Inflammation and Repair — MCQs

A 25-year-old machinist sustains an injury from a metal sliver in his left hand. Over the next few days, the wounded area becomes reddened, tender, swollen, and warm to the touch. The patient presents to the emergency room for removal of the sliver. Twenty-four hours later, endothelial cells at the site of injury release a chemical mediator that inhibits further platelet aggregation. What is this mediator of inflammation?

Q300Medium

In an inflammatory response to infection, it is found that the inflammatory infiltrate is predominated by neutrophils for several days beyond the usual 24-48 hours. Which of the following organisms is most likely the cause of infection?

Inflammation and Repair Indian Medical PG Practice Questions and MCQs

Question 291: What is chronic granulomatous disease?

A. A defect in leukocyte function (Correct Answer)
B. Associated with the formation of multiple granulomas
C. A benign neoplastic process
D. A parasitic disease

Explanation: **Chronic Granulomatous Disease (CGD)** is a primary immunodeficiency disorder characterized by a defect in phagocytic function, specifically the **NADPH oxidase enzyme complex**. ### 1. Why Option A is Correct The core pathology of CGD is a **defect in leukocyte function**. Specifically, there is a failure to produce the "respiratory burst" (reactive oxygen species like superoxide radicals). This occurs due to mutations in the genes encoding components of the NADPH oxidase enzyme (most commonly the **gp91phox** subunit, which is X-linked). Without these oxidative radicals, neutrophils and macrophages can ingest bacteria but cannot kill them, leading to persistent intracellular infections. ### 2. Why Other Options are Incorrect * **Option B:** While the name implies "granulomatous," the disease is defined by the functional leukocyte defect, not just the presence of granulomas. Granulomas form as a *secondary* compensatory mechanism because the body tries to wall off the microbes it cannot kill [1], [2]. * **Option C:** CGD is a genetic immunodeficiency, not a neoplastic (cancerous) process. * **Option D:** It is an inherited genetic disorder, not an infectious parasitic disease, though patients are highly susceptible to specific infections. ### 3. High-Yield Clinical Pearls for NEET-PG * **Inheritance:** Most common is **X-linked recessive** (70%); the rest are Autosomal Recessive. * **Organisms:** Patients are susceptible to **Catalase-positive organisms** (e.g., *Staphylococcus aureus*, *Aspergillus*, *Nocardia*, *Serratia marcescens*, and *Burkholderia cepacia*). Catalase-positive bugs destroy their own H₂O₂, leaving the defective leukocyte with no oxidative tools to use. * **Diagnostic Tests:** 1. **Nitroblue Tetrazolium (NBT) Test:** Cells fail to turn blue (Negative test). 2. **Dihydrorhodamine (DHR) Flow Cytometry:** The modern gold standard; shows decreased fluorescence. * **Morphology:** Characterized by the formation of **granulomas** in skin, liver, and GI tract [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. 198-200. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109.

Question 292: What is the most important cytokine for the synthesis and deposition of connective tissue proteins?

A. PDGF
B. FGF-2
C. TGF-β (Correct Answer)
D. MMP

Explanation: **Explanation:** **TGF-β (Transforming Growth Factor-beta)** is considered the most important cytokine involved in tissue repair and fibrosis [1]. Its primary role is to stimulate the synthesis of collagen, fibronectin, and proteoglycans while simultaneously inhibiting the degradation of the extracellular matrix (ECM) by decreasing the activity of Matrix Metalloproteinases (MMPs) [1]. This dual action makes it the central mediator in the transition from acute inflammation to permanent scar formation. **Analysis of Options:** * **PDGF (Platelet-Derived Growth Factor):** While it is a potent chemoattractant and mitogen for fibroblasts and smooth muscle cells, it acts more as an "initiator" of the proliferative phase rather than the primary driver of protein deposition [3]. * **FGF-2 (Fibroblast Growth Factor-2):** Primarily known for its role in **angiogenesis** (blood vessel formation) and the migration of fibroblasts, but it is not the chief regulator of connective tissue synthesis [1]. * **MMP (Matrix Metalloproteinases):** These are enzymes that **degrade** ECM components to allow for tissue remodeling. They are the functional opposites of TGF-β in the context of protein deposition. **High-Yield Clinical Pearls for NEET-PG:** * **TGF-β Dual Role:** It is anti-inflammatory in early stages (inhibits lymphocyte proliferation) but pro-fibrotic in later stages [1]. * **Pathological Fibrosis:** Excessive TGF-β activity is the hallmark of chronic fibrotic diseases, such as liver cirrhosis, systemic sclerosis, and pulmonary fibrosis. * **Source:** Produced by most cells in granulation tissue, particularly M2 macrophages [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 115-116. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 115. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 117-119.

