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INFLAMMATION - Comprehensive Theory Answer (PG University Exam Standard)

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DEFINITION

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CARDINAL SIGNS OF INFLAMMATION

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TYPES OF INFLAMMATION

1. Acute Inflammation - short duration (minutes to days); characterized by exudation of fluid, plasma proteins, and neutrophil emigration
2. Chronic Inflammation - prolonged duration (weeks to months); characterized by mononuclear cell infiltration, tissue destruction, and repair occurring simultaneously
3. Granulomatous Inflammation - a special form of chronic inflammation; focal aggregates of activated macrophages (epithelioid cells) ± Langhans giant cells

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PART I: ACUTE INFLAMMATION

A. Components

1. Dilation of small blood vessels leading to increased blood flow
2. Increased permeability of the microvasculature - enabling plasma proteins and leukocytes to leave the circulation
3. Emigration of leukocytes from the microcirculation, their accumulation at the focus of injury, and activation to eliminate the offending agent

B. Vascular Reactions

• Vasodilation: Induced by histamine and nitric oxide acting on vascular smooth muscle. Affects mainly postcapillary venules. Causes increased blood flow = heat and redness. It is one of the earliest manifestations.
• Increased vascular permeability: Outpouring of protein-rich fluid (exudate) into extravascular tissues. Mechanisms include:
  • Endothelial cell contraction forming intercellular gaps (most common; induced by histamine, bradykinin, leukotrienes, substance P)
  • Endothelial injury (direct vascular damage from burns, toxins, etc.)
  • Leukocyte-mediated vascular injury
  • Transcytosis (vesicular transport across endothelial cells)
  • Angiogenesis (new vessel growth with leaky walls)
• Stasis: Loss of fluid + increased diameter leads to slower flow; RBCs concentrate in small vessels (vascular congestion); leukocytes accumulate along endothelium

C. Leukocyte Recruitment (Cellular Events)

• Stasis causes leukocytes to move to the periphery (margination)
• Rolling along endothelium mediated by selectins (P-selectin, E-selectin on endothelium; L-selectin on leukocytes) and their ligands (PSGL-1, sialyl-Lewis X)

• Mediated by integrins on leukocyte surface (LFA-1/ICAM-1, VLA-4/VCAM-1)
• Chemokines (IL-8/CXCL8) activate integrins, increasing their avidity
• TNF and IL-1 upregulate integrin ligands on endothelium

• Leukocytes migrate through interendothelial junctions
• PECAM-1 (CD31) is important in this process
• Neutrophils predominate first (6-24 hours); monocytes later (24-48 hours onward) due to:
  • Short-lived neutrophils
  • Chemokine-specific monocyte attractants produced later

• Migration along chemical gradient toward the site of injury
• Exogenous chemotactic agents: bacterial products (N-formyl methionine peptides)
• Endogenous agents: C5a, LTB4, IL-8/CXCL8, platelet-activating factor

D. Leukocyte Activation and Phagocytosis

• Toll-like receptors (TLRs) - recognize pathogen-associated molecular patterns (PAMPs)
• NOD-like receptors (NLRs) - intracellular receptors
• G protein-coupled receptors responding to chemokines
• Cytokine receptors (TNF, IL-1)

1. Recognition and attachment - aided by opsonins (IgG, C3b) binding to Fc receptors and CR1/CR3 on leukocytes respectively
2. Engulfment - pseudopod extension → phagosome formation → fusion with lysosome → phagolysosome
3. Killing and degradation via:
   • Oxygen-dependent: Respiratory burst (NADPH oxidase) → superoxide → H2O2 → HOCl (myeloperoxidase system); most potent bactericidal mechanism
   • Oxygen-independent: Lysozyme, defensins, major basic protein, lactoferrin, bactericidal permeability-increasing protein (BPI)

