Pathology, Lecture 10 (Lecture Notes)

8/8/2019 Pathology, Lecture 10 (Lecture Notes)

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1020Inflammation Lec#4Ismaeel MatalqaDima M. Bani-Essa19/10/2010


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Pathology Lecture 10

Tuesday, October 19, 2010

Done by: Dima M. Bani-Essa

* You can find the slides of this lecture on Sama group website

under the name (patho slides#5 inflamation #3). So follow the slides

while you are reading this lecture in order to understand better,

especially in explaining the figures *

First, the doctor revised what he has explained in the previous

lecture quickly.

We'll start by talking about coagulation cascade and the role ofcoagulation factors in the inflammation process.

Coagulation

(Slide 2): This is a good diagram (figure 4-9, page 91 in the book)

which summarizes all the steps and the series of reactions which

occur in coagulation.

In the coagulation cascade, we have the extrinsic pathway and theintrinsic pathway, and then there's a common pathway. Just know a

couple of things; actually, we'll not go into fine details of the

coagulation because you'll learn this in the hemodynamics, but just

note here that in the extrinsic pathway, the initiative for such

reactions, when will we have coagulation? We have it, usually, if

there is stimulation of the endothelium, the basement membrane or

the surface of the platelets and this occurs either because of some

insults of the endothelium like in atherosclerosis, in some specifictypes of infections or in inflammation which also leads to the

activation of the endothelium.

Now, such activation will lead to the initiation of this cascade of

enzymatic reactions or enzymatic activation of the different factors

of coagulation.

For the extrinsic pathway, it is usually in tissue injury, which means

there should be a tissue factor, which is the thromboplastin, andplease note here that there are inactive forms of the factors which

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are in the red boxes and we call them the substrates, and we have

the active forms of these in green color which are the enzymes or

the activated factors leading to the activation of the other factors.

In most of these cascade steps, we need a cofactor which

accelerates and initiates the activation of these proenzymes or

inactive forms of the factors. So these are like (calcium) which is one

of the main cofactor. Another cofactor here is the high molecular

weight kininogen (HMWK). And collagen is another cofactor

which is initial in initiating the in-intrinsic factors.

So we have the substrate, we have the enzyme, and we have

cofactors.

Here you see the tissue factor(thromboplastin) activates factor

VII(7) into tissue factorwhich is the VIIa factor(all of these with

a are activated forms and they are in the green boxes). On the other

hand, the Hageman factorwhich is factor XII (12) gets activated

by the HMWK leading to the active form of factor XIIa and then

activation offactor XIa (11).

The common pathway is here, and you see the phospholipid service

(in yellow) which is also needed for the activation, and this with the

calcium cofactor and with those enzymes that will lead to the

activation offactor Xa(10), and this what we call it the common

pathway for the coagulation cascade, and this of course will be

followed by further activation offactor V(5).

The main task of coagulation is to culminate into the activation of

Thrombin which's factor II. So, factor II is the inactive form present in Prothrombin and gets activated by the common

pathway to Thrombin. Thrombin here is the main target to form the

mesh, it's a soluble protein which is present in the plasma and is

used to convert the Fibrinogen into an insoluble form of protein,

Fibrin, and this Fibrin forms the mesh of the blood clot or the

thrombus, so that we have a lot of fibers. This is actually the main

task of coagulation; the formation of Thrombin and then the fibrin.

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So this Fibrin gets activated by thrombin then by further activation,

this will lead to cross-linked Fibrin and the formation of the

thrombus.

Why do we get this thrombus? If we have endothelial injury or

stimulation of the endothelium, we need this coagulation to beactivated and to start functioning to do its task and purpose.

However, if this is continuous (continuous thrombus formation and

continuous Fibrin activation), this will lead to thrombosis.

Thrombosis by itself is harmful and this will lead to occlusion of the

blood vessels, so we need another mechanism to counter balance

this action which is the Fibrinolytic system, and we'll see that

later.

(Slide 3): Just to show you, this is an example (figure 4-10, page

92), here the phospholipid surface of the basement membrane, for

example, or of the endothelium or whatever it is, and you see here

there is an inactive coagulation factor which is the substrate and we

have the active coagulation factor, which is in this case IXa(9), and

this is factor X, with the presence of the cofactor which is factor

VIIIa (13) and the presence of the other cofactors like Ca++ ions,

this will lead to the activation of factor X and this in turn will activatethrombin ( factor II) into thrombin-a (IIa) etc. This is the way of

cascade reactions that occur to create such coagulation profile.

The Clotting Fibrinolytic System

- The Fibrin clots at the site of injury helps in containing the cause,

Fibrin clot provides a frame work for inflammatory cells.

