Immunology and Allergies — MCQs

Immunology and Allergies Indian Medical PG Practice Questions and MCQs

Question 51: Excessive crying is a known side effect following which vaccination?

A. Polio
B. DPT (Correct Answer)
C. BCG
D. Measles

Explanation: **Explanation:** The correct answer is **DPT (Diphtheria, Pertussis, and Tetanus)**. **Why DPT is the correct answer:** Excessive crying (defined as persistent, inconsolable crying lasting for 3 hours or more) is a well-documented systemic adverse event following immunization (AEFI) specifically associated with the **whole-cell Pertussis (wP)** component of the DPT vaccine. This reaction typically occurs within 2–24 hours of administration. It is thought to be caused by the local inflammatory response and systemic effects of the endotoxins present in the *Bordetella pertussis* bacteria. While distressing to parents, it is usually self-limiting and not a contraindication to future doses, though acellular pertussis (aP) vaccines are associated with a significantly lower incidence of this side effect. **Why other options are incorrect:** * **Polio (OPV/IPV):** Generally very well tolerated. The most serious (though rare) side effect of OPV is Vaccine-Associated Paralytic Poliomyelitis (VAPP), not excessive crying. * **BCG:** Typically causes local reactions such as a papule, ulcer, and eventual scarring at the injection site. Systemic reactions like persistent crying are rare. * **Measles:** Common side effects include fever and a transient rash occurring 5–12 days after vaccination, rather than immediate excessive crying. **High-Yield Clinical Pearls for NEET-PG:** * **Persistent Inconsolable Crying:** Occurs in approximately 1% of children receiving the wP vaccine. * **Absolute Contraindications to Pertussis vaccine:** Encephalopathy (e.g., coma, seizures) within 7 days of a previous dose. * **Triple Response:** DPT is also associated with local pain, swelling, and redness at the injection site. * **Switching to DTaP:** If a child experiences severe reactions to DTwP, the acellular version (DTaP) is preferred for subsequent doses.

Question 52: What is the most common cause for the umbilical cord to not separate by the age of 2 years?

A. Raspberry tumor
B. Leukocyte adhesion deficiency (Correct Answer)
C. Patent urachus
D. Umbilical granuloma

Explanation: **Explanation:** The normal separation of the umbilical cord typically occurs within **1 to 2 weeks** of birth. This process is mediated by **neutrophil infiltration** and the release of lysosomal enzymes, which cause the infarction and subsequent sloughing of the cord stump. **Why Leukocyte Adhesion Deficiency (LAD) is correct:** LAD (specifically Type 1) is a rare autosomal recessive primary immunodeficiency caused by a defect in the **CD18 subunit of β2-integrins**. This defect prevents leukocytes (neutrophils) from adhering to the vascular endothelium and migrating into the tissues. Because neutrophils cannot reach the umbilical site to initiate the inflammatory process required for separation, **delayed umbilical cord separation** (often beyond 3 weeks) is the classic hallmark of this condition. **Analysis of Incorrect Options:** * **Raspberry Tumor:** This is a synonym for an **Umbilical Granuloma** or occasionally a remnant of the vitellointestinal duct. It presents as a red, moist globule of tissue after the cord has already fallen off. * **Patent Urachus:** This is a failure of the urachus to obliterate, resulting in a communication between the bladder and the umbilicus. It presents with **urine leakage** from the umbilicus, not delayed cord separation. * **Umbilical Granuloma:** This is the most common cause of an umbilical mass in newborns, appearing as pink, friable tissue *after* the cord separates. It is treated with silver nitrate. **High-Yield Clinical Pearls for NEET-PG:** * **LAD Triad:** 1. Delayed separation of the umbilical cord, 2. Recurrent bacterial infections (skin/mucosa) without pus formation (cold abscesses), 3. Persistent **marked leukocytosis** (neutrophilia) even when no infection is present. * **Normal Cord Separation:** Usually occurs by 7–14 days. Separation delayed beyond **3 weeks** should trigger an investigation for LAD.

Question 53: Absent parathyroid, thymic aplasia with immunodeficiency and cardiac defects are features of which of the following syndromes?

