Immunopathology Practice Questions

Q: Which antigen is primarily involved in post-transplant rejection?

HLA-Antigen. **Explanation:** The correct answer is **HLA-Antigen (Human Leukocyte Antigen)**. **1. Why HLA-Antigen is correct:** The HLA system is the human version of the **Major Histocompatibility Complex (MHC)**, located on Chromosome 6. These surface glycoproteins are the primary markers used by the immune system to distinguish "self" from "non-self." In organ transplantation, if the donor’s HLA molecules do not match the recipient’s, the recipient’s T-cells recognize them as foreign antigens. This triggers a potent immune response (Cell-mediated via CD8+ T-cells and Humoral via B-cells), leading to graft destruction or **rejection**. **2. Why other options are incorrect:** * **Nuclear Antigens:** These are components found inside the cell nucleus (e.g., ANA, anti-dsDNA). They are primarily involved in **autoimmune diseases** like Systemic Lupus Erythematosus (SLE), not transplant rejection. * **Polysaccharides:** These are typically found in bacterial capsules (e.g., *Streptococcus pneumoniae*). They trigger T-independent immune responses but are not the mediators of graft rejection. * **DHA (Docosahexaenoic acid):** This is an omega-3 fatty acid essential for brain health; it has no antigenic role in transplant immunology. **Clinical Pearls for NEET-PG:** * **MHC Class I (HLA-A, B, C):** Present on all nucleated cells; recognized by CD8+ T-cells. * **MHC Class II (HLA-DR, DQ, DP):** Present on Antigen-Presenting Cells (APCs); recognized by CD4+ T-cells. * **Hyperacute Rejection:** Occurs within minutes due to pre-formed antibodies against ABO or HLA antigens (Type II Hypersensitivity). * **Acute Rejection:** Occurs within days to weeks; primarily T-cell mediated (Type IV Hypersensitivity). * **HLA-B27** is strongly associated with Ankylosing Spondylitis.

Q: An 8-month-old boy is evaluated because of repeated episodes of pneumococcal pneumonia. Serum studies demonstrate very low levels of IgM, IgG, and IgA. This patient's condition is related to a deficiency of which of the following proteins?

Tyrosine kinase. **Explanation:** The clinical presentation of an 8-month-old boy with recurrent pyogenic infections (specifically *Streptococcus pneumoniae*) and pan-hypogammaglobulinemia (low IgM, IgG, and IgA) is classic for **X-linked Agammaglobulinemia (XLA)**, also known as Bruton’s Agammaglobulinemia. **1. Why Tyrosine Kinase is Correct:** XLA is caused by a mutation in the **Bruton Tyrosine Kinase (BTK) gene**. This cytoplasmic tyrosine kinase is essential for B-cell signal transduction. Without functional BTK, B-cell precursors (Pre-B cells) in the bone marrow fail to mature into mature B-cells. Consequently, there is a complete absence of B-cells in the peripheral blood, leading to a lack of plasma cells and a failure to produce all classes of antibodies. **2. Why the Incorrect Options are Wrong:** * **Adenosine deaminase (ADA):** Deficiency leads to **SCID** (Autosomal Recessive). It causes the accumulation of toxic metabolites that destroy both B and T lymphocytes. * **Class III MHC gene:** These genes encode components of the complement system (C2, C4) and TNF. Deficiencies do not typically present with pan-hypogammaglobulinemia. * **Gamma chain of the IL-2 receptor:** This is the most common cause of **X-linked SCID**. It results in a lack of T-cells and NK cells, with secondary B-cell dysfunction. **Clinical Pearls for NEET-PG:** * **Age of Onset:** Symptoms typically appear after **6 months** of age, once maternal IgG wanes. * **Physical Exam:** Look for **absent or hypoplastic tonsils** and lymph nodes (due to lack of germinal centers). * **Infections:** Increased susceptibility to encapsulated bacteria (*H. influenzae, S. pneumoniae*) and certain viruses/parasites (Enteroviruses, *Giardia*). * **Diagnosis:** Flow cytometry showing **CD19+ B-cell count <2%**.

Q: A 27-year-old male patient with blood group O presents with massive intestinal bleeding and has lost half his blood volume. He is transfused with blood group AB blood. Within minutes, he develops fever, chills, dyspnea, and a dramatic drop in blood pressure. What is the most likely cause of this reaction?

Preformed anti-A and anti-B antibodies in the recipient. **Explanation:** This clinical scenario describes an **Acute Hemolytic Transfusion Reaction (AHTR)**, which is a classic example of a **Type II Hypersensitivity Reaction**. **Why Option C is correct:** Individuals with **Blood Group O** naturally possess preformed, high-titer IgM (and some IgG) antibodies against both A and B antigens (anti-A and anti-B). When blood group AB (which expresses both A and B antigens) is transfused into this patient, these preformed antibodies immediately bind to the donor's red blood cells. This triggers the **classical complement pathway**, leading to rapid intravascular hemolysis, release of inflammatory cytokines, and the clinical triad of fever, hypotension, and potential DIC. **Why other options are incorrect:** * **Option A:** Cell-mediated responses (Type IV Hypersensitivity) are delayed (taking days) and do not involve the immediate antibody-antigen binding seen in ABO incompatibility. * **Option B:** This describes a primary immune response. Production of new IgG takes 7–14 days; it cannot account for a reaction occurring "within minutes." * **Option C vs D:** In a major mismatch, the **recipient’s antibodies** attacking the **donor’s cells** (Option C) is the primary cause of life-threatening hemolysis. While the donor's plasma (Option D) contains no antibodies in this specific case (AB is the universal recipient), even if it did, the volume is usually too diluted to cause such a dramatic systemic collapse. **High-Yield Clinical Pearls for NEET-PG:** * **Universal Donor:** Blood Group O (Negative). * **Universal Recipient:** Blood Group AB (Positive). * **Mechanism:** Type II Hypersensitivity (Complement-mediated lysis). * **First Step in Management:** Stop the transfusion immediately and initiate aggressive IV fluid resuscitation to maintain renal perfusion. * **Commonest cause of AHTR:** Clerical/Administrative error (mislabeled samples).

