HDM TBL 4: Cytokine Messengers

cytokine types

• interleukins

  • pro- & anti- inflammatory [IL-]

• chemokines

• interferons

• colony-stim factors

  • hematopoiesis

• transforming growth factors

  • metabolism

pro-inflammatory cytokines [innate]

IL-1, IL-6, IL-8, IL-12, IFN-gamma, TNF-alpha

anti-inflammatory cytokines

IL-10, TGF-beta

pro-allergic cytokines [adaptive]

IL-4, IL-5, IL-13

chemokines

chemotaxis

IL-8 [CxCL-8], CCL-5

interferons

involved in viral immune response [except IFN-gamma]

IFN-alpha, IFN-beta

colony-stimulating factors [CSF]

regulate hematopoiesis

GM-CSF [Granulocyte-Macrophage CSF], G-CSF

transforming growth factors [TGF]

• involved in cell metabolism, differentiation, wound repair

• stim. fibroblasts → secretion of ECM components [collagen]

• TGF-1

cytokines w/ pleiotropic effects

exert diff biologicsal effects on diff target cells

ex. IL-6

signal transduction mechanisms

• phosphorylation-dephosphorylation

  • most common

• ubiquitination

  • less common

*attenuates T & B cells, acts as neg. feedback mech

phosphorylation-dephosphorylation mech

• phosphorylation

  • activates pathway

  • catalyzed by kinase enzyme using ATP

• dephosphorylation

  • inactivates pathway

  • catalyzed by phosphatase enzyme

• binding of cytokine or antigen w/ receptor activates primary kinase → secondary kinase → downstream proteins → phospho-relay

ubiquitination mech

• covalent addition of ubiquitin to lysine residues

  • done by ubiquitin ligase enzymes [Cbl]

  • monoubiquitination: sends proteins to lysosome for degradation

  • polyubiquitination: sends proteins to proteasome for degradation

receptor tyrosine kinases [RTKs]

• have intrinsic kinase domain

• ex. growth factors & VEGF [vascular endothelial growth facor]

• many cancer drugs target these

receptors that do not have an intrinsic kinase domain

• noncovalently associate w/ separate kinase

• phosphorylation of immune receptors occurs at tyrosine sites, known as ITAM consensus sequences

• most of cytokine & antigen receptors use this pathway

ITAM

immunoreceptor tyrosine activation motif

activation

recruits kinases

ITIM

immunoreceptor tyrosine inactivation motif

inhibitory

recruits phosphatases

GPCRs

used by chemokines, C3A, C5a

active when bound to GTP

PAMPs mainly detected by

TLRs on PM or endosomal membrane

DAMPs mainly detected by

several types of PRRS: NLR, RLR, CDS [cytoplasm], besides TLR

TLR4 detects

lipopolysaccharide [LPS] of Gram-neg bacteria

TLR2 detects

lipoteichoic acid [LTA] of Gram-pos bacteria

TLR2:TLR6 heterodimer detects

lipopeptides of bacteria

AND zymosan glycan of fungi

TLR5 detects

bacterial flagellin

TLR9 detects

DNA of bacteria, viruses, fungi, protists

TLR7 detects

viral ssRNA

TLR3 detects

viral dsRNA

M1 macrophages

secrete pro-inflamm cytokines:

• IL-1

• TNF-alpha

• IL-6

• IL-8

• IL-12

• G-CSF, GM-CSF

M2 macrophages secrete

anti-inflamm cytokines

• IL-10

• TGF-beta

Interleukin-1 [IL-1]

• major pro-inflamm cytokine

• IL-1alpha

  • synth from precursor protein, pro-IL-1alpha that have biological activity as a DAMP; stored in cytoplasm

• IL-1beta

  • no bio activity until cleaved by Caspase-1 of inflammasome

• pyrogen → induces fever!

  • MAJOR in fevers

• promotes express. of adhesion molecules on endothelium

• induces acute phase response in liver

• induces pain locally by activating prostaglandin synth.

• increases prod. of pro-inflamm cytokines

overprod. of IL-1 & overactivation of caspase-1 associated w/

rheumatoid arthritis, juvenile arthritis, gout, macrophage activation syndrome [MAS] seen in COVID-19

IL-1Ra

regulates IL -1, by blocking its action

Anakinra

• recombinant IL-1Ra

• competitively inhibits IL-R function by binding to receptor

Canakinumab

• monoclonal antibody against IL-1beta

• binds IL-1 & inhibits its binding to IL-R

deficiency of IL-1Ra [DIRA] →

rare genetic disorder

→ severe skin & bone inflammation

MyD88 deficiency & IRAK-4 deficiency

TLR4 mechanism & IL-1

• primary immune deficiencies w/ loss of IL-1R signaling & TLR signaling

• life-threatening recurrent infections + arthritis & internal abscesses caused by pyogenic bacteria due to inability to secrete sufficienct pro-inflamm cytokines

• pts fail to mount fevers during infections

NEMO deficiency syndrome

TLR4 mechanism & IL-1

• mutations in IKK-gamma gene → similar phenotype as MyD88 & IRAK-4 deficiency + ectodermal dysplasia

