Immunopathology Practice Questions

Q: Which of the following immunoglobulins is absent in Ataxia telangiectasia?

IgA. ### Explanation **Ataxia-Telangiectasia (AT)** is an autosomal recessive multisystem disorder caused by a mutation in the **ATM (Ataxia-Telangiectasia Mutated) gene** on chromosome 11 [1]. This gene is responsible for repairing double-stranded DNA breaks. #### Why IgA is the Correct Answer: The hallmark of AT is a combined immunodeficiency affecting both humoral and cellular immunity. The most characteristic laboratory finding is a **selective deficiency of IgA**, which occurs in approximately 70% of patients [1]. This occurs because the defective DNA repair mechanism impairs **class-switch recombination**, the process required to switch from IgM to other isotypes like IgA or IgE. #### Analysis of Incorrect Options: * **IgG:** While some subclasses of IgG (like IgG2) may be decreased, total IgG is usually normal or only mildly reduced compared to the profound absence of IgA. * **IgM:** IgM levels are typically **normal or elevated**. Since IgM is the first antibody produced and does not require class-switching, it remains unaffected by the ATM mutation. * **IgD:** IgD deficiency is not a clinical feature of AT and does not carry diagnostic significance for this condition. #### High-Yield Clinical Pearls for NEET-PG: * **Clinical Triad:** 1. Progressive cerebellar **ataxia** (early childhood), 2. Oculocutaneous **telangiectasia** (conjunctival "bloodshot" eyes), 3. Recurrent sinopulmonary infections [1]. * **Diagnostic Marker:** Elevated **Alpha-fetoprotein (AFP)** levels after age 2 are highly suggestive of AT. * **Malignancy Risk:** Patients have a 100x higher risk of developing lymphomas and leukemias due to genomic instability [1]. * **Radiosensitivity:** Patients are hypersensitive to **ionizing radiation** (X-rays/CT scans), which causes catastrophic DNA damage. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 250-251.

Q: Antihistone antibodies are detectable in which of the following conditions?

Drug-induced lupus erythematosus. **Explanation:** **Antihistone antibodies** are the hallmark serological marker for **Drug-induced Lupus Erythematosus (DILE)**. In this condition, certain drugs (most commonly Hydralazine, Procainamide, and Isoniazid) alter the structure of chromatin, leading to the formation of antibodies against histone proteins. These antibodies are present in over **95% of DILE cases**, making them highly sensitive for the diagnosis. Unlike systemic lupus erythematosus (SLE), DILE rarely involves the kidneys or central nervous system and typically resolves upon discontinuation of the offending drug. **Analysis of Incorrect Options:** * **A. CREST Syndrome:** Characterized by **Anti-centromere antibodies** [1]. It is a localized form of systemic sclerosis (Calcinosis, Raynaud’s, Esophageal dysmotility, Sclerodactyly, Telangiectasia). * **B. Polyarteritis Nodosa (PAN):** A systemic necrotizing vasculitis of medium-sized arteries. It is classically **ANCA-negative** and strongly associated with Hepatitis B infection. * **D. Intestinal Lymphoma:** Associated with Celiac disease (Enteropathy-associated T-cell lymphoma) or chronic infections (IPSID), but not with antihistone antibodies. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug-Induced Lupus:** Most common drugs are **H**ydralazine, **I**soniazid, **P**rocainamide (**HIP**). 2. **SLE vs. DILE:** While antihistone antibodies are seen in both, the absence of **Anti-dsDNA** and **Anti-Sm** antibodies strongly favors a diagnosis of DILE. 3. **Screening Test:** ANA (Antinuclear Antibody) is positive in both SLE and DILE, usually showing a **homogeneous/diffuse** pattern [1]. 4. **Diffuse Systemic Sclerosis:** Associated with **Anti-Scl-70** (Anti-topoisomerase I) antibodies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 228.

Q: Chediak-Higashi syndrome is characterized by which of the following defects?

