General Pathology — MCQs

General Pathology Indian Medical PG Practice Questions and MCQs

Question 1061: Deposition of protein Aβ2m is seen in which clinicopathologic category of amyloidosis?

A. Familial Mediterranean fever
B. Hemodialysis associated (Correct Answer)
C. Senile cerebral
D. Systemic senile

Explanation: **Explanation:** **A̢2m (Beta-2 Microglobulin)** is the characteristic amyloid protein associated with **Hemodialysis-associated amyloidosis** [1]. 1. **Why Option B is correct:** Beta-2 microglobulin is a component of the MHC Class I molecule found on all nucleated cells. In patients with chronic renal failure, this protein cannot be filtered by the kidneys [1]. Standard hemodialysis membranes are also inefficient at filtering A̢2m, leading to high serum concentrations [1]. Over time (usually >10 years of dialysis), the protein undergoes conformational changes and deposits as amyloid fibrils, primarily in the **synovium, joints, and tendon sheaths**, often presenting as **Carpal Tunnel Syndrome**. 2. **Why other options are incorrect:** * **A. Familial Mediterranean Fever (FMF):** This is associated with **AA (Amyloid Associated)** protein, derived from SAA (Serum Amyloid-Associated) protein during chronic inflammation [1]. * **C. Senile Cerebral:** Seen in Alzheimer’s disease, the protein involved is **A̢ (Amyloid Beta)**, derived from Amyloid Precursor Protein (APP). * **D. Systemic Senile:** Now termed "Wild-type ATTR," this involves the deposition of normal (non-mutated) **Transthyretin (TTR)**, typically in the hearts of elderly patients [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** All amyloid shows **Apple-green birefringence** under polarized light after **Congo Red** staining [1]. * **AL Amyloid:** Most common primary systemic amyloidosis (associated with Plasma Cell Dyscrasias/Multiple Myeloma). * **Transthyretin (ATTR):** Mutated form is seen in Familial Amyloid Polyneuropathies; Wild-type is seen in Senile Systemic Amyloidosis [1]. * **Calcitonin:** Pro-calcitonin derived amyloid (ACal) is seen in **Medullary Carcinoma of the Thyroid**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 264-269.

Question 1062: Which of the following is NOT associated with tumor suppressor gene dysfunction?

A. Breast cancers
B. Neurofibromatosis
C. Multiple endocrine neoplasia (Correct Answer)
D. Retinoblastoma

Explanation: ### Explanation The correct answer is **Multiple Endocrine Neoplasia (MEN)**. **1. Why Multiple Endocrine Neoplasia is the correct answer:** While many hereditary cancer syndromes involve the loss of tumor suppressor genes (TSGs), **MEN type 2 (MEN2A and 2B)** is a classic example of an **oncogene activation** [1]. It is caused by a "gain-of-function" mutation in the **RET proto-oncogene**. Unlike TSGs, which require "two hits" (loss of both alleles) to promote malignancy, oncogenes require only a single mutation to drive constitutive signaling and cell proliferation [4]. (Note: MEN1 is caused by the *MEN1* gene, which is a TSG, but in the context of this standard competitive exam question, MEN is categorized by its hallmark *RET* oncogene association). **2. Why the other options are incorrect:** * **Breast Cancers:** Frequently associated with mutations in **BRCA1 and BRCA2**, which are classic tumor suppressor genes involved in DNA repair [2]. * **Neurofibromatosis:** NF Type 1 is caused by mutations in the **NF1** gene (encoding Neurofibromin), and NF Type 2 by the **NF2** gene (encoding Merlin). Both are tumor suppressor genes that regulate cell signaling pathways like RAS. * **Retinoblastoma:** This is the "prototype" of tumor suppressor gene dysfunction [3]. It involves the **RB1** gene, leading to Knudson’s "Two-Hit Hypothesis" [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **RET Proto-oncogene:** Associated with Medullary Thyroid Carcinoma, Pheochromocytoma, and Hirschsprung disease (loss-of-function). * **Two-Hit Hypothesis:** Applies to TSGs (e.g., *RB, TP53, APC*), not oncogenes [3]. * **Li-Fraumeni Syndrome:** Caused by a germline mutation in **TP53**, the "Guardian of the Genome." * **VHL Gene:** A TSG associated with Von Hippel-Lindau syndrome (Renal cell carcinoma and hemangioblastomas). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1139-1140. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 300. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 298-300. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 297-298.

