Inflammation and Repair — MCQs

A 32-year-old woman has had a chronic cough with fever for the past month. On physical examination, her temperature is 37.5°C. A chest radiograph shows many small, ill-defined nodular opacities in all lung fields. A transbronchial biopsy specimen shows interstitial infiltrates with lymphocytes, plasma cells, and epithelioid macrophages. Which of the following infectious agents is the most likely cause of this appearance?

Q253Medium

A 5-year-old boy punctures his thumb with a rusty nail. Four hours later, the thumb appears red and swollen. The initial swelling of the boy's thumb is primarily due to which of the following mechanisms?

Q254Easy

What type of cell is primarily attracted to an acute inflammatory focus?

Q255Easy

Which prostaglandin is primarily responsible for fever?

Q256Easy

Which amino acid is useful in Neutrophil Extracellular Traps (NETs) and causes lysis of chromatin?

Q257Medium

Which of the following infections is associated with persistent neutrophil recruitment even after 24 hours of infection?

Q258Medium

A 25-year-old woman presents with a 2-week history of febrile illness and chest pain. She has an erythematous, macular facial rash and tender joints, particularly in her left wrist and elbow. A CBC shows mild anemia and thrombocytopenia. Corticosteroids are prescribed for the patient. The patient is noted to have increased serum levels of ceruloplasmin, fibrinogen, 2-macroglobulin, serum amyloid A protein, and C-reactive protein. Together, these markers belong to which of the following families of proteins?

Q259Easy

Which reactant generated by neutrophils plays an important role in bacterial killing?

Q260Easy

All of the following are positive acute phase reactants except which one?

Inflammation and Repair Indian Medical PG Practice Questions and MCQs

Question 251: Arrange the steps in cellular changes in inflammation in the correct sequence?

A. Chemotaxis, Diapedesis, Margination, Respiratory burst, Phagocytosis
B. Chemotaxis, Margination, Diapedesis, Phagocytosis, Respiratory burst
C. Phagocytosis, Margination, Chemotaxis, Diapedesis, Respiratory burst
D. Margination, Diapedesis, Chemotaxis, Phagocytosis, Respiratory burst (Correct Answer)

Explanation: ### Explanation The cellular phase of acute inflammation involves the recruitment of leukocytes from the vascular lumen to the site of injury [1]. This process follows a highly regulated, sequential cascade: 1. **Margination and Rolling:** As blood flow slows (stasis), leukocytes move from the central column to the periphery of the vessel (**Margination**). They then tumble along the endothelium via transient interactions (mediated by Selectins) [2]. 2. **Adhesion and Transmigration (Diapedesis):** Leukocytes bind firmly to the endothelium (mediated by Integrins) and crawl through the intercellular junctions to exit the vessel (**Diapedesis**) [2], [3]. 3. **Chemotaxis:** Once in the extravascular space, leukocytes migrate toward the injury site along a chemical gradient (e.g., C5a, LTB4, bacterial products) [3], [5]. 4. **Phagocytosis:** The leukocyte recognizes, engulfs, and internalizes the offending agent into a phagosome [1]. 5. **Killing (Respiratory Burst):** This is the final step where a rapid increase in oxygen consumption (Respiratory Burst) produces Reactive Oxygen Species (ROS) like superoxide and $H_2O_2$ to destroy the ingested microbe. #### Analysis of Incorrect Options: * **Options A & B:** These are incorrect because **Margination** must occur before Diapedesis [2]. Furthermore, **Chemotaxis** occurs only after the cell has exited the vessel (post-diapedesis) [3]. * **Option C:** This is incorrect because **Phagocytosis** is a late-stage event that can only happen after the leukocyte has successfully migrated to the tissue site [1]. #### NEET-PG High-Yield Pearls: * **Rolling** is mediated by **Selectins** (E, P, and L-selectin) [2], [4]. * **Firm Adhesion** is mediated by **Integrins** (ICAM-1, VCAM-1) [4]. * **Diapedesis** primarily involves **PECAM-1 (CD31)** [3]. * **Most potent chemotactic agents:** C5a, LTB4, IL-8, and Bacterial Formyl peptides [3]. * **Defect in Phagolysosome formation:** Chédiak-Higashi syndrome. * **Defect in Respiratory Burst:** Chronic Granulomatous Disease (NADPH oxidase deficiency). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 81. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Migration in the tissues toward a chemotactic stimulus, pp. 86-87. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 87-89. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 87. [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. 188-189.