E. Chemical Mediators of Inflammation

Membrane phospholipids
        ↓ (Phospholipase A2)
Arachidonic acid
    ↙              ↘
COX pathway      LOX pathway
(Cyclooxygenase)  (Lipoxygenase)
    ↓                  ↓
Prostaglandins      Leukotrienes
Thromboxanes        (LTA4, LTB4, LTC4, LTD4, LTE4)
Prostacyclin        Lipoxins (anti-inflammatory)

F. Morphologic Patterns of Acute Inflammation

1. Serous inflammation: Watery fluid with few cells (e.g., pleural effusion, skin blisters)
2. Fibrinous inflammation: Large amounts of fibrin in exudate; seen in pericarditis ("bread and butter" pericarditis)
3. Suppurative (purulent) inflammation: Pus formation (neutrophils + liquefactive necrosis); abscess
4. Ulceration: Loss of epithelial surface from combined inflammation and necrosis; seen in peptic ulcer, aphthous ulcers

G. Outcomes of Acute Inflammation

1. Complete resolution: Normal outcome when injury is limited; removal of cellular debris by macrophages, resorption of edema by lymphatics, tissue regeneration
2. Healing by scarring (fibrosis): When tissue destruction is substantial, or tissue cannot regenerate; connective tissue replaces damaged area (organization)
3. Progression to chronic inflammation: When the acute response cannot be resolved due to persistence of injurious agent or interference with normal healing

H. Systemic Effects (Acute Phase Response)

• Fever: IL-1, IL-6, TNF act on hypothalamus → PGE2 synthesis → raised thermostat
• Leukocytosis: IL-1, TNF → increased production and release from bone marrow (neutrophilia in bacterial; lymphocytosis in viral; eosinophilia in parasitic/allergic)
• Acute phase proteins: CRP, fibrinogen, serum amyloid A (SAA) - produced by liver; ESR rises due to fibrinogen
• Septic shock: Systemic vasodilation, DIC, metabolic disturbances with overwhelming infection

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PART II: CHRONIC INFLAMMATION

A. Definition

B. Causes

1. Persistent infections by organisms difficult to eradicate - mycobacteria, fungi, parasites, certain viruses; often associated with delayed-type hypersensitivity / granulomatous reactions
2. Hypersensitivity/autoimmune diseases - self-perpetuating immune reactions against autoantigens (rheumatoid arthritis, multiple sclerosis, IBD); allergic diseases (bronchial asthma)
3. Toxic agents - prolonged exposure to silica (silicosis), endogenous cholesterol deposition (atherosclerosis)

C. Morphologic Features

1. Infiltration by mononuclear cells: macrophages, lymphocytes, plasma cells
2. Tissue destruction induced by the persistent offending agent or by inflammatory cells
3. Attempts at healing via connective tissue replacement (angiogenesis + fibrosis)

D. Cells of Chronic Inflammation

• Derived from blood monocytes (half-life in tissues: several months to years)
• Tissue-resident forms: Kupffer cells (liver), microglia (CNS), alveolar macrophages, osteoclasts
• Activated by: IFN-γ (from Th1 cells), bacterial endotoxin, fibronectin, other cytokines
• Functions: phagocytosis, cytokine secretion (TNF, IL-1, IL-6, IL-12), growth factors (PDGF, TGF-β), tissue-remodeling enzymes (MMPs), NO production
• M1 macrophages (classically activated): antimicrobial, proinflammatory
• M2 macrophages (alternatively activated): anti-inflammatory, tissue repair, fibrosis

• CD4+ T helper cells: Th1 (IFN-γ) → macrophage activation; Th2 (IL-4, IL-5, IL-13) → eosinophil recruitment and IgE production; Th17 (IL-17) → neutrophil recruitment
• CD8+ cytotoxic T cells: direct killing of infected cells
• B lymphocytes → plasma cells → antibody production

