Immunopathology Practice Questions

Q: The Nitroblue tetrazolium test is used to assess the function of which cells?

Phagocytes. The **Nitroblue Tetrazolium (NBT) test** is a classic diagnostic tool used to assess the metabolic activity of **phagocytes** (specifically neutrophils and macrophages) [1]. **Why Phagocytes is correct:** During phagocytosis, these cells undergo a "respiratory burst" mediated by the enzyme **NADPH oxidase**. This process generates reactive oxygen species (superoxide radicals) to kill ingested pathogens. In the NBT test, the colorless NBT dye is added to the cells. If NADPH oxidase is functional, the superoxide radicals reduce the yellow NBT into insoluble, dark blue **formazan crystals**. A positive result (blue color) indicates normal phagocytic function [1]. **Why other options are incorrect:** * **Complement:** Complement function is typically assessed using the **CH50 assay** (for the classical pathway) or AP50 (for the alternative pathway). * **T cells:** T-cell function is evaluated via delayed-type hypersensitivity (DTH) skin tests or flow cytometry (CD3/CD4/CD8 counts). * **B cells:** B-cell function is assessed by measuring serum immunoglobulin levels or using flow cytometry (CD19/CD20 counts). **Clinical Pearls for NEET-PG:** * **Chronic Granulomatous Disease (CGD):** This is an X-linked recessive disorder caused by a deficiency in **NADPH oxidase**. Patients with CGD will have a **negative NBT test** (cells remain colorless/yellow) because they cannot produce superoxide radicals. * **Dihydrorhodamine (DHR) 123 test:** This is the modern, more sensitive flow cytometry-based gold standard that has largely replaced the NBT test for diagnosing CGD. * **Catalase-positive organisms:** Patients with defective phagocyte function (CGD) are particularly susceptible to infections by *Staphylococcus aureus*, *Aspergillus*, and *Serratia marcescens*.

Q: Chediak-Higashi syndrome is characterized by a defect in which of the following?

Lysosome fusion. **Explanation:** **Chediak-Higashi Syndrome (CHS)** is an autosomal recessive disorder caused by a mutation in the **LYST gene** (Lysosomal Trafficking Regulator). This mutation leads to a defect in **microtubule-dependent phagosome-lysosome fusion** [1]. 1. **Why Option A is Correct:** The defect in the LYST protein prevents the proper trafficking and fusion of lysosomes with phagosomes [1]. This results in the formation of **giant lysosomal granules** in various cells (neutrophils, melanocytes, and platelets) because the organelles cannot be properly distributed or fused, leading to impaired intracellular killing of bacteria [1]. 2. **Why Other Options are Incorrect:** * **B & C (T-cells and B-cells):** CHS is primarily a defect of phagocytes (innate immunity) and natural killer (NK) cells. While it causes severe immunodeficiency, it is not a primary T-cell (e.g., DiGeorge) or B-cell (e.g., Bruton’s) deficiency. * **D (Complement):** Complement deficiencies (like C3 or C5-C9 defects) involve opsonization or membrane attack complex issues, not intracellular trafficking. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Pathognomonic **giant granules** in neutrophils on peripheral smear [1]. * **Clinical Triad:** 1. **Partial Albinism** (melanocytes cannot transfer pigment granules to keratinocytes) [1]. 2. **Recurrent Pyogenic Infections** (Staph and Strep due to impaired chemotaxis/killing) [1]. 3. **Neurological symptoms** (peripheral neuropathy) [1]. * **Associated Feature:** Mild bleeding tendency due to defective dense granules in platelets [1]. * **Complication:** Risk of "Accelerated Phase" (Hemophagocytic Lymphohistiocytosis - HLH). **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.

Q: Which of the following is an example of a Type II hypersensitivity reaction?

Goodpasture syndrome. **Explanation:** **Type II Hypersensitivity** (Cytotoxic) involves **IgG or IgM** antibodies directed against specific antigens located on **cell surfaces or in the extracellular matrix**. This leads to cell destruction or tissue damage via the complement system, opsonization, or antibody-dependent cellular cytotoxicity (ADCC). **Why Goodpasture Syndrome is Correct:** In Goodpasture syndrome, autoantibodies are formed against the **alpha-3 chain of Type IV collagen** found in the glomerular and alveolar basement membranes. This is a classic "tissue-specific" reaction where antibodies bind directly to the target organ, resulting in a characteristic **linear immunofluorescence** pattern on biopsy. **Why the Other Options are Incorrect:** * **A, B, and C (PSGN, SLE, and Serum Sickness):** These are all examples of **Type III Hypersensitivity**. Unlike Type II, Type III involves the formation of **soluble antigen-antibody (immune) complexes** that circulate in the blood and deposit in various tissues (like joints, kidneys, or vessels), causing systemic inflammation and a "lumpy-bumpy" (granular) immunofluorescence pattern. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Type II:** "The **2** Gs" – **G**oodpasture and **G**rave’s disease (though Grave's is specifically Type II-non-cytotoxic/stimulatory). * **Key Distinction:** Type II is **Antibody-mediated** (fixed antigen); Type III is **Immune-complex mediated** (circulating antigen). * **Other Type II Examples:** Rheumatic fever, Myasthenia Gravis, Erythroblastosis fetalis, and Autoimmune Hemolytic Anemia (AIHA). * **Exam Tip:** If the question mentions "Linear IgG deposits" on a renal biopsy, always think Type II (Goodpasture). If it mentions "Granular deposits," think Type III (PSGN/SLE).