Question 252: A 32-year-old woman has had a chronic cough with fever for the past month. On physical examination, her temperature is 37.5°C. A chest radiograph shows many small, ill-defined nodular opacities in all lung fields. A transbronchial biopsy specimen shows interstitial infiltrates with lymphocytes, plasma cells, and epithelioid macrophages. Which of the following infectious agents is the most likely cause of this appearance?

A. Candida albicans
B. Cytomegalovirus
C. Enterobacter aerogenes
D. Mycobacterium tuberculosis (Correct Answer)

Explanation: The clinical presentation and histopathology point toward **Granulomatous Inflammation**, a hallmark of chronic inflammation. [3] **1. Why Mycobacterium tuberculosis is correct:** The patient presents with a chronic cough, low-grade fever, and a "miliary" pattern (small nodular opacities) on chest X-ray. [4] The biopsy reveals **epithelioid macrophages**, which are the defining feature of a granuloma. [2] These are activated macrophages that have developed an abundant pink cytoplasm resembling epithelial cells [3], usually under the influence of **IFN-γ** produced by TH1 cells. [1] *M. tuberculosis* is the most common cause of granulomatous inflammation characterized by these cells, often accompanied by Langhans giant cells and central caseous necrosis. [2] **2. Why the other options are incorrect:** * **Candida albicans:** Typically causes acute inflammation with neutrophils (abscess formation) or pseudohyphae/yeast forms in tissue. It does not typically present with epithelioid granulomas. * **Cytomegalovirus (CMV):** A viral infection characterized by "Owl’s eye" intranuclear inclusions. It causes interstitial pneumonitis but not epithelioid granulomas. * **Enterobacter aerogenes:** A gram-negative bacterium that causes acute pyogenic inflammation (pneumonia) characterized by a dense neutrophilic infiltrate, not a chronic granulomatous response. **NEET-PG High-Yield Pearls:** * **Epithelioid cells:** Derived from activated macrophages; they have decreased phagocytic activity but increased secretory function. [3] * **Granuloma Composition:** Lymphocytes (outer rim), epithelioid macrophages, and multinucleated giant cells (Langhans type in TB). [3] * **Miliary TB:** Represents hematogenous spread, appearing as 1-2 mm "millet seed" lesions throughout the lung. [4] * **Key Cytokine:** **TNF-α** is essential for the formation and maintenance of granulomas (Infliximab therapy can cause granuloma breakdown and TB reactivation). [1] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 380-381. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 383-384. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 320-321.

Question 253: A 5-year-old boy punctures his thumb with a rusty nail. Four hours later, the thumb appears red and swollen. The initial swelling of the boy's thumb is primarily due to which of the following mechanisms?

A. Decreased intravascular hydrostatic pressure
B. Decreased intravascular oncotic pressure
C. Increased capillary permeability (Correct Answer)
D. Increased intravascular oncotic pressure

