Immunopathology Practice Questions

Q: The prototype of type-II hypersensitivity reaction is:

Autoimmune hemolytic anemia. ### Explanation **Type II Hypersensitivity** (Cytotoxic Hypersensitivity) is mediated by **IgG or IgM** antibodies directed against antigens present on the surface of specific cells or tissues. This leads to cell destruction via the complement system, opsonization (phagocytosis), or antibody-dependent cellular cytotoxicity (ADCC). **Why Autoimmune Hemolytic Anemia (AIHA) is correct:** In AIHA, antibodies (usually IgG) are produced against self-antigens on the **Red Blood Cell (RBC) membrane**. These coated RBCs are then destroyed by splenic macrophages or complement-mediated lysis. This is a classic example of tissue-specific damage, the hallmark of Type II reactions. **Analysis of Incorrect Options:** * **Arthus Reaction (Option A):** This is a localized **Type III** hypersensitivity reaction. It involves the formation of immune complexes (antigen-antibody) that deposit in vessel walls, leading to vasculitis and necrosis. * **Systemic Lupus Erythematosus (Option B):** SLE is the prototype for **Type III** hypersensitivity. It involves circulating immune complexes that deposit in various organs (kidneys, joints, skin), causing systemic inflammation. * **Contact Dermatitis (Option D):** This is a **Type IV** (Delayed-type) hypersensitivity reaction. It is mediated by T-cells (CD4+ and CD8+) rather than antibodies, typically occurring 48–72 hours after exposure to allergens like nickel or poison ivy. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypersensitivity:** **ACID** (Type I: **A**naphylactic/Allergic; Type II: **C**ytotoxic; Type III: **I**mmune Complex; Type IV: **D**elayed). * **Other Type II Examples:** Goodpasture syndrome, Myasthenia Gravis, Graves' disease, and Rheumatic fever. * **Coombs Test:** The Direct Antiglobulin Test (Coombs test) is the gold standard for diagnosing Type II reactions involving RBCs (like AIHA and Erythroblastosis Fetalis).

Q: What is the function of IL-4?

Inhibiting IL-1. **Explanation:** Interleukin-4 (IL-4) is a key cytokine produced primarily by **Th2 cells**, mast cells, and basophils. Its primary role is to drive the humoral immune response. **Why Option A is Correct:** IL-4 acts as an **anti-inflammatory cytokine**. It downregulates the production of pro-inflammatory cytokines like **IL-1**, TNF-alpha, and IL-6. Specifically, IL-4 induces the production of the **IL-1 receptor antagonist (IL-1Ra)**, which competitively inhibits IL-1 activity, thereby limiting the inflammatory damage. **Analysis of Incorrect Options:** * **B. Chemotaxis:** This is primarily the function of **IL-8** (the major neutrophil chemoattractant) and C5a. * **C. Vasodilation:** This is mediated by chemical mediators like **Histamine**, Prostaglandins (PGE2), and Nitric Oxide (NO), rather than IL-4. * **D. Inhibiting Macrophages:** While IL-4 does antagonize the "classical activation" (M1) of macrophages, the most potent inhibitor of macrophage function is **IL-10** and **TGF-beta**. IL-4 actually promotes "alternative activation" (M2) of macrophages, which is involved in tissue repair. **High-Yield Clinical Pearls for NEET-PG:** * **Class Switching:** IL-4 is the primary driver for B-cell class switching to **IgE** and **IgG4**. (Mnemonic: *4-E-G*). * **Th2 Differentiation:** IL-4 promotes the differentiation of naive T-cells (Th0) into Th2 cells while inhibiting Th1 differentiation. * **Atopy:** Overproduction of IL-4 is associated with Type I Hypersensitivity reactions (asthma, eczema, and anaphylaxis). * **Major Anti-inflammatory Cytokines:** Remember **IL-4, IL-10, and TGF-beta**.

Q: Graft versus host reaction is mediated by which of the following?

T lymphocytes. **Explanation:** **Graft-versus-Host Disease (GVHD)** occurs when immunologically competent cells (the graft) recognize the recipient’s (the host) tissues as foreign and mount an immune attack against them. **Why T lymphocytes are correct:** The primary mediators of GVHD are **mature donor T lymphocytes**. For GVHD to occur, three conditions (Billingham’s criteria) must be met: 1. The graft must contain immunologically competent cells (specifically T cells). 2. The recipient must possess antigens lacking in the donor (making the host appear "foreign"). 3. The recipient must be immunocompromised or unable to reject the donor cells. When donor T cells (both CD4+ and CD8+) are infused, they recognize the host’s Major Histocompatibility Complex (MHC) antigens, undergo activation, and cause direct cytotoxic damage and cytokine-mediated inflammation. **Why other options are incorrect:** * **A & D (Macrophages):** While macrophages are involved in the effector phase of inflammation and tissue damage, they are not the primary mediators or initiators of the reaction. GVHD is fundamentally a T-cell-driven process. * **C (B lymphocytes):** B cells produce antibodies. While they may play a minor role in chronic GVHD, the classic graft-versus-host reaction is a **Type IV (Cell-Mediated) Hypersensitivity** response, which is the hallmark of T-cell activity. **High-Yield Clinical Pearls for NEET-PG:** * **Common Sites:** GVHD typically affects the **skin** (rash), **liver** (jaundice/elevated enzymes), and **GIT** (diarrhea). * **Common Scenarios:** Most frequently seen in **Allogeneic Bone Marrow Transplants**. It can also occur after blood transfusions in severely immunocompromised patients. * **Prevention:** To prevent transfusion-associated GVHD, blood products should be **irradiated** to inactivate donor T lymphocytes. * **Acute vs. Chronic:** Acute GVHD occurs within 100 days; Chronic GVHD occurs after 100 days.

