Inflammation + Repair

Dr. Burns lectures

Inflammation

• Inflammatio - to set on fire

• “-itis” : suffix that signifies inflammation

characteristics of inflammation

• provoked response to tissue injury initiated by:

  • chemical agents

  • cold, hear

  • trauma

  • invasion of microbes

• protective response: destroys, dilutes or confines the injurious agent

• reparative response: induces and supports tissue repair

• potentially harmful: ex: appendicitis that can burst and lead to other inflammation or death

types of inflammation

• Acute

• Chronic

Distinguished by duration, type of infiltrating inflammatory cells

cardinal signs of acute inflammation

Celcus:

• pain

• heat

• redness

• swelling

Galen:

• loss of function

Physiological Responses and Symptoms of 4 cardinal signs

• release of soluble mediators → swelling (tumor), pain (dolor)

• vasodilation → heat (calor), redness (rubor), swelling (tumor)

• increased blood flow → heat (calor), redness (rubor), swelling (tumor)

• extravasation of fluid (permeability) → swelling (tumor)

• cellular influx (chemotaxis) →swelling (tumor)

vascular events at moment of inflammation

First: brief vasoconstriction mediated by

• autonomic nerves

• direct vessel injury

• release of vasoconstrixtors: endothelin-1, thromboxane A2, serotonin)

Second: active hyperemia - increase in organ blood flow

• arteriolar smooth muscle relaxes → vasodilation

Active hyperemia

• Vasodilation

• Arteriolar smooth muscle cells relax → precapillary sphincter opens → blood flow increases → increased intravascular pressure→ tissue redness, swelling, warmth → transudate (protein-poor filtrate of plasma - LEAKY!!) leaves vessels → congestion → exudate comes in (protein-rich filtrate) → increases interstitial osmotic pressure → swelling/edema, lymphatic collapse (poor drainage)

  • exudate: protein-rich, supplies antibodies and complement to the affected area

Can swelling be beneficial?

Yes, it causes pain (dolor) → limits mobility around the affected area (loss of function)

Stasis

loss of fluid from vasculature:

• RBC concentrates (rouleaux)

• blood viscosity increases

• circulation around affected area slows down (stasis)

• neutrophils accumulate and pavement along the vessel wall 

PAGE 18

diapedesis

• neutrophils leave the inflamed vessle by

  • margination and rolling

  • adhesion and transmigration

  • chemotaxis and activation

transmigration

neutrophils rolling on the endothelium until it can embed itself into the layers and exits thru the “aperture”

chemotaxis

neutrophils follow a chemical gradient to site of injury

• soluble bacterial products

• complement components

• chemokines

• LTB ( AA metabolite)

Neutrophil activation: binding of chemotactic agents to neutrophil surface receptors (assembly of contractile elements)

how does neutrophil kill bacteria?

• opsonins: involves opsonization by IgG and C3b

• oxygen-dependent killing: simply engulfing, driven by NADPH oxidase

• pxygen-independent killing: fusion of phagocytic vacuole w lysosomes and cytoplasmic granules contaning hydrolyctic enzymes

oxygen-dependent killing (MOST EFFECTIVE)

• ROS formed thru oxidative burst:

  • glycogen → glucose

  • glucose oxidation by the hexose monophosphate shunt generates NADPH

  • increased O2 consumpion (oxidative burst)

oxygen-independent killing

• molecules inside neutrophils (granule, phagolysomes, etc) help kill bacteria

• not as potent as ROS

degradation and clean up

dead microorganisms degraded by lysosomal acid hydrolases

hydrogen peroxide broken down to water and oxygen by catalase

neutrophil-induced tissue injury

• neutrophil engulfs something too difficult to breakdown

  • degranulation occurs

  • frustrated phagocytosis

  • membranolytic substance

  • persistent leukocyte activation

mediator syystems — vasoactive amines

• histamine: vasodilation and endothelial cell contraction, EC junctional widening and increased permeability

• released by mast cells, basophils, platelets in response to

  • injury

  • immune rxns

  • anaphylatoxins

  • cytokines

  • neuropeptides

  • leukocytes-deprived histamine -releasing peptide

• histamine rxn lasts less than 30 mins (immediate transient reaction)