Explanation: **Explanation:** The clinical scenario describes the **acute inflammatory response** following a mechanical injury [3]. The cardinal signs of inflammation—redness (*rubor*) and swelling (*tumor*)—are mediated by vascular changes that occur shortly after injury [1], [3]. **Why Option C is Correct:** The hallmark of acute inflammation is **increased vascular permeability**, leading to the formation of an **exudate** [1]. Following the injury, chemical mediators (like histamine, bradykinin, and leukotrienes) cause endothelial cell contraction, creating "gaps" in the post-capillary venules [1], [2]. This allows protein-rich fluid and blood cells to move from the intravascular compartment into the interstitial tissue [1]. This increase in interstitial osmotic pressure, coupled with the fluid shift, results in localized **edema (swelling)**. **Why Other Options are Incorrect:** * **Options A & B:** For swelling to occur, hydrostatic pressure usually *increases* (due to vasodilation) and intravascular oncotic pressure *decreases* (as proteins leak out). Decreased hydrostatic pressure or increased oncotic pressure would actually favor fluid retention within the vessels, preventing swelling. * **Option D:** Intravascular oncotic pressure is maintained by plasma proteins (primarily albumin). In inflammation, these proteins leak out; therefore, the oncotic pressure inside the vessel decreases, not increases. **NEET-PG High-Yield Pearls:** * **Mechanism of Leakage:** The most common mechanism of vascular leakage in acute inflammation is **endothelial cell contraction** (immediate transient response), affecting post-capillary venules [1]. * **Exudate vs. Transudate:** * **Exudate:** High protein, high LDH, specific gravity >1.020 (Seen in inflammation). * **Transudate:** Low protein, low LDH, specific gravity <1.012 (Seen in systemic conditions like CHF or Nephrotic syndrome). * **Sequence of Events:** Vasodilation (causes redness/heat) → Increased permeability (causes swelling) → Stasis → Leukocyte margination [1]. **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. 187-188. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 101. [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. 185-186.

Question 254: What type of cell is primarily attracted to an acute inflammatory focus?

A. Monocytes
B. Plasma cells
C. Neutrophils (Correct Answer)
D. Basophils

Explanation: **Explanation:** The hallmark of **acute inflammation** is the rapid recruitment of leukocytes to the site of injury [1]. Among these, **Neutrophils** (polymorphonuclear leukocytes) are the first responders [2]. They are primarily attracted to the inflammatory focus within the first 6–24 hours [1]. This rapid recruitment is driven by their high concentration in the blood, their rapid response to chemokines (like IL-8 and C5a), and their ability to attach firmly to adhesion molecules (selectins and integrins) on activated vascular endothelium [1], [3]. **Analysis of Options:** * **A. Monocytes:** These are the second wave of cells. They typically replace neutrophils after 24–48 hours, maturing into macrophages to handle chronic inflammation and tissue repair [1], [2]. * **B. Plasma Cells:** These are differentiated B-lymphocytes associated with **chronic inflammation**, particularly in conditions like syphilis or rheumatoid arthritis. * **C. Neutrophils (Correct):** The primary cellular component of the acute inflammatory infiltrate and the chief cells in "pus" formation [2]. * **D. Basophils:** These are involved in IgE-mediated allergic reactions and parasitic infections, but are not the primary cells in general acute inflammation. **High-Yield NEET-PG Pearls:** * **Exceptions to the Rule:** While neutrophils dominate most acute inflammation, **Lymphocytes** are the first responders in viral infections, and **Eosinophils** dominate in allergic reactions or parasitic infestations. * **Chemotactic Factors:** The most potent chemoattractants for neutrophils are **IL-8, C5a, Leukotriene B4 (LTB4),** and bacterial products (N-formylmethionine) [3]. * **Lifespan:** Neutrophils are short-lived (dying via apoptosis within 24-48 hours), which is why they are replaced by longer-lived monocytes in the later stages of inflammation [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 83-89. [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. 188-193. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 87-89.

Question 255: Which prostaglandin is primarily responsible for fever?

