Inflammation Study Guide

📖 Core Concepts Inflammation – innate‑immune defence that removes injurious agents, clears damaged cells, and starts repair. Triggers – physical trauma, necrotic tissue, pathogens, toxins, allergens, auto‑immune reactions, foreign bodies. Cardinal signs – dolor (pain), calor (heat), rubor (redness), tumor (swelling), functio laesa (loss of function). Vascular response – vasodilation (histamine, NO, PG E₂) → ↑ blood flow (heat/redness); ↑ permeability → plasma exudate → edema. Cellular response – leukocyte extravasation (rolling → adhesion → diapedesis → chemotaxis); neutrophils dominate acute phase, mononuclear cells dominate chronic phase. Resolution vs. Fibrosis – active termination (lipoxins, resolvins, IL‑10, TGF‑β) restores tissue; if damage is extensive, scar (fibrosis) replaces parenchyma. Systemic spill‑over – acute‑phase proteins (CRP, serum amyloid A), leukocytosis, SIRS → sepsis if infection present. 📌 Must Remember Acute inflammation: minutes‑hours, neutrophil‑rich, resolves with removal of stimulus. Chronic inflammation: months‑years, mononuclear infiltrate, simultaneous destruction & repair. Sub‑acute: 2–6 weeks duration. Type 1 vs. Type 2: driven by Th1‑ vs. Th2‑type cytokines. Leukocyte extravasation steps: Margination → Rolling (selectins) → Activation (chemokines) → Firm adhesion (integrins ↔ ICAM/VCAM) → Diapedesis → Chemotaxis. Phagocytosis enhancers: Opsonization (C3b, IgG) → FcR & CR1 binding. Common mediators: Histamine, serotonin, PG E₂, LTB₄ (vasodilation & permeability); NO (vasodilation); complement C3a/C5a (chemotaxis). Acute‑phase protein rise → CRP ↑ → predicts cardiovascular risk independent of LDL. Eosinophilia → allergy, parasitic infection; Neutrophilia → bacterial infection. 🔄 Key Processes Leukocyte Extravasation Margination: blood flow slows at post‑capillary venules, pushing leukocytes to vessel wall. Rolling: endothelial selectins bind leukocyte carbohydrate ligands → transient tethering. Activation: chemokines (e.g., IL‑8) trigger integrin conformational change. Firm adhesion: integrins bind ICAM‑1/VCAM‑1 → stop rolling. Diapedesis: leukocyte squeezes through endothelial junctions (PECAM‑1 involvement). Chemotaxis: follows gradient of C3a, C5a, bacterial products, or IL‑8. Phagocytosis Recognition: PRRs bind PAMPs (LPS, peptidoglycan, β‑glucan). Engulfment: actin‑myosin remodeling forms phagosome. Maturation: phagosome fuses with lysosome → phagolysosome. Killing: ROS, hypochlorite, enzymes degrade microbe. Resolution of Inflammation Lipid mediator switch: prostaglandins/leukotrienes → lipoxins (via neutrophil‑derived signals). Neutrophil apoptosis → efferocytosis by macrophages. Macrophage reprogramming → release TGF‑β, IL‑10, IL‑1Ra. Clearance of mediators → down‑regulation of leukotriene synthesis, up‑regulation of anti‑inflammatory receptors. 🔍 Key Comparisons Acute vs. Chronic Time: minutes‑hours vs. months‑years. Cells: neutrophils vs. macrophages, lymphocytes, plasma cells. Outcome: resolution vs. tissue remodeling/fibrosis. Neutrophil‑dominant vs. Mononuclear‑dominant infiltrate Neutrophils → bacterial infection, purulent exudate. Mononuclear → viral/chronic infections, granulomas, auto‑immunity. Granulomatous vs. Fibrinous vs. Purulent inflammation Granulomatous: organized macrophage/epithelioid cell collections (TB, sarcoidosis). Fibrinous: protein‑rich exudate, “pseudomembrane” (serous pericarditis). Purulent: pus (neutrophils + dead cells) (pyogenic bacteria). Type 1 vs. Type 2 cytokine milieu Type 1: IFN‑γ, IL‑2 → intracellular pathogens, delayed‑type hypersensitivity. Type 2: IL‑4, IL‑5, IL‑13 → parasites, allergy, eosinophilia. ⚠️ Common Misunderstandings Inflammation ≠ infection – sterile injury (e.g., trauma) also triggers full inflammatory cascade. Fever is caused by the pathogen – it is driven by pyrogenic cytokines (IL‑1, IL‑6, TNF‑α). Edema means lymphatic obstruction – in acute inflammation it primarily reflects increased vascular permeability. All swelling is “pus” – swelling can be serous, fibrinous, or purulent; only purulent exudate contains abundant neutrophils and dead microbes. 🧠 Mental Models / Intuition “Fire alarm” analogy: injury = alarm; mediators (histamine, cytokines) = sirens that call firefighters (neutrophils). Traffic‑jam model for leukocyte recruitment: selectins = road signs (slow down), integrins = stoplights (full stop), chemokines = GPS directing cars to the site. Resolution as “turning off the lights”: lipid‑mediator switch flips the switch from “red alert” (pro‑inflammatory) to “green” (repair). 🚩 Exceptions & Edge Cases Sub‑acute inflammation (2–6 weeks) – intermediate pattern; may show mixed neutrophil/mononuclear infiltrate. Low‑grade chronic inflammation in obesity – modest 2‑3× rise in IL‑6, TNF‑α, CRP; correlates with waist circumference. Atherosclerosis – chronic inflammatory disease despite being traditionally “cholesterol‑driven”. Chronic granulomatous disease – phagocytes can ingest microbes but cannot generate ROS → persistent granulomas. 📍 When to Use Which Acute vs. Chronic descriptors – use acute when symptoms began < 2 weeks and neutrophils dominate; use chronic for > 6 weeks with mononuclear cells. Mediator‑targeted therapy – NSAIDs → block cyclooxygenase (prostaglandins); anti‑IL‑1β antibodies → treat atherosclerosis‑related inflammation. Diagnostic clue – eosinophilia → think allergy/parasitic infection; neutrophilia → bacterial infection. Histologic pattern – granulomas → order TB/ sarcoidosis work‑up; fibrinous exudate → consider serosal inflammation (pericarditis). 👀 Patterns to Recognize Neutrophil‑rich pus → pyogenic bacteria (Staph, Strep). Eosinophil surge → type 1 hypersensitivity or helminth infection. Elevated CRP + IL‑6 without infection → obesity‑related low‑grade inflammation or chronic disease flare. Presence of C3a/C5a → complement activation → rapid vasodilation & chemotaxis. Lipoxin or resolvin rise → transition from active inflammation to resolution phase. 🗂️ Exam Traps “All red, hot, swollen lesions are bacterial infections.” – viral or allergic reactions can produce similar cardinal signs via cytokine release. Choosing “chronic” because inflammation lasts > 4 weeks – remember the sub‑acute 2–6 week window; chronic is > 6 weeks. Assuming CRP is a cause of atherosclerosis – it is a marker and contributor, but not the primary etiologic factor. Confusing “vasodilation” with “increased vascular permeability.” – they are distinct: dilation → heat/redness; permeability → edema. Attributing eosinophilia to bacterial infection – eosinophils are not typical for bacterial infections; look for allergy or parasites. --- All statements are drawn directly from the provided outline; no external information has been added.