• Eosinophils: parasitic infections, allergic reactions; contain major basic protein (toxic to helminths)
• Mast cells: present in chronic reactions; produce cytokines amplifying inflammation
• Neutrophils: can persist in chronic bacterial infections (e.g., osteomyelitis)

E. Systemic Effects of Chronic Inflammation

• Amyloidosis (AA type) due to sustained SAA production
• Weight loss, anemia of chronic disease
• Cancer risk (chronic inflammation creates a microenvironment that can promote malignant transformation - e.g., H. pylori → gastric cancer; HBV/HCV → hepatocellular carcinoma; Crohn disease → colorectal cancer)

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PART III: GRANULOMATOUS INFLAMMATION

A. Definition

B. Types

C. Morphology

• Epithelioid cells: Activated macrophages with pink granular cytoplasm, indistinct cell borders; resemble epithelial cells
• Langhans giant cells: 40-50 μm; formed by fusion of activated macrophages; nuclei arranged in horseshoe/peripheral pattern at periphery of cell
• Foreign body giant cells: Nuclei scattered randomly (no particular pattern)
• Lymphocyte cuff surrounding the epithelioid cell aggregate
• Rim of fibroblasts and connective tissue in older granulomas
• Caseous necrosis: Central amorphous, structureless, eosinophilic, granular debris (complete loss of cellular architecture) - characteristic of TB. Due to hypoxia + free radical injury.

D. Common Causes of Granulomatous Inflammation

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WRITE NOTE: INFLAMMATION IN PERIODONTOLOGY

Introduction

Microbiology and Initiating Stimulus

• Aggregatibacter (Actinobacillus) actinomycetemcomitans - aggressive (juvenile) periodontitis
• Porphyromonas gingivalis - major pathogen in chronic adult periodontitis; produces gingipains (proteases)
• Prevotella intermedia - associated with pregnancy gingivitis and chronic periodontitis
• Treponema denticola, Tannerella forsythia - "red complex" with P. gingivalis (most pathogenic triad)

Pathogenesis of Periodontal Inflammation

• Acute vascular response in the gingival sulcus area
• Increased vascular permeability and exudation of fluid (gingival crevicular fluid)
• Predominantly PMNs (neutrophils) in the junctional epithelium and sulcus
• Migration of neutrophils across junctional epithelium acts as a protective barrier

• Transition to chronic inflammatory infiltrate
• Predominantly lymphocytes (mostly T-cells) appear in connective tissue
• Collagen loss begins immediately subjacent to junctional epithelium
• Altered fibroblast morphology (become vacuolated/damaged)
• Gingivitis at this stage is still reversible

• Plasma cells and B-lymphocytes predominate (shift from T- to B-cell dominated lesion)
• Dense inflammatory infiltrate; immunoglobulin production
• Junctional epithelium begins to proliferate and migrate apically (pocket formation begins)
• Collagen loss extends
• Represents chronic gingivitis - still potentially reversible

• Periodontitis proper; irreversible tissue destruction begins
• Alveolar bone resorption - mediated by osteoclast activation via RANKL/OPG pathway
• Periodontal pocket formation (true pocket with apical migration of junctional epithelium)
• Extensive plasma cells, lymphocytes, macrophages
• Destruction of periodontal ligament fibers
• This stage is irreversible without treatment

Mechanisms of Tissue Destruction in Periodontitis

• Bacterial enzymes (collagenases, proteases, hyaluronidase) directly destroy collagen and connective tissue matrix
• Lipopolysaccharide (LPS) of gram-negative organisms activates complement, stimulates cytokine release
• P. gingivalis gingipains cleave complement components and immunoglobulins

