What's covered in each note:

1. Phagocytosis and Mechanism - 3 steps with full mechanism
2. Chemotaxis - chemoattractants + G-protein mechanism
3. Role of Prostaglandins in Inflammation - synthesis pathway + table of actions + pharmacology
4. Granuloma - 2 types + full morphology + causes
5. Chemokines - classification table + key members + functions
6. Steps in Wound Healing - all 4 phases + first vs second intention + complications

1. Phagocytosis and Mechanism

Step 1 - Recognition and Attachment

• Mannose receptors - recognize terminal mannose/fucose on microbial glycoproteins (absent on mammalian cells)
• Scavenger receptors - bind modified LDL and microbial surfaces
• MAC-1 (CD11b/CD18) - integrin that binds microbes directly

• IgG antibodies (Fc receptors on phagocyte)
• C3b complement fragment (complement receptors)
• Mannose-binding lectin and collectins

Step 2 - Engulfment

• Pseudopods extend around the particle
• Plasma membrane pinches off → forms phagosome
• Phagosome fuses with lysosome → phagolysosome
• Requires actin polymerization and cytoskeletal remodeling

Step 3 - Intracellular Killing

• NADPH oxidase assembles on phagosomal membrane
• Converts NADPH + O₂ → superoxide (O₂⁻) - this is the respiratory burst
• O₂⁻ → H₂O₂ (by spontaneous dismutation)
• MPO (myeloperoxidase) + H₂O₂ + Cl⁻ → HOCl (hypochlorite) - most potent microbicidal agent; kills by halogenation and lipid peroxidation
• Defect in NADPH oxidase → Chronic Granulomatous Disease

• iNOS generates nitric oxide (NO)
• NO + O₂⁻ → peroxynitrite (ONOO⁻) → microbicidal

• Elastase, cathepsins, defensins, lysozyme
• Acid proteases degrade bacteria in acidic phagolysosome
• Leakage into extracellular space → tissue damage

2. Chemotaxis

Chemoattractants

• Bacterial N-formyl methionyl (f-Met) peptides - produced only by bacteria, not eukaryotes

1. C5a - complement fragment; most potent chemoattractant
2. Leukotriene B4 (LTB4) - arachidonic acid metabolite
3. Chemokines - especially IL-8 (CXCL8)

Mechanism

• Chemoattractants bind 7-transmembrane G protein-coupled receptors on leukocytes
• G-protein activation → second messengers (IP₃, DAG, Ca²⁺) → actin polymerization at the leading edge
• Myosin contracts at the trailing edge → net forward movement toward increasing concentration gradient

Leukocyte Selectivity

• Neutrophils: C5a, LTB4, IL-8 (CXCL8)
• Monocytes: MCP-1 (CCL2)
• Eosinophils: Eotaxin (CCL11)

3. Role of Prostaglandins in Inflammation

Synthesis

• Cell injury → phospholipase A₂ cleaves AA from membrane phospholipids
• AA → via COX-1 / COX-2 → cyclic endoperoxides (PGG₂, PGH₂)
• PGH₂ → specific prostaglandins via tissue-specific synthases

Actions in Inflammation

Key Roles in Inflammation

• Fever: PGE₂ acts on hypothalamic thermoregulatory neurons → raises temperature set point
• Pain: PGE₂ sensitizes nociceptors to bradykinin and other stimuli → hyperalgesia
• Vasodilation + edema: PGE₂ and PGI₂ dilate arterioles and increase postcapillary venule permeability

Pharmacological Relevance

• NSAIDs (aspirin, ibuprofen): Block COX-1 and COX-2 → inhibit all prostaglandin synthesis → anti-inflammatory, antipyretic, analgesic
• COX-2 selective inhibitors (coxibs): Spare COX-1 (less GI side effects)
• Corticosteroids: Inhibit phospholipase A₂ → block AA release → suppress all eicosanoids

4. Granuloma

• Represents a cellular attempt to contain an agent that is difficult to eradicate
• Name derived from its granular macroscopic appearance

Types

• Reaction to inert, non-immunogenic foreign bodies (sutures, talc, silica)
• Too large to be phagocytosed by a single macrophage
• No T-cell immune response involved
• Foreign material visible at center (refractile under polarized light)

• Caused by persistent agents inducing T cell-mediated immune response
• Agents: M. tuberculosis, fungi, parasites, sarcoidosis, berylliosis
• Th1 cells produce IFN-γ → activates macrophages (classical M1 activation)
• In schistosomiasis: Th2 response with eosinophils

