Immunopathology Practice Questions

Q: Hyperacute rejection is due to which of the following mechanisms?

Preformed antibodies. **Explanation:** **Hyperacute Rejection** is an immediate, irreversible immunological reaction occurring within minutes to hours after organ transplantation. **1. Why Option A is Correct:** The mechanism is a **Type II Hypersensitivity reaction**. It is mediated by **preformed circulating antibodies** (IgG) in the recipient’s blood. These antibodies are directed against donor antigens (typically ABO blood group antigens or HLA Class I antigens). Upon reperfusion, these antibodies bind to the donor vascular endothelium, activating the **complement system**. This leads to rapid endothelial damage, platelet aggregation, and diffuse intravascular thrombosis, resulting in the "blue graft" appearance and graft necrosis. **2. Why Other Options are Incorrect:** * **Option B:** Cytotoxic T lymphocyte (CD8+) mediated injury is the hallmark of **Acute Cellular Rejection**, which typically occurs days to weeks after transplant. * **Option C:** Endothelitis (inflammation of the vessel wall) is a feature of **Acute Antibody-Mediated Rejection**, but it is caused by *recipient* antibodies against donor tissue, not donor antibodies. * **Option D:** Macrophages play a role in chronic inflammation and delayed-type hypersensitivity but are not the primary mediators of the rapid vascular collapse seen in hyperacute rejection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Prevention:** Hyperacute rejection is prevented by **Cross-matching** (mixing recipient serum with donor lymphocytes) and ABO compatibility testing. * **Treatment:** There is no effective treatment once it starts; the graft must be **surgically removed**. * **Risk Factors:** Previous blood transfusions, multiple pregnancies, or prior organ transplants (all of which sensitize the recipient). * **Pathology:** Characterized by **Fibrinoid necrosis** of capillaries and "starry sky" appearance due to neutrophilic infiltration.

Q: Molecular mimicry is an explanation for which of the following?

Autoimmune disorders. ### Explanation **Molecular Mimicry** is a key mechanism in the pathogenesis of **Autoimmune Disorders** [1]. It occurs when there is a structural similarity between the antigens of an infectious agent (bacteria or virus) and the host’s self-antigens. When the immune system mounts a response against the pathogen, the cross-reactive antibodies or T-cells mistakenly attack the host’s own tissues, leading to loss of self-tolerance and subsequent tissue damage [1]. **Why the other options are incorrect:** * **Immune Tolerance:** This is the state of unresponsiveness to an antigen. Molecular mimicry represents a *failure* of tolerance, specifically a breakdown in peripheral tolerance. * **Hypersensitivity:** While autoimmunity involves hypersensitivity reactions (Types II, III, or IV), "Hypersensitivity" is a broad category describing exaggerated immune responses to *exogenous* antigens (like pollen or drugs). Molecular mimicry specifically explains the *trigger* for attacking *endogenous* (self) antigens [1]. * **Immunosuppression:** This refers to a reduced activation or efficacy of the immune system (e.g., HIV or chemotherapy). Molecular mimicry involves an *overactive* and misdirected immune response. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Example:** **Rheumatic Heart Disease.** Antibodies against the M-protein of *Streptococcus pyogenes* cross-react with cardiac myosin, leading to carditis. * **Guillain-Barré Syndrome (GBS):** Lipopolysaccharides of *Campylobacter jejuni* mimic gangliosides in peripheral nerves. * **Type 1 Diabetes:** Potential mimicry between Coxsackie B virus antigens and islet cell antigens (GAD65) [1]. * **Ankylosing Spondylitis:** Associated with *Klebsiella* species cross-reacting with HLA-B27. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 219-226.

Q: Which human leukocyte antigen (HLA) complex is associated with narcolepsy?

