Immunopathology Practice Questions

Q: What is the most common antibody found in Sjogren syndrome?

Anti-Ribonucleoprotein. **Explanation:** Sjögren syndrome is a chronic autoimmune disorder characterized by lymphocytic infiltration of exocrine glands, primarily the lacrimal and salivary glands. The diagnosis relies heavily on the presence of specific autoantibodies directed against **ribonucleoproteins (RNPs)** [1]. **1. Why the Correct Answer is Right:** The correct answer is **Anti-Ribonucleoprotein**. In Sjögren syndrome, the two hallmark antibodies are **SS-A (Ro)** and **SS-B (La)** [1]. Both of these are directed against small ribonucleoprotein particles. While they are not 100% specific (as they can appear in SLE), they are the most common and diagnostically significant antibodies for this condition. SS-A is found in 70-95% of cases, and SS-B is found in 60-90%. **2. Analysis of Incorrect Options:** * **A. Anti-DNA topoisomerase (Anti-Scl-70):** This is highly specific for **Diffuse Cutaneous Systemic Sclerosis**. * **B. Anti-Centromere:** This is the classic marker for **Limited Cutaneous Systemic Sclerosis (CREST syndrome)**. * **C. Anti-RNA polymerase III:** This is associated with **Diffuse Systemic Sclerosis** and indicates an increased risk for scleroderma renal crisis. **3. NEET-PG High-Yield Pearls:** * **Schirmer Test:** Used to quantify decreased lacrimation (objective evidence of keratoconjunctivitis sicca). * **Lip Biopsy:** The gold standard for diagnosis; it shows minor salivary gland involvement with focal lymphocytic aggregates (focus score). * **Malignancy Risk:** Patients with Sjögren syndrome have a **40-fold increased risk** of developing **B-cell MALT Lymphoma** (often presenting as persistent parotid swelling). * **Neonatal Lupus:** Pregnant women with Anti-Ro (SS-A) antibodies are at risk of having infants with congenital heart block. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 234-235.

Q: Which of the following is the WRONG combination regarding adhesion molecules and their corresponding CD markers?

PECAM - CD64. This question tests your knowledge of **Adhesion Molecules**, which are critical for leukocyte trafficking and the inflammatory response. In the NEET-PG exam, matching Cluster of Differentiation (CD) markers to their common names is a high-yield topic. ### **Explanation of the Correct Answer** **Option D (PECAM - CD64) is the WRONG combination.** * **PECAM-1** (Platelet Endothelial Cell Adhesion Molecule-1) is actually **CD31**. It is expressed on leukocytes and endothelial cells and is primarily responsible for **diapedesis** (transmigration of leukocytes through the endothelial junction) [1]. * **CD64** is the marker for **FcγRI**, the high-affinity receptor for IgG found on macrophages, monocytes, and neutrophils. ### **Analysis of Other Options** * **A. VCAM - CD106:** Correct. Vascular Cell Adhesion Molecule-1 (VCAM-1) is CD106. It binds to VLA-4 integrins on leukocytes and is involved in firm adhesion. * **B. ICAM - CD102:** Correct. Intercellular Adhesion Molecule-2 (ICAM-2) is CD102. It is constitutively expressed on endothelial cells. * **C. ICAM-1 - CD54:** Correct. ICAM-1 is CD54. It is upregulated by cytokines (TNF, IL-1) and is the ligand for LFA-1 (CD11a/CD18) during firm adhesion. ### **High-Yield Clinical Pearls for NEET-PG** * **Selectins (Rolling):** L-Selectin (CD62L), E-Selectin (CD62E), P-Selectin (CD62P). * **Integrins (Adhesion):** LFA-1 (CD11a/CD18) and MAC-1 (CD11b/CD18). * **LAD Type 1:** Caused by a deficiency in **CD18** (integrin β2 chain), leading to impaired firm adhesion and recurrent infections without pus formation [1]. * **LAD Type 2:** Caused by a deficiency in **Sialyl-Lewis X** (ligand for selectins), leading to impaired rolling. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 87-89.

