Inflammation and Tissue Repair - MCQs MCQs

Question 1

A 45-year-old man develops a wound infection. The tissue macrophages recognize the bacteria through pattern recognition receptors. Which of the following best describes the mechanism by which Toll-like receptors (TLRs) contribute to the inflammatory response?

Accepted Answer

They recognize pathogen-associated molecular patterns and trigger production of inflammatory mediators — TLRs are pattern recognition receptors expressed on sentinel cells like macrophages, dendritic cells, and epithelial cells. They recognize conserved microbial structures (PAMPs) in different cellular compartments - plasma membrane for extracellular microbes, endosomes for ingested microbes, and cytosol for intracellular microbes. Upon engagement, TLRs trigger signaling pathways that lead to production of inflammatory mediators including cytokines, adhesion molecules, and chemokines. They don't directly phagocytose (that's the role of phagocytic receptors), don't form membrane pores (that's complement's membrane attack complex), don't bind antibodies (that's Fc receptors), and don't release histamine (that's mast cells). ---

Question 2

A research study examines cellular responses to tissue necrosis from various causes including ischemia, trauma, and chemical injury. Which sensor mechanism is responsible for detecting damaged cells regardless of the cause of injury?

Accepted Answer

NOD-like receptors detecting uric acid and ATP — NOD-like receptors (NLRs) are cytosolic receptors that recognize diverse molecules released from damaged cells, making them the universal sensors of cell damage. These include uric acid (DNA breakdown product), ATP (from damaged mitochondria), reduced intracellular K+ (from membrane injury), and cytoplasmic DNA. NLRs activate the inflammasome, which produces IL-1, triggering inflammation. The other options are more specific: mannose-binding lectin and TLR-4 recognize microbes specifically, C3b is a complement product that assists in phagocytosis, and scavenger receptors primarily handle modified lipoproteins. Only NLRs detect damage from ANY cause - ischemia, trauma, or toxins. ---

Question 3

During an inflammatory response to bacterial infection, which sequence correctly describes the temporal pattern of leukocyte infiltration?

Accepted Answer

Neutrophils (6-24h) → monocytes (24-48h) → lymphocytes (later stages) — The typical sequence in acute inflammation shows neutrophils predominating in the first 6-24 hours, then being replaced by monocytes at 24-48 hours. Neutrophils arrive first because they're more numerous in blood, respond faster to chemokines, and attach more firmly to early adhesion molecules like P-selectin and E-selectin. Neutrophils are short-lived in tissues (undergo apoptosis within days), while monocytes survive longer and may proliferate, becoming the dominant population in prolonged reactions. Lymphocytes typically appear in later stages or in chronic inflammation. Eosinophils are seen mainly in allergic reactions and parasitic infections, not typical bacterial infections. ---

Question 4

A patient with hereditary angioedema experiences recurrent episodes of severe swelling. This condition results from deficiency of C1 inhibitor. Which of the following best explains the pathophysiology?

Accepted Answer

Excessive C3a and C5a production leads to mast cell degranulation and increased vascular permeability — C1 inhibitor (C1 INH) is a key regulatory protein that blocks activation of C1, the first protein of the classical complement pathway. Without it, there's uncontrolled complement activation producing excessive amounts of C3a and C5a - the anaphylatoxins. These fragments stimulate mast cell degranulation and histamine release, causing the vasodilation and increased vascular permeability that leads to angioedema (swelling). The membrane attack complex (MAC) is formed later in the cascade and isn't the primary issue here. Opsonization defects would cause infections, not swelling. This isn't about phagocytosis or leukocyte adhesion - it's specifically about uncontrolled complement activation causing vascular leakage. ---

Question 5

In a patient with chronic granulomatous disease (CGD), neutrophils fail to kill ingested bacteria. Which enzyme complex is deficient?

Accepted Answer

NADPH oxidase — CGD results from inherited deficiencies in components of NADPH oxidase (phagocyte oxidase), which is essential for the respiratory burst that generates superoxide (O2•) and subsequent reactive oxygen species. This enzyme complex normally assembles rapidly when neutrophils phagocytose bacteria - cytosolic components translocate to the phagosomal membrane to form the active enzyme. Without functional NADPH oxidase, neutrophils can phagocytose bacteria but cannot kill them effectively. Myeloperoxidase deficiency causes a milder problem because other microbicidal mechanisms compensate. iNOS is more important in macrophages. COX-2 and 5-lipoxygenase produce inflammatory mediators, not microbicidal substances. ---

Question 6

A 55-year-old diabetic develops a foot ulcer that fails to heal despite antibiotics. Which factor is LEAST likely contributing to impaired wound healing?