• Cytokines: IL-1β and TNF-α are key drivers; stimulate PGE2 production and activate osteoclasts; IL-6 is elevated in periodontitis
• Prostaglandins (PGE2): Produced by macrophages and fibroblasts; major mediator of bone resorption; stimulates osteoclastogenesis via RANKL upregulation
• Matrix metalloproteinases (MMPs): MMP-1 (collagenase), MMP-8, MMP-13 - degrade collagen and connective tissue matrix; produced by PMNs, macrophages, and fibroblasts
• RANKL/OPG axis: RANKL (receptor activator of NF-κB ligand) is upregulated by inflammatory mediators → binds RANK on osteoclast precursors → osteoclast differentiation and activation → alveolar bone resorption. OPG (osteoprotegerin) is the decoy receptor that blocks this pathway and is reduced in periodontitis.
• Reactive oxygen species (ROS): Generated by PMNs during respiratory burst; tissue damage when released extracellularly
• Complement activation: C3a, C5a increase vascular permeability and recruit more PMNs, amplifying inflammation

• Horizontal bone loss: Generalized, uniform loss of alveolar crest
• Vertical (angular) bone loss: Localized, angular defects adjacent to teeth; associated with more aggressive local disease

Systemic Associations of Periodontitis

Histological Features of Periodontitis

• Ulceration of pocket epithelium
• Dense infiltrate of plasma cells and lymphocytes
• Dilated capillaries, tissue edema
• Loss of principal periodontal ligament fibers
• Resorption lacunae (Howship's lacunae) with osteoclasts at alveolar bone margin
• Deepened pocket with apically migrated junctional epithelium

Gingivitis vs Periodontitis (Key Distinction)

Treatment Implications Based on Inflammatory Pathogenesis

• Mechanical plaque removal (scaling, root planing) - removes bacterial stimulus
• Antibiotics (metronidazole, doxycycline) - target anaerobic pathogens
• Host modulation therapy: Low-dose doxycycline (sub-antimicrobial) inhibits MMPs; NSAIDs reduce PGE2
• Anti-RANKL therapy: Denosumab (monoclonal antibody against RANKL) - used in systemic bone conditions, under investigation in periodontitis
• Periodontal surgery - regenerative procedures to restore lost tissues

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SUMMARY TABLE: ACUTE vs CHRONIC INFLAMMATION

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What's Included in This Answer

Main Theory: Inflammation

• Definition and 3 major components (Robbins)
• Vascular reactions: vasodilation, increased permeability, stasis
• Exudate vs transudate (with distinguishing table)
• Leukocyte recruitment: margination, rolling (selectins), firm adhesion (integrins), transmigration (PECAM-1), chemotaxis
• Leukocyte activation: TLRs, NOD-like receptors
• Phagocytosis: 3 steps, opsonins, oxygen-dependent (NADPH oxidase/MPO) and oxygen-independent killing
• Chemical mediators: complete table (histamine, PGs, leukotrienes, cytokines, complement, kinins, NO, PAF)
• Arachidonic acid pathway (COX vs LOX)
• Morphologic patterns: serous, fibrinous, suppurative, ulcerative
• Outcomes: resolution, fibrosis, chronicity
• Systemic effects: fever, acute phase proteins, leukocytosis, septic shock

• Causes: persistent infection, autoimmune/hypersensitivity, toxic agents
• Morphology: mononuclear infiltrate, tissue destruction, fibrosis
• Cells: M1/M2 macrophages, T-cell subsets (Th1/Th2/Th17), eosinophils
• Systemic effects including amyloidosis and cancer risk

• Definition, two types (foreign body vs immune)
• Full morphology: epithelioid cells, Langhans vs foreign body giant cells, caseous necrosis
• Table of diseases with granulomatous inflammation

Write Note: Inflammation in Periodontology

• Microbiology (the red complex, key pathogens)
• Page and Schroeder's 4 histological stages (initial → early → established → advanced)
• Molecular mechanisms: IL-1β, TNF-α, PGE2, MMPs, RANKL/OPG axis, ROS, complement
• Systemic associations: diabetes, CVD, preterm birth, endocarditis
• Gingivitis vs Periodontitis comparison table
• Treatment implications from inflammatory pathogenesis