Immunopathology Practice Questions

Q: Which HLA allele is associated with Graves' disease?

B8. **Explanation:** The association between the Human Leukocyte Antigen (HLA) system and autoimmune diseases is a high-yield topic for NEET-PG. Graves' disease, an autoimmune hyperthyroidism caused by stimulating antibodies against the TSH receptor, is strongly linked to **HLA-B8** and **HLA-DR3**. These alleles are often inherited together as part of a conserved extended haplotype, predisposing individuals to various organ-specific autoimmune conditions. **Analysis of Options:** * **HLA-B8 (Correct):** This Class I MHC allele is classically associated with Graves' disease, Myasthenia gravis, and Celiac disease. * **HLA-DR4:** This is primarily associated with **Rheumatoid Arthritis**, Type 1 Diabetes Mellitus, and Pemphigus vulgaris. (Mnemonic: *DR4 for 4-walled joints*). * **HLA-B27:** This is the most famous association in PG exams, linked to **Seronegative Spondyloarthropathies** (PAIR: Psoriatic arthritis, Ankylosing spondylitis, Inflammatory bowel disease-associated arthritis, and Reactive arthritis). * **HLA-DQ8:** This allele, along with DQ2, is specifically associated with **Celiac disease**. **High-Yield Clinical Pearls for NEET-PG:** * **HLA-DR3 Association:** If HLA-B8 is not in the options, look for **DR3**, as they are frequently linked in Graves' disease and Systemic Lupus Erythematosus (SLE). * **Narcolepsy:** Associated with **HLA-DR2/DQB1*0602** (Strongest known HLA association). * **Multiple Sclerosis:** Associated with **HLA-DR2**. * **Behcet’s Disease:** Associated with **HLA-B51**.

Q: What is true about Chediak Higashi syndrome?

Impaired bacteriolysis. **Explanation:** **Chediak-Higashi Syndrome (CHS)** is a rare, autosomal recessive immunodeficiency disorder characterized by a defect in the **LYST gene** (Lysosomal Trafficking Regulator). This defect leads to impaired vesicle fusion and the formation of pathognomonic **giant lysosomal granules** in neutrophils and other cells [1]. 1. **Why "Impaired Bacteriolysis" is correct:** In CHS, although neutrophils can phagocytose bacteria, the fusion of phagosomes with the giant lysosomes is defective [1]. This prevents the delivery of lytic enzymes and reactive oxygen species to the phagosome, resulting in a failure to kill ingested bacteria (impaired bacteriolysis). This leads to recurrent pyogenic infections [1]. 2. **Why other options are incorrect:** * **A. Neutrophilia:** CHS is actually associated with **neutropenia** [1]. The giant granules cause ineffective hematopoiesis in the bone marrow and increased peripheral destruction of fragile neutrophils. * **C. Autosomal Dominant:** CHS follows an **Autosomal Recessive** inheritance pattern [1]. * **D. Associated with Polycythemia:** There is no association with polycythemia. Patients often present with pancytopenia, especially during the "accelerated phase" (lymphohistiocytic infiltration). **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Tetrad:** Partial oculocutaneous albinism, recurrent pyogenic infections, progressive neurological abnormalities, and bleeding tendencies (due to dense granule deficiency in platelets) [1]. * **Peripheral Smear:** Look for **massive/giant azurophilic granules** in the cytoplasm of neutrophils and precursors [1]. * **Accelerated Phase:** A life-threatening, lymphoma-like syndrome characterized by hepatosplenomegaly and lymphadenopathy. **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: Allergic reactions are a type of hypersensitivity. To which type of hypersensitivity reaction do common allergies like hay fever and asthma belong?

