Immunopathology Practice Questions

Q: Which of the following is true regarding Chediak-Higashi syndrome?

Defect in phagocytosis. **Explanation:** **Chediak-Higashi Syndrome (CHS)** is a rare autosomal recessive disorder characterized by a defect in the **LYST gene** (Lysosomal Trafficking Regulator). This mutation leads to impaired microtubule formation and disordered intracellular trafficking of organelles. 1. **Why the correct answer is right:** The primary defect in CHS is the failure of **phagosome-lysosome fusion** [1]. While neutrophils can ingest bacteria, they cannot discharge lysosomal enzymes into the phagocytic vacuoles to kill them. This results in a profound **defect in phagocytosis** (specifically, intracellular killing). Morphologically, this is visualized as **giant peroxidase-positive granules** in neutrophils [1], which represent fused, dysfunctional lysosomes. 2. **Why the incorrect options are wrong:** * **Neutropenia:** While mild neutropenia can occur due to ineffective granulopoiesis in the bone marrow [1], the *hallmark* functional defect is the qualitative phagocytic failure, not a primary quantitative lack of cells. * **Agammaglobulinemia/IgA deficiency:** CHS is a defect of the innate immune system (phagocytes and NK cells). Humoral immunity (B-cells and antibody production) is generally intact, making these options incorrect. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Partial oculocutaneous **albinism**, recurrent pyogenic infections (Staph/Strep), and progressive neurologic abnormalities [1]. * **Hematologic finding:** Giant lysosomal granules in leukocytes and platelets (causing mild bleeding tendencies) [1]. * **The "Accelerated Phase":** A dreaded complication involving a hemophagocytic lymphohistiocytosis (HLH)-like syndrome, often triggered by EBV. * **Diagnosis:** Peripheral blood smear showing giant granules [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.

Q: What is the term for an antigen-antibody reaction due to the presence of antibody at the surface of a cell?

Type I hypersensitivity. **Explanation:** The correct answer is **Type I hypersensitivity**. This reaction is characterized by the presence of pre-formed **IgE antibodies** bound to the surface of **mast cells and basophils** via high-affinity Fc receptors (FcεRI). When a specific antigen (allergen) cross-links these surface-bound antibodies, it triggers immediate degranulation and the release of pharmacological mediators like histamine. **Why the other options are incorrect:** * **Type II (Cytotoxic):** Here, antibodies (IgG/IgM) are directed against antigens present **on the cell surface** or extracellular matrix. The antibody is in the serum and attacks the cell; it is not "at the surface" as a receptor for the antigen. * **Type III (Immune-complex):** This involves the formation of **soluble** antigen-antibody complexes in the circulation, which later deposit in tissues (e.g., kidneys, joints) and trigger inflammation. * **Type IV (Delayed-type):** This is a **cell-mediated** response involving T-lymphocytes (Th1, Th17, or CD8+), not antibodies. **NEET-PG High-Yield Pearls:** * **Type I** is the only "Immediate" hypersensitivity; others take hours to days. * **Key Mediators:** Histamine (pre-formed), Leukotrienes (LTC4, LTD4—more potent than histamine), and Eosinophilic Chemotactic Factor (ECF-A). * **Clinical Examples:** Anaphylaxis, Atopy, Urticaria, and Extrinsic Asthma. * **PK Reaction:** The Prausnitz-Küstner reaction is a classic demonstration of Type I hypersensitivity involving the transfer of serum containing IgE.

Q: Which of the following is NOT a feature of AIDS-related lymphadenopathy?

Haematoxylin bodies. **Explanation:** The question asks for the feature **not** associated with AIDS-related lymphadenopathy. **Correct Option: C. Haematoxylin bodies** Haematoxylin bodies (also known as Gross bodies) are rounded, amorphous, lilac-colored structures found in the heart, kidneys, or lymph nodes. They represent denatured nuclear material coated with antibodies and are a **pathognomonic feature of Systemic Lupus Erythematosus (SLE)**, not HIV/AIDS. **Analysis of Incorrect Options (Features of AIDS Lymphadenopathy):** The lymph node changes in HIV progress through stages known as **PGL (Persistent Generalized Lymphadenopathy)**: * **Option A (Florid reactive hyperplasia):** This is the hallmark of the early stage of HIV infection, where HIV preferentially targets CD4+ cells, leading to eventual lymphocyte depletion [1]. Lymph nodes show massive, irregularly shaped germinal centers. * **Option B (Follicle lysis):** This is a characteristic finding where small lymphocytes from the mantle zone "invade" and break up the germinal centers (the "moth-eaten" appearance). It signifies the transition toward follicular involution. * **Option D (Monocytoid B cells):** In the early stages of HIV, there is often a prominent proliferation of monocytoid B cells within the subcapsular and trabecular sinuses. **NEET-PG High-Yield Pearls:** 1. **Stages of HIV Lymphadenopathy:** Hyperplasia (Stage I) → Follicle Lysis (Stage II) → Follicular Involution/Depletion (Stage III) [1]. 2. **Warthin-Finkeldey Giant Cells:** While classically associated with Measles, these can also be seen in the hyperplastic lymph nodes of HIV patients. 3. **Castleman Disease:** HIV-positive patients have an increased risk of the multicentric variant of Castleman disease, often associated with HHV-8.

