Immunopathology Practice Questions

Q: A 9-year-old girl receives an intradermal tuberculin injection and later develops an indurated, erythematous papule 12 mm in diameter. This reaction is an example of which of the following?

Type IV hypersensitivity. ### Explanation **Correct Option: D. Type IV hypersensitivity** The clinical scenario describes a classic **Mantoux (Tuberculin) test** reaction. Type IV hypersensitivity, also known as **Delayed-Type Hypersensitivity (DTH)**, is mediated by T-lymphocytes rather than antibodies. Upon intradermal injection of PPD (Purified Protein Derivative), sensitized **Th1 cells** release cytokines (IFN-γ, IL-2), which recruit and activate macrophages. This process takes **48–72 hours** to manifest as the indurated papule described. **Analysis of Incorrect Options:** * **A. Antibody-dependent cell-mediated cytotoxicity (ADCC):** This is a mechanism associated with **Type II hypersensitivity**, where NK cells or macrophages kill target cells coated with IgG antibodies (e.g., transplant rejection). * **B. Local anaphylaxis:** This refers to **Type I hypersensitivity**, which is IgE-mediated and occurs within minutes (immediate) due to mast cell degranulation. * **C. T-cell mediated cytotoxicity:** While also a form of Type IV hypersensitivity, this specifically involves **CD8+ T-cells** directly killing target cells (e.g., viral infections or contact dermatitis). The tuberculin reaction is primarily a **CD4+ Th1-mediated** inflammatory response. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypersensitivity (Gell & Coombs):** **A**cid (Type I: **A**llergic/Anaphylactic), **C**ytotoxic (Type II), **I**mmune-Complex (Type III), **D**elayed (Type IV). * **Type IV Examples:** Mantoux test, Contact dermatitis (Nickel, Poison Ivy), Lepromin test, and Granuloma formation (Tuberculosis, Sarcoidosis). * **Key Cells:** The hallmark of Type IV is the absence of antibodies; it is entirely **cell-mediated**. * **Induration vs. Erythema:** In a Mantoux test, only the **induration** (palpable hardness) is measured, not the erythema (redness).

Q: Which of the following represents a Type 4 hypersensitivity reaction?

Contact dermatitis. ### Explanation **Correct Answer: D. Contact dermatitis** **Mechanism of Type 4 Hypersensitivity:** Type 4 hypersensitivity is a **delayed-type hypersensitivity (DTH)** mediated by **T-lymphocytes** (CD4+ Th1 cells or CD8+ cytotoxic T cells) rather than antibodies. In **Contact Dermatitis** (e.g., reaction to nickel, poison ivy, or cosmetics), small molecules called haptens penetrate the skin and bind to self-proteins. These are processed by Langerhans cells and presented to T cells. Upon re-exposure, memory T cells release cytokines (IFN-γ, IL-2), leading to macrophage activation and keratinocyte damage. The reaction typically peaks **48–72 hours** after exposure. **Analysis of Incorrect Options:** * **A. Glomerulonephritis & B. Serum sickness:** These are classic examples of **Type 3 (Immune-complex mediated)** hypersensitivity. They involve the deposition of antigen-antibody complexes in tissues, which activates the complement system and leads to neutrophil-mediated inflammation. * **C. Myasthenia gravis:** This is a **Type 2 (Antibody-mediated)** hypersensitivity. Specific IgG antibodies bind to acetylcholine receptors at the neuromuscular junction, leading to receptor degradation or blockade. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypersensitivity (Gell & Coombs):** **ACID** (Type 1: **A**naphylactic/Atopic; Type 2: **C**ytotoxic; Type 3: **I**mmune-complex; Type 4: **D**elayed). * **Other Type 4 Examples:** Mantoux (Tuberculin) test, Lepromin test, Graft rejection (cellular), and Granuloma formation (e.g., Sarcoidosis, TB). * **Key Cells:** Type 4 is the only hypersensitivity that **cannot** be transferred by serum (antibodies); it requires sensitized T-cells.

Q: HLA-B47 is associated with which of the following conditions?