- Factor Xa causes an increase in vascular permeability and

leukocytes immigration; so that's the rule of coagulation factor in

inflammation and you can see here the role of different factors in

inflammation:

- Thrombin causes leukocyte adhesion, platelets aggregation,

and generation of the fibrinopeptides and it is chemotactic. So,

if we like targeting thrombin (by a drug), this will lead to theloss of leukocyte adhesion and the loss of platelets

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aggregation, and this is the main mechanism of action of some

drugs, like warfarin (it is anticoagulant causes fibrinolysis) and

this also will lead to increment of the inflammatory action or

reactions.

- Fibrinopeptides are chemotactic and induce vasopermeability.

- FactorXIIa also activates the fibrinolytic pathway to prevent

widespread thrombosis.

- Fibrinsplit products increase vascular permeability; because

after the formation of the fibrin, they will get activated by other

mechanisms to transform these fibrins into what we call fibrin

split products, and these themselves will increase the vascular

permeability.

- Plasmin interacts with another system which is the

complement system, and it cleaves C3 to form C3a leading to

dilatation and increased permeability. Also it activates XIIa

amplifying the entire process.

So there is a very close interrelationship between the coagulation

system, the fibrinolytic system, the kinin system, and the

complement system.

So, thrombin as an inflammatory mediator binds to protease-

activated receptors (PARs) which are expressed on platelets,

endothelial cells, and smooth muscles leading to:

P-selectin mobilization

Expression of integrin ligands

Chemokine production Prostaglandin production by activating cyclooxygenase-2

Production of PAF

Production of NO

The kinin system

The kinin system leads to the formation ofbradykinin from HMWK(hight molecular weight kininogen). The effects of bradykinin are: 1)

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increased the vascular permeability. 2) Arteriolar dilatation. 3)

Bronchial smooth muscle contraction.4) Pain.

So bradykinin is one of the mediators of pain, and we'll see other

mediators of pain. They have a short half-life which can get

inactivated by kininase.

(Slide 8): The interaction between the four plasma mediator

proteins.

You see here, this is factor XII (12) gets activated by HMWK and

Prekallikerin surface, and once it is activated in this form XIIa, it

will activate the conversion of Prekallikerin into kallikerin, and

kallikerin itself activates factor XII and the transformation of HMWK

into bradykinin. Both of them; the kallikerin and the bradykinin, willactivate the Plasminogen toplasmin, and plasmin will activate the

splitting of the fibrin into fibrin split product to counterbalance the

clot formation of fibrin (fibrinolytic action the of plasmin).

And at the same time, the plasmin also will activate the other

system which is the complement system. So, we are talking about

cascades and series of reactions which are enzymicallymediated

leading to interaction between all the components of plasmaproteins.

(Slides 9 and 10): The doctor repeated the same as the discussed

above.

The Complement System in Inflammation

The C3a andC5a, we call them togetheranaphylatoxins; becausethey are mediators in anaphylaxis (exaggerated allergic reaction to

a foreign protein resulting from previous exposure to it. Sometimes

it can be fatal; anaphylatactic reaction due to mutations, drugs,

toxins... etc might be very fatal). Anaphylatoxins lead to increased

vascular permeability, and cause mast cell to secrete histamine.

C5a activates lipooxygenase pathway of AA (Arachidonic acid). It

also activates leukocytes and increased integrins affinity and it ischemotactic.

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Both of them (C3a and C5a) are opsonins; which means that they

participate in the process of opsonization of microbes and bacteria.

Plasmin and proteolytic enzymes split C3 and C5 into C3a and C5a,

respectively.

The Membrane attack complexes (C5-C9) lyse the bacterial

membranes.

(Slide 12): The complement activation pathways

We have the classical pathwayand we have the alternative

pathway.

The classical pathway is gotten activated by antigen-antibody

complexes, and you see here C1 (complement 1) which can be

formed into activated C1 and then C4+C2 leading to the classic

pathway C3 convertase and this will lead to the classic pathway

C5 convertase by the activation of C3.

The Anaphylatoxins, as we said, in the classical pathway, cause

vasodilatation and increased vascular permeability, also generated

via plasmin and lysosomal proteases. Whereas in the alternative,

pathway it is usually initiated by the microbial surfaces and

polysaccharides.

There is a newly-described pathway, we call it lectin pathway

which is, more or less, similar to the classical pathway but usuallywe don't need antibodies for the activation. So they are, actually,

three pathways: the classical pathway, the alternative pathway, and

the lectin pathway which is usually associated to the classical

pathway.