A. PGD2
B. PGE2 (Correct Answer)
C. PGF2a
D. PGI2

Explanation: **Explanation:** **Why PGE2 is the correct answer:** Prostaglandin E2 (PGE2) is the ultimate mediator of fever. During inflammation or infection, exogenous pyrogens (like bacterial LPS) stimulate immune cells to release endogenous pyrogens, primarily **IL-1 and TNF**. These cytokines travel to the hypothalamus, where they induce the enzyme **Cyclooxygenase (COX)** to convert arachidonic acid into **PGE2** [1]. PGE2 then acts on the EP3 receptors in the preoptic area of the hypothalamus, triggering a reset of the thermoregulatory set-point to a higher level, resulting in fever. This is the physiological basis for using NSAIDs (COX inhibitors) as antipyretics. **Analysis of Incorrect Options:** * **PGD2:** Primarily produced by mast cells; it is a potent chemoattractant for neutrophils and causes vasodilation and increased vascular permeability, but it does not mediate fever. * **PGF2α:** Primarily involved in uterine contractions (oxytocic effect) and bronchoconstriction. It is not a mediator of the systemic inflammatory response like fever. * **PGI2 (Prostacyclin):** Produced by vascular endothelium; it is a potent vasodilator and an inhibitor of platelet aggregation. While it contributes to the "pain" and "redness" of inflammation, it is not the primary pyrogen. **High-Yield NEET-PG Pearls:** * **PGE2 Triple Threat:** Remember PGE2 for **P**ain, **P**yrexia (Fever), and **P**atency of the Ductus Arteriosus [1]. * **Cytokine Trigger:** IL-1 is the most potent cytokine inducer of PGE2 in the hypothalamus [1]. * **Aspirin Mechanism:** Aspirin reduces fever by inhibiting COX-1 and COX-2, thereby blocking the synthesis of PGE2. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 101.

Question 256: Which amino acid is useful in Neutrophil Extracellular Traps (NETs) and causes lysis of chromatin?

A. Arginine (Correct Answer)
B. Alanine
C. Phenylalanine
D. Valine

Explanation: **Explanation:** **Neutrophil Extracellular Traps (NETs)** are extracellular fibrillar networks produced by neutrophils to trap and kill microbes. The core mechanism involves the release of nuclear chromatin into the extracellular space. **Why Arginine is the correct answer:** The key enzyme involved in NETosis is **Peptidylarginine Deiminase 4 (PAD4)**. Chromatin is normally tightly packed because of the strong electrostatic attraction between negatively charged DNA and positively charged **Arginine** and Lysine residues in histone proteins [1]. PAD4 converts these **Arginine** residues into **Citrulline** (a process called citrullination). Citrulline is neutral, which leads to the loss of positive charge on histones, causing the chromatin to lose its affinity for DNA. This results in **chromatin decondensation (lysis)** and its subsequent release from the cell to form the "trap." **Why the other options are incorrect:** * **Alanine, Phenylalanine, and Valine:** These are non-polar, hydrophobic amino acids. They do not carry the strong positive charge necessary for DNA binding in histones, nor are they substrates for the PAD4 enzyme. Therefore, they do not play a functional role in the biochemical remodeling of chromatin during NETosis. **NEET-PG High-Yield Pearls:** * **NETosis:** A specialized form of programmed cell death (distinct from apoptosis and necrosis) where the nuclear envelope ruptures. * **Components of NETs:** Chromatin (DNA + Histones) and antimicrobial granular proteins (e.g., **Myeloperoxidase**, **Neutrophil Elastase**) [2]. * **Clinical Correlation:** NETs are implicated in the pathogenesis of **Systemic Lupus Erythematosus (SLE)**, where they serve as a source of self-antigens (anti-dsDNA and anti-histone antibodies) [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 15-16. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 92-93.

Question 257: Which of the following infections is associated with persistent neutrophil recruitment even after 24 hours of infection?