Q: A 31-year-old man with AIDS complains of difficulty swallowing. Examination of his oral cavity demonstrates whitish membranes covering much of his tongue and palate. Endoscopy also reveals several whitish, ulcerated lesions in the esophagus. Which of the following enzymes converts the HIV genome into double-stranded DNA in host cells?

Reverse transcriptase. The clinical presentation of a patient with AIDS presenting with oral thrush (candidiasis) and esophageal ulcers is highly suggestive of advanced immunosuppression. The question focuses on the replication cycle of the **Human Immunodeficiency Virus (HIV)**, a retrovirus. **1. Why Reverse Transcriptase is Correct:** HIV is an RNA virus. Upon entering the host cell (CD4+ T cell), its single-stranded RNA genome must be converted into double-stranded DNA (dsDNA) to be integrated into the host genome [1]. This process is catalyzed by the enzyme **Reverse Transcriptase (RNA-dependent DNA polymerase)**. This enzyme lacks proofreading capabilities, leading to the high mutation rate characteristic of HIV. **2. Why the Other Options are Incorrect:** * **DNA Polymerase (Pol-1 & Pol-2):** These are host cell enzymes involved in eukaryotic DNA replication and repair. They synthesize DNA from a DNA template, not from the viral RNA template. * **Integrase:** This viral enzyme is responsible for inserting (integrating) the newly synthesized viral dsDNA into the host cell's nuclear DNA [1]. It acts *after* reverse transcriptase has completed its job. **Clinical Pearls for NEET-PG:** * **HIV Genes:** * *gag:* Codes for structural proteins (p24 capsid). * *pol:* Codes for enzymes (**Reverse Transcriptase, Integrase, Protease**). * *env:* Codes for envelope glycoproteins (gp120 for attachment, gp41 for fusion). * **Diagnostic Marker:** p24 antigen is the earliest detectable protein in the blood during the window period. * **Opportunistic Infection:** Esophageal candidiasis is an **AIDS-defining illness**, typically occurring when the CD4 count falls below 100 cells/mm³. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 255-256.

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

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 2

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 3

What is the most common antibody found in Sjogren syndrome?

Accepted Answer

Anti-Ribonucleoprotein

Answer

Anti-DNA topoisomerase

Answer

Anti-Centromere

Answer

Anti-RNA polymerase

Question 4

Which of the following is the WRONG combination regarding adhesion molecules and their corresponding CD markers?

Accepted Answer

PECAM - CD64

Answer

VCAM - CD106

Answer

ICAM - CD102

Answer

ICAM1 - CD54

Question 5

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 6

Acute graft-versus-host-disease (GVHD) commonly involves all of the following organs, except:

Accepted Answer

Brain

Answer

Skin

Answer

Liver

Answer

Small & large intestines

Question 7

A 31-year-old man with AIDS complains of difficulty swallowing. Examination of his oral cavity demonstrates whitish membranes covering much of his tongue and palate. Endoscopy also reveals several whitish, ulcerated lesions in the esophagus. Which of the following enzymes converts the HIV genome into double-stranded DNA in host cells?

Accepted Answer

Reverse transcriptase

Answer

DNA polymerase (Pol-1)

Answer

DNA polymerase (Pol-2)

Answer

Integrase

Question 8

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

Question 9

Biopsy of the parotid gland in Sjogren's syndrome typically shows infiltration by which type of inflammatory cell?

Accepted Answer

Lymphocytes

Answer

Neutrophils

Answer

Eosinophils

Answer

Basophils

Question 10

MHC III codes for which of the following?

Accepted Answer

TNF alpha

Answer

IL 1

Answer

HLA A

Answer

HLA B

Immunopathology — MCQs

Immunopathology — MCQs

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