L3- Cytokines and Inflammation

Question 1

Describe basic characteristics of cytokines

Answer 1

• Low molecular weight proteins (30kDa)
• Bind to specific receptors, alter gene expression
• Regular immune responses (signal)
• Made by a variety of immune cell types

• Involved in;
—Haematopoiesis
—Adaptive immunity
—Innate immunity
—Inflammation

Question 2

How often is cytokines expressed and when?

Answer 2

• Produced transiently in response to antigen
• Cytokines specificity is determined by receptor expression
• Receptor expression can vary depending on cell activation state

Question 3

Due to the potency of cytokines, what happens when the systemic inflammation can’t be resolved?

Answer 3

It can lead to increasing concentrations of cytokines in the systemic circulation (“cytokine storm”). This continued cytokine production can have a deleterious effect on the host, with the development of hypotension, intravascular thrombosis, pulmonary edema, and hemorrhage; if this process is left unchecked, it can lead to multiple organ failure and death. This condition often is referred to as the systemic inflammatory response syndrome (SIRS). This term describes the clinical manifestations of widespread endothelial inflammation that leads to increased vascular permeability. This condition is the initiating pathologic process in a group of diverse disorders, such as bacterial sepsis, ischemia, burn injury, trauma and tissue injury, and hemorrhagic shock.

-Can reflect severe infections or autoimmunity

Question 4

Cytokines usually act on same cell that produces the cytokines is called ______ and acting on nearby cells is called ______.

Answer 4

Same cell: Autocrine

Different cell: paracrine

Question 5

What does the term pleiotropism in relation to cytokines mean?

Also list a positive and negative reason for this action.

Answer 5

Each cytokines has multiple biological actions.

Positive: provides diversity of actions

Negative: May limit clinical utility of cytokines because of unwanted effects

Question 6

What is the effect of redundancy of multiple cytokines sharing the same or similar biological activities?

Answer 6

Blocking any one cytokine may not achieve a desired effect

Question 7

Th1 effector CD4+ helper T cell defining cytokines is _____ with the principle target cell being _____. The major immune reaction is _____ to host defense against ______. Plays a role in this disease ______.

Answer 7

Defining cytokine: IFN-y

Principle target cells: macrophages

Major immune reaction: macrophage activation

Host defense: intracellular pathogens

Role in disease: Autoimmunity; chronic inflammation

Question 8

Th2 effector CD4+ helper T cell defining cytokines is _____ with the principle target cell being _____. The major immune reaction is _____ to host defense against ______. Plays a role in this disease ______.

Answer 8

Defining cytokines; IL-4, IL-5, IL-13

Principal target cell: Eosinophils

Major immune reactions: IgE production; Eosinophil and mast cell activation; alternative macrophage activation

Host defense: Helminths

Role in disease: Allergy

Question 9

Th17 effector CD4+ helper T cell defining cytokines is _____ with the principle target cell being _____. The major immune reaction is _____ to host defense against ______. Plays a role in this disease ______.

Answer 9

Defining cytokines: IL-17, IL-22

Principal target cells: Neutrophils

Major immune reactions: Neutrophil recruitment and activation

Host defense: extracellular bacteria and fungi

Role in disease: Autoimmunity; inflammation

Question 10

Tfh effector CD4+ helper T cell defining cytokines is _____ with the principle target cell being _____. The major immune reaction is _____ to host defense against ______. Plays a role in this disease ______.

Answer 10

Defining cytokines: IL-21 (and IFN-y or IL-4)

Principal target cells: B cells

Major immune reaction: Antibody production

Host defense: extracellular pathogens

Role in disease: Autoimmunity (autoantibodies)

Question 11

What is the 3 main responses of activated macrophages following Th1 cell stimulation?

Answer 11

1. Enhanced killing capacity of bacteria by phagocytosis
2. Secretion of cytokines (TNF, IL-1, IL-12,); chemokines
3. Increased expression of MHC and co-stimulators (B7 molecules (CD80, CD86))

Question 12

What receptor and cytokine is responsible for classical macrophage activation?

Answer 12

IFN-y and CD40L

Question 13

What effect does Th2 cells have on macrophages?