• serotonin: vasodilatory effects similar to histamine

  • found in platelet granules

  • release triggered by platelet aggrevation and platelet activating factor

mediator systems — plasma protein systems

clotting:

hemostasis - vasoconstriction & plug (loose clot) formation

• vasoconstriction

• platelet activation: multiple factors, positive feedback

• aggregation

• loose clot

coagulation and clot formation - clotting cascade

2 pathways:

• intrinsic pathway: contact activation pathway

• extrinsic pathway: tissue factor pathway

both pathways join the common pathway where they convert Factor 10 → Active factor 10 which converts Prothrombin → Thrombin , Fibrinogen uses thrombin → fibrin → cross-linked fibrin that is important in stablizing blood clots

plasma protein system

• clotting system

• kinin system

• fibrinolytic system

• complement system

kinin system

• hageman factor (in both clotting and kinin systems) lead to the production of Bradykinin

• Bradykinin is important for increasing vessle permeability, vasodilation, pain (directly stimulate pain receptors), short lasting (30mins)

fibrinolytic system

• dissolves the clot

• bleeding stops

• vessel repaired

• endothelial tissue and platelet acts on plasminogen to make plasmin, thrombin from kinin system also indirectly act on plsminogen to make plasmin

• plasmin: cut the fibrin into fragments → dissolves blood clots

complement systems

• assists antibody in killing bacteria

• 3 pathways:

  • classical pathway: triggered by antibodies or C-reactive protein (made in liver) → bind to foreign cell membrane and kill them

    • C1 binds to C-reactive protein → split into C2 and C4 → split into C2a C2b and C4a C4b → C2b + C4b = C2bC4b aka C3 convertase → C3 split into C3a and C3b → C3b IS THE ACTIVE ELEMENT

  • alternative: triggered by C3b binding to bacterial cell wall

    • does not require C1,C2,C4 or specific antibody → more important than classical and lectin pathways in initial defense

    • factor B + C3b = C3bB → Factor D split Factor B into Ba (leaves) and Bb = C3bBb (unstable/short-lived) → Factor P + C3bBb = C3bBbP (stabilizes c3 convertase) →

  • lectin: main functional cell is Mannose that has structure and function very similar to C1 but gets recognized by lectin → C4bC2b = C3 convertase → C4bC2bC3b aka C5 convertase split into C5a and C5b

all pathways goes thru C3 convertase step to make C3a + C3b

arachidonic acid (AA)

• product of membrane phospholipid

• cyclooxygenase pathway act on AA → PGW PGD PGF PGI (vasodilation)

• lipoxygenase pathway act on AA → leukotrienes → LTA → LTB (chemotaxis) or LTC → LTC → LTD → LTE (bronchospasm/bronchoconstriction — vascular permeability , vasoconstriction)

C3a, C4a, C5a main characteristic / fucntion

they are all anaphylatoxin, main job is to trigger mast cell degranulation and increase vascular permeability

how does the different systems of mediators connect to each other?

The Kallikrein in Kinin cascade can trigger plasmin production in fibrinolytic system and boost activity

The plasmin in fibrinolytic system cuts fibrin from the clotting cascade and can also act on C3 and C5 in complement cascade and boost activity

What is the role of NSAIDS (aspirin medicine)

it blocks the cyclooxygenase pathway and prevent the production of prostroglandins → prevent vasodilation

what is role of corticosteroids X (steroid medicine) ?

it blocks the phospholipases → prevents arachidonic acids production → no vasodilation or vasoconstriction → alleviate inflammation symptoms

cytokines and chemokines

• protein cell product that act as a message to other cells, tell them how to behave

• released by many cell types

• IL1, TNF, IL6 activate endothelium and allow leukocyte recruitment

• IFN-y activates macrophages/neutrophils, boosting killing ability

• IL8 (chemokine) potent chemotactic factor for neutrophils

• IL6 (cytokine) acts on hepatocytes to increase fibrinogen production → promotes clot formation

inflammation and resolution

1. immediate transient rxn: neutrophil recruited → phagocytosis → apoptosis , leaky vessels → edema

2. monocytes migrate into the tissues → become macrophage → clear out dead neutrophils