Type I. **Explanation:** **Correct Answer: A. Type I Hypersensitivity** Type I hypersensitivity, also known as **Immediate Hypersensitivity**, is mediated by **IgE antibodies**. When a predisposed individual is exposed to an allergen (like pollen or dander), IgE binds to the surface of **mast cells and basophils** via Fc receptors. Upon re-exposure, the allergen cross-links these IgE molecules, triggering degranulation and the release of vasoactive amines like **histamine**. This leads to rapid clinical manifestations such as vasodilation and bronchoconstriction, characteristic of hay fever, extrinsic asthma, and anaphylaxis. **Why the other options are incorrect:** * **Type II (Cytotoxic):** Mediated by **IgG or IgM** antibodies directed against antigens on specific cell surfaces or tissues (e.g., ABO incompatibility, Rh incompatibility, Myasthenia Gravis). * **Type III (Immune-Complex):** Caused by the deposition of **antigen-antibody complexes** in tissues, leading to complement activation and inflammation (e.g., SLE, Post-streptococcal glomerulonephritis, Arthus reaction). * **Type IV (Delayed-type):** This is **cell-mediated** (T-cells), not antibody-mediated. It takes 48–72 hours to manifest (e.g., Mantoux test, contact dermatitis, graft rejection). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (ACID):** **A**naphyalctic (I), **C**ytotoxic (II), **I**mmune-Complex (III), **D**elayed (IV). * **Key Cells:** Mast cells are the primary effectors in Type I; T-lymphocytes/Macrophages in Type IV. * **Atopy:** Refers to the genetic predisposition to develop Type I reactions. * **Coombs and Gell Classification:** This is the formal name for the four-type classification system of hypersensitivity.

Question 1

Which of the following conditions is NOT associated with HLA-B27?

Accepted Answer

Systemic lupus erythematosus (SLE)

Answer

Ankylosing spondylitis

Answer

Juvenile rheumatoid arthritis

Answer

Reactive arthritis

Question 2

Which HLA allele is associated with Graves' disease?

Accepted Answer

B8

Answer

DR4

Answer

B27

Answer

DQ8

Question 3

What is true about Chediak Higashi syndrome?

Accepted Answer

Impaired bacteriolysis

Answer

Neutrophilia

Answer

Autosomal dominant

Answer

Associated with polycythemia

Question 4

All of the following are true regarding innate immunity except:

Accepted Answer

In Bruton's agammaglobulinemia, opsonization is impaired.

Answer

NADPH oxidase generates superoxide ions.

Answer

Chediak-Higashi syndrome is due to defective phagolysosome formation.

Answer

Myeloperoxidase action is mainly due to hypochlorous acid (HOCl).

Question 5

Human immunodeficiency virus (HIV) affects the immune response. What is the primary change it brings about?

Accepted Answer

Defect in cell-mediated immunity

Answer

A gammaglobulinemia

Answer

Defect in complement system

Answer

Defect in natural killer cells

Question 6

Autoimmunity is caused by which of the following mechanisms?

Accepted Answer

Defective negative selection of T-cells in the thymus

Answer

The pressure of forbidden clones

Answer

Expression of cryptic antigens

Answer

Inappropriate expression of MHC proteins

Question 7

Allergic reactions are a type of hypersensitivity. To which type of hypersensitivity reaction do common allergies like hay fever and asthma belong?

Accepted Answer

Type I

Answer

Type II

Answer

Type III

Answer

Type IV

Question 8

An 8-year-old boy presents with recurrent infections since infancy, hepatosplenomegaly, lymphadenopathy, and eczema-like dermatitis. Peripheral blood smear examination during a staphylococcal infection reveals impaired or absent neutrophil bactericidal capacity. What is the most likely cause of this child's illness?

Accepted Answer

Defect in the enzyme NADPH oxidase

Answer

Defect in the enzyme adenosine deaminase (ADA)

Answer

Defect in the IL-2 receptor

Answer

Developmental defect at the pre-B stage

Question 9

All of the following are disorders of phagocyte function, except?

Accepted Answer

X-linked SCID

Answer

Chronic granulomatous disease

Answer

Chediak-Higashi syndrome

Answer

Myeloperoxidase deficiency

Question 10

What is the best investigation for diagnosing amyloidosis?

Accepted Answer

Rectal biopsy

Answer

Colonoscopy

Answer

CT scan

Answer

Upper GI endoscopy

Immunopathology — MCQs

Immunopathology — MCQs

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