Immunology and Allergies Practice Questions

Q: In a 5-year-old boy with a history of recurrent pyogenic infections by bacteria with polysaccharide-rich capsules, which of the following investigations should be done?

IgA and IgG2 deficiency. **Explanation:** The correct answer is **D. IgA and IgG2 deficiency.** **Medical Concept:** The immune response to **encapsulated bacteria** (such as *Streptococcus pneumoniae*, *Haemophilus influenzae* type b, and *Neisseria meningitidis*) relies heavily on the production of antibodies against their **polysaccharide-rich capsules**. In humans, the antibody response to polysaccharide antigens is primarily mediated by the **IgG2 subclass**. Clinically, isolated IgG2 deficiency is rare; it most commonly occurs in association with **Selective IgA deficiency**. This combined deficiency significantly impairs the body's ability to opsonize and clear encapsulated organisms, leading to recurrent sinopulmonary and pyogenic infections. **Analysis of Options:** * **Option A (IgA deficiency):** While IgA deficiency is the most common primary immunodeficiency, it is often asymptomatic. Recurrent pyogenic infections specifically by encapsulated bacteria point more strongly toward a defect in the IgG subclass responsible for polysaccharide antigens. * **Option B (IgG1 deficiency):** IgG1 is the most abundant subclass and primarily responds to protein antigens (e.g., toxoids). Deficiency usually leads to a decrease in total IgG levels. * **Option C (IgG2 deficiency):** While IgG2 deficiency explains the susceptibility to encapsulated bacteria, it is frequently associated with IgA deficiency in clinical practice, making Option D the more comprehensive and clinically accurate choice. **High-Yield Pearls for NEET-PG:** * **IgG1 & IgG3:** Respond to **protein** antigens (e.g., viral proteins, tetanus toxoid). * **IgG2 & IgG4:** Respond to **polysaccharide** antigens. * **Selective IgA Deficiency:** Patients are at risk of **anaphylaxis** during blood transfusions due to anti-IgA antibodies. * **Wiskott-Aldrich Syndrome:** Another high-yield condition featuring low IgM and poor response to polysaccharide antigens.

Q: Which of the following conditions is treated with Intravenous Immunoglobulin (IVIG)?

Kawasaki disease, Bruton's disease, Guillain-Barré syndrome. **Explanation:** Intravenous Immunoglobulin (IVIG) is a blood product containing pooled IgG antibodies from thousands of donors. It functions through multiple mechanisms: providing passive immunity in immunodeficiency and exerting anti-inflammatory/immunomodulatory effects in autoimmune and neurological disorders. **Why Option B is Correct:** * **Kawasaki Disease:** IVIG is the gold standard treatment (along with Aspirin) to prevent coronary artery aneurysms. It reduces systemic inflammation by neutralizing bacterial superantigens and inhibiting cytokine production. * **Bruton’s Agammaglobulinemia (X-linked Agammaglobulinemia):** Since these patients lack B-cells and cannot produce their own antibodies, lifelong IVIG replacement is essential to prevent recurrent pyogenic infections. * **Guillain-Barré Syndrome (GBS):** IVIG acts as an immunomodulator that neutralizes pathogenic autoantibodies attacking the peripheral nerves, accelerating recovery. **Why Other Options are Incorrect:** * **Wegener’s Granulomatosis (Granulomatosis with Polyangiitis) & Polyarteritis Nodosa (PAN):** These are systemic vasculitides primarily managed with **Corticosteroids** and cytotoxic agents like **Cyclophosphamide** or Rituximab. While IVIG is occasionally used in refractory cases, it is not the primary or standard treatment. Options A, C, and D are incorrect because they include these conditions as primary indications. **NEET-PG High-Yield Pearls:** * **Kawasaki Dose:** 2 g/kg as a single infusion. Most effective if given within the first 10 days of fever. * **ITP Connection:** IVIG is also a first-line treatment for acute Immune Thrombocytopenic Purpura (ITP) to rapidly increase platelet counts by blocking Fc receptors on splenic macrophages. * **Contraindication:** IVIG is contraindicated in patients with **Selective IgA deficiency** due to the risk of anaphylaxis (anti-IgA antibodies).

Q: A patient presents with thrombocytopenia, eczema, and recurrent infections. What is the most probable diagnosis?

