Immunopathology Practice Questions

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

Di George syndrome. **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.

Q: All of the following statements regarding Antineutrophil Cytoplasmic Antibodies (ANCA) are true, EXCEPT:

There are three principal classifications of ANCA.. **Explanation:** The correct answer is **D** because there are only **two** principal classifications of ANCA based on immunofluorescence patterns: **cANCA** (cytoplasmic) and **pANCA** (perinuclear). While a third pattern, xANCA (atypical), is sometimes described in inflammatory bowel disease, it is not considered a "principal" classification in the context of systemic vasculitis. **Analysis of Options:** * **Option A (Incorrect):** This is a true statement. **Proteinase-3 (PR3)** is the major antigen for cANCA. It is located in the azurophilic granules of neutrophils. cANCA is highly specific (approx. 90%) for **Granulomatosis with Polyangiitis (Wegener's)**. * **Option B (Incorrect):** This is a true statement. **Myeloperoxidase (MPO)** is the primary target for pANCA [1]. It is associated with Microscopic Polyangiitis (MPA), Churg-Strauss Syndrome (EGPA), and Pauci-immune Crescentic Glomerulonephritis [1]. * **Option C (Incorrect):** This is a true statement. Unlike cANCA, which is highly specific for vasculitis, **pANCA** can be found in non-vasculitic conditions such as Primary Sclerosing Cholangitis (PSC), Ulcerative Colitis, and Rheumatoid Arthritis. **High-Yield Clinical Pearls for NEET-PG:** * **cANCA/PR3-ANCA:** Associated with Granulomatosis with Polyangiitis (GPA). * **pANCA/MPO-ANCA:** Associated with Microscopic Polyangiitis (MPA) and Eosinophilic Granulomatosis with Polyangiitis (EGPA) [1]. * **Diagnostic Gold Standard:** The current recommendation is to use **ELISA** to confirm the specific antigen (PR3 or MPO) after an initial screening with **Indirect Immunofluorescence (IIF)**. * **Monitoring:** ANCA titers often correlate with disease activity; a rise in titers may predict a relapse. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 917-918.

Q: A patient presents with generalized edema, sweating, flushing, tachycardia, and fever after a bee sting. What type of hypersensitivity reaction is most likely responsible?

IgE mediated reaction. **Explanation:** The clinical presentation of generalized edema, flushing, tachycardia, and sweating following a bee sting is a classic manifestation of **Anaphylaxis**, which is a **Type I Hypersensitivity Reaction**. **1. Why Option B is Correct:** Type I hypersensitivity is an **IgE-mediated reaction**. Upon re-exposure to an allergen (bee venom), specific IgE antibodies already bound to the surface of **mast cells and basophils** cause cross-linking. This triggers immediate degranulation and the release of potent vasoactive mediators like **histamine**, leukotrienes, and prostaglandins. These mediators cause systemic vasodilation (flushing, tachycardia), increased vascular permeability (edema), and smooth muscle contraction. **2. Why the other options are incorrect:** * **Option A (T cell mediated):** This refers to **Type IV (Delayed) Hypersensitivity**. It involves sensitized T-lymphocytes and typically occurs 48–72 hours after exposure (e.g., Mantoux test or contact dermatitis), not immediately. * **Option C (IgG mediated):** IgG is primarily involved in **Type II** (Cytotoxic, e.g., Autoimmune hemolytic anemia) and **Type III** (Immune-complex, e.g., SLE or Serum Sickness) reactions. While IgG can sometimes play a role in subacute reactions, the rapid systemic collapse seen here is classically IgE-driven. * **Option D (IgA mediated):** IgA is involved in mucosal immunity. It is not a primary mediator of systemic hypersensitivity reactions. **High-Yield Clinical Pearls for NEET-PG:** * **Gell and Coombs Classification:** Remember the mnemonic **ACID** (Type I: **A**naphylactic/Atopic; Type II: **C**ytotoxic; Type III: **I**mmune Complex; Type IV: **D**elayed). * **Drug of Choice:** Intramuscular **Epinephrine (1:1000)** is the first-line treatment for anaphylaxis. * **Diagnostic Marker:** Serum **tryptase** levels can be measured shortly after the event to confirm mast cell degranulation.

Q: Which of the following is NOT a type II hypersensitivity reaction?

