Immunopathology — MCQs

Immunopathology Indian Medical PG Practice Questions and MCQs

Question 311: What is the prototype of type-II hypersensitivity reaction?

A. Arthus reaction
B. Systemic lupus erythematosus
C. Autoimmune hemolytic anemia (Correct Answer)
D. Contact dermatitis

Explanation: **Explanation:** **Type II Hypersensitivity** (Antibody-mediated cytotoxicity) occurs when IgG or IgM antibodies bind to antigens on specific cell surfaces or tissues [2]. This leads to cell destruction via complement activation, opsonization (phagocytosis), or Antibody-Dependent Cellular Cytotoxicity (ADCC) [2]. **Why Autoimmune Hemolytic Anemia (AIHA) is the correct answer:** AIHA is the classic prototype of Type II hypersensitivity. In this condition, antibodies are directed against antigens on the surface of the patient's own Red Blood Cells (RBCs) [1]. These antibody-coated RBCs are then destroyed by macrophages in the spleen or through complement-mediated lysis [1]. [3] **Analysis of Incorrect Options:** * **A. Arthus Reaction:** This is the prototype for **Type III** hypersensitivity (localized). It involves the deposition of immune complexes in vessel walls, leading to vasculitis. * **B. Systemic Lupus Erythematosus (SLE):** This is a systemic **Type III** hypersensitivity reaction characterized by circulating antigen-antibody complexes that deposit in various organs (kidneys, joints). * **C. Contact Dermatitis:** This is a **Type IV** (Delayed-type) hypersensitivity reaction mediated by T-cells (CD4+ and CD8+), not antibodies. **High-Yield NEET-PG Pearls:** * **Mnemonic for Type II:** "Cytotoxic" (C for Cell-bound). * **Other Examples:** Goodpasture syndrome, Myasthenia Gravis, Graves' disease, Rheumatic fever, and Erythroblastosis Fetalis [2]. * **Key Distinction:** Type II involves antigens fixed on **cells/tissues**, whereas Type III involves **soluble** antigens forming circulating complexes [2]. * **Direct Coombs Test:** Used to detect the Type II antibodies bound to RBCs in AIHA [3]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 602-603. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 213-214. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 651-652.

Question 312: Immunosuppressive drugs are less effective in which type of graft rejection?

A. Acute cellular rejection
B. Acute humoral rejection (Correct Answer)
C. Chronic rejection
D. None of the above

Explanation: The effectiveness of immunosuppressive therapy depends on the underlying mechanism of the immune response. **Why Acute Humoral Rejection is the correct answer:** Acute humoral rejection (also known as **Antibody-Mediated Rejection or AMR**) is mediated by pre-formed or newly synthesized antibodies against donor HLA antigens [1]. These antibodies cause damage via the complement cascade (classical pathway) and antibody-dependent cellular cytotoxicity (ADCC), leading to necrotizing vasculitis and fibrinoid necrosis [2]. Standard immunosuppressive drugs (like Cyclosporine, Tacrolimus, or Mycophenolate) primarily target **T-cell activation and proliferation** [3]. Since AMR is driven by B-cell products (antibodies) already in circulation, these drugs are significantly less effective. Management instead requires plasmapheresis, IVIG, or Rituximab. **Analysis of Incorrect Options:** * **Acute Cellular Rejection:** This is primarily mediated by T-cells (CD8+ cytotoxic and CD4+ Th1 cells) [2]. Because most conventional immunosuppressants are designed to inhibit T-cell signaling (calcineurin inhibitors) or IL-2 production, this type of rejection usually responds very well to steroid pulses or adjustments in maintenance therapy [3]. * **Chronic Rejection:** While chronic rejection is difficult to treat because it involves irreversible fibrosis and intimal thickening (arteriosclerosis), the question asks where drugs are *less effective* in an acute/active context. Chronic rejection is a slow, progressive failure rather than a failure of drug mechanism against an active immune surge. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperacute Rejection:** Occurs within minutes; mediated by pre-formed antibodies; Type II Hypersensitivity [2]. * **Acute Humoral Rejection Hallmark:** Look for **C4d deposition** in peritubular capillaries on immunofluorescence. * **Chronic Rejection Hallmark:** Characterized by **"Graft Arteriosclerosis"** (intimal fibrosis) and organ atrophy. * **Acute Cellular Rejection Hallmark:** Characterized by mononuclear (lymphocytic) infiltrate and **tubulitis** in renal grafts [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 213-214. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 242. [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. 180-181.