Wiskott Aldrich syndrome. ### Explanation **Correct Option: A. Wiskott-Aldrich Syndrome (WAS)** Wiskott-Aldrich Syndrome is an **X-linked recessive** primary immunodeficiency caused by a mutation in the **WASp gene**, which leads to defects in the actin cytoskeleton of hematopoietic cells. The classic clinical triad presented in the question is: 1. **Thrombocytopenia:** Characteristically presents with **micro-thrombocytes** (small platelets) and bleeding tendencies (e.g., petechiae, epistaxis). 2. **Eczema:** Typically develops in early infancy. 3. **Recurrent Infections:** Due to combined B-cell and T-cell dysfunction (predisposing to encapsulated bacteria and opportunistic infections). **Why Incorrect Options are Wrong:** * **B. Agammaglobulinemia (Bruton’s):** Presents with recurrent sinopulmonary infections starting after 6 months of age (when maternal IgG wanes). It does not feature eczema or thrombocytopenia. * **C. Chediak-Higashi Syndrome:** Characterized by **oculocutaneous albinism**, peripheral neuropathy, and giant cytoplasmic granules in neutrophils. While it involves infections, the classic triad of WAS is absent. * **D. Lazy Leukocyte Syndrome:** A defect in neutrophil chemotaxis and mobility. Patients present with recurrent skin infections and gingivitis, but not with eczema or small-platelet thrombocytopenia. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** X-linked Recessive (mostly affects males). * **Lab Findings:** Low IgM, normal/low IgG, and **elevated IgA and IgE**. * **Platelet Morphology:** WAS is the only condition where **small platelets** are a hallmark feature. * **Mnemonic (WATER):** **W**iskott **A**ldrich, **T**hrombocytopenia, **E**czema, **R**ecurrent infections. * **Complications:** Increased risk of autoimmune diseases and **B-cell lymphomas**. * **Treatment:** Hematopoietic stem cell transplant is the definitive cure.

Q: All of the following are true about Wiskott-Aldrich syndrome except:

Large size platelets. **Explanation:** Wiskott-Aldrich Syndrome (WAS) is an X-linked recessive disorder caused by a mutation in the **WASp gene**, which is critical for actin cytoskeleton remodeling in hematopoietic cells. **Why Option C is the correct answer (The Exception):** In WAS, the hallmark hematological finding is **microthrombocytopenia**. Patients have a low platelet count and, characteristically, **small-sized platelets**. Finding large platelets (megathrombocytes) would instead point toward conditions like Bernard-Soulier Syndrome or ITP. **Analysis of Incorrect Options (True statements about WAS):** * **A. Bloody diarrhea:** This is often the earliest clinical manifestation in infancy due to severe thrombocytopenia and platelet dysfunction. * **B. Immunoglobulin profile:** The classic pattern is **low IgM**, normal to low IgG, and **elevated IgA and IgE**. This imbalance contributes to the underlying immunodeficiency. * **D. Atopic dermatitis:** Eczema is a core component of the clinical triad and is typically severe and difficult to manage. **Clinical Pearls for NEET-PG:** * **The Classic Triad:** 1. Thrombocytopenia (Microplatelets), 2. Eczema, 3. Recurrent Infections (especially encapsulated organisms like *S. pneumoniae*). * **Mnemonic:** **TIE** (Thrombocytopenia, Infections, Eczema). * **Inheritance:** X-linked Recessive (affects males). * **Complications:** High risk of **Non-Hodgkin Lymphoma** and autoimmune hemolytic anemia. * **Definitive Treatment:** Hematopoietic stem cell transplant (HSCT).

Q: Which of the following are true about Henoch-Schönlein purpura (HSP)?

