Pathology, Lecture 8 (lecture Notes)

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

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In The Name Of Allah

Pathology Lecture 8

Tuesday 12-10-2010

Dona By: Esra' Soudi

Before we start I will remind you about many notes:

1) I've put many photos in this tfree3 because the lecture today was

based on slides & diagrams.

2) The exam will be at Saturday (30/ 10/2010) we have two times

for two sections ....you can go later and check your e-mail to know your

computers number the Dr not allow for any student who don't knowhis/her lab..okalso the Dr said that the material in both sections is

the sameand exam will be the same

3) The doctor advises you to read your material from your book

4) The doctor is angry from students who leave the hall before Dr

Finishes

I will start my lecture:

Last lecture we stopped at this slide. Today, we will talk in details

about the process of extravasation of leukocytes to the site of

infection, and the specific steps about adhesive molecules that

activate such extravasation or movement of leukocytes from inside the

blood vessels to outside (the site of infection).

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You remember that we said that initially the leukocytes which margin

at the periphery of blood vessels stick in a transient way to the

endothelium and we called this rolling.

After this, they will have a more firm adhesion and then they will

transmigrate from the intercellular spaces to the outside environment

which is the extracellular matrix or the connective tissue site. The

processes of rolling, adhesion, firm adhesion, and transmigration are

controlled by a group of cellular adhesion molecules and ligands that we

call: (selectins and integrins).

So what are the selectins and intigrins?Selectins: Receptors that are expressed on the surfaces of

endothelial cells and leukocytes that bind to selected sugars

(sialylated oligosaccharides). They have specific binding sites for

the oligosaccharides and thats why we call them selectins,

because this means they are selective to become apparent or bind

to the ligands which are polysaccharides. They are normally not

expressed on the resting endothelial cells, but are expressed

within 30 minutes of stimulation, by the chemokines or othercytokines that we will see later on. These chemokines and cytokines

will transform the endothelial cells or leukocytes from low affinity

for binding to high affinity (or fast off).

This mean when the cells are in a resting state, they will have

these receptors inside the intracellular space. Then, by the

stimulation they will go through redistribution and transformation

which transforms these receptors to the surfaces. Thus, theybecome high affinity receptors (expressed on the surfaces).

There are many different types of selectins :2


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E-selectin: expressed on Endothelial cells

P-selectin: expressed on Platelets & Endothelial cell

L-selectin: expressed on different types of Leukocytes

Integrins: obligate heterodimers containing two distinct chains,

called the (alpha) and (beta) subunits (selectin has only a single

chain). Integrins only appear on leukocytes (selectin: on leukocytes&

platelets &endothelial cells).

Integrins bind to ligands present in:

Extracellular matrix

Complement systemSurface of other cells

Integrin have cytoplasmic domains and surface receptors which

bind or connect to the cytoskeleton of the cells, which leads to

cytoskeleton transformation, and these transformations will lead to

changes in cell shape allowing it to transmigrate. (Note: the cellmustchange its shape in order to transmigrate.)

Integrin-cytoskeletal interactions involve ligand binding to the

integrins extracellular domain and the clustering of the integrin

and this is induced by chemokines. This interaction will cause

cytoskeletal changes which will cause locomotion of the cell.

(Remember: the main function of the cytoskeleton is locomotion of

any type of cells from inside opposite to the outside).

Reminder: the difference between migration and transmigration,migration is the movement of leukocytes from inside to the outside,

but transmigration is the movement of leukocytes within endothelial

cells.

Follow me step by step to know the sequence of extravasation:

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1) Weak adhesion and rolling: which are mediated by selectin OR

firm adhesion.

2) Firm adhesion : which is mediated by two factors:

Ig (immunoglobulin), super-family molecules expressed on

endothelial cells such as:

- ICAM-1 (Intra-Cellular Adhesion Molecule )

- VCAM-1 (Vascular Cell Adhesion Molecule)

Integrins expressed on leukocytes:

a) LFA-1 (the leukocyte function-associated antigen), another name is:

(CD11a/CD18): we used these integrins to test immunodeficiency >binds with ICAM-1

b) Mac-1 (CD11b/CD18)ligand (expressed on the endothelial cells)

c) P150,95 (CD11c/CD18)

d) VLA-4 (Very Late Activation antigen 1) >> binds with VCAM-1

NOW Look at these two diagrams:

A

Leukocytes have three receptors:

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1. Sialyl-Lewis x-modified glycoprotein that bind with the selectin

on the endothelial cells....(P-selectin and E-selectin )

2. L- Selectin which binds with L-selectin ligand on the endothelial

cells.

3. Integrins which are found in a low affinity state in two situations

A) Normal flow

B) Rolling or not firm adhesion.

Now we will explain in details the sequence of extravasation of

leukocytes to the infectious ar ea..JUST follow me...

FIRST: in the rolling state and after the macrophages go to theinfection site and secrete cytokines (kemokines), adhesion occurs

between:

A. Sialyl-Lewis x-modified glycoprotein & P-selectin

B. Sialyl-Lewis x-modified glycoprotein & E-selectin

C. L-selectin & L-selectin ligand on the endothelial cell.

IMPORTANT NOTE: in the rolling state integrins still have low

affinity until they arrive to the firm adhesion state.

