Cytokines - Langer 4/6/16

Question 1

body has to coordinate the actions of a large number of organs, tissues, etc at the CELLULAR LEVEL

communication is key

describe multiple modes of comm used by the body on this front

Answer 1

1. cell-cell contact via interaction of membrane proteins

ex. TCR-MHC interactions

2. secretion of “signal proteins” that bind membrane receptors on target cells

ex cytokines

3. secretion of other small molecules that bind membrane receptors on target cells

ex. eicosanoids, prostaglandins involved with infl response

Question 2

general properties of cytokines

Answer 2

• proteins
• synth’d and secreted in response to external stimuli
• often transient (controled by transc, post-transl mechs)
• pleiotropic : one cytokine can have diff effects on many cell types
  
  • can depend on time of exposure, concentration of cytokine
• redundant : diff cytokines can have same/overlapping effects
• autocrine, paracrine, endocrine effects

Question 3

pleiotropy of cytokines

Answer 3

one cytokine can have diff effects on many cell types

• can depend on time of exposure, concentration of cytokine
  ex. IL1
• hepatocytes → synth of acute phase proteins
• osteoclasts → bone resorption
• neutrophils → increased adhesion to endothelium

one way to understand pleiotropic effects of cytokines : cytokines “answer” a question

• same answer can have diff effects depending on the question being asked → diff cells at diff stages are asking diff Qs, so cytokines may affect them differently

Question 4

experimental methods to discover cytokines

Answer 4

1. [historical] cellular assay
2. [genomic era] “in silico”

• look for relationship to known cytokines
• downside: you’ll only find things that look structurally similar to the sequence you’re using as baseline

Question 5

general ROLES of cytokines

Answer 5

1. developmental : formation of immune system → stimulation of cell production, prolif, diff
2. homeostasis : maintenance → targeting cells to immune tissues for formation/organization
3. response to infection/infl

Question 6

major classes of cytokines

Answer 6

cytokines

• generally soluble proteins, >18kD
• signal through receptors coupled to protein kinases → growth, diff, fx of immune system cells
• produce local and systemic manifestations of disease

chemokines (= chemotactic cytokine)

• smaller (8-10 kD)
• signal through G protein coupled receptors (GCPRs) → chemotactic effects (attract infl/effector cells to site of chemokine prod), cellular activation, devptal targeting of cells to organs

Question 7

general properties of IL/IFNs

Answer 7

interleukins/interferons

• induced/produced transiently when and where needed
  
  • unregulated or chronic production can cause damage
• mechanism: bind to specific cell-surface receptor proteins → intracellular signaling cascade → changes in transcription/other pathways
• pleiotropy, i.e. cells may undergo many diff changes and/or diff cells may respond differently

Question 8

cytokine therapeutics:

IFNalpha, IFN beta

Answer 8

broad spectrum antiviral

(hepB, hepC, treatment of MS)

Question 9

cytokine therapeutics:

IL2

Answer 9

in vitro growth of T cells for T cell therapies

some anti-tumor apps

Question 10

cytokine therapeutics:

GM-CSF

Answer 10

growth factor for neutrophils follwing bone marrow transplant

neutropenia following chemo

Question 11

cytokine therapeutics:

IFN-gamma

Answer 11

chronic granulomatous disease

(poor killing of bacteria by neutrophils)

Question 12

cytokine therapeutics:

epo

Answer 12

anemia

myelodysplasia

Question 13

specfic cytokines and their roles

• IFN1
• IL1/TNFalpha
• cytokines in T cell and B cell diff and maturation
• chemokines

Answer 13

• IFN1 : antiviral protection
• IL1/TNFalpha : inflammation
• cytokines in T cell and B cell diff and maturation
• chemokines

Question 14

Type I interferons

basics

gen mechanism

Answer 14

globular proteins with 5 alpha helices

whole family encoded in a cluster on chr9

• 13 IFNalpha, IFNbeta, IFNepsilon, IFNomega, IFNkappa : prob evolved through duplication/divergence
• receptor: IFNAR = IFNAR1 + IFNAR2

general mechanism

IFN binds to IFNAR (heterodimer) → stimulates Jak/STAT pathway → cascade which eventually hits nuclear ISRE (ifn stimulatory resp element) → stimulate ISG (ifn stimulated genes) → transc/transl of proteins that have cellular effect

• direct antiviral effects
• apoptosis
• stimulation of adaptive and innate immune resp
  
  • MHC induction
  • NK cell activation
  • DC maturation
  • Th1 biasing
  • B-cell class switching → IgG (viruses vs allergens)

Question 15

IFN1

what if the stimulus is an immune complex instead of a virus?