Stevens-Johnson syndrome. **Explanation:** Hypersensitivity reactions are classified based on the immune mechanism involved. **Type II hypersensitivity** (Cytotoxic) involves IgG or IgM antibodies binding to antigens on specific cell surfaces or tissues, leading to cell destruction via the complement system or phagocytosis. **Why Stevens-Johnson Syndrome (SJS) is the correct answer:** SJS is a **Type IV (Delayed-type) hypersensitivity reaction**, specifically a T-cell mediated cytotoxic response. It involves the activation of CD8+ cytotoxic T-lymphocytes and Natural Killer cells, which release proteins like granulysin and perforin. This leads to widespread keratinocyte apoptosis and epidermal detachment. It is not mediated by antibodies, which is the hallmark of Type II. **Analysis of incorrect options (Type II Reactions):** * **Drug-induced hemolytic anemia:** Drugs (like penicillin) act as haptens, binding to RBC membranes. Antibodies then target these drug-coated cells, leading to hemolysis. * **Drug-induced thrombocytopenia:** Similar to hemolytic anemia, drugs bind to platelets, triggering antibody-mediated destruction. * **Hemolytic disease of the newborn (HDN):** Maternal IgG antibodies cross the placenta and attack fetal Rh+ red blood cells. **NEET-PG High-Yield Pearls:** * **Mnemonic for Hypersensitivity:** **ACID** (Type I: **A**llergic/Anaphylactic; Type II: **C**ytotoxic; Type III: **I**mmune-Complex; Type IV: **D**elayed). * **SJS vs. TEN:** They are differentiated by the percentage of body surface area (BSA) involved: SJS 30%. * **Common SJS Triggers:** Sulfonamides, Antiepileptics (Phenytoin, Carbamazepine), and Allopurinol.

Q: Type II hypersensitivity is mediated by which component?

Antibody-mediated. **Explanation:** Type II hypersensitivity is primarily defined as **Antibody-mediated (Cytotoxic) hypersensitivity**. It occurs when IgG or IgM antibodies bind to specific antigens located on the surface of cells or within the extracellular matrix. This binding leads to cell destruction or dysfunction through three main pathways: opsonization/phagocytosis, complement-mediated lysis, or antibody-dependent cellular cytotoxicity (ADCC). **Analysis of Options:** * **Option B (Correct):** The hallmark of Type II is the direct binding of antibodies to fixed antigens on target cells. Examples include Autoimmune Hemolytic Anemia and Myasthenia Gravis. * **Option A (Incorrect):** While the **Complement system** is often *activated* during a Type II reaction (leading to the Membrane Attack Complex), it is an effector mechanism triggered by the initial antibody binding, not the primary mediator itself. * **Option C (Incorrect):** **Immune complex-mediated** refers to **Type III hypersensitivity**, where soluble antigen-antibody complexes circulate and deposit in tissues (e.g., SLE, Serum Sickness). * **Option D (Incorrect):** **Cell-mediated** refers to **Type IV (Delayed) hypersensitivity**, which involves T-lymphocytes and macrophages rather than antibodies (e.g., Mantoux test, Contact dermatitis). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (ACID):** **A**naphylactic (I), **C**ytotoxic (II), **I**mmune-Complex (III), **D**elayed (IV). * **Key Examples of Type II:** Erythroblastosis Fetalis (Rh incompatibility), Goodpasture syndrome, Pemphigus vulgaris, and Rheumatic fever. * **Distinction:** Type II involves **fixed** antigens; Type III involves **soluble** antigens. * **Special Type II:** Graves’ disease and Myasthenia Gravis are "Type II non-cytotoxic" because the antibody alters cell function without killing the cell.

Q: Wheal and flare reaction is what type of hypersensitivity reaction?