A. Tuberculosis
B. Virus
C. Pseudomonas (Correct Answer)
D. Protozoa

Explanation: In the standard cellular response of acute inflammation, **neutrophils** are the first responders, typically dominating the infiltrate during the first **6–24 hours** [3]. They are subsequently replaced by **monocytes/macrophages** after 24–48 hours due to the shorter lifespan of neutrophils and the delayed recruitment of mononuclear cells [3]. **Why Pseudomonas is the correct answer:** *Pseudomonas aeruginosa* is a notable exception to this rule. In *Pseudomonas* infections, **neutrophils are recruited continuously for several days** (persistent recruitment). This is primarily due to the specific chemoattractants produced by the bacteria and the sustained release of cytokines that prolong the neutrophilic phase, making the infiltrate appear "acute" for a longer duration. **Analysis of Incorrect Options:** * **A. Tuberculosis:** This is a chronic granulomatous infection. The predominant cells are **epithelioid macrophages** and lymphocytes, not neutrophils [1], [2], [4]. * **B. Virus:** In most viral infections, **lymphocytes** are the first cells to arrive at the site of injury, rather than neutrophils (except in specific cases like viral encephalitis) [1]. * **C. Protozoa:** These infections typically elicit a **lymphocytic or eosinophilic** response depending on the organism and tissue involved [1]. **High-Yield NEET-PG Pearls:** 1. **Standard Sequence:** Neutrophils (6–24 hrs) $\rightarrow$ Macrophages (24–48 hrs). 2. **Exceptions to the Rule:** * **Pseudomonas:** Persistent neutrophils for several days. * **Viral Infections:** Lymphocytes may be the first responders. * **Hypersensitivity/Allergy/Parasites:** Eosinophils may dominate [1]. 3. **Neutrophil Lifespan:** They undergo apoptosis within 24–48 hours after entering tissues, which is why their persistence in *Pseudomonas* requires constant new recruitment. **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. 195-196. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360. [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. 192-193. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 109-110.

Question 258: A 25-year-old woman presents with a 2-week history of febrile illness and chest pain. She has an erythematous, macular facial rash and tender joints, particularly in her left wrist and elbow. A CBC shows mild anemia and thrombocytopenia. Corticosteroids are prescribed for the patient. The patient is noted to have increased serum levels of ceruloplasmin, fibrinogen, 2-macroglobulin, serum amyloid A protein, and C-reactive protein. Together, these markers belong to which of the following families of proteins?

A. Acute phase proteins (Correct Answer)
B. Anaphylatoxins
C. Inhibitors of platelet activation
D. Protease inhibitors

Explanation: ### Explanation **Correct Option: A. Acute phase proteins** The clinical presentation (malar rash, joint pain, fever, and cytopenia) is highly suggestive of **Systemic Lupus Erythematosus (SLE)** [1], [3], an inflammatory autoimmune disorder. The proteins mentioned—**Ceruloplasmin, Fibrinogen, $̡_2$-macroglobulin, Serum Amyloid A (SAA), and C-reactive protein (CRP)**—are classic examples of **Acute Phase Reactants (APRs)**. APRs are plasma proteins whose concentrations increase (positive APRs) or decrease (negative APRs, e.g., Albumin, Transferrin) by at least 25% during inflammation [2]. Their synthesis is primarily stimulated by pro-inflammatory cytokines, specifically **IL-6, IL-1, and TNF-$̑$**, acting on the liver [2]. **Analysis of Incorrect Options:** * **B. Anaphylatoxins:** These are fragments of complement proteins (**C3a, C4a, C5a**) that trigger mast cell degranulation and increase vascular permeability. While involved in inflammation, they do not include fibrinogen or ceruloplasmin. * **C. Inhibitors of platelet activation:** While some APRs (like fibrinogen) are involved in coagulation, the group as a whole does not function to inhibit platelets. In fact, inflammation often promotes a pro-thrombotic state. * **D. Protease inhibitors:** While $̡_2$-macroglobulin and $̑_1$-antitrypsin act as protease inhibitors, other listed proteins like CRP (an opsonin) and Fibrinogen (a clotting factor) do not share this function. --- ### NEET-PG High-Yield Pearls * **ESR vs. CRP:** CRP is a rapid responder (rises and falls quickly), whereas ESR (driven largely by **Fibrinogen**) is a slower marker of chronic inflammation. * **Negative APRs:** Remember the mnemonic **"TAP"** (Transferrin, Albumin, Pre-albumin/Transthyretin) – these levels *decrease* during acute inflammation. * **Serum Amyloid A (SAA):** Prolonged elevation of SAA in chronic inflammation (like RA or Bronchiectasis) leads to **Secondary (AA) Amyloidosis**. * **Hepcidin:** An important APR that sequesters iron, leading to **Anemia of Chronic Disease**. **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] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 110-111. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 685-686.

Question 259: Which reactant generated by neutrophils plays an important role in bacterial killing?