Question 1063: Metastatic calcification is not seen in which of the following?

A. Kidney tubules
B. Fundal glands of stomach
C. Alveoli of lungs
D. Media of Monkeberg degeneration (Correct Answer)

Explanation: **Explanation:** The core concept tested here is the distinction between **Dystrophic** and **Metastatic calcification**. **1. Why Option D is Correct:** **Mönckeberg medial calcific sclerosis** is a classic example of **Dystrophic calcification**. In this condition, calcium deposits occur in the tunica media of medium-sized muscular arteries (like the femoral or radial arteries) despite **normal serum calcium levels**. It is associated with aging and cellular degeneration. Metastatic calcification, by definition, occurs in normal tissues due to **hypercalcemia** (elevated serum calcium) [2]. **2. Why Options A, B, and C are Incorrect:** Metastatic calcification preferentially affects tissues that have an **internal alkaline environment** due to the excretion of acids [1]. High pH (alkalinity) favors the precipitation of calcium salts. * **Kidney Tubules (A):** Excrete acid ($H^+$ ions), making the tubular cells alkaline [1]. * **Fundal Glands of Stomach (B):** Excrete hydrochloric acid ($HCl$), leaving the gastric mucosa alkaline [1]. * **Alveoli of Lungs (C):** Lose carbon dioxide ($CO_2$), which increases the local pH [1]. These three sites are the most common locations for metastatic calcification. **Clinical Pearls for NEET-PG:** * **Dystrophic Calcification:** Normal serum calcium; occurs in dead/dying tissues (e.g., Atherosclerosis, Psammoma bodies, Caseous necrosis). * **Metastatic Calcification:** High serum calcium; occurs in normal tissues (e.g., Hyperparathyroidism, Vitamin D toxicity, Milk-alkali syndrome) [3]. * **Morphology:** On H&E stain, both types appear as **basophilic (blue/purple)**, amorphous granular clumps [1]. * **Special Stains:** Von Kossa (black) and Alizarin Red S (red) are used to identify calcium. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 76-77. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 134-135. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 127-128.

Question 1064: A 50-year-old male with a history of excessive alcohol consumption presents with signs of alcoholic hepatitis. Microscopic examination of a liver biopsy reveals characteristic inclusions within hepatocytes. These inclusions are primarily composed of what substance?

A. Immunoglobulin
B. Excess plasma proteins
C. Basement membrane material
D. Prekeratin intermediate filaments (Correct Answer)

Explanation: **Explanation:** The clinical presentation of a chronic alcoholic with hepatitis and characteristic inclusions points to **Mallory-Denk bodies** (Mallory hyaline) [1]. These are eosinophilic, rope-like cytoplasmic inclusions found within hepatocytes [1]. **1. Why the correct answer is right:** Mallory-Denk bodies are composed of tangled masses of **prekeratin intermediate filaments** (specifically Cytokeratin 8 and 18) complexed with other proteins like ubiquitin and p62. They represent a failure of the hepatocyte's cytoskeleton to degrade damaged proteins, leading to their accumulation [1]. While most classically associated with **Alcoholic Liver Disease**, they are also seen in Non-alcoholic steatohepatitis (NASH), Wilson disease, and Primary Biliary Cholangitis [1]. **2. Why the incorrect options are wrong:** * **A. Immunoglobulins:** These form **Russell bodies**, which are eosinophilic inclusions found in the endoplasmic reticulum of plasma cells (seen in Multiple Myeloma). * **B. Excess plasma proteins:** Accumulation of proteins like albumin or alpha-1-antitrypsin (AAT) can cause eosinophilic droplets [1], but they are not the primary component of Mallory bodies. AAT deficiency specifically shows PAS-positive, diastase-resistant globules [1]. * **C. Basement membrane material:** This is associated with collagen deposition (fibrosis) in the Space of Disse but does not form intracellular inclusions in hepatocytes [1]. **Clinical Pearls for NEET-PG:** * **Mallory-Denk Bodies:** Eosinophilic, "twisted-rope" appearance. * **Stain:** They can be highlighted using **Ubiquitin** immunohistochemical stains. * **Councilman Bodies:** These are different; they represent apoptotic hepatocytes (acidophilic bodies) commonly seen in Yellow Fever and Viral Hepatitis. * **Reinke Crystals:** Rod-shaped inclusions seen in Leydig cell tumors. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 388-390.