Q: A patient develops wheeze and hemolysis 48 hours after receiving penicillin, with no prior history of drug allergy. Antibody for penicillin is positive. What type of hypersensitivity reaction is this?

Type II. **Explanation:** The correct answer is **Type II Hypersensitivity (Cytotoxic)**. In this scenario, penicillin acts as a **hapten**, binding to the surface of red blood cells (RBCs). This modifies the cell membrane, making it appear foreign to the immune system. Specific IgG or IgM antibodies then bind to these penicillin-coated RBCs, leading to complement activation or phagocytosis, resulting in **drug-induced hemolytic anemia**. **Why other options are incorrect:** * **Type I (Immediate):** Mediated by IgE and mast cell degranulation. It typically occurs within minutes to hours of exposure (anaphylaxis, urticaria). While the patient has a wheeze, the presence of hemolysis and the 48-hour timeline point toward a cytotoxic mechanism rather than classical IgE-mediated anaphylaxis. * **Type III (Immune Complex):** Involves the deposition of antigen-antibody complexes in tissues (e.g., Serum Sickness). It does not typically present with direct hemolysis of RBCs. * **Type IV (Delayed):** T-cell mediated and usually presents as contact dermatitis or Stevens-Johnson Syndrome (SJS) 48–72 hours later. It does not involve antibodies or acute hemolysis. **High-Yield Clinical Pearls for NEET-PG:** * **Penicillin is unique:** It can cause all four types of hypersensitivity reactions. * **Type II Mechanism:** Remember the mnemonic **"Cy-2-toxic"**—antibodies (IgG/IgM) target antigens on specific cell surfaces. * **Coombs Test:** Drug-induced Type II hemolysis will typically show a **Positive Direct Antiglobulin Test (DAT/Direct Coombs)**. * **Other Type II Examples:** Goodpasture syndrome, Myasthenia Gravis, Rheumatic fever, and Erythroblastosis fetalis.

Question 1

Autoimmunity can be caused due to all of the following except:

Accepted Answer

Negative selection of T cells in thymus

Answer

Forbidden clones

Answer

Expression of cryptic antigens

Answer

Inappropriate expression of MHC proteins

Question 2

Bruton's agammaglobulinemia is due to which defect?

Accepted Answer

B-cell defect

Answer

IgA deficiency

Answer

IgM deficiency

Answer

IgG deficiency

Question 3

Myasthenia gravis is associated with which of the following conditions?

Accepted Answer

Thymic hyperplasia

Answer

Thymoma

Answer

Thymic carcinoma

Answer

Lymphoma

Question 4

The Nitroblue tetrazolium test is used to assess the function of which cells?

Accepted Answer

Phagocytes

Answer

Complement

Answer

T cells

Answer

B cells

Question 5

Chediak-Higashi syndrome is characterized by a defect in which of the following?

Accepted Answer

Lysosome fusion

Answer

T-cells

Answer

B-cells

Answer

Complement

Question 6

Which of the following is an example of a Type II hypersensitivity reaction?

Accepted Answer

Goodpasture syndrome

Answer

Post-streptococcal glomerulonephritis (PSGN)

Answer

Systemic lupus erythematosus (SLE)

Answer

Serum sickness

Question 7

In acute solid organ Graft versus Host Disease, which of the following is not a characteristic feature?

Accepted Answer

Preformed antibodies are involved

Answer

Occurs within 100 days of transplantation

Answer

Skin is the most common organ involved

Answer

May lead to cholestatic jaundice

Question 8

A patient develops wheeze and hemolysis 48 hours after receiving penicillin, with no prior history of drug allergy. Antibody for penicillin is positive. What type of hypersensitivity reaction is this?

Accepted Answer

Type II

Answer

Type I

Answer

Type III

Answer

Type IV

Question 9

For each patient with a specific medical condition, select the most likely immune dysfunction.

Accepted Answer

Mixed T- and B-cell deficiency/dysfunction

Answer

B-cell deficiency/dysfunction

Answer

T-lymphocyte deficiency/dysfunction

Answer

Neutropenia

Question 10

T cell dependent tubercular antigens stimulate the production of which of the following antibodies?

Accepted Answer

IgG and IgA

Answer

IgM

Answer

IgG

Answer

IgG, IgM, IgA, IgE

Immunopathology — MCQs

Immunopathology — MCQs

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