Type I. **Explanation:** The **Wheal and Flare reaction** is the classic clinical manifestation of **Type I (Immediate) Hypersensitivity**. **Why Type I is Correct:** Type I hypersensitivity is mediated by **IgE antibodies** bound to the surface of mast cells and basophils. Upon re-exposure to an allergen, cross-linking of these IgE molecules triggers degranulation, releasing primary mediators like **histamine**. * **The Wheal:** Histamine increases vascular permeability, leading to localized edema (soft swelling). * **The Flare:** Histamine causes vasodilation of surrounding arterioles, resulting in erythema (redness). This reaction typically occurs within minutes, which is why it is used in "Skin Prick Tests" to identify allergens. **Why Other Options are Incorrect:** * **Type II (Antibody-mediated):** Involves IgG or IgM attacking antigens on specific cell surfaces or tissues (e.g., Erythroblastosis fetalis, Myasthenia gravis). It does not produce an immediate wheal. * **Type III (Immune-complex mediated):** Caused by the deposition of antigen-antibody complexes in tissues, leading to complement activation (e.g., Arthus reaction, SLE). The Arthus reaction is inflammatory but occurs over 4–10 hours, not minutes. * **Type IV (Delayed-type):** Mediated by T-cells rather than antibodies. The reaction (e.g., Mantoux test) takes 48–72 hours to develop and is characterized by induration rather than a soft wheal. **High-Yield Clinical Pearls for NEET-PG:** * **Coombs and Gell Classification:** Type I (Anaphylactic), Type II (Cytotoxic), Type III (Immune-complex), Type IV (Delayed). * **Key Cells:** Mast cells are the central effector cells in Type I reactions. * **Common Examples of Type I:** Anaphylaxis, Urticaria, Atopic dermatitis, and Allergic rhinitis. * **The Arthus Reaction (Type III)** is often confused with the Wheal and Flare; remember that Arthus is delayed (hours) and involves localized vasculitis.

Question 1

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

Accepted Answer

Di George syndrome

Answer

Autoimmune polyglandular syndrome

Answer

Pendred syndrome

Answer

Lesch-Nyhan syndrome

Question 2

A 40-year-old man presents with a chronic cough and fever for several months. Chest radiography shows a diffuse reticulonodular pattern. Microscopic examination of a transbronchial biopsy reveals focal areas of inflammation containing epithelioid cell granulomas, Langhans giant cells, and lymphocytes. These findings are typical for which of the following types of hypersensitivity immunologic responses?

Accepted Answer

Type IV

Answer

Type II

Answer

Type III

Answer

Type I

Question 3

All of the following statements regarding Antineutrophil Cytoplasmic Antibodies (ANCA) are true, EXCEPT:

Accepted Answer

There are three principal classifications of ANCA.

Answer

Proteinase-3, found in neutrophil azurophilic granules, is the primary antigen for cANCA.

Answer

Myeloperoxidase is the main target antigen for pANCA.

Answer

A pANCA staining pattern is linked to nonvasculitic conditions, including rheumatic and other autoimmune diseases.

Question 4

A patient presents with generalized edema, sweating, flushing, tachycardia, and fever after a bee sting. What type of hypersensitivity reaction is most likely responsible?

Accepted Answer

IgE mediated reaction

Answer

T cell mediated cytotoxicity

Answer

IgG mediated reaction

Answer

IgA mediated hypersensitivity reaction

Question 5

Which of the following tests should be done to optimize graft uptake in bone marrow transplant?

Accepted Answer

HLA matching

Answer

Blood grouping

Answer

Culture for infection

Answer

All of the above

Question 6

Which of the following is NOT a type II hypersensitivity reaction?

Accepted Answer

Stevens-Johnson syndrome

Answer

Drug-induced hemolytic anemia

Answer

Drug-induced thrombocytopenia

Answer

Hemolytic disease of the newborn

Question 7

Type II hypersensitivity is mediated by which component?

Accepted Answer

Antibody-mediated

Answer

Complement-mediated

Answer

Immune complex-mediated

Answer

Cell-mediated

Question 8

Which HLA association is seen with Myasthenia gravis?

Accepted Answer

HLA-B8

Answer

HLA-B27

Answer

HLA-B51

Answer

HLA-B47

Question 9

A skin biopsy study of a Systemic Lupus Erythematosus (SLE) patient, using C-labeled human IgG antiserum, shows deposition of irregular particles at the dermoepidermal junction. What does this finding indicate?

Accepted Answer

Immune complex deposits

Answer

Anti-nuclear antibody

Answer

Anti-collagen antibody

Answer

Anti-epithelial antibody

Question 10

Wheal and flare reaction is what type of hypersensitivity reaction?

Accepted Answer

Type I

Answer

Type II

Answer

Type III

Answer

Type IV

Immunopathology — MCQs

Immunopathology — MCQs

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