Accepted Answer

Excessive neutrophil extracellular trap formation — Diabetic ulcers result from multiple factors: ischemia from vascular disease (atherosclerosis) reduces oxygen delivery needed for healing; neuropathy removes protective pain sensation allowing continued trauma; metabolic abnormalities (hyperglycemia, insulin resistance) impair cellular functions; and the wounds are prone to infection. These are all documented contributors. NET formation, while it can occur in infections, is not a major mechanism of impaired healing in diabetes - in fact, impaired immune function in diabetes might reduce NET formation. The question asks for the LEAST likely contributor, and excessive NET formation doesn't fit the pathophysiology of diabetic wound healing failure the way the other factors do. ---

Question 7

A researcher studying leukocyte recruitment observes that blocking E-selectin on endothelial cells reduces but doesn't eliminate neutrophil rolling. Which molecule likely compensates?

Accepted Answer

P-selectin — Leukocyte rolling is mediated specifically by selectins, not integrins. E-selectin and P-selectin are both expressed on activated endothelium and both mediate rolling by binding to sialylated oligosaccharides on leukocytes. P-selectin is rapidly expressed (within minutes) by redistribution from Weibel-Palade bodies, while E-selectin expression takes 1-2 hours after cytokine stimulation. So if E-selectin is blocked, P-selectin can still mediate rolling. ICAM-1 and VCAM-1 are ligands for integrins and mediate firm adhesion, not rolling. LFA-1 and MAC-1 are integrins on leukocytes that bind to ICAM-1 for firm adhesion. Only P-selectin performs the same rolling function as E-selectin. ---

Question 8

During acute inflammation, what causes the conversion of a "marginating pool" of neutrophils to become available in circulation?

Accepted Answer

Accelerated release from bone marrow due to cytokines like TNF and IL-1 — The question addresses the immediate increase in circulating neutrophils (leukocytosis) that occurs early in inflammation. This happens because cytokines like TNF and IL-1 cause accelerated release of granulocytes from bone marrow storage pools, including both mature and immature neutrophils (causing a "left shift"). This is a rapid response utilizing already-produced cells. CSF production increases marrow proliferation but takes longer to affect counts. Selectin expression would cause neutrophils to stick to vessels, not increase circulation. Integrin affinity changes help neutrophils exit vessels. Reduced apoptosis isn't the primary mechanism for the rapid leukocytosis. The marginating pool refers to cells already in circulation but along vessel walls - they're mobilized by the acute phase response. ---

Question 9

A patient receives a COX-2 selective inhibitor for chronic arthritis but develops a myocardial infarction. What best explains this adverse effect?

Accepted Answer

Selective inhibition of endothelial PGI2 production without affecting platelet TxA2 favors thrombosis — This is a critical clinical point about selective COX-2 inhibitors. Endothelial cells produce prostacyclin (PGI2) via COX-2, which is a vasodilator and inhibits platelet aggregation. Platelets produce thromboxane A2 (TxA2) via COX-1, which promotes vasoconstriction and platelet aggregation. Selective COX-2 inhibitors block endothelial PGI2 production but leave platelet TxA2 production intact (since platelets use COX-1). This tips the balance toward thrombosis, especially in patients with cardiovascular risk factors. The arachidonic acid shunting concept isn't the mechanism here. These drugs don't primarily work by affecting adhesion molecules or cytokines. The hepatocyte explanation is incorrect and unrelated. ---

Question 10

In examining a tissue biopsy showing chronic inflammation, which finding would most strongly suggest immune-mediated rather than infectious etiology?

Accepted Answer

Organized lymphoid follicles with germinal centers (tertiary lymphoid organs) — Tertiary lymphoid organs - organized lymphoid follicles resembling lymph nodes - form in chronically inflamed tissues particularly in autoimmune diseases like rheumatoid arthritis (synovium) and Hashimoto thyroiditis (thyroid). Their formation suggests persistent immune activation against self or environmental antigens rather than microbes. Neutrophils are typical of acute bacterial infections. Granulation tissue is a general repair response seen in both infectious and non-infectious inflammation. Eosinophils can be seen in parasitic infections AND allergic conditions. Fibrin deposition occurs in many inflammatory contexts. Only the tertiary lymphoid organs specifically suggest chronic immune-mediated disease with persistent antigen stimulation and local lymphocyte proliferation. ## SECTION 2: VASCULAR REACTIONS AND MEDIATORS ---

Question 11

A burn patient develops edema at the injury site. Examination of the fluid shows high protein content and cellular debris. What term best describes this fluid?

