The Innate Immune Response

Question 1

Immunology

Answer 1

is the study of the physiological mechanisms that humans
and other animals use to defend their bodies from invasion by other
organisms

• Your body defends you from all things that are not you – we call
  these things that are not you “anitgens”

Question 2

Antigen

Answer 2

are any molecule that binds specifically to an antibody, also any molecule that can produce peptides that bind specifically to a T-cell receptor

Question 3

Intrinsic epithelial barriers

to infection

Answer 3

• Skin, mucosa, epithelium = MECHANICAL barriers
• Enzymes in tears, sweat, saliva = CHEMICAL barriers

• There are good bacteria in your body = MICROBIOLOGICAL barrier – you need these in our gut to keep pathogenic bacteria from being able to
grow (healthy bacteria are taking up all the resources and space

Question 4

Breaking the Physical

Barrier

Answer 4

As soon as you break barrier (stab yourself with an explorer) you start recruiting inflammatory cells to this area; INNATE IMMUNE RESPONSE IS FIRST!!! at the same time, inflammatory cells that are at the site of infection (dendritic cells) are going to change states and “schlep” off to the nearest lymph node; once they get to the lymph node, they will get ADAPTIVE IMMUNITY started

Question 5

Breaking the

Microbiological Barrier

Answer 5

• This can happen if you were on antibiotics and killed off good bacteria, leaving space for pathogenic bacteria to grow
• Vomiting and diarrhea until you can combat this; i.e. neutrophils and red blood cells leak into gut between injured and epithelial cells

Question 6

Nonspecific Immune Cells Part of Innate

Immune Response

Answer 6

• Neutrophils
• Macrophages
• Dendritic cells
• Natural killer cells
• Mast cells
• Eosinophils/basophils

Question 7

Soluble Molecules

Answer 7

• Complement
• Antibodies (secreted by B-cells)
• Cytokines (secreted by any cell)
• Chemokines
• Vasoactive mediators

Question 8

Specific Immune Cells

Answer 8

• B cells

* T cells

Question 9

Small Lymphocytes

Answer 9

Production of antibodies (B cells) or cytotoxic and helper functions (T cells)

Question 10

Plasma Cells

Answer 10

Fully differentiated form of B cell that secretes antibodies

Question 11

Natural Killer Cell

Answer 11

kills cells infected with certain viruses

Question 12

Neutrophil

Answer 12

Phagocytosis and killing of microorganisms

Question 13

Eosinophil

Answer 13

Killing of anti-body coated PARASITES through release of granule contents

Question 14

Basophil

Answer 14

Controlling immune responses to parasites

Question 15

Dendritic Cell

Answer 15

Activation of T cells and intitiation of adaptive immune responses

Question 16

Mast cells

Answer 16

Expulsion of parasites from body through release of granules containing HISTAMINE AND OTHER ACTIVE AGENTS

Question 17

Monocyte

Answer 17

Circulating precursor cell to macrophage

Question 18

Marcophage

Answer 18

Phagocytosis and killing of microorganisms. Activation of T cells and initiation of immune responses

Question 19

Dichotomies

Answer 19

Innate (nonspecific cells) VS. Adaptive (specific cells)

Humoral (mediated by antibodies) VS. Cell Mediated Immunnity (CMI) mediated by TH1 T cells and macrophages

Question 20

Innate Immunity

Answer 20

•Fast and will show up within hours of
Infection
• Fixed # of things; they do their specific job and then die
• Limited number of specificties
• Constant during response
• Innate does not recognize viruses and can only recognize certain antigens on bacteria

**BOTH ARE NECESSARY TO REMOVE AN INFECTION!!!!!!!!!!!!**

Question 21

Adaptive Immunity

Answer 21

• Longer response (days to weeks)
• Is specific to each pathogen and each person
• Gets better over time
• Variability: meaning that it is very specific to that pathogen; numerous highly selective specificites

