Immunopathology Practice Questions

Q: What is the distinguishing characteristic of a positive delayed-type hypersensitivity skin test?

Induration. **Explanation:** **Delayed-Type Hypersensitivity (DTH)** is a Type IV hypersensitivity reaction mediated by T-cells (specifically Th1 cells) rather than antibodies. **Why Induration is the correct answer:** The hallmark of a positive DTH skin test (such as the Mantoux/Tuberculin test) is **induration** (a firm, raised area). This occurs because sensitized T-cells are recruited to the site of antigen injection, where they release cytokines (IFN-γ, TNF-α). These cytokines activate macrophages and cause an influx of mononuclear cells and fibrin deposition in the extravascular space. This cellular infiltration and local edema create the characteristic firmness or "hardness" known as induration. **Why other options are incorrect:** * **Erythema:** While redness (erythema) often accompanies the reaction due to vasodilation, it is **not** used for measurement. Erythema can occur in Type I (immediate) reactions or non-specific irritation; only induration reflects the T-cell mediated cellular response. * **Necrosis:** This is a sign of an exaggerated or severe reaction (e.g., a strongly positive Mantoux test), but it is not the standard distinguishing characteristic of a positive test. * **Vasculitis:** This is typically associated with Type III hypersensitivity (Immune-complex mediated), such as the Arthus reaction, involving complement activation and neutrophil infiltration, rather than T-cell responses. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** DTH reactions typically peak at **48–72 hours** (hence "delayed"). * **Key Cells:** The "effector" cell is the **Macrophage**, but the "initiator" is the **CD4+ Th1 cell**. * **Examples:** Tuberculin test (Mantoux), Lepromin test, and Contact Dermatitis (e.g., Nickel or Poison Ivy). * **Measurement:** In a Mantoux test, always measure the **transverse diameter of induration**, not the erythema.

Q: Which complement component is encoded by the given site?

Complement component C3. ***Complement component C3*** - **C3** is encoded on **chromosome 19p13.3** and serves as the central component of the complement system, playing a crucial role in both classical and alternative pathways. - It is the most abundant complement protein in plasma and undergoes cleavage to form **C3a** (anaphylatoxin) and **C3b** (opsonin) during complement activation. *Tumor necrosis factor* - **TNF-α** is encoded on **chromosome 6p21.3** within the **MHC class III region**, not on chromosome 19. - It functions as a pro-inflammatory cytokine involved in **systemic inflammation** and **apoptosis**, not as a complement component. *Interleukin-2* - **IL-2** is encoded on **chromosome 4q26-q27**, which is distinct from the complement C3 locus. - It serves as a **T-cell growth factor** promoting lymphocyte proliferation and activation, not involved in complement cascade. *Beta-2 microglobulin* - **β2-microglobulin** is encoded on **chromosome 15q21.1**, not on chromosome 19 where C3 is located. - It forms part of **MHC class I molecules** and is involved in antigen presentation, not complement function.

Question 1

Nude mice are able to accept xenografts because they lack which type of immune cell?

Accepted Answer

T cells

Answer

B cells

Answer

NK cells

Answer

LAK cells

Question 2

All of the following statements about Ataxia-Telangiectasia are true, except?

Accepted Answer

Selective absence of IgM

Answer

Autosomal Recessive disorder

Answer

Lymphoreticular malignancy

Answer

Progressive Cerebellar ataxia

Question 3

What is the distinguishing characteristic of a positive delayed-type hypersensitivity skin test?

Accepted Answer

Induration

Answer

Erythema

Answer

Necrosis

Answer

Vasculitis

Question 4

In familial Mediterranean fever, which protein undergoes mutation?

Accepted Answer

Pyrin

Answer

Perforin

Answer

Atrial natriuretic factor

Answer

Immunoglobulin light chain

Question 5

The immediate type of hypersensitivity in which histamine does not play a major role is:

Accepted Answer

Arthus reaction

Answer

Urticaria

Answer

Asthma

Answer

Anaphylaxis

Question 6

Epithelial granuloma is caused by which of the following?

Accepted Answer

Helper T-cells

Answer

Neutrophil

Answer

Cytotoxic T-cells

Answer

NK cells

Question 7

Pinch purpura is seen in which of the following conditions?

Accepted Answer

Primary systemic amyloidosis

Answer

Vitamin C deficiency

Answer

Purpura fulminans

Answer

Kawasaki disease

Question 8

What is the most common tumor associated with AIDS?

Accepted Answer

Kaposi's sarcoma

Answer

Carcinoma

Answer

Melanoma

Answer

Ewing's sarcoma

Question 9

A 24-year-old man is infected with HIV during a sexual encounter. During the asymptomatic latent phase of his infection, the virus is actively proliferating and can be found in association with which of the following?

Accepted Answer

Follicular dendritic cells in lymph nodes

Answer

B lymphocytes

Answer

Ganglion cells

Answer

Oligodendrocytes

Question 10

Which complement component is encoded by the given site?

Accepted Answer

Complement component C3

Answer

Tumor necrosis factor

Answer

Interleukin-2

Answer

Beta-2 microglobulin

Immunopathology — MCQs

Immunopathology — MCQs

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