Defects in phagolysosome function. **Explanation:** **Chediak-Higashi Syndrome (CHS)** is an autosomal recessive disorder caused by a mutation in the **LYST (Lysosomal Trafficking Regulator) gene**. This mutation leads to a defect in protein trafficking, resulting in the failure of phagosomes to fuse with lysosomes [1]. 1. **Why Option A is Correct:** The hallmark of CHS is the formation of **giant lysosomal granules** in neutrophils and other cells [1]. Because of the LYST gene mutation, lysosomes cannot properly fuse with phagosomes to form **phagolysosomes** [1]. This prevents the effective digestion of engulfed bacteria, leading to recurrent pyogenic infections. 2. **Why Incorrect Options are Wrong:** * **Option B:** Macrophage production is generally normal; the defect lies in their intracellular function. * **Option C:** Leukocyte adhesion defects (LAD) are caused by deficiencies in integrins (CD18) or ligands, preventing leukocytes from migrating out of blood vessels. * **Option D:** While microbicidal activity is ultimately impaired, this is a broad term. Specifically, CHS is a defect of **degranulation/fusion**, whereas Chronic Granulomatous Disease (CGD) is the classic example of a primary defect in microbicidal activity (NADPH oxidase deficiency) [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Peripheral Smear:** Pathognomonic **giant azurophilic granules** in neutrophils [1]. * **Clinical Tetrad:** 1. Recurrent pyogenic infections (Staph and Strep) [1]. 2. **Partial Oculocutaneous Albinism** (melanocytes cannot distribute melanin) [1]. 3. Progressive Neuropathy [1]. 4. Bleeding tendencies (due to defective dense granules in platelets) [1]. * **Associated Finding:** Neutropenia and Natural Killer (NK) cell deficiency [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 245-246.

Question 1

NADPH oxidase deficiency causes impaired immunity. Which of the following processes is affected?

Accepted Answer

Chronic granulomatous disease

Answer

Chediak-Higashi syndrome

Answer

Leukocyte adhesion defect type 1

Answer

Leukocyte adhesion defect type 2

Question 2

Which of the following immunoglobulins is absent in Ataxia telangiectasia?

Accepted Answer

IgA

Answer

IgG

Answer

IgM

Answer

IgD

Question 3

Lack of leukocyte adhesion molecules (LAM) is associated with which of the following?

Accepted Answer

Delayed separation of the umbilical cord

Answer

Normal leukocyte chemotaxis

Answer

Complement opsonization

Answer

Neutropenia

Question 4

A 23-year-old woman develops a skin rash after prolonged sun exposure and has a malar rash on physical examination. Laboratory studies show a positive ANA test result with a titer of 1:1024 and a "rim" pattern, along with a positive anti-double-stranded DNA test. Her hemoglobin is 12.1 g/dL, hematocrit is 35.5%, MCV is 89 mm
3, platelet count is 109,000/mm
3, and WBC count is 4500/mm
3. Which of the following findings is most likely to be shown by a WBC differential count?

Accepted Answer

Monocytosis

Answer

Basophilia

Answer

Eosinophilia

Answer

Neutrophilia

Question 5

Serum sickness is which type of hypersensitivity reaction?

Accepted Answer

Type III

Answer

Type I

Answer

Type II

Answer

Type IV

Question 6

Which of the following complement factors is present in the final common terminal pathway?

Accepted Answer

C5

Answer

C4

Answer

C3

Answer

Factor B

Question 7

Antihistone antibodies are detectable in which of the following conditions?

Accepted Answer

Drug-induced lupus erythematosus

Answer

CREST syndrome

Answer

Polyarteritis nodosa

Answer

Intestinal lymphoma

Question 8

Which of the following is an example of Type IV hypersensitivity?

Accepted Answer

Granulomatous reaction

Answer

Serum sickness

Answer

Shwartzman reaction

Answer

Arthus reaction

Question 9

Chediak-Higashi syndrome is characterized by which of the following defects?

Accepted Answer

Defects in phagolysosome function

Answer

Defects in macrophage production

Answer

Defects in leukocyte adhesion

Answer

Defects in microbicidal activity

Question 10

Chediak-Higashi syndrome is characterized by which of the following defects?

Accepted Answer

Defects in phagolysosome function

Answer

Defects in macrophage production

Answer

Defects in leukocyte adhesion

Answer

Defects in microbicidal activity

Immunopathology — MCQs

Immunopathology — MCQs

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