Question 293: Which of the following events occurs first in wound healing?

A. Thin continuous epithelial cover appears
B. Fibroblasts lay down collagen fiber
C. Granulation tissue fills the wound
D. Neutrophils line the wound edge (Correct Answer)

Explanation: **Explanation:** Wound healing by primary intention follows a predictable chronological sequence. The correct answer is **D (Neutrophils line the wound edge)** because the inflammatory phase is the immediate response to injury. **1. Why Option D is correct:** Within **24 hours** of injury, neutrophils appear at the margins of the incision, moving toward the fibrin clot [1]. They are the first cells to arrive to clear debris and prevent infection. This marks the beginning of the acute inflammatory phase, which precedes the proliferative and remodeling phases. **2. Why the other options are incorrect:** * **Option A (Thin epithelial cover):** This occurs by **24–48 hours**. Epithelial cells from the edges migrate and proliferate along the dermis, meeting in the midline beneath the surface scab to form a thin layer [1]. * **Option B (Fibroblasts lay down collagen):** This occurs during the proliferative phase, typically starting around **day 3** and peaking at **day 5 to 2 weeks** [1]. Fibroblasts are responsible for structural integrity, not the initial response [2]. * **Option C (Granulation tissue fills the wound):** Granulation tissue (characterized by angiogenesis and fibroblast proliferation) typically peaks by **day 3 to 5** [1]. It serves as the "scaffolding" for later tissue repair [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Day 1:** Neutrophils infiltrate; Clot forms [1]. * **Day 3:** Macrophages replace neutrophils; Granulation tissue starts forming [1]. * **Day 5:** Neovascularization (angiogenesis) reaches its peak; Collagen bridges the incision [1]. * **Week 2:** Proliferation of fibroblasts and continued collagen accumulation. * **Month 2:** Connective tissue devoid of inflammation, covered by intact epidermis. * **Tensile Strength:** At 1 week, strength is ~10% of unwounded skin; it reaches ~70-80% by 3 months but rarely returns to 100%. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 117-119. [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. 105-106.

Question 294: Caseous necrosis in granuloma is NOT found in which of the following conditions?

A. Tuberculosis
B. Leprosy (Correct Answer)
C. Histoplasmosis
D. All of the above

Explanation: ### Explanation The core concept tested here is the distinction between **caseating** and **non-caseating** granulomas. Caseous necrosis is a form of cell death characterized by a "cheese-like," friable, white appearance, typically associated with a strong delayed-type hypersensitivity (Type IV) response [1]. **Why Leprosy is the correct answer:** In **Leprosy** (Hansen’s disease), the granulomas formed—whether in the Tuberculoid (paucibacillary) or Lepromatous (multibacillary) poles—are typically **non-caseating** [2], [3]. While Tuberculoid leprosy features well-formed epithelioid granulomas, they lack the central "cheesy" necrosis characteristic of Tuberculosis [2]. **Analysis of Incorrect Options:** * **Tuberculosis (A):** This is the classic prototype of caseating granulomatous inflammation [1]. The necrosis is caused by the host's immune response to the lipid-rich cell wall of *Mycobacterium tuberculosis*. * **Histoplasmosis (C):** Fungal infections, particularly *Histoplasma capsulatum* and *Coccidioides*, frequently mimic Tuberculosis by producing granulomas with central caseous-like necrosis. * **All of the above (D):** This is incorrect because Tuberculosis and Histoplasmosis are well-known causes of caseation. **High-Yield Clinical Pearls for NEET-PG:** * **Non-caseating granulomas:** Think of Sarcoidosis (most common), Leprosy, Crohn’s disease, Berylliosis, and Cat-scratch disease. * **Caseating granulomas:** Think of Tuberculosis, Histoplasmosis, and Coccidioidomycosis. * **Asteroid bodies & Schaumann bodies:** These are microscopic inclusions frequently found in the non-caseating granulomas of **Sarcoidosis**. * **Langhans Giant Cells:** These are peripheral arrangements of nuclei in a horseshoe shape, commonly seen in TB, but can also appear in other granulomatous diseases [4]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 383-384. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 638-639. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109.

