Immunology and Allergies — MCQs
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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?
Delayed separation of the umbilical cord stump is a characteristic feature of which condition?
Maternal antibodies do not provide protective immunity to the neonate against which of the following diseases?
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?
A four-year-old child presents with mild fever, malaise, purpura, arthritis, abdominal pain, and microscopic hematuria. What would be the most likely diagnosis?
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?
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?
Eye involvement is seen in which of the following subtypes of Juvenile Rheumatoid Arthritis?
DiGeorge syndrome is associated with all of the following except?
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?
Immunology and Allergies Indian Medical PG Practice Questions and MCQs
Question 41: 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?
- A. There is progressive loss of T lymphocytes in the peripheral blood and in the T-cell zones (paracortical areas) of the lymph nodes.
- B. Low IgM and IgG levels. (Correct Answer)
- C. High levels of IgA.
- D. Patients are prone to developing B-cell lymphomas.
Explanation: ### **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.
Question 42: Delayed separation of the umbilical cord stump is a characteristic feature of which condition?
- A. Chediak Higashi syndrome
- B. Chronic granulomatous disease
- C. Leukocyte adhesion deficiency (Correct Answer)
- D. All of the above
Explanation: **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.
Question 43: Maternal antibodies do not provide protective immunity to the neonate against which of the following diseases?
- A. Diphtheria
- B. Pertussis
- C. Tetanus
- D. Polio (Correct Answer)
Explanation: **Explanation:** The transfer of maternal antibodies (IgG) via the placenta provides passive immunity to the neonate, protecting them against several vaccine-preventable diseases during the first few months of life. However, the effectiveness of this protection depends on the type of pathogen and the nature of the maternal immune response. **Why Polio is the Correct Answer:** While maternal IgG antibodies against Polio are transferred across the placenta, they do not provide **protective immunity** to the neonate. Poliovirus primarily infects the gastrointestinal tract. Serum IgG can prevent systemic spread (viremia) and paralytic polio, but it does not provide local mucosal immunity (IgA) in the infant's gut. Therefore, the neonate remains susceptible to infection and colonization by the virus. Furthermore, maternal antibody levels for polio are often insufficient to prevent infection in the infant, necessitating early vaccination. **Analysis of Incorrect Options:** * **Diphtheria & Tetanus:** Maternal antibodies (anti-toxins) against Diphtheria and Tetanus are highly efficient at crossing the placenta. If the mother is adequately immunized, these antibodies provide robust protection to the neonate against the effects of the toxins produced by *C. diphtheriae* and *C. tetani*. * **Pertussis:** Although maternal antibodies against Pertussis are transferred, their protective efficacy is relatively short-lived compared to Tetanus. However, they still provide a baseline level of protection that reduces the severity of the disease in early infancy, which is why "cocooning" and maternal Tdap vaccination are recommended. **NEET-PG High-Yield Pearls:** * **IgG** is the only immunoglobulin class that crosses the placenta (via neonatal Fc receptors). * **Measles:** Maternal antibodies are highly protective and can interfere with the Measles vaccine if given too early (hence the 9-month schedule). * **Exceptions:** Maternal antibodies do **not** provide protection against **Pertussis** (partially/short-lived) and **Polio** (lack of mucosal immunity). * **Breast milk** provides passive **IgA**, which offers local intestinal protection that placental IgG cannot provide.
Question 44: 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?
- A. DiGeorge syndrome
- B. Isolated IgA deficiency
- C. Wiskott Aldrich syndrome
- D. X-linked agammaglobulinemia of Bruton (Correct Answer)
Explanation: ### 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.
Question 45: A four-year-old child presents with mild fever, malaise, purpura, arthritis, abdominal pain, and microscopic hematuria. What would be the most likely diagnosis?
- A. Thrombasthenia
- B. Idiopathic thrombocytopenic purpura
- C. Systemic lupus erythematosus
- D. Henoch-Schonlein purpura (Correct Answer)
Explanation: ### Explanation **Correct Answer: D. Henoch-Schonlein purpura (HSP)** **Why it is correct:** Henoch-Schönlein Purpura (now termed **IgA Vasculitis**) is the most common systemic vasculitis in children. It is a small-vessel vasculitis characterized by the deposition of **IgA-dominant immune complexes**. The diagnosis is clinical, based on the classic tetrad presented in this case: 1. **Palpable Purpura:** Typically involving the lower extremities and buttocks (non-thrombocytopenic). 2. **Arthritis/Arthralgia:** Migratory, usually affecting knees and ankles. 3. **Abdominal Pain:** Due to bowel wall edema or intussusception. 4. **Renal Involvement:** Presenting as hematuria or proteinuria (HSP nephritis). **Why the other options are incorrect:** * **A. Thrombasthenia (Glanzmann’s):** This is a qualitative platelet disorder (defect in GpIIb/IIIa). It presents with mucosal bleeding and epistaxis, not with arthritis, abdominal pain, or systemic vasculitic features. * **B. Idiopathic Thrombocytopenic Purpura (ITP):** While ITP presents with purpura, the spots are usually "flat" (petechiae/ecchymosis) rather than palpable. Crucially, ITP lacks systemic features like arthritis, abdominal pain, or hematuria. * **C. Systemic Lupus Erythematosus (SLE):** While SLE can cause arthritis and hematuria, it is rare in a 4-year-old (more common in adolescent females) and typically presents with a malar rash and positive ANA/anti-dsDNA markers. **NEET-PG High-Yield Pearls:** * **Trigger:** Often follows an Upper Respiratory Tract Infection (URTI). * **Platelet Count:** Characteristically **normal** in HSP (distinguishes it from ITP). * **Most common complication:** Intussusception (typically **ileo-ileal**, unlike the usual ileo-colic type). * **Prognosis:** Generally excellent; long-term prognosis depends entirely on the severity of **renal involvement**. * **Biopsy:** Shows leukocytoclastic vasculitis with IgA deposits on immunofluorescence.