DR2. Narcolepsy, particularly Type 1 (narcolepsy with cataplexy), has one of the strongest known genetic associations in medicine [1]. The correct answer is **HLA-DR2**, specifically the subtype **HLA-DRB1*1501** and its closely linked allele **HLA-DQB1*0602**. 1. **Why HLA-DR2 is correct:** Over 95% of patients with narcolepsy and cataplexy carry the HLA-DR2/DQB1*0602 complex. This association supports the autoimmune theory of the disease, where the immune system selectively destroys **hypocretin (orexin)-producing neurons** in the lateral hypothalamus. Hypocretin is essential for maintaining wakefulness and regulating REM sleep. 2. **Why other options are incorrect:** * **HLA-DR3:** Associated with autoimmune conditions like Type 1 Diabetes Mellitus, SLE, and Graves' disease. * **HLA-DR4:** Classically associated with Rheumatoid Arthritis and Type 1 Diabetes Mellitus. * **HLA-B27 (related to B4):** HLA-B alleles (like B27) are typically associated with seronegative spondyloarthropathies (e.g., Ankylosing Spondylitis), not sleep disorders. **Clinical Pearls for NEET-PG:** * **The Pentad of Narcolepsy:** Excessive daytime sleepiness (earliest symptom), Cataplexy (most specific), Hypnagogic hallucinations, Sleep paralysis, and Fragmented nocturnal sleep. * **Diagnosis:** Gold standard is the **Multiple Sleep Latency Test (MSLT)** showing a mean sleep latency <8 minutes and ≥2 Sleep Onset REM Periods (SOREMPs). * **CSF Findings:** Low or absent **Hypocretin-1 (Orexin-A)** levels in the cerebrospinal fluid are diagnostic for Type 1 Narcolepsy [1]. * **Treatment:** Modafinil is the first-line for daytime sleepiness; Sodium Oxybate is the drug of choice for cataplexy.

Question 1

A 30-year-old male presents with rapidly progressive renal failure over 3 weeks, haematuria, and red cell casts in urine. Serum creatinine has risen from 1.2 to 7.8 mg/dL within one month. ANCA is positive. The renal biopsy is shown in Image 3. Which of the following statements best describes the cellular composition and origin of the lesion most prominently seen in this biopsy?

Accepted Answer

A. Proliferating parietal epithelial cells of Bowman's capsule and infiltrating macrophages forming a compressive extra-capillary lesion

Answer

B. Proliferating visceral epithelial cells (podocytes) with mesangial expansion forming a segmental sclerosing lesion

Answer

C. Proliferating endothelial cells and mesangial cells with subendothelial immune deposits forming a diffuse proliferative lesion

Answer

D. Proliferating tubular epithelial cells with interstitial fibroblasts forming a periglomerular fibrotic lesion

Question 2

Secondary amyloidosis complicates which of the following conditions?

Accepted Answer

Chronic osteomyelitis

Answer

Pneumonia

Answer

Chronic glomerulonephritis

Answer

Irritable bowel syndrome

Question 3

Hyperacute rejection is due to which of the following mechanisms?

Accepted Answer

Preformed antibodies

Answer

Cytotoxic T lymphocyte mediated injury

Answer

Endothelitis caused by donor antibodies

Answer

Circulating macrophage mediated injury

Question 4

Which of the following cells do not act as antigen-presenting cells?

Accepted Answer

T-cells

Answer

B-cells

Answer

Macrophages

Answer

Osteoclasts

Question 5

Which of the following is NOT a disorder of phagocytosis?

Accepted Answer

Wiskott-Aldrich syndrome

Answer

Job's syndrome

Answer

Chediak-Higashi syndrome

Answer

Myeloperoxidase deficiency

Question 6

Molecular mimicry is an explanation for which of the following?

Accepted Answer

Autoimmune disorders

Answer

Immune tolerance

Answer

Hypersensitivity

Answer

Immunosuppression

Question 7

Erythroblastosis fetalis is an example of which type of hypersensitivity reaction?

Accepted Answer

Type II

Answer

Type I

Answer

Type III

Answer

Type IV

Question 8

Which human leukocyte antigen (HLA) complex is associated with narcolepsy?

Accepted Answer

DR2

Answer

DR3

Answer

DR4

Answer

B4

Question 9

A patient on treatment with penicillin developed pallor, but without shortness of breath, urticaria, or wheezing. Investigations revealed antibodies against penicillin in his blood. What is the most likely type of hypersensitivity reaction that occurred in this patient?

Accepted Answer

Type II hypersensitivity

Answer

Type I hypersensitivity

Answer

Type III hypersensitivity

Answer

Type IV hypersensitivity

Question 10

Which one of the following are the most important antigen-presenting cells in humans?

Accepted Answer

Langerhan's cells/histiocytes

Answer

Macrophages

Answer

Plasma cells

Answer

Lymphocytes

Immunopathology — MCQs

Immunopathology — MCQs

On this page

Practice by Chapter

Want unlimited practice?