Q: Which of the following interleukins is characteristically produced in a T helper cell type 1 (TH1) response?

IL-2. The differentiation of CD4+ T cells into specific subsets is a high-yield topic in immunology. **T helper 1 (TH1)** cells are primarily involved in cell-mediated immunity and the activation of macrophages to destroy intracellular pathogens [1]. **Why IL-2 is Correct:** TH1 cells are characterized by the production of **IL-2**, **IFN-γ (Interferon-gamma)**, and **TNF-β** [2]. * **IL-2** acts as a potent T-cell growth factor, promoting the proliferation of T-cytotoxic (CD8+) cells and NK cells [2]. * The differentiation into the TH1 subset is driven by IL-12 and IFN-γ, under the influence of the master transcription factor **T-bet**. **Why the Other Options are Incorrect:** * **IL-4, IL-5, and IL-10** are characteristic products of the **TH2 response** [1]. * **IL-4:** Induces B-cell class switching to **IgE** and promotes TH2 differentiation (inhibiting TH1) [1], [2]. * **IL-5:** Responsible for the activation and chemotaxis of **eosinophils**, crucial in helminthic infections [1]. * **IL-10:** An anti-inflammatory cytokine that inhibits TH1 cytokine production and MHC II expression, effectively "turning off" the cell-mediated immune response [1]. **NEET-PG High-Yield Pearls:** * **TH1:** Secretes IL-2, IFN-γ; deals with intracellular pathogens (e.g., *M. tuberculosis*); associated with Type IV hypersensitivity. * **TH2:** Secretes IL-4, IL-5, IL-10, IL-13; deals with extracellular parasites and allergens; associated with Type I hypersensitivity [1]. * **Transcription Factors:** TH1 uses **T-bet**, while TH2 uses **GATA-3**. * **Leprosy Link:** Tuberculoid leprosy shows a strong TH1 response (contained), while Lepromatous leprosy shows a dominant TH2 response (disseminated).

Question 1

The prototype of type-II hypersensitivity reaction is:

Accepted Answer

Autoimmune hemolytic anemia

Answer

Arthus reaction

Answer

Systemic Lupus Erythematosus (SLE)

Answer

Contact dermatitis

Question 2

Acute cellular rejection following solid organ transplantation typically occurs within which timeframe?

Accepted Answer

Between 5 to 30 days of transplantation

Answer

Within minutes to hours of transplantation

Answer

Within 48 hours of transplantation

Answer

Beyond 30 days after transplantation

Question 3

Which antibody is commonly seen in antiphospholipid syndrome?

Accepted Answer

Anticardiolipin

Answer

Anti-b2GPI

Answer

ANA

Answer

Anti-Sm

Question 4

What is the function of IL-4?

Accepted Answer

Inhibiting IL-1

Answer

Chemotaxis

Answer

Vasodilation

Answer

Inhibiting macrophages

Question 5

Which of the following is not an example of immune complex disease?

Accepted Answer

Contact dermatitis

Answer

Systemic lupus erythematosus

Answer

Arthus reaction

Answer

Post-streptococcal glomerulonephritis

Question 6

A 40-year-old female presented with hemoptysis and hematuria. Lab studies show the presence of anti-basement membrane antibodies, and the patient's symptoms improved with plasmapheresis. Which of the following diseases is of the same hypersensitivity category as this disease?

Accepted Answer

Myasthenia gravis

Answer

Systemic lupus erythematosus

Answer

Seasonal allergies

Answer

Poison ivy rash

Question 7

Graft versus host reaction is mediated by which of the following?

Accepted Answer

T lymphocytes

Answer

Macrophages

Answer

B lymphocytes

Answer

T lymphocytes and macrophages

Question 8

MHC Class I molecules are primarily involved in the presentation of which type of antigens?

Accepted Answer

Endogenous antigens

Answer

Exogenous antigens

Answer

Self antigens not presented to T cells

Answer

Bacterial antigens presented to B cells

Question 9

Nude mice are used in genetics research due to which of the following properties?

Accepted Answer

Xenografts can be sustained for weeks

Answer

Absence of thymus

Answer

Severe combined immunodeficiency mice are the same as nude mice

Answer

They can generate mature T lymphocytes

Question 10

Which of the following interleukins is characteristically produced in a T helper cell type 1 (TH1) response?

Accepted Answer

IL-2

Answer

IL-4

Answer

IL-5

Answer

IL-10

Immunopathology — MCQs

Immunopathology — MCQs

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