Question 1065: The SYT-SSXI gene fusion is associated with which of the following entities?

A. Liposarcoma
B. Rhabdomyosarcoma
C. Synovial sarcoma (Correct Answer)
D. Ewing's sarcoma

Explanation: **Explanation:** The correct answer is **Synovial sarcoma**. **1. Why Synovial Sarcoma is Correct:** Synovial sarcoma is characterized by a highly specific reciprocal translocation, **t(x;18)(p11;q11)** [1]. This translocation results in the fusion of the **SYT** gene (also known as SS18) on chromosome 18 with the **SSX** gene (SSX1, SSX2, or rarely SSX4) on the X chromosome [1]. The resulting **SYT-SSX** fusion protein acts as an aberrant transcriptional regulator that disrupts chromatin remodeling (SWI/SNF complex), leading to oncogenesis. Despite its name, this tumor does not arise from synovial cells but from multipotent mesenchymal stem cells [1]. **2. Why Other Options are Incorrect:** * **Liposarcoma:** Associated with different mutations depending on the subtype. Well-differentiated/dedifferentiated liposarcomas typically show **MDM2 amplification** (12q13-15), while Myxoid liposarcoma is characterized by **t(12;16)** involving the **FUS-CHOP** genes. * **Rhabdomyosarcoma:** Alveolar rhabdomyosarcoma is associated with **t(2;13)** or **t(1;13)**, resulting in **PAX3-FOXO1** or **PAX7-FOXO1** fusions, respectively. * **Ewing’s Sarcoma:** Characterized by **t(11;22)(q24;q12)**, which creates the **EWS-FLI1** fusion gene. **3. NEET-PG High-Yield Pearls:** * **Morphology:** Synovial sarcoma can be **Biphasic** (spindle cells + epithelial-like glands) or **Monophasic** (spindle cells only) [1]. * **Immunohistochemistry (IHC):** Positive for **TLE1** (highly sensitive/specific), Cytokeratin, and EMA. * **Location:** Most common in the deep soft tissues of the lower extremities (near joints) in young adults [1]. * **Radiology:** Often shows "speckled" calcifications on X-ray. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1225-1226.

Question 1066: Caseous necrosis is typically seen in which of the following conditions?

A. Tuberculosis (Correct Answer)
B. Sarcoidosis
C. Cryptococcal infection
D. Gangrene

Explanation: **Explanation:** **Caseous necrosis** is a unique form of cell death that combines features of both coagulative and liquefactive necrosis [1]. It is characterized by a "cheese-like" (caseous) appearance—grossly white, friable, and soft. Microscopically, it presents as an eosinophilic, amorphous, granular debris surrounded by a granulomatous inflammatory border [1], [2]. * **Tuberculosis (Correct):** This is the classic prototype of caseous necrosis [1]. It is caused by the body's delayed hypersensitivity reaction (Type IV) to *Mycobacterium tuberculosis*. The lipid-rich cell wall of the mycobacteria (specifically mycolic acids) contributes to the characteristic "cheesy" texture of the necrotic center [2]. **Why other options are incorrect:** * **Sarcoidosis:** While sarcoidosis is a granulomatous disease, it typically presents with **non-caseating granulomas** [3]. The absence of central necrosis is a key histopathological differentiator from tuberculosis [3]. * **Cryptococcal infection:** Fungal infections like Cryptococcus often cause a "soap bubble" appearance in the brain or chronic inflammation, but they do not typically manifest as classic caseous necrosis unless there is significant immune interaction [2]. * **Gangrene:** This is a clinical term. **Dry gangrene** is primarily coagulative necrosis due to ischemia, while **wet gangrene** involves liquefactive necrosis due to superimposed bacterial infection. **High-Yield Pearls for NEET-PG:** * **Microscopic hallmark:** Loss of tissue architecture (unlike coagulative) and presence of "tombstone" Langhans giant cells [4]. * **Dystrophic Calcification:** Caseous centers are frequent sites for calcium deposition [1]. * **Syphilis:** Associated with **Gummatous necrosis**, which is similar to caseous but has a more "rubbery" consistency. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, p. 55. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 383-384. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 198-200. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109.

Question 1067: What is the role of major histocompatibility complex protein?