Accepted Answer

Exudate — An exudate is extravascular fluid with HIGH protein content and cellular debris, indicating increased vascular permeability from inflammation. Transudates have LOW protein (mostly albumin), little/no cells, and result from osmotic or hydrostatic imbalance WITHOUT increased permeability (seen in heart failure, liver disease). Effusions are fluid accumulations in body cavities and can be either exudates or transudates. Pus is a specific type of exudate rich in neutrophils and microbes (purulent/suppurative inflammation). Serous fluid is typically cell-poor and seen in mild injuries like blisters. The burn causes inflammatory vascular permeability changes, leaking protein-rich fluid with debris - defining an exudate. ---

Question 12

Which mechanism accounts for the immediate transient phase of increased vascular permeability in acute inflammation?

Accepted Answer

Histamine-induced endothelial cell contraction creating interendothelial gaps — The immediate transient response (within seconds to minutes, lasting 15-30 minutes) is caused by histamine and other vasoactive mediators inducing endothelial cell contraction in venules, creating gaps between cells. This is the FIRST and fastest mechanism. Direct endothelial injury causes immediate but sustained leakage (hours to days) - not transient. Leukocyte-dependent injury comes later after cells are recruited. VEGF and angiogenesis are processes in tissue repair, not acute permeability changes. The delayed prolonged response (2-12 hours onset, lasting days) results from mild endothelial damage. Only histamine-mediated contraction fits the "immediate transient" pattern. ---

Question 13

A patient with septic shock shows elevated levels of multiple cytokines. Which combination is most directly responsible for the fever?

Accepted Answer

IL-1 and TNF inducing COX-2 and PGE2 production in hypothalamus — Fever is caused by IL-1 and TNF (endogenous pyrogens) acting on hypothalamic vascular cells to upregulate cyclooxygenase (COX), which produces prostaglandins, especially PGE2. PGE2 then stimulates neurotransmitter production that resets the body's temperature set-point higher. This is why NSAIDs and aspirin (COX inhibitors) reduce fever by blocking prostaglandin synthesis. IL-8 and MCP-1 are chemokines for leukocyte recruitment, not fever. IL-6 does contribute to systemic responses but works primarily through acute phase proteins. IL-17 recruits neutrophils but doesn't directly cause fever. TGF-β is actually anti-inflammatory. The IL-1/TNF → COX-2 → PGE2 pathway is the classic fever mechanism. ---

Question 14

In studying arachidonic acid metabolism, a researcher finds that alternatively activated (M2) macrophages produce different lipid mediators than classically activated (M1) macrophages. What explains the transition from pro-inflammatory to anti-inflammatory lipid mediators?

Accepted Answer

Switch from leukotriene to lipoxin production — The switch from leukotrienes (pro-inflammatory) to lipoxins (anti-inflammatory) is a key mechanism for terminating inflammation. Lipoxins are generated from arachidonic acid by the lipoxygenase pathway (like leukotrienes) but have opposite effects - they inhibit neutrophil chemotaxis and adhesion. This represents an active termination mechanism. Lipoxins require transcellular biosynthesis - neutrophils make precursors that platelets convert to active lipoxins. This isn't about COX-1 vs COX-2 (those make prostaglandins, not lipoxins). Increased thromboxane would be prothrombotic. Reduced phospholipase A2 would decrease ALL eicosanoid production. Enhanced 5-lipoxygenase could increase either leukotrienes OR lipoxins depending on the downstream enzymes. ---

Question 15

A patient takes aspirin for pain relief. Which effect is directly related to irreversible acetylation of cyclooxygenase?

Accepted Answer

Reduced production of both PGI2 and TxA2 — Aspirin irreversibly acetylates and inactivates BOTH COX-1 and COX-2, preventing prostaglandin synthesis. This affects both platelet TxA2 (promoting aggregation) and endothelial PGI2 (inhibiting aggregation). The irreversible nature is why aspirin's antiplatelet effect lasts the lifespan of platelets (~7-10 days) even though aspirin itself is cleared quickly. Aspirin doesn't affect the lipoxygenase pathway that makes leukotrienes and lipoxins. It doesn't increase arachidonic acid availability - it blocks its conversion via cyclooxygenases. Understanding that aspirin hits BOTH COX enzymes and affects prostaglandin (not leukotriene) production is key. ---

Question 16

During acute inflammation, complement activation produces several bioactive fragments. Which function is specifically performed by C3b?