Answer 15

in a situation like lupus, immune complexes can be mistaken for virus!

→ IFN constantly being made → autoimmunity

Question 16

IL2

Answer 16

T cell growth factor

Question 17

IL4, IL5

Answer 17

B cell growth, survival, diff

Question 18

IFN-gamma

Answer 18

activates macrophages (produced by T cells)

Question 19

IL10

Answer 19

inhibits immune responses (except when activating them…)

Question 20

cytokine receptor families

• IL2, IL4
• IFNalpha, IFNbeta, IL10
• TNFalpha
• IL1
• chemokines

Answer 20

• IL2, IL4 : Type I cytokine (hematopoeitin) receptors - dimeric
• IFNalpha, IFNbeta, IL10 : Type II cytokine receptors - dimeric
• TNFalpha : TNF receptor family - trimeric
• IL1 : IL1 receptor family
• chemokines : Gprotein coupled receptors

**cytokine receptor families sometimes have common subunits (ex. gamma-c)

• mutation in that subunit gene → more than one signal affected (ex. mutation in gamma-c → X-SCID, severe combined immunodeficiency due to mutation on X chromosome)

Question 21

inflammatory cytokines

Answer 21

IL1 & TNFalpha (and IL6)

“pro-inflammatory” cytokines

• major producers: monocytes and macrophages, esp in response to bacteria
  
  • can be produced by several other cell types
• effect dependent on level and persistence of production
  
  • low : local infl + stimulates body’s response to damage/infection
  • high : shock, disseminated intravascular coagulation (DIC), death
  • chronic : weight loss, loss of conn tissue and bone
• typical sepsis cascade: LPS → TNF → IL1 → IL6 in “waves”

Question 22

role of cytokines in T cell and B cell devpt and diff

Answer 22

IL2 is the key growth factor for proliferation of all T cells → acts via IL2 receptor

diff combos of other cytokines present work together to lead to diff specific outcomes during differentiation

ex. Th1 cell devpt

DCs and macrophages interact with mibrobes, produce IL12 (maturation of naive T cell)

NK cells produce IFN-gamma (T cell diff)

• combo of IL12 and IFNgamma → STAT4 and STAT1 respectively → tf Tbet → Th1 cells

Question 23

chemokines

• size
• major effects
• structural relationships based on… & naming

Answer 23

small proteins

signal chemotaxis and “homing”, modulate cell adhesion

signal through GPCRs → activate cellular G proteins

• over 20 known receptors, with some overlap (“promiscuity”) → multiple chemokines can interact with some receptors, producing similar effects

structural family relationships based on Cys in structure

• C chemokines - 1 Cys = CCLx
• CC - 2 Cys = CCL
• CXC - 2 Cys sep by 1 a.a. = CXCLx
• CX3C - 2 Cys sep by 3 a.a. = CX3CLx
• XCL - other a.a. patterns

Question 24

chemokine & receptor expression

Answer 24

• expression can be constitutive or inducible
• can be modified by cell maturation, diff, cytokine action
• cells can express characteristic chemokine receptors, but can also express multiple chemokine receptors → highly sensitive immune response

Question 25

real life:

chemokine receptors and HIV

Answer 25

dominant receptor for HIV : CD4 protein on T cells

• sufficient for viral attachment, NOT INFECTION

need either CXCR4 (T cells) or CCR5 (macrophages, some T cells) to get infection

→ some people with mutations in CCR5 are resistant to infection

implication: CXCR4 and CCR5 are routes to look at for HIV therapies