Question 313: Which is considered the best serological marker for Systemic Lupus Erythematosus (SLE)?

A. Anti-Sm antibodies
B. Anti-ds DNA antibodies (Correct Answer)
C. Anti-Histone antibodies
D. Anti-Ro (SS-A) antibodies

Explanation: **Explanation:** The diagnosis of Systemic Lupus Erythematosus (SLE) relies on a combination of clinical features and serological markers [3]. While **Antinuclear Antibody (ANA)** is the best *screening* test due to its high sensitivity (95-98%) [1], **Anti-dsDNA antibodies** are considered the best overall marker for diagnosis and management [4]. **Why Anti-dsDNA is the correct answer:** 1. **High Specificity:** It is highly specific for SLE (nearly 100%). 2. **Disease Activity:** Unlike other markers, its titers fluctuate with disease activity [2]. High titers often correlate with **Lupus Nephritis**. 3. **Prognostic Value:** It is used to monitor flares and response to treatment. **Analysis of Incorrect Options:** * **Anti-Sm (Smith) antibodies:** These are the *most specific* markers for SLE [2]. However, they are only present in 20-30% of patients and do not correlate with disease activity, making Anti-dsDNA a better clinical marker for overall management. * **Anti-Histone antibodies:** These are the hallmark of **Drug-Induced Lupus** (e.g., caused by Hydralazine, Procainamide, or Isoniazid) [2]. They are usually absent in idiopathic SLE. * **Anti-Ro (SS-A) antibodies:** These are associated with **Sjögren’s syndrome**, Neonatal Lupus (congenital heart block), and Subacute Cutaneous Lupus [2]. **NEET-PG High-Yield Pearls:** * **Best Screening Test:** ANA (High sensitivity, low specificity) [1]. * **Most Specific Marker:** Anti-Sm antibody [2]. * **Marker for Lupus Nephritis:** Anti-dsDNA. * **Marker for Drug-Induced Lupus:** Anti-Histone [2]. * **Marker for Neonatal Lupus:** Anti-Ro (SS-A) [2]. * **Antiphospholipid Syndrome (APS):** Look for Anti-cardiolipin antibodies or Lupus Anticoagulant (associated with recurrent abortions and thrombosis) [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 226-227. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 228. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 226. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 639-640.

Question 314: Local lymph nodules are enlarged near an infected wound. Histological examination reveals an increased amount of macrophages, lymphocytes, lymphatic follicles in the cortical layer, and a large amount of plasma cells. What process in the lymphatic nodules represents these histological changes?

A. Antigen stimulation (Correct Answer)
B. Acquired insufficiency of the lymphoid tissue
C. Tumour transformation
D. Innate insufficiency of the lymphoid tissue

Explanation: ### Explanation **1. Why "Antigen Stimulation" is Correct:** The histological findings described—**follicular hyperplasia** (increased follicles in the cortical layer), **lymphocytic proliferation**, and **plasmacytosis** (increased plasma cells)—are classic features of a **reactive lymphadenitis** [1]. When an infected wound introduces foreign antigens, the regional lymph nodes mount an immune response [4]. * **B-cell response:** Antigens stimulate B-lymphocytes in the follicles to proliferate and differentiate into **plasma cells** (found in the medullary cords) [2], which produce antibodies [3]. * **T-cell response:** Lymphocytes in the paracortical areas proliferate to handle the cellular immune response. * **Macrophage activity:** Increased macrophages (sinus histiocytosis) occur to phagocytose debris and present antigens [5]. This "reactive" state is the direct result of **antigenic stimulation**. **2. Why Other Options are Incorrect:** * **B & D (Acquired/Innate Insufficiency):** Immunodeficiency states (like DiGeorge syndrome or AIDS) would show the opposite: lymphoid depletion, hypocellularity, and absent follicles or germinal centers. * **C (Tumour Transformation):** While lymphoma causes lymphadenopathy, it typically presents with a **loss of normal architecture** (effacement of sinuses and follicles) and a monomorphic cell population [4], rather than the organized increase of multiple cell types (macrophages, lymphocytes, and plasma cells) seen here. **3. NEET-PG High-Yield Pearls:** * **Follicular Hyperplasia:** Indicates a **B-cell** response (e.g., Rheumatoid arthritis, early HIV, toxoplasmosis) [4]. * **Paracortical Hyperplasia:** Indicates a **T-cell** response (e.g., Viral infections, post-vaccination). * **Sinus Histiocytosis:** Characterized by prominent macrophages in the lymphatic sinusoids; often seen in nodes draining **malignant tumors**. * **Plasma cells** in the lymph node are the hallmark of the humoral immune response transition [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 592-593. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 551-552. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 206-207. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 549-551. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 85-86.