Q: Which is the most common complement protein deficiency?

C2. **Explanation:** The complement system is a vital component of innate immunity. Among all the inherited complement deficiencies, **C2 deficiency** is the most common (Option B). **Why C2 is the correct answer:** C2 deficiency is an autosomal recessive condition and is the most frequently reported complement protein defect in Western populations. It is often associated with an increased risk of autoimmune diseases, particularly **Systemic Lupus Erythematosus (SLE)**, because C2 is essential for the classical pathway's role in clearing immune complexes. Interestingly, many individuals with C2 deficiency remain asymptomatic because the alternative pathway remains intact to handle bacterial pathogens. **Analysis of Incorrect Options:** * **C1 (Option A):** Deficiency of C1 (C1q, C1r, or C1s) is rare. It is most strongly associated with the development of SLE (over 90% of C1q-deficient individuals develop SLE). [1] * **C3 (Option C):** C3 is the central molecule for all three complement pathways. While not the most common, it is the **most severe** deficiency. Patients present with recurrent, life-threatening pyogenic bacterial infections (e.g., *S. pneumoniae*) and Type III hypersensitivity reactions. * **C4 (Option D):** C4 deficiency is also associated with SLE-like syndromes but is less common than C2 deficiency. **NEET-PG High-Yield Pearls:** 1. **Most common deficiency:** C2. 2. **Most severe deficiency:** C3. 3. **C1 esterase inhibitor deficiency:** Leads to **Hereditary Angioedema** (characterized by low C4 levels). 4. **C5-C9 (MAC) deficiency:** Increases susceptibility to **Neisseria** infections (meningitis and gonorrhea). 5. **CH50 Assay:** Used to screen the classical pathway; it will be low/zero in C1-C8 deficiencies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 228.

Question 1

Which of the following is true regarding Chediak-Higashi syndrome?

Accepted Answer

Defect in phagocytosis

Answer

Neutropenia

Answer

Agammaglobulinemia

Answer

IgA deficiency

Question 2

Which of the following antigen-presenting cells does not express MHC Class II molecules?

Accepted Answer

Follicular cells of the thyroid

Answer

Microglia of the brain

Answer

Langerhans cells of the skin

Answer

Dendritic cells of lymphoid tissues

Question 3

NADPH oxidase deficiency causes which of the following conditions?

Accepted Answer

Chronic granulomatous disease

Answer

Chédiak-Higashi syndrome

Answer

Leukocyte adhesion defect type 1

Answer

Leukocyte adhesion defect type 2

Question 4

Steven Johnson Syndrome is seen with what kind of hypersensitivity reaction?

Accepted Answer

Type 4

Answer

Type 1

Answer

Type 2

Answer

Type 3

Question 5

What is the term for an antigen-antibody reaction due to the presence of antibody at the surface of a cell?

Accepted Answer

Type I hypersensitivity

Answer

Type II hypersensitivity

Answer

Type III hypersensitivity

Answer

Type IV hypersensitivity

Question 6

Anaphylactic shock is caused by which type of hypersensitivity reaction?

Accepted Answer

Type I

Answer

Type II

Answer

Type III

Answer

Type IV

Question 7

In patients with myasthenia gravis, the characteristic autoantibody is directed against which of the following?

Accepted Answer

Acetylcholine receptors

Answer

Acetylcholine

Answer

Acetylcholine vesicles in the nerve terminal

Answer

Actin-myosin complex of the muscle

Question 8

Which of the following is NOT a feature of AIDS-related lymphadenopathy?

Accepted Answer

Haematoxylin bodies

Answer

Florid reactive hyperplasia

Answer

Follicle lysis

Answer

Collection of monocytoid B cells in sinuses

Question 9

Which is the most common complement protein deficiency?

Accepted Answer

C2

Answer

C1

Answer

C3

Answer

C4

Question 10

Which of the following statements regarding the Human Leukocyte Antigen (HLA) complex is incorrect?

Accepted Answer

Class-I molecules are homodimers, whereas Class-II molecules are heterodimers.

Answer

Class-I antigens are expressed in all nucleated cells and platelets.

Answer

Class-II molecules are involved in the induction of helper T-cells.

Answer

Class-I molecules are involved in the induction of cytotoxic T-cells.

Immunopathology — MCQs

Immunopathology — MCQs

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