Q: The image shows a cellular finding in a peripheral blood smear. This finding is most characteristic of which condition?

Systemic Lupus Erythematosus. ***Systemic Lupus Erythematosus*** - The image shows an **LE cell** (Lupus Erythematosus cell), which is a neutrophil or macrophage containing an engulfed **hematoxylin body** (nuclear chromatin material). - This finding is pathognomonic for **SLE** and results from anti-nuclear antibodies coating cell nuclei, leading to phagocytosis by neutrophils. *Tuberculosis* - Characterized by **epithelioid cell granulomas** with **Langhans giant cells** and **caseous necrosis** in tissue sections. - Peripheral blood smears do not show specific cellular findings like LE cells, but may show nonspecific changes like anemia. *Leprosy* - Microscopic findings include **acid-fast bacilli** within **foamy macrophages** (Virchow cells) in tissue sections. - Blood smears are typically normal and do not demonstrate the **nuclear chromatin engulfment** seen in LE cells. *Malaria* - Blood smears show **ring-form trophozoites**, **schizonts**, or **gametocytes** within **red blood cells**. - The parasitic forms are intracellular within RBCs, not the **neutrophilic engulfment of nuclear material** characteristic of LE cells.

Question 1

Which of the following is NOT a feature of DiGeorge Syndrome?

Accepted Answer

Features include hypercalcemia

Answer

Caused due to deletion of the long arm of Chromosome 22

Answer

Featured with cleft palate

Answer

Associated with cardiac septal defects

Question 2

All of the following immunodeficiency diseases are due to chromosomal instability or defective repair of genes, except:

Accepted Answer

Chediak-Higashi syndrome

Answer

Ataxia telangiectasia

Answer

Bloom syndrome

Answer

Seckel syndrome

Question 3

Which antigen is primarily involved in post-transplant rejection?

Accepted Answer

HLA-Antigen

Answer

Nuclear antigen

Answer

Polysaccharide

Answer

DHA

Question 4

Thymoma is associated with which of the following conditions?

Accepted Answer

Myasthenia gravis

Answer

Hypergammaglobulinemia

Answer

Systemic lupus erythematosus

Answer

Multiple sclerosis

Question 5

Which of the following organs can cause an antigen reaction when exposed in self-blood?

Accepted Answer

Eye lens

Answer

Kidney

Answer

Liver

Answer

Platelets

Question 6

An 8-month-old boy is evaluated because of repeated episodes of pneumococcal pneumonia. Serum studies demonstrate very low levels of IgM, IgG, and IgA. This patient's condition is related to a deficiency of which of the following proteins?

Accepted Answer

Tyrosine kinase

Answer

Adenosine deaminase

Answer

Class III MHC gene

Answer

Gamma chain of the IL-2 receptor

Question 7

Hematoxylin bodies are seen in which of the following conditions?

Accepted Answer

Systemic Lupus Erythematosus (SLE)

Answer

Polyarteritis Nodosa (PAN)

Answer

Disseminated Intravascular Coagulation (DIC)

Answer

Wegener's Granulomatosis

Question 8

A 27-year-old male patient with blood group O presents with massive intestinal bleeding and has lost half his blood volume. He is transfused with blood group AB blood. Within minutes, he develops fever, chills, dyspnea, and a dramatic drop in blood pressure. What is the most likely cause of this reaction?

Accepted Answer

Preformed anti-A and anti-B antibodies in the recipient

Answer

A cell-mediated response against AB antigens

Answer

IgG production by the recipient in response to AB antigens

Answer

Preformed anti-A and anti-B antibodies of the blood donor

Question 9

The image shows a cellular finding in a peripheral blood smear. This finding is most characteristic of which condition?

Accepted Answer

Systemic Lupus Erythematosus

Answer

Tuberculosis

Answer

Leprosy

Answer

Malaria

Question 10

A 12-year-old boy presents with a 5-day history of sore throat. His temperature is 38.7°C (103°F). Physical examination reveals inflamed tonsils and swollen cervical lymph nodes. Trafficking and recirculation of blood-borne lymphocytes through the cervical lymph nodes in this patient occurs primarily at which of the following locations?

Accepted Answer

High endothelial venules

Answer

Afferent lymphatic vessel

Answer

Efferent lymphatic vessel

Answer

Hassall corpuscles

Immunopathology — MCQs

Immunopathology — MCQs

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