopenia leading to recurrent fractures. * **Facial dysmorphy (D):** Characteristic "coarse facies" include a broad nasal bridge, deep-set eyes, a prominent forehead (frontal bossing), and a protruding jaw. **High-Yield Clinical Pearls for NEET-PG:** * **The "F's" of Job Syndrome:** **F**acies (coarse), **F**ractures (pathological), **F**ailed eruption of primary teeth (retained deciduous teeth), **F**ungal infections (candidiasis), and **F**ull of IgE. * **Pathophysiology:** STAT3 mutation leads to a failure of Th17 cell differentiation, resulting in impaired neutrophil recruitment to sites of infection. * **Differentiating Feature:** Unlike other immunodeficiencies, HIES involves both the immune system and the connective tissue/skeletal system.

Question 18: All of the following are seen in 22q 11.2 deletion syndrome except?

A. B cell immunodeficiency
B. Learning disabilities (Correct Answer)
C. Increased incidence of psychiatric disorders like schizophrenia in adulthood
D. Facial abnormalities

Explanation: **Explanation:** 22q11.2 Deletion Syndrome (encompassing DiGeorge Syndrome and Velocardiofacial Syndrome) is a microdeletion disorder characterized by the mnemonic **CATCH-22**: **C**onotruncal cardiac defects, **A**bnormal facies, **T**hymic hypoplasia, **C**left palate, and **H**ypocalcemia. **Why Option B is the "Except":** The question asks for what is *not* typically seen. However, there is a nuance in medical literature: **Learning disabilities, psychiatric disorders, and facial abnormalities are all classic features of 22q11.2 deletion.** In the context of this specific question (often seen in older PG entrance patterns), the "Except" is **B-cell immunodeficiency**. The primary immunological defect in DiGeorge syndrome is **T-cell deficiency** due to thymic hypoplasia (failure of the 3rd and 4th pharyngeal pouches). While severe cases may show secondary antibody issues, the hallmark is a T-cell defect, not a primary B-cell immunodeficiency (like X-linked Agammaglobulinemia). *Note: If the question implies all are features, it may be technically flawed as B, C, and D are all present. However, in competitive exams, B-cell deficiency is the most "incorrect" immunological statement.* **Analysis of other options:** * **Psychiatric disorders (C):** There is a significantly increased risk (up to 25-30%) of developing schizophrenia and bipolar disorder in early adulthood. * **Facial abnormalities (D):** Characteristic features include a bulbous nose, low-set ears, micrognathia, and hypertelorism. * **Learning disabilities (B):** Most patients have mild-to-moderate intellectual disabilities or specific learning impairments. **Clinical Pearls for NEET-PG:** * **Most common cardiac defect:** Interrupted aortic arch (Type B) or Tetralogy of Fallot. * **Immunology:** Low T-cell count; patients are susceptible to viral, fungal, and protozoal infections. * **Diagnosis:** Confirmed via **FISH** (Fluorescence In Situ Hybridization) or MLPA. * **Hypocalcemia:** Presents as neonatal tetany or seizures due to parathyroid hypoplasia.

Question 19: A 6-year-old child presented to the OPD with an eczematous rash. On evaluation, the child was found to have fever and a platelet count of 80,000. On enquiry, there were multiple hospitalizations for recurrent infections. What is the most likely diagnosis?

A. Bruton's agammaglobulinemia
B. Chediak-Higashi syndrome
C. Wiskott-Aldrich syndrome (Correct Answer)
D. Severe combined immunodeficiency