A. Autoimmune polyglandular syndrome
B. Pendred syndrome
C. Di George syndrome (Correct Answer)
D. Lesch-Nyhan syndrome

Explanation: **Explanation** **DiGeorge Syndrome (DGS)** is the correct answer. It is a primary immunodeficiency caused by the **maldevelopment of the 3rd and 4th pharyngeal pouches** during embryonic life. This leads to a classic triad of clinical features: 1. **Thymic Aplasia/Hypoplasia:** Results in T-cell deficiency and recurrent viral/fungal infections. 2. **Parathyroid Hypoplasia:** Leads to hypocalcemia and neonatal tetany. 3. **Conotruncal Cardiac Defects:** Most commonly Tetralogy of Fallot or Interrupted Aortic Arch. **Analysis of Incorrect Options:** * **Autoimmune Polyglandular Syndrome (APS):** A group of rare diseases characterized by autoimmune destruction of multiple endocrine glands (e.g., Addison’s disease, hypoparathyroidism, and mucocutaneous candidiasis in Type 1). It is not associated with thymic aplasia or congenital cardiac defects. * **Pendred Syndrome:** An autosomal recessive disorder characterized by sensorineural hearing loss and goiter (thyroid dysfunction). It does not involve the immune system or parathyroid glands. * **Lesch-Nyhan Syndrome:** An X-linked recessive disorder caused by a deficiency of the enzyme HGPRT. It presents with hyperuricemia, gout, and characteristic self-mutilating behavior, unrelated to the pharyngeal pouch development. **High-Yield Clinical Pearls for NEET-PG:** * **Genetics:** Most cases are due to a **22q11.2 microdeletion** (detected via FISH). * **CATCH-22 Mnemonic:** **C**ardiac defects, **A**bnormal facies, **T**hymic hypoplasia, **C**left palate, **H**ypocalcemia. * **Immunology:** Patients have low T-cell counts but normal B-cell counts (though antibody production may be impaired). * **Radiology:** Look for the **absence of a thymic shadow** on a neonatal chest X-ray.

Question 54: A 10-year-old child presents with recurrent palpable purpura on the buttocks, arthralgias, colicky abdominal pain, diarrhea, and microscopic hematuria. What is the most likely diagnosis?

A. Influenza
B. Immune complex vasculitis (Correct Answer)
C. Juvenile rheumatoid arthritis
D. Systemic lupus erythematosus (SLE)

Explanation: The clinical presentation described is the classic tetrad of **Henoch-Schönlein Purpura (HSP)**, now commonly referred to as **IgA Vasculitis**. ### **Explanation of the Correct Answer** HSP is a small-vessel **Immune Complex Vasculitis** characterized by the deposition of IgA-dominant immune complexes in the walls of capillaries, venules, and arterioles. * **Palpable Purpura:** Non-thrombocytopenic bruising, typically on gravity-dependent areas (buttocks and lower extremities). * **Arthralgia:** Migratory polyarthralgia, usually affecting knees and ankles. * **Gastrointestinal involvement:** Colicky pain and diarrhea due to bowel wall edema/hemorrhage. * **Renal involvement:** Microscopic hematuria (IgA nephropathy) is the most common renal manifestation. ### **Why Other Options are Incorrect** * **A. Influenza:** This is a viral respiratory illness presenting with fever, cough, and myalgia, not systemic vasculitis or purpura. * **C. Juvenile Rheumatoid Arthritis (JRA):** While it causes joint pain, it does not typically present with palpable purpura or colicky abdominal pain. Systemic JRA (Still’s disease) presents with a salmon-pink evanescent rash, not purpura. * **D. Systemic Lupus Erythematosus (SLE):** While SLE can cause hematuria and joint pain, the hallmark is a malar rash and positive ANA/anti-dsDNA. It is less common than HSP in a 10-year-old presenting with this specific tetrad. ### **NEET-PG High-Yield Pearls** * **Most common** systemic vasculitis in children. * **Preceding trigger:** Often follows an Upper Respiratory Tract Infection (URTI), specifically Group A Streptococcus. * **Biopsy findings:** Leukocytoclastic vasculitis with **IgA and C3 deposition** on immunofluorescence. * **Complication:** Intussusception (usually ileo-ileal) is a serious GI complication to watch for. * **Treatment:** Mostly supportive; steroids are used for severe GI or renal involvement but do not prevent chronic kidney disease.