Answer 13

Th2 cytokines inhibit classical macrophage activation and stimulate the alternative pathway of macrophage activation – clearance and repair of tissues damaged in eg. allergic and parasite-specific immune reactions

Question 14

Which cytokines are responsible for shutting down the activation of inflammatory macrophages, thus terminating these potentially damaging reactions

Answer 14

IL-4 and IL-13

Question 15

Which cytokine of Th2 cells is responsible for B cell activation to produce antibodies?

Answer 15

IL-4

Question 16

Which cytokines of Th2 cells is responsible for intestinal mucus secretion and peristalsis?

Answer 16

IL-4 and IL-13

Question 17

Which cytokines of Th2 cells is responsible for Eosinophil activation?

Answer 17

IL-5

Question 18

What are the 3 major effects of Th17 cells?

Answer 18

1. Stimulate the recruitment of neutrophils and, to less extent, monocytes, thus inducing the inflammation that accompanies many T cell–mediated adaptive immune responses
2. Anti-microbial peptides (IL-17; IL-22 makes this happen)
3. Increased barrier integrity (IL-22)

Question 19

List some chemokine characteristics?

Answer 19

• Chemokines are a family of >40 small proteins of similar structures
• They bind to 7 Transmembrane G-protein coupled receptors
• The 7tm receptors have 7 transmembrane helices embedded within the cell membrane, linked to GTP-binding proteins which cause cell activation

Question 20

Recruited leukocytes must migrate towards site of infection or damage within the affected tissues to perform their antimicrobial and phagocyte functions. This is achieved by………..

Answer 20

Detection of cytokine gradients, since concentration of chemokine is highest at the source of chemokine production, leukocytes move from an area of low concentration to an area of high concentration.

Receptors are up-regulated to be at a greater concentration towards side of cell where chemokine concentration is greatest and moves in that direction.

Question 21

Briefly explain the innate immune response to an infection.

Answer 21

• Macrophages encountering bacteria or other types of microorganisms in tissue are triggered to release cytokines that increase the permeability of blood vessels, allowing fluids, proteins and cells to pass into tissues
• Macrophages also secrete cytokines, which direct migration of neutrophils to site of infection; release inflammatory mediators to cause pain
• Phagocytosis and activation of bactericidal mechanisms; antigen presentation

Question 22

What is inflammation?

Answer 22

Inflammation is a tissue reaction that delivers mediators of host defense—circulating cells and proteins—to sites of infection and tissue damage

Question 23

List 4 acute inflammatory responses

Answer 23

• Inflammation involves recruitment of cells and leakage of plasma proteins through blood vessels and activation of these cells and proteins in the extravascular tissues
• The initial release of histamine, TNF, prostaglandins, and other mediators by mast cells and macrophages causes an increase in local blood flow and exudation of plasma proteins
• These contribute to redness, warmth, and swelling, which are characteristic features of inflammation
• This is often followed by a local accumulation in the tissue of phagocytes, mainly neutrophils and blood monocytederived macrophages, in response to cytokines

Question 24

How are macrophages activated?

Answer 24

Macrophages are activated by microbial products such as endotoxin (LPS) and by T cell cytokines such as IFN-γ

Question 25

Monocytes are inactivated macrophages. T or F

Answer 25

True

Question 26

What is the role of macrophages in both innate and adaptive immune response?

Answer 26

Activated macrophages phagocytose and kill microorganisms, secrete proinflammatory cytokines, and present antigens to CD4+ helper T cells

Question 27

What are the macrophages called in the CNS?

Answer 27

Microglia cells

Question 28

What are the macrophages called in the liver?

Answer 28

Kupffer cells

Question 29

What are macrophages called in the lung?

Answer 29

Alveolar cells

Question 30

What are macrophages called in bone?