The alternative pathway is helped by some factors like factor B,

factor D and properdin and then leads to the alternative pathway

C3 convertase leading to what we call it the membrane attack

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complex (MAC), and we will see that MAC is the main one in

digesting and attacking the microbes.

(Slide 13): Here you see, again, the microbe classical, the

alternative and the lectin pathways, and you see here the C3b in the

alternative pathway will lead to recognition of bound C3b by phagocyte C3b receptor leading to phagocytosis. Also, for the

alternative pathway, this will lead to the formation of MAC and this is

mainly to do with lyses of the microbe. Whereas for C5a and C3a

and their role in inflammation, they are involved in the activation of

further leukocytes and in destruction of microbes by leukocytes.

For the classical pathway, we need antigen-antibody complexes for

activation, while in the alternative pathway we need a microbe ormicrobe's metabolites or oligosaccharides to get it activated, but in

the lectin pathway we have the mannose binding lectin with the

other antigens but there's no need for the antibodies.

Defects in the Complement System

Deficiency of C3 susceptibility to infections; so the

patients who come, esp. the children, to the clinic of the

infectious diseases complaining of recurrent infections, wemake them immuno-profiling, in one of these immuno-profiling

we look for complement deficiency, we measure the

complements C3, C5 etc. C3 deficiency, because it's one of

the main actions of destruction of the microbes, it will lead to

susceptibility to infections.

Deficiency of C2 and C4 has been proofed to increase thesusceptibility to Systemic Lupus Erythematosus (SLE).

Deficiency of late components (MAC) is specifically known to

increase the susceptibility to Neisseria infections.

Decrease inhibitors of C3 and C5 convertase. You know

that C3 is a cascade and after finishing its action, we need an

inhibitor for it. So inhibitors are needed to stop the action of C3;

because every C3's action continues, this will lead to adverse

results or adverse reactions. So if there's a decrease in the

inhibitors of C3, this means there is continuation of action of C3and C5, in which we have a decrease in the decade

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accelerating factor (DAF) which is one of the inhibitors of C3,

leading to hemolytic anemia.

The decrease in levels of C1 inhibitor which initiates

(referring to C1) the complement will lead to a very well-known

serious disease, we call it angioneurotic edema. Because of theextravasation of the fluid and the continuous initiation of this

reaction, this will lead to edema and this edema in the skin, in

the larynx, in the GI tract and different parts of the body. (here,

the doctor mentioned something about edema in the larynx

and how it leads to death but I couldn't hear it clearly).

The Arachidonic Acid Metabolism

Cell membrane has a component of phospholipid A2 and under

the action of phospholipase A2. These phospholipids can lead to

the formation of platelet activation factor or AA metabolites.

We have two main pathways for the AA metabolism: one of them

is the Cyclooxygenase and the other is Lipooxygenase.

You see here the products of cyclooxygenase pathway are mainlyprostaglandins (F2, D2, I2) andthromboxanes (A2) and we will

see later that PGI2 (prostacyclin) and TXA2 (thromboxanes A2)

have opposite functions, although they are produced via the same

pathway.

The lipooxygenase products are leukotrienes (LTC4, LTD4, and

LTE4) and other products like Hete.

(Slide 16): this is very important:

There are some other lipooxygenases that we are not interested

about at this moment leading to the formation of Hpete and Hete.

We are interested about the two main pathways; the

cyclooxygenase and the lipooxygenase.

For the lipooxygenase, we have the main 5-lipooxygenase and we

have the 12-lipooxygenase which is another subtype of the

lipooxygenase leading to the formation oflipoxins.

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In summary, for AA metabolites; we have two main pathways:

the cyclooxygenase and the lipooxygenase. The cyclooxygenase

leads to the formation of prostaglandins and thromboxanes. The

lipooxygenase leads to the formation of leukotrienes and there is

subset on this leading to the formarion of what we call lipoxin

(this is a newly-described pathway in the AA metabolism, by the

way. So you may not find this in all the books, it is probably in the

8th edition, you might not find it in the 7th edition).

Cyclooxygenase leads to prostaglandin formation which is PGG2

and then prostaglandin H2 (PGH2) which also lead to the

formation of prostacyclin I2 (PGI2) and this is the most important

one of these prostaglandins and this (referring to PGH2), also, can

get activated to thromboxane A2 (TXA2). Prostacyclin causesvasodilatation and inhibits platelets aggregation, on the other

hand, thromboxane A2 causes vasoconstriction and promotes

platelets aggregation. So PGI2 and TXA2 are opposite in terms of

function.