Question 55: Which of the following statements regarding Bloom syndrome is true?

A. Raised IgM
B. Absent IgA
C. Decreased IgM (Correct Answer)
D. Raised IgE

Explanation: **Explanation:** **Bloom Syndrome** is a rare autosomal recessive disorder characterized by chromosomal instability due to a mutation in the **BLM gene** (DNA helicase). This defect leads to impaired DNA repair and a high frequency of sister chromatid exchanges. **1. Why the correct answer is right:** Patients with Bloom syndrome exhibit a progressive combined immunodeficiency. The most consistent laboratory finding is **hypogammaglobulinemia**, characterized by **decreased levels of IgG, IgA, and IgM**. While all classes are typically low, the reduction in **IgM** is a hallmark feature often tested in exams. This deficiency leads to increased susceptibility to recurrent sinopulmonary infections (otitis media and pneumonia). **2. Why the incorrect options are wrong:** * **Raised IgM (Option A):** This is characteristic of Hyper-IgM Syndrome (CD40L deficiency), not Bloom syndrome. * **Absent IgA (Option B):** While IgA is decreased in Bloom syndrome, "absent" is more characteristic of Selective IgA Deficiency. * **Raised IgE (Option C):** Elevated IgE is the hallmark of Job Syndrome (Hyper-IgE Syndrome) or Wiskott-Aldrich Syndrome, not Bloom syndrome. **3. High-Yield Clinical Pearls for NEET-PG:** * **Triad:** Telangiectatic erythema (butterfly distribution on the face), photosensitivity, and severe growth retardation (proportionate dwarfism). * **Cytogenetics:** High frequency of **Sister Chromatid Exchange (SCE)**—the "gold standard" for diagnosis. * **Malignancy:** Extremely high risk of early-onset cancers (leukemias, lymphomas, and carcinomas). * **Key Association:** "Bird-like" facies (narrow face, prominent nose).

Question 56: DPT vaccine is contraindicated in which of the following conditions?

A. Family history of convulsions and neurological illness
B. Acute upper respiratory infection
C. Malnutrition
D. Evolving neurological illness (Correct Answer)

Explanation: **Explanation:** The DPT vaccine contains the **Whole-cell Pertussis (wP)** component, which is highly reactogenic and associated with neurological adverse events. The primary medical concern is that administering the vaccine during an active, unstable, or progressive neurological condition can mask the disease progression or trigger severe encephalopathy. **Why "Evolving Neurological Illness" is the Correct Answer:** Absolute contraindications for the Pertussis component include: 1. **Evolving/Progressive Neurological Disorders:** Conditions like uncontrolled epilepsy, infantile spasms, or progressive encephalopathy. Vaccination is deferred until the neurological status is stabilized. 2. **Encephalopathy:** Any encephalopathy occurring within 7 days of a previous DPT dose that is not attributable to another cause. **Analysis of Incorrect Options:** * **A. Family history of convulsions:** A personal or family history of stable seizures is **not** a contraindication. These children are at a slightly higher risk of post-vaccination febrile seizures, but the benefits of protection outweigh the risks. * **B. Acute upper respiratory infection:** Mild illnesses (with or without low-grade fever) are considered "false contraindications." Vaccination should only be deferred in cases of severe systemic illness to avoid diagnostic confusion. * **C. Malnutrition:** Malnourished children are at a higher risk of complications from Pertussis and Diphtheria; therefore, they should be prioritized for vaccination. **NEET-PG High-Yield Pearls:** * **DT vs. DPT:** If a child has a contraindication to the Pertussis component, the **DT (Diphtheria and Tetanus)** vaccine is administered instead. * **Acellular Pertussis (aP):** The aP vaccine (found in DTaP) has a significantly lower risk of fever and febrile seizures compared to the whole-cell (wP) version. * **Age Limit:** The DPT vaccine is generally not recommended for children above **7 years** of age due to increased reactogenicity; Tdap or Td is used instead.