A. Transduce signals to T cells after antigen recognition
B. Mediate immunoglobulin class switching
C. Present antigens for recognition by the T cell antigen receptor (Correct Answer)
D. Enhance the secretion of cytokines

Explanation: ### Explanation **Correct Answer: C. Present antigens for recognition by the T cell antigen receptor** The primary physiological role of the **Major Histocompatibility Complex (MHC)**, known as Human Leukocyte Antigen (HLA) in humans, is to display peptide fragments of proteins (antigens) on the cell surface for recognition by T lymphocytes [1]. T cells are "MHC-restricted," meaning they cannot recognize "naked" or soluble antigens; they only recognize antigens when they are nestled within the peptide-binding groove of an MHC molecule [2]. * **MHC Class I:** Found on all nucleated cells; presents endogenous antigens (e.g., viral or tumor proteins) to **CD8+ Cytotoxic T cells** [3]. * **MHC Class II:** Found on professional Antigen Presenting Cells (APCs) like dendritic cells, macrophages, and B cells; presents exogenous antigens to **CD4+ Helper T cells** [1], [2]. **Why other options are incorrect:** * **Option A:** Signal transduction after antigen recognition is primarily the role of the **CD3 complex** and **ζ (zeta) chains**, which are associated with the T-cell receptor (TCR) [2]. * **Option B:** Immunoglobulin class switching is mediated by the interaction between **CD40** (on B cells) and **CD40 Ligand** (on T cells), along with specific cytokines (e.g., IL-4 for IgE). * **Option C:** While MHC-TCR binding triggers T-cell activation, the *secretion* of cytokines is a downstream effector function of the activated T cell, not a direct role of the MHC molecule itself. **High-Yield Clinical Pearls for NEET-PG:** * **MHC Genes:** Located on the **Short arm of Chromosome 6** [2]. * **MHC Class I structure:** Composed of an $\alpha$ heavy chain and a **$\beta_2$-microglobulin** (non-polymorphic). * **MHC Class II structure:** Composed of $\alpha$ and $\beta$ chains (both polymorphic) [1]. * **HLA Associations:** * **B27:** Ankylosing spondylitis, Reactive arthritis. * **DR3/DR4:** Type 1 Diabetes Mellitus. * **DQ2/DQ8:** Celiac Disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 202-203. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 156-157. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208.

Question 1068: All of the following are true about Xanthogranulomatous inflammation, except:

A. Associated with tuberculosis (Correct Answer)
B. Characterized by yellow granulomas
C. Presence of giant cells
D. Presence of foam cells

Explanation: **Explanation:** **Xanthogranulomatous inflammation** is a rare, destructive form of chronic inflammation characterized by the massive accumulation of lipid-laden macrophages (foam cells) [1]. **Why Option A is the Correct Answer (The Exception):** Xanthogranulomatous inflammation is **not** typically associated with *Mycobacterium tuberculosis*. Tuberculosis is the classic example of **caseating granulomatous inflammation**, characterized by central necrosis and Langhans giant cells [2], [3]. In contrast, xanthogranulomatous inflammation is most commonly associated with chronic infections caused by **Proteus mirabilis** or **Escherichia coli**, often in the setting of urinary or biliary obstruction (e.g., Xanthogranulomatous Pyelonephritis) [1]. **Analysis of Incorrect Options:** * **Option B (Yellow granulomas):** Grossly, the affected tissue appears bright yellow or golden-orange due to the high lipid content within the infiltrating macrophages [1]. * **Option C (Giant cells):** Histology reveals a pleomorphic infiltrate including Touton giant cells, plasma cells, and lymphocytes alongside the predominant macrophages [1]. * **Option D (Foam cells):** The hallmark of this condition is the presence of **xanthoma cells** (foamy macrophages), which are histiocytes that have ingested lipids from destroyed cell membranes [1]. **NEET-PG High-Yield Pearls:** 1. **Xanthogranulomatous Pyelonephritis (XPN):** Often presents with a "Bear's Paw" sign on CT scan; it is a "great imitator" as it can mimic Renal Cell Carcinoma (RCC) [1]. 2. **Touton Giant Cells:** These are characteristic giant cells where nuclei form a ring around a central non-foamy cytoplasm, surrounded by a peripheral foamy cytoplasm. 3. **Key Association:** Always look for a history of staghorn calculi or chronic biliary obstruction in clinical vignettes [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 939-940. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 383-384.

