immunology handouts friday

8/2/2019 Immunology Handouts Friday

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Innate Immune System:

Anatomical Barriers:

Mechanical- skin, mucous membranes, mucociliary escalator Chemical- sweat, skin, saliva, tears, HCl (stomach acid), defensins, surfactant Biological-normal flora competing with pathogensHumoral Components Complement Cytokines

Cellular Components:

Neutrophils-phagocytosis Monocytes-become macrophages in the tissue Macrophages-phagocytosis NK cells-killing virus infected and malignant cells Eosinophils- killing parasites and helmiths (worms)

Phagocytosis and Intracellular Killing:

Phagocytes: Neutrophils

Characteristic, multilobular nucleus Granules in cytoplasm- PRIMARY (contain lysozyme, cationic proteins, lysozyme, defensins,

elastase and MPO). SECONDARY contain lysozyme, NADPH oxidase, lactoferrin.

Phagocytes: Macrophages

Kidney shaped nucleus Lysosomes contain lysozyme Not many granules

Phagocyte Response to Infection:

1. THE SOS SignalsThese molecules send an SOS signal to the phagocyte to alert them of an infection. These are:

N-formyl methionine containing peptides Clotting system peptides Complement products Cytokines

2. Phagocyte ResponseOnce the phagocyte has been alerted, the phagocyte responds by:

Vascular adherence: it sticks to the endothelial cells via adhesion molecules such as P selectinand E-selectin.

Diapedesis: phagocyte moves in between the endothelial cells Chemotaxis: substances sent from the infected tissue (chemoattractants) attract the phagocyte

into the tissue.

Activation: the phagocyte becomes activated Phagocytosis and killing


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3. Initiation of phagocytosis:Attachment of the phagocyte to the pathogen happens via receptors:

Complement receptors Scavenger receptors Receptor for IgG FcR (if antibodies against the pathogen have been produced). This is a good

example of how the innate and acquired immune systems are linked.

Toll-like receptors- which recognise broad patterns on bacterial cell walls.4. Phagocytosis: Attachment Phagosome formation (pathogen contained in the phagosome) Granule/lysosome fusion Phagolysosome formation

How is the bacteria killed in the phagolysosome?

Via chemical reactions which use up oxygen (hence they are given the name RESPIRATORY BURST) that

produce free radicals such as superoxide anions which are toxic using the enzyme myeloperoxidase.

Other substances can also kill the pathogen such as lactoferrin which is found in the phagocyte granules

and defensins and cationic proteins. These are oxygen independent mechanisms.

In addition, macrophages have another mechanism of killing which involves Nitric oxide which can be

toxic to pathogens.

NON-SPECIFIC KILLER CELLS

Several different cells including NK and LAK cells, K cells, activated macrophages and eosinophils are

capable of killing foreign and altered self target cells in a non-specific manner. These cells play an

important role in the innate immune system.

1. NK and LAK cells

Natural killer (NK) cells are also known as large granular lymphocytes (LGL) because they resemble

lymphocytes in their morphology, except that they are slightly larger and have numerous granules. NK

cells can be identified by the presence ofCD56 and CD16 and a lack of CD3 cell

surface markers. NK cells are capable of

killing virus-infected and malignant target

cells but they are relatively inefficient in

doing so. However, upon exposure to IL-2

and IFN-gamma, NK cells become


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lymphokine-activated killer (LAK) cells, which are capable of killing malignant cells. Continued exposure

to IL-2 and IFN-gamma enables the LAK cells to kill transformed as well as malignant cells. LAK cell

therapy is one approach for the treatment of malignancies.

How do NK and LAK cells distinguish a normal cell from a virus-infected or malignant cell? NK and LAK

cells have two kinds of receptors on their surface a killer activating receptor (KAR) and a killer

inhibiting receptor (KIR). When the KAR encounters its ligand, a killer activating ligand (KAL) on the

target cell the NK or LAK cells are capable of killing the target. However, if the KIR also binds to its ligand

then killing is inhibited even if KAR binds to KAL. The ligands for KIR are MHC-class I molecules. Thus, if a

target cell expresses class I MHC molecules it will not be killed by NK or LAK cells even if the target also

has a KAL which could bind to KAR. Normal cells constitutively express MHC class I molecules on their

surface, however, virus infected and malignant cells down regulate expression of class I MHC. Thus, NK

and LAK cells selectively kill virus-infected and malignant cells while sparing normal cells.

