10-14 - Acute Inflammation 1b (Levitt).txt

What is it?

• series of reactions of vascularized tissue to injury

What is its purpose?

• defend against foreign substances (infection)
• dispose of dead / dying tissue
• immobilize injured area
• compartmentalize area

1. Vasodilation

2. Increased permeability of microvasculature (venules)

3. Vascular stasis in small vessels

First few seconds

• immediate vasoconstriction (lasts ~30 seconds)

First hour

• gradual vasodilation (beginning of ""bleeding"")
• begin hemostasis (hemostasis = opposite of hemorrhage)
• mast cell degranulation
• margination of WBCs (adhesion of white blood cells to the endothelial cells of blood vessels)
• being large-scale neutrophil response

After first hour

• hemoconcentration from edema (increased permeability)
• ischemia
• growing interaction of chemical mediators
• emigration of larger WBCs
• complement system

• Histamine from mast cells
• Bradykinin (a vasoactive peptide)
• Prostaglandins (arachidonic acid metabolites)

It is a change in vascular flow and caliber during acute inflammation

• consists of terminal arterioles, capillaries, and post-capillary venules
• bloow flow controlled by contraction / relaxation of pre-capillary sphincters

Normal: Hydrostatic pressure (pushing blood out from blood vessel into extravascular fluid) is balanced with oncotic pressure (form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system)

Acute: Hydrostatic >> Oncotic (net flow OUT of capillaries into extravascular fluid)

The vessels become leaky resulting in exudation of fluid and resultant tissue edema. Mechanisms include:

• formation of intercellular gaps in endothelium
• • immediate transient response (15-30 minutes)
  • • endothelial cells contract, widening intercellular gaps in small venules
    • histamine, bradykinin, leukotrienes, substance P
  • delayed, sustained response (4-6 hours to days)
  • • endothelial cells undergo cytoskeletal changes that disrupt junctions in venules & capillaries
    • cytokines IL-1, TNFa, IFNg
• direct injury resulting in endothelial cell necrosis (ex: burns)
• • immediate sustained response
• • • immediate leakage that continues until thrombosis / repair
    • affects ALL types of vessels (hours)
  • delayed prolonged leakage
  • • similar to direct injury leakage
    • doesn't start for 2-12 hours
    • lasts hours - days
    • ex: sunburn
• leukocyte mediated endothelial injury
• • inflammation results in PMN adhesion to vessel, degranulation, release of enzymes, and local injury to vessel wall
  • seen in lungs and kidneys

Greater in venules than in capillaries because

• venules have more H2 receptors than capillaries
• V. endothelium have more contractile elements
• Inter-endothelial junctions are looser in venules

• 1) Margination, rolling, and adhesion
• 2) Migration
• 3) Chemotaxis
• 4) Attachment of neutrophils
• 5) Phagocytosis
• 6) Degranulation of neutrophils

2. Activation of endothelial cells
4. Loose adhesion and rolling
6. Firm adhesion
8. Transmigration

• Disruption of laminar flow by stasis and increased viscosity
• Leukocytes roll/tumble along endothelial surface, gradually becoming adherent

• Proposed mechanism of adherence
• • Activation of cell-specific receptors (adhesins) on both leukocytes and endothelial cells (Selectins)

• Underlying stimulus causes the release of mediators which activate the endothelium causing selectin to be moved to the surface
• TNFa and IL-1 stimulate production of E selection (presenet on endothelial cells) and ICAM
• Histamine, thrombin & PAF (platelet activating factor) cause P-selectin to move from Weibel-Palade bodies to cell surface
• Increase strenght of binding of integrins (conformational change)

• Selectins - E-selectin (present in endothelial cells), P-selectin (platelet cells), L-selectin (leukocytes)
• Immunoglobulins - ICAM-1 & VCAM-1
• Integrins: LFA-1, Mac-1, VLA-4
• Mucin-like glycoproteins

(Activation of endothelial cells = #1 of M,R,&A of cellular inflammation)

Occurs in postcapillary venules

#2 of M,R,&A of cellular inflammation; M,R,&A = first step of cellular inflammation

• Selectins transiently bind to receptors
• PMN's bounce of roll along endothelial surface

#3 of M,R,&A of cellular inflammation; M,R,&A = first step of cellular inflammation

• leukocytes firmly adhere to and flatten along endothelial surface
• occurs in postcapillary venules
• Mediated by CD11/18 integrns on leukocytes surface and ICAM-1 on endothelial cells

#4 of M,R,&A of cellular inflammation; M,R,&A = first step of cellular inflammation

• Called ""diapedesis""
• Mediated by ICAM and PECAM
• Neutrophils follow chemoattractants into tissues