Question 1069: Which of the following is a DNA repair defect?

A. Bloom syndrome (Correct Answer)
B. Incontinentia pigmenti
C. Aplastic Anemia
D. Tuberous sclerosis

Explanation: ### Explanation **Bloom Syndrome (Correct Answer)** Bloom syndrome is a classic example of a **DNA repair defect** (specifically a chromosomal instability syndrome) [1]. It is caused by a mutation in the **BLM gene**, which encodes a member of the **RecQ helicase** family. DNA helicases are essential for unwinding DNA during replication and repair. A deficiency leads to genomic instability, characterized by a high frequency of sister chromatid exchanges and a predisposition to various cancers [2]. **Analysis of Incorrect Options:** * **Incontinentia pigmenti:** This is an X-linked dominant genodermatosis caused by mutations in the **IKBKG gene** (NEMO). It affects the skin, teeth, and CNS but is not primarily a DNA repair defect. * **Aplastic Anemia:** This is a clinical syndrome of bone marrow failure. While some inherited forms (like Fanconi Anemia) involve DNA repair defects, "Aplastic Anemia" itself is a broad hematological diagnosis often caused by autoimmune destruction or toxins [1]. * **Tuberous sclerosis:** This is a neurocutaneous syndrome (phakomatosis) caused by mutations in **TSC1 (Hamartin)** or **TSC2 (Tuberin)** genes. These genes act as tumor suppressors via the mTOR pathway, not DNA repair. **High-Yield Clinical Pearls for NEET-PG:** * **Bloom Syndrome Triad:** Telangiectatic erythema (butterfly distribution on the face), photosensitivity, and growth retardation (dwarfism). * **Cytogenetic Hallmark:** "Quadriradial figures" in lymphocytes and increased sister chromatid exchange (SCE). * **Other DNA Repair Defects (Must-know):** * **Xeroderma Pigmentosum:** Defect in Nucleotide Excision Repair (NER) [1]. * **HNPCC (Lynch Syndrome):** Defect in Mismatch Repair (MMR). * **Ataxia Telangiectasia:** Defect in ATM gene (dsDNA break repair) [1]. * **Fanconi Anemia:** Defect in DNA cross-link repair [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 322-323. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 226-227.

Question 1070: Which feature is NOT shared between T cells and B cells?

A. Antigen-specific receptors
B. Class I MHC receptors
C. Positive selection during development (Correct Answer)
D. All of the above

Explanation: **Explanation:** The correct answer is **C. Positive selection during development.** While both T and B lymphocytes undergo complex maturation processes, the mechanisms of selection differ significantly. [1], [2] 1. **Why Option C is correct:** * **T Cells:** Undergo **both** positive and negative selection in the thymus. Positive selection ensures that T cells can recognize self-MHC molecules (MHC restriction). [2] * **B Cells:** Undergo **negative selection** (to eliminate self-reactive clones) in the bone marrow, but they **do not undergo positive selection**. [2] Since B cells recognize intact antigens directly via their B-cell receptors (BCR) and are not MHC-restricted, there is no biological requirement for positive selection to "test" MHC binding. [3] 2. **Why other options are incorrect:** * **Option A (Antigen-specific receptors):** Both cell types possess unique, clonally distributed receptors generated by V(D)J recombination—the **TCR** for T cells and the **BCR (surface IgM/IgD)** for B cells. [4] * **Option B (Class I MHC receptors):** All nucleated cells in the human body express MHC Class I molecules on their surface. [5] Since both T and B cells are nucleated leukocytes, they both express MHC Class I. **High-Yield NEET-PG Pearls:** * **Site of Maturation:** T cells mature in the **Thymus**; B cells mature in the **Bone Marrow**. [1] * **Negative Selection:** Both cells undergo this to prevent autoimmunity (Central Tolerance). Failure of this process leads to autoimmune diseases. [2] * **MHC Restriction:** T cells are "MHC restricted" (CD4+ to MHC II; CD8+ to MHC I), whereas B cells can recognize free, soluble antigens. [3] * **Receptor Diversity:** Generated by the **RAG-1 and RAG-2 genes**. Mutations in these genes lead to Omenn Syndrome or SCID. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 158-160. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 220-221. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 155-156. [5] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 156-157.

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