Cytokines, actue phase reaction and definsins

Question 1

What symptoms does inflammation cause?

Answer 1

Swelling - increased vascular permeability
Redness - vasodilation and cell recruitment
Heat - Cell recruitment, localised increase in cell metabolism
Pain - sensitisation of pain receptors
Loss of function - reduced movement and compromised organ function

Failure to resolve inflammation can lead to fibrosis, septic shock or chronic inflammation

Question 2

What are the three types of cells that detect pathogens?

Answer 2

T and B cells:
Individual T and B cells are highly selective for a specific pathogen species - have immune memory

Innate immune cells: Less selective - recognises broad classes of pathogens and not specific species - no memory

Question 3

How do the innate immune cells detect pathogens?

Answer 3

Via PAMPs (pathogen associated molecular patterns) - molecules or structures that are specific for microbes and viruses and not visible on host cells

Question 4

How are PAMPs recognised?

Answer 4

By Pattern recognition receptors (PRR):
PRR are invariant germline encoded receptors that are expressed on innate immune cells and in some cases T cells, B cells and endothelial cells there are several classes

Question 5

What are the classes of PRR mentioned in the lecture?

Answer 5

Toll-like receptors 
NOD like receptors 
C-type lectin receptors 
DNA receptors 
RNA receptors (RIG-I, Mda5)

Question 6

How do cytokines regulate the immune response?

Answer 6

Pathogen –> PRR –> cell activation –> secretion of cytokines –> co-ordinated immune response

Question 7

What are cytokines?

Answer 7

Small proteins that mediate cell-cell communication during immune reactions. Produced by cells in the immune system, main action in immune responses by can target non-immune cells. Stimulate cytokine receptors which are specific, act to modulate immune cell function or attract cells to specific locations

Question 8

What are the three sub-classes of cytokines?

Answer 8

Chemokines, interleukins and TNF family.

Question 9

What are chemokines?

Answer 9

They are a sub-class of cytokines and can have a homeostatic or inflammatory effect on leukocyte migration. They are divided into four groups which are based on the position of the cysteine residue that mediates the formation of disulphide bridges in 3D structures.
Groups:
XCL, CCL, CXCL and CX3CL

Question 10

Describe host defense peptides

Answer 10

They are peptides that can inactivate prokaryotic cells or viruses found to be produced by both prokaryotic and eukaryotic organisms, there are two types, cathelicidin and definsins (alpha, ß, and theta)

Question 11

What are the three main mechanisms of HDP?

Answer 11

• disruption of membrane integrity
• Bind precursors of cell wall formation to inhibit the formation of the bacterial cell wall and block bacterial replication
• target intracellular proteins to disrupt cell function

Question 12

Describe the three types of definsins

Answer 12

Alpha: Restricted to certain mammalian species, main expression in myeloid (neutrophils and some macrophages) and paneth cells
ß: Found in vertebrates and invertebrates, expressed in immune cells (macrophages, granulocytes and NK cells) and epithelial cells
Theta: Restricted to old world monkeys, are expressed on cyclic peptides.

Question 13

Describe the function of cytokines

Answer 13

Mainly act to modulate the function of their target cells, different cytokines have specific receptors, can act in autocrine or paracrine fashion, some regulate immune cell development, hemostatsis, others act in pro-inflammatory or anti-inflammatory responses. Some are monomeric, others are dimers or trimers.

Question 14

How are cytokines released by macrophages?

Answer 14

They are released in response to stimulation of a PRR, requires de-novo transcription and translation of cytokine genes (closely regulated)
Made with pro-sequence that allows their transport into the ER and they subsequent secretion via the secretory vessels.
Exception: IL-1 and TNF
IL1-b requires processing by the inflamasome whilst TNF is initially transported to cell surface where it is expressed as a PM protein, cleaved by protease and releases mature TNF from membrane

Question 15

After release, the plasma promotes systematic changes in response to infections. What are they?

Answer 15

TNF: attracts neutrophils
IL-1ß: T cell polarisation
IL-6: Promotes neutrophil and B cell survival and proliferation, T cell polarisation.
IFNß: antiviral response, promotes IL-10 production by macrophages
IL-10: inhibits TNF, IL-6 and IL-12 production by macrophages
IL-12: Th1 driven T cell responses and NK cell activation

Question 16

What is the acute phase response?

Answer 16

Involves the changes in the plasma concentrations of specific proteins in response to inflammation. This is driven by cytokines produced during localised inflammatory responses, it is systematic with no localised effects. The changes are due to the altered protein synthesis in the liver, some acute phase proteins (APP) are increased (positive APP) whilst others are decreases (-ve APP) The time course of all APPs is not the same

Question 17

What are the functions of APP?

Answer 17

Preventing spread of infection - C reactive protein, SAP and complement proteins

Wound healing - fibrinogen, coagulation and Von Willebrant factor

Preventing systemic inflammation - C reactive protein, SAP, proteinase inhibitors (neutralizes lysosomal proteases realeased by neutrophils) haptoglobin (prevents ion loss) Maganese superoxide dismutase (scavenger of free radicals) and Serum amyloid A (lipid binding)

Question 18

What are the two stages of response in T helper cell polarisation?

Answer 18

Stage 1: Antigen presentation: antigen is presented on MHC class II molecules on an antigen presenting cell (e.g. dendritic cells) and is recognised by the T cell receptor (TCR) of a naïve CD4 T cell. This stimulates the T cell proliferate

Stage 2: Polarisation: response to cytokines secreted by the APC or other nearby immune cells the Th cell will polarize to take on specific characteristics

Question 19

T helper cell polarization?

Answer 19

Naïve CD4 T cell recieves different signals to determine the class.
Th1 (IL-12 signal): promotes killing by macrophages, responses to intracellular pathogens
Th17 (TGFß/IL-6/IL-1ß/IL-23 signals): Anti-fungal and anti-tumor immunity. Auto-reactive Th17 cells are a major driving factor of the pathogenesis of autoimmune disorders
Th2 (IL-4 signal): Promotes antibody production by B cells, anti-worm immune responses
Treg Immunosupressive - TGFß signals

Question 20

Cytokines in Disease?

Answer 20

Chronic inflammation drives pathology in many diseases such as autoimmune disorders, autoinflammatory disorders, cardiovascular disease, neurodegeneration and diabetes

chronic inflammation is driven by excessive production of proinflammatory cytokines. Blocking cytokine function has become an important therapeutic strategy

Question 21

Name examples of autoinflammatory disorders and what they result in

Answer 21

Familial Mediterranean Fever (FMF)
Neonatal Onset Multisystem Inflammatory Disease NOMID)
Tumor Necrosis Factor (TNF) Receptor-Associated Periodic Syndrome (TRAPS)
Deficiency of the interleukin-1 Receptor Antagonist (DIRA)
Behçet’s Disease

Most result from genetic mutations that increase IL-1 production of signalling, TRAPS results from a mutation in the TNF receptor