Question 315: Which of the following is a large granular lymphocyte?

A. NK cell (Correct Answer)
B. B-lymphocyte
C. T-lymphocyte
D. Macrophage

Explanation: ### Explanation **Correct Option: A (NK cell)** Natural Killer (NK) cells are the classic example of **Large Granular Lymphocytes (LGLs)**. Morphologically, they are larger than resting B or T cells and possess a characteristic abundant pale cytoplasm containing distinct azurophilic (proteolytic) granules. These granules contain **perforins and granzymes**, which are essential for the NK cell's primary function: inducing apoptosis in virally infected or tumor cells without prior sensitization (Innate Immunity) [1]. **Incorrect Options:** * **B & C (B and T-lymphocytes):** Most circulating B and T cells are **small lymphocytes**. They have a high nuclear-to-cytoplasmic (N:C) ratio, a thin rim of agranular cytoplasm, and dense chromatin. While some activated T-cells (CD8+ cytotoxic T-cells) can appear as LGLs, NK cells are the definitive answer for this classification in standard pathology. * **D (Macrophage):** Macrophages are derived from monocytes and are part of the myeloid lineage, not the lymphoid lineage. They are much larger than lymphocytes and possess a kidney-shaped nucleus with vacuolated cytoplasm, rather than the specific "large granular lymphocyte" morphology. **High-Yield Clinical Pearls for NEET-PG:** * **Surface Markers:** NK cells are identified by the presence of **CD56** and **CD16** (Fc̲RIII) and the **absence of CD3**. * **Mechanism:** They utilize **KIRs (Killer Cell Immunoglobulin-like Receptors)** to detect the absence of MHC Class I molecules on target cells ("Missing Self" hypothesis) [1]. * **LGL Leukemia:** A rare lymphoproliferative disorder characterized by a persistent increase in large granular lymphocytes, often associated with rheumatoid arthritis and neutropenia (Felty’s syndrome). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 200-201.

Question 316: Which granulomatous condition is associated with hypercalcemia?

A. Tuberculosis
B. Sarcoidosis (Correct Answer)
C. Berylliosis
D. Systemic Lupus Erythematosus

Explanation: **Explanation:** **Correct Answer: B. Sarcoidosis** The primary mechanism behind hypercalcemia in sarcoidosis [1] is the **extra-renal synthesis of 1,25-dihydroxyvitamin D (Calcitriol)**. In this condition, activated epithelioid macrophages within the non-caseating granulomas [2] express the enzyme **1-alpha-hydroxylase**. This enzyme converts 25-hydroxyvitamin D into its active form, 1,25-dihydroxyvitamin D, independent of Parathyroid Hormone (PTH) regulation. Elevated calcitriol levels lead to increased intestinal calcium absorption and increased bone resorption, resulting in hypercalcemia and hypercuria. **Analysis of Incorrect Options:** * **A. Tuberculosis:** While TB is a granulomatous disease and can occasionally cause hypercalcemia via a similar mechanism, it is far less characteristic than in Sarcoidosis. * **C. Berylliosis:** This is an occupational lung disease causing non-caseating granulomas similar to sarcoidosis [2]. While hypercalcemia can occur, it is significantly rarer and not the defining biochemical feature for exam purposes. * **D. Systemic Lupus Erythematosus (SLE):** SLE is an autoimmune connective tissue disorder characterized by immune complex deposition (Type III Hypersensitivity), not granuloma formation. It is typically associated with renal failure or cytopenias, not hypercalcemia. **NEET-PG High-Yield Pearls:** * **Biochemical Profile:** In Sarcoidosis, you will see **↑ Calcium, ↑ Vitamin D, and ↓ PTH** (due to negative feedback). * **ACE Levels:** Elevated Angiotensin-Converting Enzyme (ACE) is a common marker produced by granulomas. * **Kveim-Siltzbach Test:** Historically used for diagnosis (though now largely replaced by biopsy showing non-caseating granulomas). * **Asteroid & Schaumann Bodies:** Characteristic microscopic findings within the giant cells of sarcoid granulomas [2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 667-668. [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. 198-200.