Congenital adrenal hyperplasia. **Explanation:** The correct answer is **Congenital Adrenal Hyperplasia (CAH)**. The association between HLA (Human Leukocyte Antigen) alleles and specific diseases is a high-yield topic in immunopathology. **HLA-B47** is specifically linked to 21-hydroxylase deficiency, the most common cause of Congenital Adrenal Hyperplasia [1]. This association occurs because the gene encoding the 21-hydroxylase enzyme (*CYP21A2*) is located within the Major Histocompatibility Complex (MHC) locus on Chromosome 6, leading to strong linkage disequilibrium between the HLA-B47 allele and the defective enzyme gene. **Analysis of Incorrect Options:** * **A. Myasthenia gravis:** This autoimmune neuromuscular disorder is most commonly associated with **HLA-DR3** and **HLA-B8**. * **B. Behcet’s disease:** This systemic vasculitis has a very strong and classic association with **HLA-B51**. * **C. Abacavir hypersensitivity:** A critical pharmacogenetic association exists between the antiretroviral drug abacavir and **HLA-B*57:01**. Testing for this allele is mandatory before starting the drug to prevent life-threatening hypersensitivity reactions. **High-Yield Clinical Pearls for NEET-PG:** * **HLA-B27:** Associated with Seronegative Spondyloarthropathies (Ankylosing spondylitis, Reiter’s syndrome, Psoriatic arthritis, Enteropathic arthritis). * **HLA-DR3/DR4:** Associated with Type 1 Diabetes Mellitus. * **HLA-DQ2/DQ8:** Associated with Celiac disease. * **HLA-DR2:** Associated with Multiple Sclerosis and Goodpasture syndrome. * **HLA-DR4:** Associated with Rheumatoid Arthritis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1130-1133.

Question 1

A 14-month-old child has had multiple infections since birth, including pneumonia with Pseudomonas aeruginosa, adenovirus, and Aspergillus fumigatus; diarrhea with Isospora belli; otitis media with Haemophilus influenzae; and urinary tract infection with Candida albicans. Laboratory studies show hemoglobin, 13.2 g/dL; hematocrit, 39.7%; platelet count, 239,100/mm3; and WBC count, 3450/mm3 with 85% segmented neutrophils, 6% bands, 2% lymphocytes, and 7% monocytes. Serum immunoglobulin levels are IgG, 118 mg/dL; IgM, 14 mg/dL; and IgA, 23 mg/dL. The child dies of pneumonia. At autopsy, a hypoplastic thymus, small lymph nodes that lack germinal centers, and scant gut-associated lymphoid tissue are seen. Which of the following is the most likely cause of this disease?

Accepted Answer

Adenosine deaminase deficiency

Answer

Abnormal CD40 ligand

Answer

BTK gene mutation

Answer

Chromosome 22q11 deletion

Question 2

A 9-year-old girl receives an intradermal tuberculin injection and later develops an indurated, erythematous papule 12 mm in diameter. This reaction is an example of which of the following?

Accepted Answer

Type IV hypersensitivity

Answer

Antibody-dependent cell-mediated cytotoxicity

Answer

Local anaphylaxis

Answer

T-cell mediated cytotoxicity

Question 3

Which Human Leukocyte Antigen (HLA) class is associated with CD4?

Accepted Answer

HLA class II

Answer

HLA class I

Answer

HLA class III

Answer

All of them

Question 4

What condition is indicated by a lymphocyte phenotype test?

Accepted Answer

Severe Combined Immunodeficiency (SCID)

Answer

Agammaglobulinemia

Answer

Sepsis

Answer

Acute leukemia

Question 5

All of the following regarding acute graft rejection are true, except?

Accepted Answer

Preformed antibodies against graft are the main causative factor.

Answer

CD8+ T-cells directly destroy the graft.

Answer

It is the principal cause of early graft failure.

Answer

Cytokines secreted by CD4+ T-cells cause inflammation which destroys the graft.

Question 6

Interleukin-6 is persistently raised in which of the following conditions?

Accepted Answer

Behcet's disease

Answer

Kawasaki disease

Answer

Viral encephalitis

Answer

HIV encephalitis

Question 7

Which of the following represents a Type 4 hypersensitivity reaction?

Accepted Answer

Contact dermatitis

Answer

Glomerulonephritis

Answer

Serum sickness

Answer

Myasthenia gravis

Question 8

TRALI is usually due to?

Accepted Answer

High titre anti-HLA antibodies in donor plasma

Answer

High titre anti-HLA antibodies in recipient plasma

Answer

Low titre anti-HLA antibodies in donor plasma

Answer

HPA-la on the platelet glycoprotein IIa receptor

Question 9

Common variable hypogammaglobulinemia shows which of the following?

Accepted Answer

Normal B cell count

Answer

Decreased B cell count

Answer

Increased B cell count

Answer

Absent B cells

Question 10

HLA-B47 is associated with which of the following conditions?

Accepted Answer

Congenital adrenal hyperplasia

Answer

Myasthenia gravis

Answer

Behcet's disease

Answer

Abacavir hypersensitivity

Immunopathology — MCQs

Immunopathology — MCQs

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