Answer 30

Osteoclasts

Question 31

Explain how phagocytosis works

Answer 31

* Neutrophils and macrophages express receptors that specifically recognize microbes, and binding of microbes to these receptors is the first step in phagocytosis. Some of these receptors are pattern recognition receptors, including C-type lectins * Phagocyte receptors bind to PAMPs and opsonins including antibody molecules and complement proteins * Ingested foreign particles are enclosed within a phagosome, that breaks away from plasma membrane * Phagosome fuses with lysosome to create phagolysosome, that contains antimicrobial molecules

Question 32

Phagosome fuses with lysosome to create phagolysosome, that contains which antimicrobial molecules.....?

Answer 32

* Reactive oxygen species * Nitric oxide * Proteolytic enzymes

Question 33

Gram negative bacteria have LPS on their cell wall. This is sensed by which PRR?

Answer 33

TLR4

Question 34

Explain how a fever develops?

Answer 34

1. A macrophage ingests a gram negative bacterium 2. The bacterium is degraded in a vacuole, releasing endotoxins that induce the macrophage to produce IL-1 3. IL-1 is released by the macrophage into the bloodstream, through which it travels to the hypothalamus of the brain 4. IL-1 induces the hypothalamus to produce prostaglandins, which reset the bodies thermostat to a higher temperature, producing fever 🥵

Question 35

Neutrophils and monocytes migrate to extravascular sites of infection or tissue damage by .....

Answer 35

Binding to venular endothelial adhesion molecules and in response to chemoattractants eg. chemokines produced by tissue cells reacting to infection or injury.

Question 36

Describe rolling and binding of venues to endothelial adhesions molecules

Answer 36

Leukocyte rolling describes the low affinity adhesive interaction between leukocytes and the vascular endothelium whereby the force of blood flow induces a rotational motion (i.e., rolling) of the leukocyte along the vascular wall TNF and IL-1 mediators act on the cell wall to up regulated modules and involved in binding of leukocytes to vessel * In response to TNF and IL-1, venular endothelial cells express an adhesion molecule of the selectin family called E-selectin. * Other stimuli, including thrombin, cause rapid translocation of P-selectin to the endothelial surface. * Circulating neutrophils and monocytes express surface carbohydrates that bind specifically to the selectins. The neutrophils become tethered to the endothelium, flowing blood disrupts this binding, the bonds reform downstream, and this repetitive process results in the rolling of the leukocytes along the endothelial surface.

Question 37

What adhesion molecules are involved with getting the phagocytes to site of infection or tissue damage?

Answer 37

Lectin-like adhesion glycoproteins, called the selectins, mediate leukocyte rolling, while the firm adhesion and subsequent transendothelial migration of leukocytes are mediated by the interaction of integrins (CD11/CD18, VLA-4) on leukocytes with immunoglobulin-like adhesion molecules on ECs (e.g., ICAM-1, VCAM-1). The expression of P-selectin, E-selectin ICAM-1, and VCAM-l on venular EC are temporally coordinated to ensure that the processes of leukocyte rolling and firm adhesion/emigration can occur for several hours after the initiation of an inflammatory response.

Question 38

Explain L-selectin on leukocytes

Answer 38

Leukocytes also express an adhesion molecule belonging to the selectin family (L-selectin) as well as counter-receptors for EC selectins (PSGL-1). L-selectin is constitutively expressed on most leukocytes, where it is situated on the tips of microvillus cell surface protrusions at a high density. L-selectin mediates leukocyte rolling by interacting with P- and E-selectins expressed on EC. Upon activation of the leukocyte, L-selectin is rapidly shed from the cell surface via a protease-dependent mechanism. P-selectin glycoprotein ligand-1 (PSGL-1) is the most important selectin ligand expressed on leukocytes. PSGL-1 expressed on neutrophils and monocytes is constitutively active and can bind to P- and E-selectins, as well as L-selectin.

Question 39

Explain integrins role

Answer 39

* Leukocytes express another set of adhesion molecules - integrins that integrate extrinsic signals into cytoskeletal alterations. Leukocyte integrins, such as LFA-1 and VLA-4, are present in a low-affinity state on unactivated cells. * Chemokines produced by tissue macrophages and endothelial cells bind to proteoglycans on the luminal surface of endothelial cells and are thus displayed at a high concentration to the leukocytes that are rolling on the endothelium.