SECOND: firm adhesion state, when cells (such as macrophages,

fibrin, and leukocytes) produce more chemokines. These chemokines

will be delivered to the endothelial cells by proteoglycans which can be

found in the cell membrane, so proteoglycans expose the chemokines to

the integrin, then conformation occurs (converting integrin from low

affinity to high affinity OR what we called firm adhesion. Integrins

are now ready for adhesion or binding.... look at this diagram...

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THIRD: migration within endothelial cells (transmigration), this is

activated by chemokines. Chemokines (cytokines) will lead to some

changes in the cytoskeleton of the cell itself, so the cell change its

shape and size and will try to create some pseudopods ( ,

which is a method of locomotion in Amoeba.)

The type of chemokine which activate transmigration is (CD31) OR

(PECAM-1) >> Platelet Endothelial Cell Adhesion Molecule - 1

Look at this diagram...

The leukocytes can damage the basement membrane of the endothelial

cells by glycogenosis and other enzymes to create more spaces

between endothelial cells through the transmigration.

FORTH: migration to the site of infection.

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This diagram explain s what we've said before

This is another diagram that shows the function of cytokines

P-selectin is normally within Weibel-Palade bodies, which are not

expressed on the surface of the endothelial cells, but when these

bodies are activated by cytokines (such as Histamine and Thrombin). P-

selectins are released on the surface of cells. This process is called

upregulation (redistribution) of selectin.

Endothelial and Leukocyte Adhesion Molecule Interactions

This table is very important: ENDOTHELIUM WBC FUNCTION

P & E-selectins Sialyl-Lewis X Rolling

GlyCAM-1, CD34 L-selectin Rolling

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VCAM-1 VLA-4 Adhesion

ICAM-1 CD11/CD18 Adhesion,

(LFA1, MAC1)

CD31 (PECAM-1 CD31 Transmigration

Q: Are the integrins and selectins part of WBC's?

A: They are only receptors, expressed on the endothelial cells &

WBC's

General Structure of CAM Families :

1) Lectin domain which is

polysaccharides, binds withmucin-like CAMs (ligand)

2)a & b integrins which

usually bind with Ig-

superfamily (ICAM &VCAM).8

Leukocytes

Endothelial cells


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Chemotaxis:Migration (movement) of cells along a chemical

gradient (to the site of infection) by the different type of chemo-

attractants. Chemotaxis increases the affinity of Integrin to the

adhesion molecule, and increases the affinity of Integrins to the

adhesion molecule.

Chemotactic factors:

a) Soluble bacteial products, e.g. N-formyl-methioninetermini

If there is bacteria which has special substance likeN-

formyl-methionine termini in the infectious area, this

chemical substance attract leukocytes.

b) Complement system products, e.g. C5a (sequence of

proteins which activate after activation of any part).

c) Lipooxygenase pathway of arachidonic acid metabolism,e.g. LTB4

d) Cytokines, e.g. IL-8

Diapedesis: Transmigration of leukocytes between endothelial cells

at the intercellular junctions. This process is activated by PECAM-1

(CD31)/PECAM-1 interaction.

Q: Which type of leukocyte come first to the site of infection?

A: Neutrophils because we have acute inflammation at the beginning of

infection (predominance of neutrophils).

Effects of Chemotactic Factors on Leukocytes:

Stimulates locomotion9


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Degranulation of lysosomal enzymes

Production of AA ( arachidonic acid )metabolites

Modulation of the numbers and affinity of leukocyte adhesion

molecules

Look at this diagram please

This is sequence of events following injury:

We take here as example which is myocardial infarction ( (

There is ischemic necrosis, and necrosis will initiate an inflammatory

process (transmigration of neutrophils because we have acute

inflammation). Follow me step by step to understand sequence of

events following the injury:

1) We start by edema (accumulation of fluid in the extracellularmatrix)

2) After that (exactly after two days ), we start with delivery of

neutrophils to the site of infection (acute inflammation)

3) Finally macrophages arrive to eliminate from necrotic (dead) cells

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Q: What are the types of cells responsible for releasing

chemokines?

A: chemokines have different sources; they can be released from the

cells or plasma proteins (this will be explained later on.)

The Dr Focus on this diagram:

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We have here four types of receptors on the plasma membrane:

1) Seven a-helical transmembrane receptors(composed of seven

helixes (rod shaped)). These receptors have intracellular and

extracellular domains. In addition, these receptors bind with many

ligands (such as lipid mediators which can be bacterial product or any

kind of products from dead tissue, chemokines or soluble bacterial

product ( e.g N-formyl-methionyl peptides), they will bind to these

receptors (seven a-helical transmembrane receptor).

2) Toll-like receptor binds with microbe which has LPS

(LipoPolySacchride)Ligands at specific region called CD14

3) Cytokine receptor: activated by different types of cytokines like

INF (InterFeroN).

4) Phagocytic receptor

I must remind you that all the information on the diagram above is very

important.

Really I did my best

Forgive me if there are any mistakes

Done by: Esraa Mofleh Al-Saudi (PharmD)

Thanks a lot for Basma Deeb & Bayan Abu khalil who gave me this chance

to participate in tfree3'

Also thanks a lot for Rawan Al-Zubaidi & Hanan al-Fayoomi who helped mein this lecture

* Sama Girls Correction Team *

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Pathology, Lecture 8 (lecture Notes)