Question 57: Nezelof's syndrome is characterized by recurrent episodes of which of the following conditions?

A. Appendicitis
B. Cholecystitis
C. Intestinal obstruction
D. Pneumonia (Correct Answer)

Explanation: **Explanation:** **Nezelof’s Syndrome** is a rare congenital immunodeficiency characterized by **isolated T-cell deficiency** despite the presence of a normal or near-normal thymus gland (unlike DiGeorge Syndrome). Because T-cells are essential for orchestrating the immune response against intracellular pathogens, these patients are highly susceptible to opportunistic infections. 1. **Why Pneumonia is Correct:** Patients with Nezelof’s Syndrome suffer from recurrent, severe sinopulmonary infections. **Pneumonia** is the most common clinical presentation, often caused by opportunistic organisms such as *Pneumocystis jirovecii*, viruses (CMV, RSV), and fungi. The lack of cell-mediated immunity prevents the body from clearing these respiratory pathogens, leading to chronic lung damage. 2. **Why Incorrect Options are Wrong:** * **Appendicitis and Cholecystitis (A & B):** These are typically acute surgical conditions related to luminal obstruction or chemical inflammation. While infections can trigger them, they are not the hallmark recurrent manifestations of primary immunodeficiencies. * **Intestinal Obstruction (C):** While these patients may suffer from chronic diarrhea or malabsorption due to intestinal infections (like Giardiasis), mechanical intestinal obstruction is not a characteristic feature of T-cell dysfunction. **Clinical Pearls for NEET-PG:** * **Triad of Nezelof’s:** Lymphopenia (T-cell), normal/hypoplastic thymus, and preserved (though often non-functional) humoral immunity. * **Differentiation:** Unlike SCID, there is some B-cell function; unlike DiGeorge, there are no parathyroid or cardiac defects (CATCH-22). * **Key Presentation:** Look for a pediatric patient with failure to thrive, chronic diarrhea, and recurrent **Pneumocystis pneumonia**.

Question 58: Which of the following is NOT a characteristic feature of Macrophage Activation Syndrome?

A. Activation of CD8+ T cells
B. Low levels of plasma ferritin (Correct Answer)
C. Presence of a cytokine storm
D. It is an alternative name for hemophagocytic lymphohistiocytosis

Explanation: **Explanation:** **Macrophage Activation Syndrome (MAS)** is a life-threatening complication of systemic inflammatory disorders, most commonly **Systemic Juvenile Idiopathic Arthritis (sJIA)**. It is considered a form of secondary Hemophagocytic Lymphohistiocytosis (HLH). **Why Option B is the correct answer:** In MAS, there is an extreme elevation of **plasma ferritin** (often >10,000 ng/mL). Ferritin is not just a storage protein here; it is an acute-phase reactant secreted by activated macrophages. Therefore, **low levels of plasma ferritin** are never seen in MAS; hyperferritinemia is a hallmark diagnostic criterion. **Analysis of Incorrect Options:** * **Option A:** MAS is driven by the uncontrolled proliferation and **activation of CD8+ T cells** and macrophages. These cells infiltrate organs, leading to tissue damage. * **Option C:** The pathophysiology involves a massive **cytokine storm**, specifically involving high levels of Pro-inflammatory cytokines like **IL-1, IL-6, IL-18, and IFN-gamma**, which leads to multi-organ failure. * **Option D:** MAS is clinically and pathologically indistinguishable from **secondary HLH**. While HLH is often used for genetic/familial forms, MAS is the term specifically used when it occurs in the context of autoimmune/rheumatologic diseases. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Persistent high fever, hepatosplenomegaly, and cytopenias. * **Laboratory Hallmarks:** High Ferritin, **High Triglycerides**, and **Low Fibrinogen** (due to consumption). * **Paradoxical Finding:** A sudden **drop in ESR** (due to low fibrinogen) in a previously inflamed patient is a strong red flag for MAS. * **Treatment:** High-dose corticosteroids (Methylprednisolone) and Cyclosporine; IL-1 inhibitors (Anakinra) are also effective.