2. K cells

Killer (K) cells are not a morphologically distinct type of cell. Rather a K cell is any cell that mediates

antibody-dependent cellular cytotoxicity (ADCC). In ADCC antibody acts as a link to bring the K cell and

the target cell together to allow killing to occur. K cells have on their surface an Fc receptor for antibody

and thus they can recognize, bind and kill target cells coated with antibody. Killer cells which have Fc

receptors include NK, LAK, and macrophages which have an Fc receptor for IgG antibodies and

eosinophils which have an Fc receptor for IgE antibodies.


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COMPLEMENT:

It is a system of around 30 different proteins. It was discovered at the end of the 19th century.

Complement Functions:

Host Benefit:

opsonisation to enhance phagocytosis (think of opsonins as like the condiments that cover apathogen and make it more tempting to "eat" by the phagocyte).

phagocyte activation and attraction lysis of bacteria and infected cells regulation of antibody responses clearance of immune complexes clearance of apoptotic cells

There are three pathways

Classical Pathway Lectin Pathway Alternative Pathway


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The three pathways provide essentially three routes towards the same end result, the same cake!

THE COMPLEMENT COOKBOOK!

THE CLASSICAL PATHWAY RECIPE!

Ingredients:

C1 complex- which has three bits stuck onto each other- q, r, s

C2

C3

C4

a good bacterial/pathogen surface with bound antibodies for the cooking to take place on

Method:

Add some C1 complex into the hot pan (bacterial cell wall). This will cause the complex to become

activated.

Then throw in some C4 with the C1. The C1 will cleave the C4 into C4a, C4b. Remove the C4a from the

pan and discard. Notice that the C4b will bind to the wall.

Chuck in some C2 now. C1 will also cleave C2 into C2a and C2b. Remove the C2b from the mixture anddiscard. Notice that C2a will bind to the C4b.

You have now made C3 convertase, an enzyme! However, we're not done cooking just yet. Add in some

C3 to complete the recipe and add in some extra flavour. C3 will split into C3a and C3b. Remove the C3a

from the mixture and discard. C3b will join to C1, C2a and the C4b.

You have now successfully made C5 convertase!


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THE LECTIN PATHWAY RECIPE! " THE EXOTIC RECIPE"

Ingredients:

MBL-mannose binding lectin

MASP1

MASP2

C4

C2

a good bacterial/pathogen surface with bound antibodies for the cooking to take place on, make sure

the pan is coated with mannose.

(most bacteria has mannose which is a sugar on the surface)

Method:

Add in some MBL, ensure this sticks to the mannose on the surface.

Add in some MASP1 and MASP2. Ensure they stick on to the MBL. This now acts just like C1 of the

classical pathway.

Add in C4 and watch the MASP1/2/MBL complex cleave it into C4b which sticks to the pan and C4a

which you can discard from the pan. Add in C2 and watch it be cleaved into C2a and C2b (which you can

discard). C2a sticks to C4b.

Add in C3 which gets cleaved into C3a (discard) and C3b which can bind to C4b and C2a. This is now C5

convertase!

You have now successfully made C5 convertase!

For advanced chefs! To make this dish into a michelin star masterpiece follow the recipe for Lytic

Attack Pathway!


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Note! Don't waste the C2b and the C3a and C4a, these can be used to make opsonins,

chemoattractants and prokinin.

THE MASTERPIECE! THE LYTIC PATHWAY- JUST FOR PROS!

Ingredients:

C5, C6, C7, C8, C9

a good bacterial/pathogen surface with bound antibodies for the cooking to take place on,

Using the C5 convertase that you made with any of the 3 above recipes, add in some C5. Watch it being

cleaved into C5a and C5b. Discard the C5a. Use the C5b to bind to the pan. Add in C6, C7, C8 and lots

and lots of C9. Assemble the mixture to form a transmembrane protein pore i.e. MAC.


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ACQUIRED IMMUNITY

Humoral Immunity- in a sheet

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