Question 40

Explain leukocyte Migration

Answer 40

* Leukocytes adherent to the endothelium crawl to and then through the junctions between endothelial cells, exiting the blood vessels * Within the tissue, leukocytes migrate along extracellular matrix fibers, directed by concentration gradients of chemokines, including chemokines and complement fragments C5a and C3a * Chemokine concentrations are highest where the microbes are located, and leukocytes have chemokine receptors that stimulate migration toward their source

Question 41

Neutrophil chemotaxis involves which cytokines?

Answer 41

IL-8; TNF-y; C5a

Question 42

Neutrophil phagocytosis uses which anti-microbial molecules?

Answer 42

Superoxide | Hydrogen peroxide

Question 43

Neutrophil can kill microbes by degranulation, releasing which anti-microbial molecules?

Answer 43

Lysozyme; NADPH oxidase; Myeloproxidase

Question 44

Explain neutrophil NETS

Answer 44

Neutrophil extracellular traps (NETs); are web-like structures of DNA and fibre that trap and kill microbes extracellularly Contains chromatin fibres decorated with anti-microbial peptides and enzymes such as neutrophil elastase

Question 45

List the three killing mechanisms of neutrophils

Answer 45

Phagocytosis; Degranulation; Neutrophil extracellular traps (NETs)

Question 46

Neutrophil extracellular traps (NETs) can entrap what type of pathogens?

Answer 46

NET-inducing stimuli include whole bacteria as well as cell surface components of Gram-positive and Gram-negative bacterial lipoteichoic acid and LPS

Question 47

Provide an example of a species that NETs can trap

Answer 47

Notable examples of bacteria that potently induce NETs include Staphylococcus aureus, Streptococcus sp., Haemophilus influenzae, Mycobacterium tuberculosis

Question 48

Provide an example when NETs can be an issue for autoimmune diseases

Answer 48

Excessive NET formation contributes to autoimmune and other inflammatory diseases eg. in cystic fibrosis, pathogens such as Pseudomonas aeruginosa thrive in the lungs of affected patients and NETs accumulate, promoting chronic lung obstruction; Clinical lung isolates from cystic fibrosis patients acquire a mucoid phenotype that makes P. aeruginosa less sensitive to NET inhibition – microbes adapt to resist NET-mediated growth suppression

Question 49

List key inducers of inflammation in infection and autoimmune disease “Pro-inflammatory”

Answer 49

TNF; IL-1; IL-6; IL-12

Question 50

Explain what TNF is

Answer 50

TNF is a mediator of the acute inflammatory response to bacteria and other infectious microbes * Under "normal" conditions, TNF-a is an inducer of local inflammatory response. Activated macrophages are stimulated to secrete TNF-a TNFa produces the following physiological effects: * Activates the vascular endothelium * Increases vascular permeability * Increased fluid drainage to lymph nodes

Question 51

How does TNF activate vascular endothelium?

Answer 51

The endothelial cells will begin expressing a different assortment of receptors that recruit leukocytes out of the blood and into the tissue • This also allows for increased platelet adhesion to the activated endothelial vessels

Question 52

How does TNF increase vascular permability?

Answer 52

* Increased entry of Immunoglobulin G into the infected tissue * Increases entry of Complement proteins from the plasma to the tissue * Increased access to leukocytes and activated lymphocytes for extravasation into the infection microenvironment

Question 53

IL-1 is also a mediator of the acute inflammatory response and has many similar actions as TNF. T or F?

Answer 53

True

Question 54

IL-6 is another important cytokine in acute inflammatory responses that has both local and systemic effects. List a few.

Answer 54

* It induces the synthesis of acute phase reactants by the liver, stimulates neutrophil production in the bone marrow, and promotes the differentiation of IL-17–producing helper T cells. * IL-6 is synthesized by mononuclear phagocytes, DCs, vascular endothelial cells, fibroblasts, and other cells in response to PAMPs and in response to IL-1 and TNF.

Question 55

Which cytokine is a major contributor to inflammation in several human inflammatory diseases, including rheumatoid arthritis, and antibodies specific for this cytokine receptor are used to treat some forms of arthritis?

Answer 55

IL-6

Question 56

Which cells express IL-12?