Palpable purpura and Kidneys commonly affected. **Explanation:** Henoch-Schönlein Purpura (HSP), now commonly referred to as **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**. **Why Option D is Correct:** The classic clinical tetrad of HSP includes **palpable purpura** (without thrombocytopenia), arthritis/arthralgia, abdominal pain, and **renal involvement**. Renal involvement (HSP Nephritis) occurs in approximately 30-50% of patients and is a major determinant of long-term prognosis. It typically manifests as hematuria or proteinuria. **Analysis of Incorrect Options:** * **Option A:** HSP is an immune-complex-mediated vasculitis, not a Pauci-immune vasculitis. **C-ANCA** is specifically associated with Granulomatosis with Polyangiitis (Wegener's), not HSP. * **Option B:** While palpable purpura is the hallmark sign, this option is incomplete compared to Option D, as renal involvement is a critical systemic feature of the disease. * **Option C:** This is a common distractor. In HSP, the purpura is **non-thrombocytopenic**. The platelet count is typically normal or even elevated (as an acute phase reactant). If a patient has purpura with a low platelet count, the diagnosis is more likely Immune Thrombocytopenic Purpura (ITP). **High-Yield Clinical Pearls for NEET-PG:** * **Trigger:** Often follows an Upper Respiratory Tract Infection (URTI). * **Biopsy:** Skin biopsy shows **Leukocytoclastic vasculitis** with IgA deposition on immunofluorescence. * **Gastrointestinal:** Can lead to **Intussusception** (characteristically ileo-ileal). * **Treatment:** Mainly supportive; steroids are used for severe GI symptoms or renal involvement but do not prevent chronic kidney disease.

Q: Wiskott-Aldrich syndrome is characterized by all of the following features except:

Increased IgM levels. **Explanation:** Wiskott-Aldrich Syndrome (WAS) is a rare primary immunodeficiency caused by a mutation in the **WAS gene**, which encodes the **WASP protein**. This protein is crucial for actin cytoskeleton remodeling in hematopoietic cells, affecting both platelet formation and immune cell function. **Why Option D is correct:** In Wiskott-Aldrich Syndrome, the characteristic immunoglobulin profile is **decreased IgM**, with **elevated IgA and IgE** levels. IgG levels are typically normal or slightly low. The defect in the WASP protein leads to a poor polysaccharide antibody response, resulting in low IgM. Therefore, "Increased IgM levels" is the incorrect feature. **Analysis of incorrect options:** * **Option A (X-linked recessive):** This is the classic mode of inheritance for WAS. It primarily affects males. * **Option B (Atopic dermatitis/Eczema):** Eczema is a hallmark clinical feature, usually appearing in early infancy and resembling atopic dermatitis. * **Option C (Thrombocytopenia):** This is often the earliest sign. Patients present with **microthrombocytopenia** (small, few platelets), leading to mucosal bleeding, petechiae, or bloody diarrhea. **NEET-PG High-Yield Pearls:** * **Classic Triad:** "TIE" — **T**hrombocytopenia (micro-platelets), **I**mmunodeficiency (recurrent infections), and **E**czema. * **Platelet Morphology:** It is the only condition characterized by **small platelets** (low Mean Platelet Volume). * **Malignancy Risk:** Patients have a significantly increased risk of developing Non-Hodgkin Lymphoma and autoimmune diseases. * **Definitive Treatment:** Hematopoietic stem cell transplant (HSCT).

Q: A full-term baby boy is delivered after an uneventful pregnancy and is well for the first 2 years of his life. He receives all his immunizations without any complications. Starting around his second birthday, the mother begins to note frequent upper respiratory tract infections, and the child is hospitalized three times for pneumonia. Laboratory testing would most likely reveal a deficiency of which of the following immunoglobulins in this child?

IgA. **Explanation:** The clinical presentation is characteristic of **Selective IgA Deficiency**, the most common primary immunodeficiency. **Why IgA is the correct answer:** IgA is the primary immunoglobulin found in mucosal secretions (respiratory, GI, and urogenital tracts). It acts as the first line of defense against pathogens. A deficiency leads to recurrent sinopulmonary infections (sinusitis, pneumonia) and gastrointestinal infections (e.g., *Giardia*). The child remained healthy for the first two years because IgA deficiency often presents later in childhood, and many patients remain asymptomatic. Crucially, the patient tolerated **vaccinations** (which are mostly systemic/IM) without complications, indicating that his humoral (IgG/IgM) and cellular immunity are intact. **Why other options are incorrect:** * **IgG Deficiency (C):** IgG is the most abundant serum antibody. A deficiency (like X-linked Agammaglobulinemia) usually presents after 6 months of age (once maternal IgG wanes) with severe, systemic pyogenic infections. These patients also react poorly to live vaccines. * **IgM Deficiency (D):** Isolated IgM deficiency is rare. IgM is the first antibody produced in response to an antigen; its absence would lead to severe disseminated infections early in life. * **IgD (B):** IgD functions primarily as an antigen receptor on B-cell surfaces; its isolated deficiency is not a recognized cause of recurrent respiratory infections. **NEET-PG High-Yield Pearls:** * **Most Common:** Selective IgA Deficiency is the most common primary immunodeficiency. * **Associated Conditions:** High association with **Celiac disease**, autoimmune disorders, and atopy. * **The "Anaphylaxis" Rule:** Patients with IgA deficiency are at high risk of **anaphylaxis during blood transfusions** because they develop anti-IgA antibodies. * **Diagnosis:** Serum IgA levels < 7 mg/dL with normal IgG and IgM levels.