**BOTH ARE NECESSARY TO REMOVE AN INFECTION!!!!!!!!!!!!**

Question 22

Two Places for Pathogens to Live

Answer 22

o Extracellular - Complement/toll-like receptors (not in intracellular)

o Intracellular - TD8 cell (only in intracellular) and DC

but other than these difference they are pretty much the same responses

FOR EXTRACELLULAR, you start out with dendritic cells and neutrophils; EVERYTHING IS DRIVEN BY RECEPTORS!! For complement/toll-like receptors

FOR INTRACELLULAR. You start with dendritic cells but there are no receptors against viruses and there is no effect by complement (one exception); if they worked on viruses (which look like host cells) they would be attacking host cells all the time which is how AUTOIMMUNE diseases work

Question 23

Extracellular First

Responders

Answer 23

• Proteins
o Antibodies
o Complement (helps recruit immune cells)

• Innate immune cells (all are receptors for bacterial proteins)
o Dendritic cells
o Neutrophils
o Macrophages

• If a cell doesn’t have a receptor, it will not respond!

Question 24

Complement

Answer 24

• A group of proteins that exist in inactive forms in the serum at all times
• When you disrupt the capillary bed (poke yourself), the proteins in the serum migrate into the tissue and can start working very quickly
• Conversion is done by activated forms of complement protein’s activating

Question 25

Classical Pathway Summary

Answer 25

1) Already existing antibodies to extracellular bacteria bind to the bacterial antigen 2) C1 binds to IGM (antibody) 3) Once it binds, C1 will then grab a hold of the next two pieces (C2 AND C4) and convert them to their active form 4) Once C2 and C4 are active and bind to the bacteria, they can convert the next piece: C3 5) C3 (ONCE ACTIVE) then binds to the bacteria and converts the NEXT piece: C5 6) C3 cleaves C5 and C5 converts C6,C7,C8 7) C6,C7,C8 form a complex which activates C9 8) C9 polymerizes and now you cause a hole in the bacteria and IT DIES

Question 26

Alternate Pathway Summary

Answer 26

In the absence of an antibody, C3 can self-cleave and combine with other things and become a C3 convertase in order to cleave itself • C3 --> C3a + C3b ``` o C3a (chemotaxis) – C3a goes away and becomes a chemotactic factor – goes off into the blood stream to start telling immune cells to go in that direction (recruits neutrophils and monocytes to site of infection) ``` o C3b binding causes opsonization (coating with butter) - There is a receptor on neutrophils that recognize C3 - One of the properties of neutrophils and macrophages is phagocytosis -We coat something with C3b and this gives it a high affinity for neutrophils and macrophages to phagocytose them • Membrane Attack Complex (MAC ATTACK!) – formation of a pore