MORPHOLOGY (H&E)

1. Epithelioid cells - activated macrophages; abundant pink granular cytoplasm; indistinct cell borders; elongated "footprint" nuclei; resemble epithelial cells
2. Lymphocytic cuff - collar of CD4+ T lymphocytes surrounding the epithelioid cell aggregate
3. Langhans giant cells - 40-50 μm multinucleated cells formed by fusion of activated macrophages; nuclei arranged in horseshoe/peripheral pattern
4. Rim of fibroblasts - in older granulomas; connective tissue encapsulation
5. Caseous necrosis (in TB) - central zone of necrosis; granular, cheesy appearance grossly; amorphous eosinophilic granular debris on histology

Common Causes

• Tuberculosis (most classic - with caseation)
• Sarcoidosis (non-caseating)
• Fungal infections (Histoplasma, Coccidioides)
• Schistosomiasis
• Berylliosis, Silicosis
• Crohn disease
• Syphilis

5. Chemokines

Classification (Based on Cysteine Residue Arrangement)

Key Members

• IL-8 (CXCL8) - secreted by macrophages and endothelial cells; activates and recruits neutrophils; induced by microbes, IL-1, TNF
• MCP-1 (CCL2) - recruits monocytes to sites of inflammation
• Eotaxin (CCL11) - selectively recruits eosinophils (allergy, asthma)
• Fractalkine (CX3CL1) - membrane-bound form promotes adhesion; soluble form is chemoattractant

Functions

• Produced in response to microbes and inflammatory stimuli
• Increase integrin affinity on leukocytes → promote firm adhesion to endothelium
• Direct leukocyte migration in tissues toward infection/damage site

• Produced in normal tissues to maintain tissue architecture
• Organize T and B lymphocytes into discrete zones in lymph nodes and spleen

Clinical Note

• HIV uses CXCR4 (T cell co-receptor) and CCR5 (macrophage co-receptor) as entry co-receptors
• Individuals with CCR5 mutations are resistant to HIV infection

6. Steps in Wound Healing

• First intention (primary union): clean, well-apposed wound; minimal scar; mainly epithelial regeneration (e.g., surgical incision)
• Second intention (secondary union): large/infected wound; more granulation tissue, wound contraction, significant scarring

The 4 Phases of Wound Healing

Phase 1 - Hemostasis (Minutes to Hours)

• Vessel injury → platelet aggregation → blood clot (fibrin) formation
• Fibrin clot seals wound and acts as provisional scaffold
• Platelets release PDGF, TGF-β → initiate repair cascade

Phase 2 - Inflammation (Hours - Day 1-3)

• Neutrophils arrive within 24 hours → clear bacteria and debris
• By day 2-3, monocytes arrive → differentiate into macrophages
• Macrophages are the critical orchestrators of repair:
  • Phagocytose debris and dead neutrophils
  • Release PDGF, FGF, VEGF, TGF-β → drive proliferative phase

Phase 3 - Proliferation / Granulation Tissue (Days 3-5 onward)

• Angiogenesis: VEGF-A drives endothelial cell proliferation and new capillary sprouting; FGF-2 also contributes
• Granulation tissue forms = new capillaries + proliferating fibroblasts + loose ECM; soft, pink, granular
• Fibroblast proliferation: PDGF, FGF-2, TGF-β → fibroblasts deposit type III collagen initially
• Re-epithelialization: keratinocytes migrate from wound edges under the scab to resurface the wound

Phase 4 - Remodeling (Weeks to Months)

• Type III collagen gradually replaced by stronger type I collagen
• MMPs (matrix metalloproteinases) degrade excess ECM, balanced by TIMPs
• Vascularity decreases; granulation tissue → avascular fibrous scar
• Wound contraction: myofibroblasts (α-SMA positive) contract the wound
• Final tensile strength = 70-80% of normal (never reaches 100%)

Factors Impairing Wound Healing

Complications of Wound Healing

• Hypertrophic scar - excess collagen within wound margins; regresses over months
• Keloid - scar extends beyond original wound margins; does not regress; genetic predisposition; commoner in dark-skinned individuals
• Proud flesh (exuberant granulation) - excessive granulation tissue above skin level; blocks re-epithelialization; needs cautery/excision
• Wound dehiscence - wound re-opens; risk factors: obesity, malnutrition, infection

Reference: Robbins, Cotran & Kumar - Pathologic Basis of Disease, Chapter 3: Inflammation and Repair