Question 295: What governs the strength of a wound after 2 months?

A. Collagen cross-linking (Correct Answer)
B. Excess collagen deposition
C. Both collagen cross-linking and excess collagen deposition
D. None of the above

Explanation: **Explanation:** The tensile strength of a healing wound is primarily determined by the **quality and organization** of collagen, rather than just the quantity. **Why Option A is Correct:** By the end of the first month, the peak of collagen synthesis is reached. However, the wound has only regained about 20–30% of its original strength. From the 2nd month onwards, the increase in strength is attributed to **collagen remodeling** [1]. This involves a structural shift from Type III to **Type I collagen** and, most importantly, the formation of **covalent cross-links** between collagen fibers (catalyzed by the enzyme lysyl oxidase) [1]. This cross-linking increases fiber diameter and structural stability, eventually allowing the wound to reach approximately 70–80% of the strength of unwounded skin by 3 months [1]. **Why Other Options are Incorrect:** * **Option B:** Excess collagen deposition does not necessarily equate to strength. In fact, an imbalance where deposition exceeds degradation leads to pathological scarring, such as **Keloids** or **Hypertrophic scars**, which are structurally inferior to normal tissue [2]. * **Option C:** As explained, strength after the 2nd month is a result of structural modification (cross-linking), not continued net accumulation of collagen [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Tensile Strength Timeline:** * End of 1st week: ~10% [1] * End of 3rd month: ~70–80% (Plateaus here; it rarely reaches 100%) [1]. * **Vitamin C:** Essential for the hydroxylation of proline and lysine; deficiency leads to poor cross-linking and wound dehiscence (Scurvy). * **Zinc:** A necessary cofactor for **Matrix Metalloproteinases (MMPs)**, which are essential for the remodeling phase. * **Type III vs. Type I:** Granulation tissue is rich in Type III collagen; mature scars are predominantly Type I. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 119-121. [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. 106-107.

Question 296: Which of the following statements regarding wound healing is NOT true?

A. Impaired by radiation
B. Impaired by hematoma
C. Impaired by infection
D. Stimulated by steroids (Correct Answer)

Explanation: **Explanation:** Wound healing is a complex process involving inflammation, proliferation, and remodeling. The correct answer is **D** because **steroids inhibit, rather than stimulate, wound healing.** **1. Why "Stimulated by steroids" is FALSE:** Glucocorticoids (steroids) are potent anti-inflammatory agents. They impair wound healing by: * **Inhibiting TGF-β production:** This reduces collagen synthesis and fibroblast proliferation [1]. * **Weakening the scar:** Resulting in decreased tensile strength and increased risk of wound dehiscence [1]. * *Clinical Note:* In some cases, surgeons use topical steroids to prevent excessive scarring (keloids). **2. Why the other options are TRUE (Factors impairing healing):** * **Radiation (A):** Ionizing radiation damages dividing cells (fibroblasts and epithelial cells) and causes microvascular injury, leading to poor blood supply and chronic non-healing wounds. * **Hematoma (B):** A collection of blood acts as a physical barrier between wound edges and provides a rich medium for bacterial growth, increasing the risk of infection. * **Infection (C):** This is the **single most important local cause** of delayed wound healing [1]. It prolongs the inflammatory phase and causes persistent tissue injury through the release of toxins and degradative enzymes [1]. **High-Yield NEET-PG Pearls:** * **Vitamin C deficiency (Scurvy):** Inhibits hydroxylation of proline/lysine, leading to defective collagen cross-linking and wound breakdown [1]. * **Zinc deficiency:** Impairs epithelialization and fibroblast proliferation (Zinc is a cofactor for DNA polymerase and MMPs). * **Diabetes Mellitus:** The most common systemic cause of impaired wound healing due to microangiopathy and impaired neutrophil function [1], [2]. * **First Intention vs. Second Intention:** Healing by second intention involves significant **wound contraction**, mediated primarily by **myofibroblasts** [3], [4], [5]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 116-117. [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. 110-111. [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. 88-89. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 119-121. [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. 105-106.

Question 297: Which cytokine is primarily responsible for fibrosis?