3. macrophage physically changes from M1 (pro-inflammatory) into M2 (pro-resolving) → tissue repair & regeneration (healing)

inflammation outcome

acute inflammation → healing with or without scars (fibrosis)

acute inflammation → pus formation (abscess)→ healing with scars (fibrosis)

acute inflammation → chronic inflammation (worsen/persistent injury) → healing with scars (fibrosis)

chronic inflammation

prolonged process (wks-months-yrs) in which 3 processes are occuring SIMULTANEOUSLY:

1. active inflammation

2. tissue destruction by inflammatory cells

3. tissue healing (repair & fibrosis): attemps at repair, neovasculation

granulomatous inflammation

• special case of chronic inflammation

• characterized by granulomas — organized collection of macrophages

• not preceded by acute, neutrophil-mediated inflammation

• circumscribed lesion, often nodular and surrounded by collagen fibers

• not a tumor

pathology of inflammation

• serous inflammation

  • watery, protein-poor effusion, excess alveolar fluid

• fibrinous inflammation

  • fibrin accumulation

  • indicative of severe inflammation

  • seen in many bacterial infections

purulent inflammation

• pus forming bacteria

• pus is rich in dead and dying neutrophils, lytic enzymes, fibrin

• localized collection of pus = abscess

ulcerative inflammation

• necrotic and eroded eopthelial surface

• commonly affects stomach or intestines

• defined as a defect in the epithelium but may extend into deeper connective tissue

pseudomembranous inflammation

• ulcerative inflammation + fibrinopurlent exudation = pseudomembranous inflammation

• fibrin + pus + cellular debris + mucus form a pseudomembrane over an ulcer

fever

• IL1,TNF and IL6 are regulated by cyclooxygenase which convert AA to prostaglandin → vasoDILATION

• NSAIDS blocks cyclooxygenase → blocks prostagandin production → blocks vasoDILATION → reduce blood flow → REDUCE FEVER

leukocytosis

• elevated WBC count

• bacterial infection

• parasitic infection

• viral infection

increased erythrocyte sedimentation rate

• test performed w anticoagulated blood in upright tube

• sedimentation rate is reported in mm/h

• during inflammation, fibrinogen is high and causes RBC to stick to each other (rouleaux) and sedimen faster

• age and sex can effect sedimentation rate

tissue regeneration

• involves restitution of tissue identitcal to that lost of by injury

• healing: fibroproliferative response that patches a tissue defect by laying down connective tissue → fibrosis and scar formation

the sequence of healing

1. inflammatory response to eliminate the initial stimulus and initiate ECM deposition

2. proliferation & migration of parenchy al and connective tissue cells

3. formation of granulation tissue

4. synthesis of ECM proteins

5. tissue remodeling

6. wound contraction and development of wound strength

granulation tissue

• consist of fibroblasts and vascular endothelial cells proliferation in the loose matrix

• appear pink, soft and granular

• ECM looks edematous b/c new vessels are leaky allowing protein and RBC escape

• new blood vessels regress after 1-2 wks, the site will appear less red

• weeks to months after, fibroblasts will secrete enxymes to breakdown collagen 3 and secrete collagen 1

• eventually, repairedarea will have 70-80% of its initial strength

cells involved in proliferation and repair

• labile cells

• stable cells

• permanent cells

labile cells

• continuouslt dividng/mitotic cells

• stem cells found in basal layer of skin, mucosa of internal organs, and limbus surrounding the cornea

• cell divisiion occurs at a regular rate and differentiated daughter cells replace shed superficial cells

• takes part in tissue regeneration post-injury

stable cells

• quescent , facultative mitotic cells

• don’t normally divide, can stimulate to divide

• takes part in tissue regeneration post-injury

ex: liver regeneration after partial hepatectomy

permanent cells

• nondividing, postmitotic cells

• never divide

• if injured, will be repaired by fibrosis scarring

• does not regenerate

ex: neuron cells

clinical wound healing

• first intention/primary healing

• secondary intention/secondary healing

first intention/primary healing

• little tissue loss

• minimal scarring occurs

• wounds can be closed w sutures

secondary intention/secondary healing

• healing of large wounds where sutures is impossible

• debris removal performed daily to encourage wound closure and allow granulation tissue formation

• myifibroblasts help bring wound edges together

• granulation results in a BROAD scar