Question 317: Which of the following is NOT a feature of DiGeorge syndrome?

A. Results from failure of development of the third and fourth pharyngeal pouches
B. Absent thyroid
C. Absent parathyroid glands
D. B cell defect (Correct Answer)

Explanation: **Explanation:** DiGeorge Syndrome (22q11.2 deletion syndrome) is a classic T-cell immunodeficiency resulting from the **maldevelopment of the 3rd and 4th pharyngeal pouches** [3]. **Why Option D is the correct answer:** DiGeorge syndrome is primarily a **T-cell defect** due to thymic hypoplasia or aplasia [1][3]. While B-cell numbers are usually normal, there may be a secondary impairment in antibody production because B-cells require "T-cell help" to function optimally [2]. However, the primary, hallmark defect is cellular (T-cell) immunity, making "B cell defect" the least characteristic feature among the choices. **Analysis of other options:** * **Option A:** This is the core embryological pathogenesis. The 3rd and 4th pouches fail to differentiate into the thymus and parathyroid glands [3]. * **Option B:** While the thyroid gland itself develops from the thyroid diverticulum (not the 3rd/4th pouches), the **C-cells (parafollicular cells)** of the thyroid are derived from the 4th pouch (ultimobranchial body). In clinical practice and exams, "absent thyroid" is often used loosely in this context to refer to the associated midline defects or C-cell absence, though the thymus and parathyroids are the primary targets. * **Option C:** Absence of parathyroid glands leads to **hypocalcemic tetany**, a classic presenting sign in neonates with this syndrome [1]. **High-Yield Clinical Pearls (CATCH-22):** * **C**ardiac defects (Interrupted aortic arch, Truncus arteriosus, Tetralogy of Fallot) [3]. * **A**bnormal facies (Low set ears, cleft palate) [3]. * **T**hymic hypoplasia (T-cell deficiency → recurrent viral/fungal infections) [1]. * **C**left palate. * **H**ypocalcemia (due to parathyroid aplasia) [3]. * **22**q11.2 deletion (detected via **FISH**) [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1107-1108. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 246-247. [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. 167-168.

Question 318: Which of the following is an autoimmune disease?

A. Sjogren's syndrome
B. Mikulicz's disease
C. Rheumatoid arthritis
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**, as all three conditions are characterized by an immune-mediated attack on self-antigens, leading to chronic inflammation and tissue destruction. 1. **Sjogren’s Syndrome:** This is a systemic autoimmune disorder primarily affecting the exocrine glands (lacrimal and salivary) [1]. It is characterized by lymphocytic infiltration (B and T cells), leading to the classic "sicca complex" (dry eyes and dry mouth) [1]. It is often associated with antibodies like **Anti-Ro (SS-A)** and **Anti-La (SS-B)** [1]. 2. **Mikulicz’s Disease:** Historically confused with Sjogren’s, it is now recognized as a part of **IgG4-related disease (IgG4-RD)**. It involves the autoimmune-mediated symmetrical enlargement of lacrimal, parotid, and submandibular glands. Unlike Sjogren’s, it shows elevated serum IgG4 levels and responds well to steroids. 3. **Rheumatoid Arthritis (RA):** A classic systemic autoimmune disease primarily targeting the synovium of joints [2]. It involves Type III and Type IV hypersensitivity reactions, driven by **Rheumatoid Factor (RF)** and **Anti-CCP antibodies**. **Clinical Pearls for NEET-PG:** * **Sjogren’s Syndrome:** Carries a 40-fold increased risk of developing **B-cell Non-Hodgkin Lymphoma** (MALToma) [1]. * **Mikulicz’s Syndrome vs. Disease:** "Syndrome" refers to glandular enlargement due to other causes (Sarcoidosis, Leukemia), while "Disease" is the specific IgG4-related autoimmune entity. * **Schirmer’s Test:** Used to quantify tear production in Sjogren’s syndrome (positive if <5mm in 5 minutes). * **Lip Biopsy:** The gold standard for diagnosing Sjogren’s, showing focal lymphocytic sialadenitis [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 234-236. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 676-679.

Question 319: Graft versus host disease is due to?