A. TGF-beta (Correct Answer)
B. TNF-alpha
C. IL-7
D. IL-10

Explanation: **Explanation:** **TGF-beta (Transforming Growth Factor-beta)** is the single most important cytokine involved in the process of fibrosis [1]. In the context of chronic inflammation and tissue repair, TGF-beta acts as a potent fibrogenic agent by: 1. **Stimulating fibroblast proliferation** and their transformation into myofibroblasts [2]. 2. **Increasing the synthesis of collagen** and fibronectin [1]. 3. **Decreasing the degradation of the extracellular matrix (ECM)** by inhibiting metalloproteinases (MMPs) and increasing the activity of tissue inhibitors of metalloproteinases (TIMPs). **Analysis of Incorrect Options:** * **TNF-alpha:** A potent pro-inflammatory cytokine primarily involved in acute inflammation, leukocyte recruitment, and the formation of granulomas. While it can influence repair, it is not the primary driver of fibrosis [1]. * **IL-7:** Primarily involved in lymphopoiesis (the production and maturation of B and T cells) within the bone marrow and thymus. It has no significant role in collagen deposition. * **IL-10:** An anti-inflammatory cytokine that functions to limit and terminate the inflammatory response by inhibiting macrophages and Th1 cells. It generally opposes the processes that lead to excessive tissue damage. **High-Yield Clinical Pearls for NEET-PG:** * **TGF-beta Dual Role:** It is also a potent anti-inflammatory agent that helps "turn off" the immune response, but its persistence leads to pathological scarring (e.g., Liver Cirrhosis, Pulmonary Fibrosis). * **VEGF:** Remember this as the primary cytokine for **Angiogenesis** [1]. * **FGF-2:** Important for both angiogenesis and fibroblast migration [1]. * **Mnemonic:** Think of **TGF-beta** as the **"Tough Great Finisher"**—it finishes the repair process by making the tissue "tough" (fibrotic). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 115-119. [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. 88-89.

Question 298: Granulation tissue appearance is due to -

A. Thrombosed capillaries
B. Chronic inflammatory cells
C. Budding ends of capillaries (Correct Answer)
D. Densely packed collagen

Explanation: ### Explanation **Correct Answer: C. Budding ends of capillaries** **Mechanism:** Granulation tissue is the hallmark of early tissue repair. Its characteristic appearance—a soft, pink, granular surface—is primarily due to **angiogenesis** (neovascularization) [1, 2]. During the proliferative phase of healing, newly formed, fragile capillaries "bud" and sprout from pre-existing vessels [3]. These budding ends, along with proliferating fibroblasts and a loose extracellular matrix, give the tissue its distinct granular texture [2]. **Analysis of Incorrect Options:** * **A. Thrombosed capillaries:** While some hemorrhage may occur due to the leakiness of new vessels, thrombosis is not a defining feature of granulation tissue; rather, the tissue is highly vascularized to provide nutrients for repair [1]. * **B. Chronic inflammatory cells:** Although macrophages and plasma cells are present in granulation tissue, they do not contribute to its macroscopic "granular" appearance [1]. * **D. Densely packed collagen:** This is a feature of **fibrosis (scarring)**. In granulation tissue, collagen (mainly Type III) is sparse and loosely arranged [1]. As the tissue matures into a scar, cellularity and vascularity decrease while collagen density increases. **High-Yield NEET-PG Pearls:** * **Components of Granulation Tissue:** (1) New capillaries (angiogenesis), (2) Fibroblasts, (3) Edematous extracellular matrix [2]. * **Key Growth Factor:** **VEGF** (Vascular Endothelial Growth Factor) is the most important driver of angiogenesis in granulation tissue [3]. * **Evolution:** Granulation tissue (Type III Collagen) $\rightarrow$ Mature Scar (Type I Collagen). * **Clinical Note:** Do not confuse *granulation tissue* with a *granuloma* (a collection of epithelioid macrophages seen in chronic inflammation) [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 117-119. [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. 105-106. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 115-116.

Question 299: A 25-year-old machinist sustains an injury from a metal sliver in his left hand. Over the next few days, the wounded area becomes reddened, tender, swollen, and warm to the touch. The patient presents to the emergency room for removal of the sliver. Twenty-four hours later, endothelial cells at the site of injury release a chemical mediator that inhibits further platelet aggregation. What is this mediator of inflammation?