The other prostaglandins like the PGD2 and PGE2 cause

vasodilatation (the same as prostacyclin) and increased vascular

permeability.For the lipooxygenase, this will lead to the Hpete and Hete which

is one of the chemotactics leading to chemotaxis, then to the

leukotrienes. Leukotrienes A4 (LTA4) lead to leukotrienes B4

which act as a chemotactant, and the other leukotrienes cause

vasoconstriction, bronchospasm and increased vascular

permeability. So the actions of leukotrienes are, more or less, like

thromboxane, In addition to this, leukotrienes also have their

effect on the smooth muscle of the bronchi leading to

bronchospasm.

For the liopxin A4(LXA4) and lipoxin B4 (LZB4), they inhibit

neutrophil adhesion and chemotaxis, so they have, more or less,

like anti-inflammatory or inhibitory effect on the action of other

leukotriene.

Look at these main steps; we can block this step (step of action of

phospholipase) by steroids and glucocorticoids. Actually, this is

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the main target of the action of steroids, they are the magic

medication, and they are used a lot in many diseases. If we look

at the site of action, we can appreciate why steroids are helpful in

many diseases, actually, because they will inhibit all these

processes.

For the cyclooxygenase there are some more specific ones, they

are COX-1 and COX-2 inhibitors which block the cyclooxygenase

like the aspirin and indomethacin.

Non-steroidal anti-inflammatory medications are used to be acting

specifically on the cyclooxygenase but this has been found to

inhibit the prostaglandins and we will see later that prostaglandin

is needed as a protective mechanism and for mucus secretion inthe stomach and that's why those who are taking a non-steroidal

anti-inflammatory medications are advised to take such

medications after meals, and if you have any gastric problems

you shouldn't take them; because they inhibit the action of

prostaglandin which is the protective mechanism in the stomach

and this, of course, will aggravate direct mechanical and chemical

activation of the gastric mucosa. New medications have been

invented which are COX-2 and don't interfere with theprostaglandin action and therefore they are more selective and

safe.

The main two mediators of pain in inflammation are Bradykinin

and PGE2.

Platelet-activating Factor is another chemical mediator which is

generated from membranes phospholipids by phospholipase A2. It

aggregates and degranulates platelets, is a potent vasodilatorand bronchoconstrictor, and increases vascular permeability. Its

effects on the leukocytes are:

Increase adhesion to endothelial cells Chemotactic Degranulation Oxygen burst

The Cytokines

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The cytokines are hormone-like polypeptides produced by cells,involved in cell-to-cell communication; they have pleiotropiceffects which means that they can exert their effects withopposite functions, sometimes. Secretion is transient and theyhave their effect either in autocrine (at the same place), paracrine

(in adjacent areas) or endocrine (through the blood stream). Sothey can exert their function either locally at the site of infection,in the adjacent area or through the blood stream.

The Classes of Cytokines

We can divide them into these 5 main classes:

Regulators of lymphocyte function Interleukin 2 (IL-2) stimulates proliferation Transforming grow factor (TGF) inhibits lymphocytes

growth

Primary responders to injury (innate immunity) Interleukin 1 (IL-1) and tumor necrosis factor (TNF)

Activators of cell mediated immunity Interferon (INF-) and interleukin 12 (IL-12)

Chemotactics Interleukin 8 (IL-8)

Hematopoietic growth factors Interleukin 3 (IL-3) and Granulocyte-macrophage colony-

stimulating factor (GM-CSF)

TNF and IL-1 are the most important of these cytokines, they are

produced mainly by macrophages and their secretion isstimulated by: bacterial products, immune complexes,endotoxins, physical injury or other cytokines and they haveeffects on endothelial cells, leukocytes, fibroblasts, and acute

phase reactions.

(Slide 24): this summarized the major effects of IL-1 & TNF. Sobacterial products, immune complexes, toxins, physical injury and

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other cytokines will activate microphages which will produce TNFand IL-1 but they can be produced by other cells but microphagesare the main source of these mediators.

We have the acute-phase reactions of inflammation whichinclude: fever, increase sleep, decrease appetite, increase theacute phase proteins which we measure them in the blood andHemodynamic effect leading to shock and neutrophilia. All thesewe call them acute-phase reactions which are the initial multi-stations of infections.

The endothelial effect of these cytokines will lead to increase inthe leukocyte adherence, increase in the production of PGI2,increase in the procoagulant activity (and therefore the activationof coagulation cascase), increase the anticoagulant activity and

increase in the production of IL-1, IL-8, IL-6 and PDGF.

The fibroblast effects: increase proliferation, increase collagensynthesis, increase collagenases, increase proteases and increasePGE synthesis. And we will see the importance of these effects onthe fibroblast in the regeneration and repair process.

And they have other effects on the leukocytes by further cytokinesecretion (IL-1, IL-6).

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Pathology, Lecture 10 (Lecture Notes)

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