Question 27

Function of C3

Answer 27

``` (1) Opsonin (receptors on these cells) • Macrophages/monocytes • Dendritic cells • Neutrophils • B cells ``` (2) Convertase – cleaves itself and gives us huge amplification loop to create massive amounts of complement (3) Activation of B cells – if there is a mutation in C3b you won’t get antibodies (cannot live)

Question 28

How to Control Complement?

Answer 28

• Inactivating factors > SOLUBLE: molecules floating around in the the serum which inactivate complement on bacterial AND host tissues > MEMBRANE BOUND: inactivate complement ONLY FOUND ON HOST CELLS so the only cells that will inactivate the complement stuck to it are host cells which means the complement on bacteria are still active; this is how we protect our cells • If you are going to design a complement system to inactivate complement factors, you might want to start with C1 or C3

Question 29

C1INH (C1 Inhibitory | Factor)

Answer 29

• C1 neutralizer keeps it inactive (C1INH) so it can't cleave anymore • Lack of C1 inhibitory factor is the cause of hereditary angioedema

Question 30

C4-binding protein

Answer 30

Membrane bound C-4 binding protein will Bind to the C4 so that it will not cleave C3 and no Pores will be formed on that cell to destroy (saves the host cells from destruction) OCCURS ONLY ON HOST CELLS

Question 31

Soluble factors H and I

Answer 31

cleave the convertase part of C3 so it can't convert but still have the oponsin for macrophages to eat and B-cells can still be activated **Leaves a receptor (iC3b) for macrophages and neutrophils to still eat**

Question 32

DAF

Answer 32

DAF splits up the alternate pathway of C3 Membrane bound DAF can inactivate the alternate form of C3 so stop production of C3 and thus activation of C5 so that it cannot form the MAC attack on host cells AGAIN THIS IS ONLY ON THE HOST CELLS!! IT WILL STILL WORK ON THE BACTERIAL CELLS

Question 33

MCP

Answer 33

Membrane bound MCP does a similar thing to DAF in preventing C3 from converting so you cant get the whole pathway on HOST CELLS

Question 34

CD59

Answer 34

• Host factor that prevents polymerization of C9 (prevents formation of pore) – so you can’t poke a hole in your own cells • Keeps complement from doing damage to host cells, only bacteria, which is what we want

Question 35

How does Complement start Inflammation?

Answer 35

* C3a, C5a are anaphylatoxins * Alter the vascular endothelium * Recruit inflammatory cells (Neutrophils are the first ones to arrive and the monocytes are shortly thereafter)

Question 36

Anaphylatoxins

Answer 36

* Endothelium is a kind of epithelium – meaning it has tight junctions * If you are neutrophil/macrophage/proteins you cannot get through tight junctions * Activating anaphylatoxins increases vascular permeability, allowing antibodies and complements to the site of infection

Question 37

The Initial Response to | Extracellular Bacteria

Answer 37

``` • Complement (START) • C3b – Receptors • C3a, C5a –Inflammatory mediators • Cell recruitment o Neutrophils o Monocytes - macrophages ```

Question 38

How do you recognize an Extracellular Bacteria?

Answer 38

PATHOGEN ASSOCIATED MOLECULAR PATTERNS (PAMP)

Question 39

Pathogen Associated Molecular Patterns (PAMPs)

Answer 39

A unique glycoprotein structure to bacteria and our immune system has evolved to have receptors to recognize these structures

Question 40

Examples of PAMP

Answer 40

Methionine- Lysine-Phenylalanine is the first amino acids for all bacterial protein (fMLP) and the "f" stands for formulated (stick a formyl group on Met - which hosts cannot do) and because every bacteria has this, we have a receptor for it LPS is on gram neg. bacteria - we have a receptor for that Glycan and Mannose cannot be made by eukaryotes but we have a receptor against them on neutrophils, macrophages, and monocytes and dendritic cells These receptors on the immune cells bind and allow phagocytosis of the bacteria and are called TOLL-LIKE RECEPTORS CONVERSELY, VIRUSES are INTRACELLULAR and are MADE IN HOST and HAVE HOST STRUTURES (we do not have TOLL-LIKE RECEPTORS for viruses)

Question 41

Toll Receptors

Answer 41

are the receptors that recognize PAMPs and also mediate how the immune system will respond Toll receptors are on the neutrophil and monocytes • A family of receptors - 10 members - Cell membrane receptors (extracellular) - Internal receptors (intracellular) • There are TLRs against the PAMPs that are not found on host cells

Question 42

Sensing microbial products inside and outside human cells by different Toll-like receptors

Answer 42

• Different TLRs activate different second messengers • Different second messengers turn on different parts of the immune system • First actions of immune response include TLRs on dendritic cells and macrophages and neutrophils which bind to extracellular pathogens and initiate the immune response • Depending on which type of toll-like receptor is binding the pathogen, That is going to change the way the neutrophil, Dendritic cell or macrophage. What cytokines that Cell will secret which influences what type of T cells are activated (is it primarily humoral or cell mediated)