A. Plasmin
B. Prostaglandin (PGI2) (Correct Answer)
C. Serotonin
D. Thrombin

Explanation: ### Explanation The clinical presentation describes a classic acute inflammatory response (rubor, tumor, calor, dolor) following a mechanical injury [1][2]. The question focuses on the physiological "braking mechanism" that prevents excessive clot formation once the initial injury is addressed. **Why Prostaglandin (PGI2) is Correct:** **Prostacyclin (PGI2)** is a potent vasodilator and a powerful **inhibitor of platelet aggregation** [1]. It is synthesized and released by healthy vascular endothelial cells [1]. In the context of inflammation and repair, PGI2 acts as a physiological antagonist to **Thromboxane A2 (TXA2)** (secreted by platelets) [1]. While TXA2 promotes vasoconstriction and aggregation to stop bleeding, PGI2 ensures the patency of the vessel and prevents the thrombus from extending beyond the site of injury. **Analysis of Incorrect Options:** * **A. Plasmin:** This is the primary enzyme responsible for **fibrinolysis** (breaking down existing fibrin clots). While it limits clot size, it does not directly inhibit the initial process of platelet aggregation. * **C. Serotonin (5-HT):** Released from platelet dense granules during activation, serotonin acts as a **vasoconstrictor** to limit blood loss; it does not inhibit aggregation [1]. * **D. Thrombin:** This is a pro-coagulant enzyme that converts fibrinogen to fibrin and is one of the most potent **activators** of platelet aggregation. **NEET-PG High-Yield Pearls:** * **The PGI2/TXA2 Balance:** This is a favorite exam topic. Remember: **P**rostacyclin **P**revents aggregation (Endothelium), while **T**hromboxane **T**riggers aggregation (Platelets) [1]. * **Aspirin Mechanism:** Low-dose aspirin irreversibly inhibits COX-1 in platelets (reducing TXA2). Since platelets lack a nucleus, they cannot synthesize new enzymes, leading to a prolonged anti-platelet effect. Endothelial cells can synthesize new COX enzymes to produce PGI2, maintaining the antithrombotic balance [1]. * **Mediators of Vasodilation:** Prostaglandins (PGI2, PGE1, PGE2, PGD2) and Nitric Oxide (NO) [1][2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 95-96. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 101.

Question 300: In an inflammatory response to infection, it is found that the inflammatory infiltrate is predominated by neutrophils for several days beyond the usual 24-48 hours. Which of the following organisms is most likely the cause of infection?

A. Pseudomonas (Correct Answer)
B. Staphylococci
C. Fungi
D. Virus

Explanation: ### Explanation In the standard timeline of acute inflammation, **neutrophils** predominate the cellular infiltrate for the first 6–24 hours. They are typically replaced by **monocytes/macrophages** within 24–48 hours because neutrophils are short-lived and undergo apoptosis quickly [3]. **Why Pseudomonas is the correct answer:** Certain exceptions exist to this classic timeline. In infections caused by **Pseudomonas aeruginosa**, neutrophils are recruited continuously and remain the dominant cell type for **several days** (up to 2–4 days or longer). This is due to the specific chemotactic signals and the persistent nature of the pathogen's virulence factors, which sustain a prolonged neutrophilic response. **Analysis of Incorrect Options:** * **Staphylococci:** These typically follow the classic pattern of acute inflammation (neutrophils followed by macrophages), although they are potent inducers of pus (pyogenic) [1], [4]. * **Fungi:** While some fungi can cause a mixed inflammatory response, they are more characteristically associated with **granulomatous (chronic) inflammation** or eosinophilic infiltrates [2]. * **Viruses:** Viral infections typically bypass the neutrophilic stage and are characterized by a **lymphocytic** infiltrate from the outset [1]. **NEET-PG High-Yield Pearls:** * **Classic Sequence:** Neutrophils (6–24 hrs) $\rightarrow$ Macrophages (24–48 hrs). * **Exceptions (Prolonged Neutrophils):** *Pseudomonas* infections. * **Exceptions (Early Lymphocytes):** Viral infections. * **Exceptions (Early Eosinophils):** Hypersensitivity reactions (Asthma/Allergy) and Parasitic infections. * **Key Chemotactic Agents for Neutrophils:** IL-8, LTB4, C5a, and Bacterial products (N-formyl methionine). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 109-110. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 103-104. [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. 193-194.

Practice by Chapter

Acute Inflammation: Vascular Events

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Acute Inflammation: Cellular Events

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Chemical Mediators of Inflammation

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Chronic Inflammation

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Granulomatous Inflammation

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Systemic Effects of Inflammation

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Wound Healing

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Tissue Regeneration

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Fibrosis and Repair

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Resolution of Inflammation

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