A. NADPH oxidase
B. Hexose monophosphate shunt
C. G proteins
D. Superoxide anion (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Superoxide anion** The primary mechanism for bacterial killing in neutrophils is the **Respiratory Burst** (Oxidative Burst). Upon activation, neutrophils undergo a rapid increase in oxygen consumption [1]. The enzyme **NADPH oxidase** (phox) transfers electrons from NADPH to molecular oxygen ($O_2$), reducing it to the **Superoxide anion ($O_2^{\bullet-}$)** [2]. This superoxide anion is the first reactive oxygen species (ROS) generated in the phagolysosome and serves as the precursor for other potent microbicides like hydrogen peroxide ($H_2O_2$) and hypochlorous acid (HOCl) [1]. **Analysis of Incorrect Options:** * **A. NADPH oxidase:** This is the **enzyme** (protein complex) that catalyzes the reaction, not the reactant/product itself [2]. While essential, the question asks for the "reactant" (chemical species) generated. * **B. Hexose monophosphate (HMP) shunt:** This is the metabolic pathway that provides the necessary **NADPH** required for the respiratory burst. It is a supportive metabolic process, not the killing agent. * **C. G proteins:** These are signaling molecules involved in chemotaxis and leukocyte activation (e.g., GPCRs), but they do not have direct bactericidal activity. **High-Yield Clinical Pearls for NEET-PG:** * **Chronic Granulomatous Disease (CGD):** Caused by a genetic deficiency in **NADPH oxidase**. Patients cannot produce superoxide anions, leading to recurrent infections with **catalase-positive organisms** (e.g., *S. aureus*, *Aspergillus*). * **Nitroblue Tetrazolium (NBT) Test:** Historically used to diagnose CGD. Normal neutrophils turn the dye blue (positive), while CGD cells remain colorless. * **MPO-Halide System:** The most potent bactericidal system in neutrophils [1]. Myeloperoxidase (MPO) converts $H_2O_2$ and $Cl^-$ into **HOCl (bleach)** [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 91. [2] 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. 59.

Question 260: All of the following are positive acute phase reactants except which one?

A. Albumin (Correct Answer)
B. Serum amyloid A (SAA)
C. C-reactive protein (CRP)
D. Fibrinogen

Explanation: **Explanation:** Acute-phase reactants (APRs) are proteins whose plasma concentrations increase or decrease by at least 25% in response to inflammation, infection, or tissue injury. These changes are primarily mediated by cytokines like **IL-6, IL-1, and TNF-α** acting on the liver [1]. **1. Why Albumin is the correct answer:** Albumin is a **Negative Acute Phase Reactant**. During inflammation, the liver prioritizes the synthesis of "positive" reactants (like CRP) to aid the immune response, leading to a downregulation of albumin production. Additionally, increased vascular permeability during inflammation causes albumin to leak into the extravascular space. Other negative APRs include **Transferrin** and **Transthyretin (Prealbumin)**. **2. Analysis of Incorrect Options (Positive APRs):** * **Serum Amyloid A (SAA):** A major positive APR. Prolonged elevation of SAA in chronic inflammation can lead to Secondary (AA) Amyloidosis. * **C-reactive protein (CRP):** The most well-known positive APR [1]. It acts as an opsonin, fixing complement and facilitating phagocytosis. It is a sensitive but non-specific marker of systemic inflammation. * **Fibrinogen:** A positive APR that plays a role in coagulation. High levels of fibrinogen cause RBCs to form stacks (rouleaux), which is the primary reason for an **elevated Erythrocyte Sedimentation Rate (ESR)** during inflammation. **Clinical Pearls for NEET-PG:** * **Most sensitive marker:** CRP (rises within 6–10 hours). * **ESR vs. CRP:** CRP reflects the current inflammatory status more accurately than ESR, as ESR is an indirect measure influenced by RBC morphology and hematocrit. * **Procalcitonin:** A specific positive APR used to distinguish bacterial infections from viral or non-infectious causes. * **Hepcidin:** A positive APR that sequesters iron, leading to **Anemia of Chronic Disease**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 110-111.

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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