Answer 56

Dendritic cells (DCs) and phagocytes produce IL-12 in response to pathogens during infection.

Question 57

Which cytokine is a heterodimeric pro-inflammatory cytokine that; * induces production of interferon-γ(IFN-γ) * favours the differentiation of T helper 1 (TH1) cells * forms a link between innate resistance and adaptive immunity?

Answer 57

IL-12

Question 58

List localised and systemic effects of TNF-α release under normal conditions

Answer 58

Under normal conditions, TNF-α is an inducer of local inflammatory response

Question 59

List localised and systemic effects of TNF-α release under severe conditions

Answer 59

* The presence of infection in the bloodstream, or sepsis, is accompanied by a massive release of TNF-α by macrophages in the liver, spleen, and other sites throughout the body * Systemic release of TNF-α into the bloodstream causes vasodilation, which leads to a loss of blood pressure and increased vascular permeability, leading to a loss of plasma volume and eventually shock, known as septic shock because the underlying cause is a bacterial infection * TNF-α release in septic shock also triggers blood clotting in small vessels throughout the body--disseminated intravascular coagulation (DIC) --which leads to massive consumption of clotting proteins, so that the patient’s blood cannot clot appropriately

Question 60

What is disseminated intravascular coagulation?

Answer 60

TNF-α release in septic shock also triggers blood clotting in small vessels throughout the body--disseminated intravascular coagulation (DIC) --which leads to massive consumption of clotting proteins, so that the patient’s blood cannot clot appropriately • DIC frequently leads to the failure of vital organs such as the kidneys, liver, heart, and lungs, which are quickly compromised by the failure of normal perfusion; consequently, septic shock has a high mortality rate

Question 61

What is sepsis?

Answer 61

A systemic complication of severe infection, usually bacterial Clinically characterized by fever, fast heart and respiratory rates, metabolic abnormalities, and mental disturbances

Question 62

Bacterial sepsis is most often initiated by which part of bacteria? What signalling is involved?

Answer 62

LPS (also called endotoxin) released from gram-negative bacteria or lipoteichoic acid released from gram-positive bacteria, which may enter the blood stream. TLR signaling is then induced in cells in many organs by LPS or lipoteichoic acid, leading to the production of TNF and other cytokines, including IL-12, IFN-γ, and IL-1

Question 63

What happens with most severe cases of sepsis called septic shock?

Answer 63

There is vascular collapse and disseminated intravascular coagulation, caused by the effects of high doses of TNF

Question 64

How can we test for severe septic shock?

Answer 64

The concentration of serum TNF may be predictive of the outcome of severe sepsis. Septic shock can be reproduced in experimental animals by administration of LPS, lipoteichoic acid, or TNF

Question 65

What drugs have been trialled in patients with sepsis?

Answer 65

Antagonists of TNF can prevent mortality in the experimental models, but clinical trials with anti-TNF antibodies or with soluble TNF receptors have not shown benefit in patients with sepsis. The cause of this therapeutic failure is not known, but it may be because other cytokines elicit the same responses as TNF

Question 66

How quickly is the onset of acute inflammation?

Answer 66

Rapid (minutes or hours)

Question 67

How quickly is the onset of chronic inflammation?

Answer 67

Insidious or follow acute inflammation (days)

Question 68

What is the duration of acute inflammation?

Answer 68

Short (minutes to days)

Question 69

What is the duration for chronic inflammation?

Answer 69

Long (weeks to years)

Question 70

What predominant inflammatory cell is present in acute inflammation?

Answer 70

Neutrophils

Question 71

What predominant inflammatory cell is present in chronic inflammation?

Answer 71

Lymphocytes and macrophages

Question 72

What is the bodily effects of acute inflammation?

Answer 72

Exudation of fluid and plasma proteins (edema)

Question 73

What is the bodily effects of chronic inflammation?

Answer 73

Proliferation of blood vessels, fibrosis, tissue destruction, scarring

Question 74

What tissue damage can you expect for acute inflammation?

Answer 74

Usually mild and self limited

Question 75

What tissue damage can you expect from chronic inflammation?

Answer 75

Often severe and progressive