A. Immunocompetent T cells in graft tissue (Correct Answer)
B. Immunocompetent T cells in host
C. Immunocompetent B cells in graft tissue
D. Immunocompetent B cells in host

Explanation: ### Explanation **Graft-versus-Host Disease (GVHD)** occurs when immunologically competent cells (or their precursors) are transplanted into recipients who are immunologically compromised [1]. **Why Option A is Correct:** The fundamental mechanism of GVHD involves **immunocompetent T cells** (specifically CD4+ and CD8+ T cells) present in the **donor (graft) tissue**. These donor T cells recognize the recipient’s (host) HLA antigens as foreign. Once activated, they proliferate and mount an immune attack against the host's tissues, primarily targeting the skin, liver, and gastrointestinal tract [1], [2]. **Analysis of Incorrect Options:** * **Option B & D:** GVHD is defined by the graft attacking the host. If the **host’s** immune cells (T or B cells) were the primary effectors, the process would be termed **Graft Rejection** (Host-versus-Graft), where the recipient's immune system attacks the transplanted organ [3]. * **Option C:** While B cells are involved in the chronic phase of GVHD through autoantibody production, the primary mediators and the "initiators" required for the disease to occur are **T cells**. Without donor T cells, GVHD does not develop [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Billingham’s Criteria:** For GVHD to occur, three conditions must be met: (1) The graft must contain immunocompetent cells, (2) The recipient must be HLA-incompatible, and (3) The recipient must be immunocompromised (unable to reject the graft). * **Common Scenarios:** Most frequently seen in **Allogeneic Bone Marrow/Stem Cell Transplantation**, but can also occur in solid organ transplants rich in lymphoid tissue (e.g., liver) or non-irradiated blood transfusions [1]. * **Acute vs. Chronic:** Acute GVHD occurs within 100 days (presents with rash, jaundice, and diarrhea); Chronic GVHD occurs after 100 days (resembles systemic sclerosis or lichen planus) [1]. * **Graft-versus-Leukemia Effect:** In leukemia patients, a mild degree of GVHD is often beneficial as the donor T cells also attack residual leukemic cells [2]. **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. 182-183. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 244-245. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 239-240.

Question 320: Onion skin spleen is seen in which of the following conditions?

A. Systemic Lupus Erythematosus (SLE) (Correct Answer)
B. Sjogren's syndrome
C. Thrombotic thrombocytopenic purpura
D. Henoch Schonlein purpura

Explanation: **Explanation:** The correct answer is **Systemic Lupus Erythematosus (SLE)**. **1. Why SLE is correct:** The "onion skin" appearance of the spleen is a classic histopathological hallmark of SLE [1]. It refers to **concentric periarterial fibrosis** around the penicilliary arteries (small splenic arteries). This occurs due to the deposition of immune complexes and subsequent fibroblastic proliferation, creating layers that resemble the skin of an onion [1]. While not pathognomonic, it is highly characteristic of SLE and can occur even in the absence of clinical splenomegaly [1], [2]. **2. Why other options are incorrect:** * **Sjogren's syndrome:** Primarily involves lymphocytic infiltration of exocrine glands (lacrimal and salivary) [3]. While it shares autoimmune features with SLE, it does not typically manifest with concentric splenic fibrosis. * **Thrombotic Thrombocytopenic Purpura (TTP):** Characterized by microthrombi in small vessels (microangiopathy). While it affects the spleen, the pathology involves hyaline thrombi, not concentric fibrosis. * **Henoch-Schonlein Purpura (HSP):** An IgA-mediated small-vessel vasculitis. It typically presents with a triad of palpable purpura, arthralgia, and abdominal pain, but does not involve the "onion skin" splenic lesion. **3. NEET-PG High-Yield Pearls:** * **Libman-Sacks Endocarditis:** Another classic SLE pathology involving small, sterile, non-bacterial vegetations on *both* sides of the heart valves (most commonly mitral). * **Wire-loop lesions:** Seen in the kidney (Lupus Nephritis Class IV) due to subendothelial immune complex deposits [5]. * **Hematoxylin Bodies (LE bodies):** Denatured nuclei of damaged cells found in various tissues in SLE [4]. * **Differential Diagnosis:** "Onion skinning" of the **bone** is seen in **Ewing’s Sarcoma**, while "onion skinning" of the **bile ducts** is seen in **Primary Sclerosing Cholangitis**. Do not confuse these with the "onion skin spleen" of SLE. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 226. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 639-640. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 236. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 230. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 232.

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Cells and Tissues of the Immune System

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Innate Immunity

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Hypersensitivity Reactions

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Autoimmune Diseases

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Immunodeficiency Disorders

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Transplantation Immunopathology

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Immune Response to Infections

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Immunologic Laboratory Techniques

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Tumor Immunology

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