Explanation: ### **Explanation** The clinical triad of **eczema, thrombocytopenia (low platelet count), and recurrent infections** is the classic presentation of **Wiskott-Aldrich Syndrome (WAS)**. **1. Why Wiskott-Aldrich Syndrome is Correct:** WAS is an **X-linked recessive** primary immunodeficiency caused by a mutation in the **WASp gene**, which is essential for actin cytoskeleton remodeling in hematopoietic cells. * **Thrombocytopenia:** The hallmark is micro-thrombocytopenia (small-sized platelets). A count of 80,000 in this child explains the bleeding tendency. * **Eczema:** Typically develops in early childhood, resembling atopic dermatitis. * **Recurrent Infections:** Due to combined B-cell and T-cell dysfunction, leading to susceptibility to encapsulated bacteria (e.g., *S. pneumoniae*) and opportunistic infections. **2. Why Other Options are Incorrect:** * **Bruton’s Agammaglobulinemia:** An X-linked B-cell defect characterized by absent B-cells and low immunoglobulins. It presents with recurrent sinopulmonary infections but **does not** cause thrombocytopenia or eczema. * **Chediak-Higashi Syndrome:** Characterized by partial albinism, peripheral neuropathy, and **giant cytoplasmic granules** in neutrophils. While it features infections, the classic triad of WAS is absent. * **Severe Combined Immunodeficiency (SCID):** Presents much earlier (usually <6 months) with severe failure to thrive, chronic diarrhea, and persistent candidiasis. It involves a total lack of T-cell function. **3. High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** X-linked Recessive (only males affected). * **Lab Findings:** Low IgM, Normal/High IgA and IgE, Low/Normal IgG. * **Platelet Morphology:** Characteristically **small platelets** (low Mean Platelet Volume - MPV). * **Mnemonic (TIE):** **T**hrombocytopenia, **I**mmunodeficiency, **E**czema. * **Complications:** Increased risk of autoimmune diseases and **B-cell lymphomas**. * **Definitive Treatment:** Hematopoietic stem cell transplant (HSCT).

Question 20: An 8-year-old boy presents with recurrent infections since infancy, hepatosplenomegaly, lymphadenopathy, and eczema-like dermatitis. Peripheral blood smear examination during a staphylococcal infection reveals impaired or absent neutrophil bactericidal capacity. What is the most likely cause of this child's illness?

A. Defect in the enzyme NADPH oxidase (Correct Answer)
B. Defect in the enzyme adenosine deaminase (ADA)
C. Defect in the IL-2 receptor
D. Developmental defect at the pre-B stage

Explanation: **Explanation:** The clinical presentation of recurrent infections, hepatosplenomegaly, lymphadenopathy, and dermatitis, combined with impaired neutrophil bactericidal capacity, is classic for **Chronic Granulomatous Disease (CGD)**. **1. Why Option A is Correct:** CGD is caused by a **defect in the NADPH oxidase enzyme complex**, which is responsible for the "respiratory burst." This defect prevents the generation of superoxide radicals and hydrogen peroxide ($H_2O_2$) within phagocytes. While neutrophils can still ingest bacteria, they cannot kill **catalase-positive organisms** (e.g., *Staphylococcus aureus*, *Aspergillus*, *Serratia*) because these organisms neutralize their own $H_2O_2$, leaving the neutrophil with no oxidative means to eliminate them. This leads to persistent intracellular infections and the formation of granulomas (causing lymphadenopathy and hepatosplenomegaly). **2. Why Other Options are Incorrect:** * **Option B (ADA deficiency):** This causes **Severe Combined Immunodeficiency (SCID)**. It presents with profound lymphopenia (both B and T cells) and failure to thrive, rather than isolated neutrophil dysfunction. * **Option C (IL-2 receptor defect):** This is the most common cause of **X-linked SCID**. It results in a lack of T cells and NK cells, leading to severe opportunistic infections (e.g., *Pneumocystis jirovecii*, *Candida*) very early in life. * **Option D (Pre-B stage defect):** This refers to **X-linked Agammaglobulinemia (Bruton’s)**. It presents with a lack of B cells and low antibodies, primarily leading to recurrent sinopulmonary infections by encapsulated bacteria (e.g., *S. pneumoniae*). **Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Dihydrorhodamine (DHR) 123 flow cytometry (replaces the older Nitroblue Tetrazolium/NBT test). * **Inheritance:** Most commonly **X-linked recessive** (CYBB gene). * **Key Organisms:** *S. aureus*, *Burkholderia cepacia*, *Nocardia*, and *Aspergillus*. * **Prophylaxis:** Patients are often maintained on lifelong TMP-SMX and Itraconazole.

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Development of Immune System

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Primary Immunodeficiency Disorders

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Atopic Dermatitis

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Drug Allergies

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Anaphylaxis

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Urticaria and Angioedema

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Autoimmune Disorders

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Immunotherapy

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