Question 46: 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?
- A. IgA
- B. IgG 1
- C. IgG 2 (Correct Answer)
- D. IgA + IgG 2
Explanation: **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.
Question 47: 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?
- A. Acquired hypogammaglobulinemia
- B. Wiskott-Aldrich syndrome (Correct Answer)
- C. DiGeorge syndrome
- D. Selective IgA deficiency
Explanation: **Explanation:** The clinical presentation of the **"Classic Triad"**—recurrent infections, eczema, and thrombocytopenia (presenting as epistaxis/petechiae)—in a young boy is pathognomonic for **Wiskott-Aldrich Syndrome (WAS)**. **1. Why Wiskott-Aldrich Syndrome is correct:** WAS is an **X-linked recessive** immunodeficiency caused by a mutation in the *WASP* gene, which affects actin cytoskeleton remodeling in hematopoietic cells. This leads to: * **Microthrombocytopenia:** Small-sized platelets and low platelet counts (the most common cause of death is hemorrhage). * **Immunodeficiency:** Impaired T-cell function and B-cell responses, leading to recurrent respiratory infections. * **Characteristic Labs:** Low IgM, **elevated IgE and IgA**, and normal/low IgG. **2. Why other options are incorrect:** * **Acquired hypogammaglobulinemia (CVID):** Usually presents in the 2nd-3rd decade of life with low levels of all immunoglobulin classes (IgG, IgA, IgM). It does not typically feature thrombocytopenia or eczema. * **DiGeorge Syndrome:** Caused by 22q11.2 deletion (3rd/4th pharyngeal pouch defect). It presents with the CATCH-22 mnemonic (Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcemia). It is not associated with thrombocytopenia. * **Selective IgA Deficiency:** The most common primary immunodeficiency. Most patients are asymptomatic or present with respiratory/GI infections and anaphylaxis during blood transfusions. It does not cause petechiae or eczema. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** X-linked Recessive (only males affected; history of affected uncle is a key clue). * **Platelet Morphology:** WAS is unique because platelets are **abnormally small** (low Mean Platelet Volume). * **Malignancy Risk:** Patients have a significantly increased risk of Non-Hodgkin Lymphoma and autoimmune diseases. * **Definitive Treatment:** Hematopoietic stem cell transplant (HSCT).
Question 48: Eye involvement is seen in which of the following subtypes of Juvenile Rheumatoid Arthritis?
- A. Seropositive pauciarticular JRA, late onset
- B. Seronegative pauciarticular JRA, late onset
- C. Seronegative polyarticular JRA, early onset
- D. Seronegative pauciarticular JRA, early onset (Correct Answer)
Explanation: ### 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.
Question 49: DiGeorge syndrome is associated with all of the following except?
- A. Hyperthyroidism
- B. Small jaws
- C. 22q11 deletion
- D. Hypocalcemia (Correct Answer)
Explanation: **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 50: 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?
- A. Bruton X-linked agammaglobulinemia
- B. DiGeorge syndrome
- C. Isolated IgA deficiency
- D. Severe combined immunodeficiency (Correct Answer)
Explanation: ### Explanation **Correct Answer: D. Severe Combined Immunodeficiency (SCID)** **Why it is correct:** Severe Combined Immunodeficiency (SCID) is a pediatric emergency characterized by a profound defect in both **T-cell and B-cell immunity**. The most common autosomal recessive form of SCID is caused by a **deficiency of Adenosine Deaminase (ADA)**. * **Pathophysiology:** ADA is essential for the purine salvage pathway. Its deficiency leads to the accumulation of toxic metabolites (deoxyadenosine and dATP) within lymphocytes. These metabolites are lymphotoxic, leading to the apoptosis of precursors and a "virtual absence" of lymphocytes in the blood and peripheral lymphoid organs (thymus, lymph nodes, tonsils). * **Clinical Presentation:** Patients present in early infancy (usually <6 months) with recurrent, severe infections (viral, bacterial, fungal, and opportunistic like *Pneumocystis jirovecii*), failure to thrive, and chronic diarrhea. **Why the other options are incorrect:** * **A. Bruton X-linked agammaglobulinemia:** This is a pure B-cell defect (BTK gene mutation). While B-cells are absent, T-cell numbers and function remain normal. * **B. DiGeorge Syndrome:** This involves thymic hypoplasia (22q11.2 deletion) leading to isolated T-cell deficiency. B-cell numbers are typically normal, though antibody production may be impaired due to lack of T-cell help. * **C. Isolated IgA Deficiency:** The most common primary immunodeficiency; it involves a selective lack of IgA. Most patients are asymptomatic, and lymphocyte counts are normal. **NEET-PG High-Yield Pearls:** * **CXR Finding:** Absence of a thymic shadow is a classic radiological sign of SCID. * **Inheritance:** X-linked SCID (IL-2 receptor gamma chain mutation) is the most common overall; ADA deficiency is the most common **autosomal recessive** form. * **Treatment:** Hematopoietic stem cell transplant (HSCT) is the definitive treatment. ADA deficiency is also notable for being the first disease treated with **gene therapy**. * **Contraindication:** Live vaccines (e.g., BCG, OPV, Rotavirus) are strictly contraindicated.
Practice by Chapter
Development of Immune System
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Primary Immunodeficiency Disorders
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Secondary Immunodeficiency Disorders
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Allergic Rhinitis
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Asthma in Children
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Atopic Dermatitis
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Food Allergies
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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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