Question 1

A previously healthy eight-year-old boy presented to the emergency department with high-grade fever, arthralgia, pruritic erythematous rash, and lymphadenopathy. He had completed 8 days of a 10-day course of cefaclor for an upper respiratory tract infection. Which of the following possibilities should be initially suspected?

Accepted Answer

Type III Hypersensitivity Reaction

Answer

Kawasaki Disease

Answer

Anaphylaxis

Answer

Henoch-Schonlein purpura

Question 2

In a 5-year-old boy with a history of recurrent pyogenic infections by bacteria with polysaccharide-rich capsules, which of the following investigations should be done?

Accepted Answer

IgA and IgG2 deficiency

Answer

IgA deficiency

Answer

IgG1 deficiency

Answer

IgG2 deficiency

Question 3

Which of the following conditions is treated with Intravenous Immunoglobulin (IVIG)?

Accepted Answer

Kawasaki disease, Bruton's disease, Guillain-Barré syndrome

Answer

Kawasaki disease, Polyarteritis nodosa, Wegener's granulomatosis

Answer

Wegener's granulomatosis, Bruton's disease, Guillain-Barré syndrome

Answer

Kawasaki disease, Wegener's granulomatosis, Bruton's disease

Question 4

A patient presents with thrombocytopenia, eczema, and recurrent infections. What is the most probable diagnosis?

Accepted Answer

Wiskott Aldrich syndrome

Answer

Alpha-beta-gamma-globulinemia

Answer

Chediak-Higashi syndrome

Answer

Lazy leukocyte syndrome

Question 5

All of the following are true about Wiskott-Aldrich syndrome except:

Accepted Answer

Large size platelets

Answer

Bloody diarrhea during infancy

Answer

Low IgM and elevated IgA and IgE

Answer

Atopic dermatitis

Question 6

Which of the following are true about Henoch-Schönlein purpura (HSP)?

Accepted Answer

Palpable purpura and Kidneys commonly affected

Answer

Palpable purpura and C-ANCA positivity

Answer

Palpable purpura

Answer

Palpable purpura and Thrombocytopenia

Question 7

A 4-month-old boy presented with spontaneous nose bleeds and bloody diarrhea. He has a history of recurrent chest and ear infections, leading to frequent hospitalizations. Examination revealed atopic dermatitis and petechiae all over the body. Laboratory findings suggested abnormally low platelet counts along with eosinophilia. The gene involved in this condition is located on which chromosome?

Accepted Answer

X-chromosome

Answer

Chromosome 21

Answer

Chromosome 23

Answer

Chromosome 1

Question 8

Wiskott-Aldrich syndrome is characterized by all of the following features except:

Accepted Answer

Increased IgM levels

Answer

X-linked recessive mode of inheritance

Answer

Atopic dermatitis and eczema during infancy

Answer

Thrombocytopenia

Question 9

A 7-month-old boy has had multiple bouts of otitis media, sinusitis, bronchitis, oral candidiasis, and multiple viral infections. Cessation of the recurrent infections follows successful engraftment of a bone marrow transplant. What is the basis of the clinical improvement?

Accepted Answer

Maturation of donor lymphoid progenitor cells.

Answer

Direct transfusion of antibody-producing B cells.

Answer

Direct transfusion of donor CD4+ and CD8+ lymphocytes.

Answer

Donor suppression of recipient cytotoxic T cells.

Question 10

A full-term baby boy is delivered after an uneventful pregnancy and is well for the first 2 years of his life. He receives all his immunizations without any complications. Starting around his second birthday, the mother begins to note frequent upper respiratory tract infections, and the child is hospitalized three times for pneumonia. Laboratory testing would most likely reveal a deficiency of which of the following immunoglobulins in this child?

Accepted Answer

IgA

Answer

IgD

Answer

IgG

Answer

IgM

Immunology and Allergies — MCQs

Immunology and Allergies — MCQs

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