Accepted Answer

Opsonization of microbes for phagocytosis — Each complement fragment has specific roles. C3b covalently attaches to microbial surfaces and acts as an opsonin - it's recognized by complement receptors on phagocytes (neutrophils and macrophages), promoting phagocytosis. C3a and C5a are anaphylatoxins that stimulate mast cell histamine release and cause increased permeability. C5a (not C3b) is the main chemotactic fragment for leukocytes. C5b initiates formation of the membrane attack complex (C5b-9). Complement doesn't directly activate the kinin system (that's a separate plasma protein cascade). This question tests whether you know the specific functions of different complement products. ---

Question 17

A research study examines endothelial changes during inflammation. Which molecule is most important for converting rolling neutrophils to firmly adherent cells?

Accepted Answer

Chemokines activating integrins to high-affinity state — The progression from rolling to firm adhesion requires integrin activation. Chemokines (produced at injury sites and displayed on endothelial proteoglycans) bind to rolling leukocytes and trigger inside-out signaling that converts integrins (LFA-1, MAC-1, VLA-4) from low to high affinity states. These high-affinity integrins then bind firmly to endothelial ligands (ICAM-1, VCAM-1), arresting the cells. E-selectin and P-selectin mediate rolling (weak, transient interactions) - not firm adhesion. PECAM-1 is involved in transmigration through the endothelium (diapedesis), not adhesion to it. L-selectin also mediates rolling. Only chemokine activation of integrins causes the critical transition to firm adhesion. ---

Question 18

A patient with paroxysmal nocturnal hemoglobinuria (PNH) experiences episodes of red blood cell lysis. This results from:

Accepted Answer

Loss of GPI-anchored proteins DAF and CD59 that normally protect cells — PNH results from acquired deficiency of the enzyme that creates GPI (glycophosphatidylinositol) anchors. This causes loss of GPI-anchored complement regulatory proteins, particularly DAF (decay accelerating factor, which prevents C3 convertase formation) and CD59 (which inhibits MAC formation). Without these protections, complement activation on the patient's own RBCs leads to MAC-mediated cell lysis. RBCs are particularly vulnerable because they're sensitive to complement lysis. C1 INH deficiency causes angioedema. Factor H deficiency causes atypical hemolytic uremic syndrome with glomerular damage. The problem isn't excessive MAC production or antibodies - it's loss of normal cellular protection against complement. ---

Question 19

In comparing tissue responses to injury, which scenario would MOST likely result in resolution rather than scarring?

Accepted Answer

Lobar pneumonia with preserved lung architecture — Resolution (complete restoration to normal) requires: (1) limited or short-lived injury, (2) little tissue destruction, (3) cells capable of regeneration, and (4) intact structural framework. Lobar pneumonia fills alveoli with inflammatory exudate but the underlying lung architecture (alveolar walls, basement membranes) remains intact. Once bacteria are cleared, the exudate can be resorbed/digested and type II pneumocytes can regenerate, restoring normal lung. Myocardial infarction kills permanent cells (cardiomyocytes) that can't regenerate - only scarring possible. Liver abscess with collapsed reticulin destroys the framework needed for regeneration despite hepatocytes being capable of proliferation. Burns destroying dermis eliminate appendages that can't regenerate. Deep ulcers with destroyed framework heal by scarring. ---

Question 20

What distinguishes serous from fibrinous inflammation?

Accepted Answer

Fibrinous inflammation involves larger molecules leaking due to greater vascular permeability — The key difference is the SIZE of molecules that leak and the degree of vascular permeability. Serous inflammation has mild permeability increase allowing cell-poor fluid (like plasma ultrafiltrate) to escape - seen in blisters or mild peritoneal irritation. Fibrinous inflammation has GREATER permeability allowing large molecules like fibrinogen to escape and form fibrin deposits - characteristic of inflammation in pericardium, pleura, meninges. Serous inflammation actually has FEWER cells than purulent/fibrinous. Both can occur in body cavities. Fibrinous inflammation can be caused by non-infectious stimuli (cancer cells, uremia). Both represent acute inflammation, not chronic. The molecular size/permeability distinction is fundamental. ## SECTION 3: CHRONIC INFLAMMATION ---

Question 21

A patient with tuberculosis shows granulomas with central necrosis on biopsy. What type of necrosis characterizes tuberculous granulomas?