#3 of cellular inflammation

Chemotaxis = ability to direct the motion of inflammatory cells in response to chemical gradients

Chemotactic agents bind cell membrane receptors which result in phosphorylation cascade & transduction within the cell resulting in release of Ca2+ ions in cytoplasm. This results in 3 important changes in the cell

2. Movement via actin myosin contraction
4. Activation of the cell causing arachidonic acid metabolism, degranulation, & modulation of adhesion molecules
6. Phagocytosis

• Exogenous mediators
• • N-formyl methionine terminal amino acids from bacteria
  • Lipids from destroyed or damaged membranes (including LPS)
• Endogenous mediators
• • Complement proteins (C5a)
  • Cytokines, particularly IL-8
  • Arachidonic acid products (LTB4) - a leukotriene

#4 of cellular inflammation

Attachment of neutrophils to the offending agent: this is done via opsonins which coat the agents:

2. IgG-FC naturally occuring Ab to particle
4. C3b & C3bi generated by activation of complement by immune or non-immune mechanisms
6. Collectins - lectins of plasma bind to microbe walls (innate immunity)

#5 of cellular inflammation

• promoted by opsonins (C3b & specific IgG)
• opsonins coat the bacteria & act as a bridge between the bacteria & the PMN surface receptors for C3b and the FC portion of IgG
• phagosome fuses with lysosomes (phagolysosomes)
• neutrophils & macrophages = primary phagocytic cells
• • Sequential events
  • • Opsonization
    • Attachment
    • Ingestion
    • Killing

#6 of cellular inflammation

Degranulation of neutrophiles leading to enzymatic degradation of the offending agent

• Reactive Oxygen Species
• • Myeloperoxidase reacts with H2O2 to form reactive oxidant (hypochlorous radical) that kills bacteria
  • O2--(NADPH)-->O2---(dismutase)-->H2O2-- (myeloloperoxidase+Cl)-->HOCl + H2O
• Enzymes
• • Lysosomes contain enzymes which punch holes in the bacterial membrance including lysozyme, lactoferrin, bactericidal permeability increasing protein and defensins
• Acid Hydrolases
• • Digest the cellular debris in the phagolysosomes

#6 of cellular inflammation

• Primary - contain serine proteases, lysozyme & phospholipase A2
• Secondary - similar to primary but also contain lactoferrin and collagenase
• Tertiary - present at leading edge of migrating PMNs, contain gelatinases that are capable of degrading basement membrane

Bacteriocidal

• Oxygen dependent
• • Oxygen radicals
  • • H2O2
    • • formed via NADPH oxidase
    • Hydroxyl radical
    • Singlet oxygen
• • Mechanisms utilizing oxygen metabolites
  • • Myeloperoxidase-halide system
    • • Formation of hypohalous acids (HClO most important)
      • probably the primary bactericidal agent in neutrophils
    • Direct damage by radicals
• Non-oxidative bacterial killing
• • Lysosomal hydrolases (primary & secondary granules)
  • Bactericidal / permeability-increasing proteins (primary granules --> affects Gram(-))
  • Defensins (primary)
  • Lactoferrin (secondary - chelates iron)
  • Lysozyme (primary & secondary, lysosomes)
  • Bactericidal proteins of eosinophils

• Can migrate through intact plasma membranes
• Initiate lipid peroxidation
• React with DNA
• Oxidize sulfhydryl groups of proteins
• Degrade extracellular matrix components

General mechanism of tissue injury by inflammatory cells:

• Lysozomes released into extracellular space
• Degrade matrix & cause cell injury
• Activated leukocytes release ROS & arachidonic acid metabolites which can injur tissue & endothelial cells

Usually lysozome enzymes function with protease activity

Protection by anti-proteases

• a1-anti-trypsin
• a2-macroglobulin

• adhesion
• phagocytosis
• microbicidal

• leukocyte adhesion disorders
• Chediak-Higashis Syndrome
• • autosomal recessive
  • defective intracellular transport protein
  • inability to lyse bacteria
  • cannot secrete lysozymes into the phagosome
• Chronic granulomatous disease
• • X-linked
  • no oxidative burst (deficient NADPH oxidase with absent H2O2 production
• Myeloperoxidase deficiency

Leukocyte adhesion deficiency-1

• recurrent bacterial infections
• inflammatory lesions lack neutrophil infiltrate
• high numbers of neutrophils in circulation
• neutrophils from patient can roll, but do not stick
• transfuse patients with normal neutrophils & they can emigrate

Mechanism

• absence of integrins on neutrophils
• mutation in n-terminal region of integrin B chain inhibits proper integrin assembly
• normal function is restored following transfection of patient cells with cDNA for beta chain