Question 59: Antibodies to which of the following infections are NOT transmitted to a child?

A. Measles
B. Pertussis (Correct Answer)
C. Diphtheria
D. Polio

Explanation: **Explanation:** The transfer of maternal antibodies to the fetus occurs primarily via the placenta (IgG) and provides passive immunity during the first few months of life. However, the efficiency of this transfer varies significantly depending on the specific pathogen. **Why Pertussis is the correct answer:** Maternal antibodies against **Bordetella pertussis** are not efficiently transferred across the placenta. Even if the mother has high titers from previous infection or vaccination, the levels of transplacental IgG are insufficient to provide clinical protection to the neonate. This creates an "immunity gap," making infants highly vulnerable to whooping cough until they receive their own primary immunization (starting at 6 weeks). This is why the **Tdap vaccine** is specifically recommended for pregnant women during the third trimester—to maximize the temporary transfer of antibodies. **Analysis of Incorrect Options:** * **Measles:** Maternal IgG against measles is very efficiently transferred. These antibodies typically protect the infant for 6–9 months, which is why the Measles/MR vaccine is traditionally delayed until 9 months of age to avoid neutralization by maternal antibodies. * **Diphtheria & Polio:** Protective levels of antitoxins (Diphtheria) and neutralizing antibodies (Polio) are successfully transmitted to the fetus, provided the mother is immune. **High-Yield NEET-PG Pearls:** * **IgG** is the only immunoglobulin that crosses the placenta (via neonatal Fc receptors). * **Passive immunity** is strongest against Measles, Mumps, Rubella, and Tetanus. * **Poorly transmitted antibodies:** Pertussis and Hemophilus influenzae type b (Hib). * **Clinical Correlation:** Because pertussis antibodies are not naturally protective in neonates, the "cocooning strategy" (vaccinating close contacts) is often employed.

Question 60: Henoch-Schonlein purpura is characterized by which of the following findings, except?

A. Thrombocytopenia (Correct Answer)
B. Glomerulonephritis
C. Arthralgia
D. Abdominal pain

Explanation: **Explanation:** **Henoch-Schönlein Purpura (HSP)**, now commonly referred to as **IgA Vasculitis**, is the most common systemic small-vessel vasculitis in children. It is characterized by the deposition of IgA-dominant immune complexes in the walls of small vessels. **Why Thrombocytopenia is the correct answer:** The hallmark of HSP is **palpable purpura** occurring in the **absence of thrombocytopenia** or coagulopathy. In fact, the platelet count in HSP is typically **normal or even elevated** (thrombocytosis) as part of the acute phase response. If a patient presents with purpura and a low platelet count, clinicians should investigate other causes like Immune Thrombocytopenic Purpura (ITP) or leukemia. **Analysis of other options:** * **Glomerulonephritis:** Occurs in about 30-50% of cases. It typically manifests as hematuria or proteinuria due to IgA deposition in the mesangium (pathologically identical to IgA Nephropathy). * **Arthralgia:** Migratory polyarthralgia or arthritis (usually affecting knees and ankles) is seen in 75% of patients. It is non-deforming. * **Abdominal pain:** Colicky abdominal pain is common due to submucosal hemorrhage and edema. It can lead to complications like **intussusception** (typically ileo-ileal). **NEET-PG High-Yield Pearls:** * **Classic Triad:** Palpable purpura (without thrombocytopenia), arthritis, and abdominal pain. * **Most common trigger:** Upper respiratory tract infection (Group A Strep is common). * **Diagnosis:** Primarily clinical; however, skin biopsy shows **leukocytoclastic vasculitis** with IgA deposition. * **Prognosis:** Generally excellent, but long-term prognosis depends entirely on the severity of **renal involvement**.

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Development of Immune System

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Primary Immunodeficiency Disorders

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Secondary Immunodeficiency Disorders

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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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