Question 43

Activation of Different Toll-Like Receptors

Answer 43

• Secondary Messenger systems • Transcription Factors • Differentiation of T cells o CD4 T cells o CD8 T cells o T reg cells • If you make an antibody response against mycobactiera, you die quickly, if you make a cell mediated response you live longer – for everything else it doesn’t really matter as much if you have an antibody or cell-mediated immune response

Question 44

Macrophage Activation (TLR)

Answer 44

• Neutrophils show up first (phagocytosis), followed by monocytes which differentiate into macrophages • TLR makes the macrophage phagocytic ``` • Cytokine secretion by macrophages o IL-1 (IL-18)/IL-6/TNFa o CXCL8 (IL- (chemokine – recruits other cells) o IL-12 ```

Question 45

Cytokines

Answer 45

Cytokines are small soluble proteins (short-lived) with a lot different functions and lots of overlap released by cells

Question 46

IL-1 beta = interleukin 1 beta and TNF- alpha = tumor necrosis factor alpha

Answer 46

These two cytokines also activate endothelium so that you have spaces between endothelial cells to make it easier for immune cells to get into the extracellular space

Question 47

IL-6

Answer 47

IL-6 goes off to bone marrow to upregulate the production of macrophages/neutrophils; also goes to the hypothalamus to cause fever (so does IL-1) **bacteria replicates slower in higher temps**

Question 48

CXCL8

Answer 48

Is a chemokine (similar to cytokines but its job is to recruit cells); tells macrophages/monocytes in bone marrow to go to site of infection

Question 49

IL-12

Answer 49

Activates another innate immune cell called a NATURAL KILLER CELL In the absence of natural killer cell the IL-12 can kill some bacteria

Question 50

General Principles of | Cytokine Biology

Answer 50

* Pleiotrophic: every cytokine has many activities * Redundant: activities of cytokines are so important that more than one cytokines can do the same activity • Broad activity > Non-immune effects in addition to immune functions * Families (structurally similar and similar functions) * Second messengers: receptor turns on second messenger, which turns on a transcription factor

Question 51

Cytokine Receptors

Answer 51

All cytokines work through receptors and, LIKE CYTOKINES, RECEPTORS COME IN FAMILIES • Variable structure – by changing the structure you can change the function of the cytokine • Shared chains – this is why you have redundant function o gp130 o gammac o ßc

Question 52

IL-1 (IL-18) (interleukin)

Answer 52

Macrophage ctyokine o Soluble inflammatory mediators o Activate vascular endothelium o IFNg production o Systemic effects - goes to liver and cause C reactive proteins to go the bone marrow and increase production of innate cell and go to hypothalamus to cause fever o Dendritic cells

Question 53

TNFa (tumor necrosis factor)

Answer 53

o Soluble inflammatory mediator o Activate vascular endothelium o Collapse venous return (ONLY TNFa does this) o IL-1 production - Wickedly potent activator OSTEOCLASTS!!!! (in tissue of mouth destroys bone) o Systemic effects- goes to liver and cause C reactive proteins o Dendritic cells o Apoptosis

Question 54

Why is collapse of venous return good?

Answer 54

- By clamping off venous return, the bacteria can only go into the lymphatic system, drain into lymph node, and destroy it (prevents bacterial spreading) - BUT what if you had cells throughout the body that could do this? > anaphylaxis shock!!!

Question 55

Adhesion and Diapedesis

Answer 55

``` • Diapedesis allows leukocytes to go through the endothelium to the site of infection • Leukocytes roll along the endothelium and look for a space to crawl out of the blood vessel wall into the surrounding connective tissue • When it rolls it makes and breaks low affinity interactions with molecules on the endothelium • Red blood cells, on the other hand, do not interact with the vessel wall • This is only in the veins, not the arteries ``` ``` CXCL8 on the endothelium binds to the receptor on a neutrophil, stopping it from rolling, which allows neutrophils/monocytes to go through the cells (diapedesis) to the site of infection ```