Accepted Answer

Caseous necrosis — Tuberculous granulomas specifically show caseous necrosis - grossly it has a cheese-like appearance, and microscopically it appears as amorphous, structureless, eosinophilic granular debris with complete loss of cellular details. This is distinct from coagulative necrosis (where cell outlines are preserved, seen in infarcts) and liquefactive necrosis (complete digestion of cells, seen in brain infarcts and abscesses). Caseous necrosis results from hypoxia and free radical injury within granulomas. Fat necrosis occurs in adipose tissue (pancreatitis, breast trauma). Gangrenous necrosis refers to coagulative necrosis in limbs with superimposed bacterial infection. The term "caseating granuloma" is pathognomonic for TB, though other mycobacteria can cause similar lesions. ---

Question 22

A researcher studies macrophage polarization. M1 (classically activated) macrophages are induced by IFN-γ and microbial products, while M2 (alternatively activated) are induced by IL-4 and IL-13. Which functional difference best distinguishes these populations?

Accepted Answer

M1 produce ROS and NO for microbicidal activity; M2 produce growth factors for tissue repair — The M1/M2 distinction is functional, not based on origin or basic capabilities. M1 macrophages are specialized for killing - they produce ROS (via NADPH oxidase), NO (via iNOS), lysosomal enzymes, and pro-inflammatory cytokines (IL-1, IL-12, IL-23, TNF, chemokines). Their job is microbicidal activity. M2 macrophages are specialized for ending inflammation and promoting repair - they produce anti-inflammatory cytokines (IL-10, TGF-β) and growth factors that stimulate tissue repair and fibrosis. BOTH types can phagocytose and present antigens. BOTH can derive from monocytes (though tissue-resident macrophages have embryonic origins). The cytokine production is reversed in choice e. The key is recognizing M1 = destruction/inflammation vs M2 = repair/resolution. ---

Question 23

A 60-year-old with rheumatoid arthritis shows synovial biopsy with organized lymphoid follicles containing germinal centers. What does this finding suggest?

Accepted Answer

Persistent immune activation with local lymphocyte proliferation — Tertiary lymphoid organs (organized lymphoid follicles resembling lymph nodes) form in chronically inflamed tissues when there's persistent immune activation against self-antigens (autoimmunity) or environmental antigens. They're seen in RA synovium, Hashimoto thyroiditis, and other chronic immune-mediated diseases. These structures contain B cells, T cells, follicular dendritic cells, and show ongoing immune responses with germinal center formation. This indicates persistent, active immune disease - not acute infection (which wouldn't show organized follicles), not transition phase (these are established chronic changes), not malignancy (though chronic inflammation is a risk factor, organized follicles alone don't indicate transformation), and not resolution (which would show decreasing inflammation and fibrosis). ---

Question 24

In examining a lung biopsy from a patient with sarcoidosis, noncaseating granulomas are seen. What distinguishes noncaseating from caseating granulomas?

Accepted Answer

Noncaseating granulomas have absent central necrosis — Caseating vs noncaseating refers to the presence/absence of central necrosis. Caseating granulomas (TB, some fungi) have central caseous necrosis surrounded by epithelioid macrophages and Langhans giant cells. Noncaseating granulomas (sarcoidosis, Crohn disease, foreign body reactions) have collections of epithelioid macrophages and often giant cells BUT lack the central necrotic zone. BOTH types contain epithelioid macrophages (that's what makes them granulomas). BOTH can have giant cells (Langhans type or foreign body type). Neither typically has neutrophils (those indicate suppurative/purulent inflammation, not granulomatous). Noncaseating doesn't indicate etiology - both immune and some infections cause noncaseating granulomas. The sole distinction is presence/absence of that characteristic central necrosis. ---

Question 25

A patient with Crohn disease shows intestinal biopsy with noncaseating granulomas and dense chronic inflammatory infiltrate. What is the proposed pathogenesis?

Accepted Answer

Immune reaction against intestinal bacteria or self antigens — Crohn disease is an inflammatory bowel disease thought to result from inappropriate, unregulated immune responses against normal intestinal bacteria (commensal flora) and possibly self antigens in genetically susceptible individuals. This is an immune-mediated granulomatous inflammation. While early theories suggested persistent mycobacterial infection (Mycobacterium avium subspecies paratuberculosis), this has not been definitively proven and isn't the accepted primary pathogenesis. It's not a simple foreign body reaction (which wouldn't cause the systemic disease manifestations). The immune deficiency theory is backwards - it's excessive/inappropriate immunity, not deficient. The Th2/helminth explanation is wrong - Crohn's is primarily Th1/Th17 mediated. Understanding that IBD represents dysregulated immunity against normal gut contents is key. ---

Inflammation and Tissue Repair - MCQs MCQs

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