  • abnormal growth of skin, sweat glands, hair, nails, teeth, mucous membranes

tumor necrosis factor-alpha [TNF-alpha]

• potent pro-inflamm cytokine prod. by activated macrophages following PRR stim

• [Nk, Th1, & CD8+ T cells can also produce it]

• local effects:

  • stim macrophages for more inflamm cytokines

  • stim express. of adhesion molecules on endothelium

  • induces permeability of BV by modifying adherens junctional proteins

  • activates platelet → coagulation & limits pathogen spread

  • excess → chronic inflamm & tissue damage

• systemic effects:

  • acute phase response in liver

  • fever at hypothalamus

  • disseminated intravascular coagulation [DIC]

  • Sepsis

  • septic shock

  • *systemic effects typically triggered by bacterial cell wall components & superantigens

Infliximab & Adalimumab

monoclonal antibodies that bind & block TNF-alpha signals

excess TNF-alpha →

give rise or worsen inflammatory disorders like:

• ulcerative colitis

• crohn disease

• rheumatoid arthritis

• psoriasis

etanercept

fusion protein that mimics TNF-alpha receptors & acts as decoy receptor to neutralize it

disseminated intravascular coagulation [DIC]

• wide platelet activation → formation of micro-clots thru-out vasculature

• can → PE, stroke, neutropenia + thrombocytopenia, multiple organ failure

*excessive TNF-alpha

interleukin-6 [IL-6]

• pro-inflamm cytokine made by macrophage, vascular smooth muscle,& adipocytes following PAMP-PRR stim

• pleiotropic effects

  • primary role = inflamm

  • induces acute phase response in liver

  • in CNS, fever

  • in bones, promotes osteoclast activity

  • in bone marrow, promotes neutrophil formation

  • promotes macrophage polarization from pro-inflamm M1 state to anti-inflamm M2 phenotype

  • stim. T cells & promotes antibody prod by B cells

overproduction of IL-6 →

autoimmune disorders:

• T1DM

• SLE

• rheumatoid arthritis

• juvenile arthritis

• Behcet’s disease

Behcet’s disease

AKA Silk Road Disease [common in middle east & east asia]

• chronic, multisystem inflamm disorder

• vasculitis [BV inflamm], affecting & damaging both arteries & veins

• painful oral ulcers, genital ulcers, eye inflamm [uveitis]

• elevated IL-6 levels

  • linked to ocular & neurological complications

Tocilizumab

• monoclonal antibody against IL-6R

• blocks IL-6 from binding to its receptor → prevents inflamm

interleukin-8 [IL-8 or CXCL8]

• major chemotactic factor for neutrophils

  • prod at site of infection

• also activates expression of integrin LFA-1 on neutrophils so it can bind selectin ICAM-I on endothelial cells, promoting tight binding of neutrophil to endothelium → its diapedesis & migration

CCL2

major chemotactic factor for monocytes

interleukin-12 [IL-12]

• prod. in response to infection w/ intracellular bacteria, fungi, parasites

  • monocytes & DC can also produce it

• promotes innate & cell-mediated immunity

  • stim. NK, Th1, CD8+ T cells to secret IFN-gamma

IFN-gamma response

activates macrophages for granuloma formation

deficiency of IL-12 or IL-12R →

impaired IFN-gamma response

• pts show selective & extreme susceptibility to infections w/ intracellular bacteria [Mycobacterium spp. -Tb, Listeria]

overexpression of IL-12 →

seen in Crohn disease, psoriasis, & psoriatic arthritis

Filgrastim

• recombinant human G-CSF

  • increases neutrophil count

*G-CSF commonly used in pts with neutropenia after chemotherapy or bone marrow transplant

Sagramostim

recombinant human GM-CSF

• increases most leukocytes & monocytes

multiple sclerosis [MS]

• decreased levels of IL-10 → continous inflamm & demyelination

inflammatory bowel disease [Crohn’s disease & ulcerative colitis]

• mutations in IL-10 or its receptor, IL-10R → overactive immmune responses in gut → uncontrolled gut inflamm

TGF-beta

• anti-inflamm

• promotes wound healing & tissue repair by stim Fb prolif & collagen synth

overprod. of TGF-beta →

excessive synth & deposition of collagen & other ECM proteins → fibrosis → systemic sclerosis [scleroderma] & pulmonary fibrosis

→ excessive scar formation [hypertrophic scars & keloids]

defective TGF-beta signaling →

Loeys-Dietz syndrome

• connective tissue disorder caused by loss of function mutation in TGF-beta pathway genee [TGRBR, SMAD]

• disrupts normal tissue development, ECM maintenance, wound repair, immune regulation

• pts exhibit arterial aneurysms, vascular dissections, craniofacial abnormalities [scoliosis, joint laxity] & translucent skin w/ easy bruising

  • Hypertelorism = increased distance btwn eyes

Type 1 interferons [IFNs]

• antiviral response, secreted by almost all cells

• TLR7 induces synth of

  • IFN-alpha & IFN-beta

  • uses MyD88 & TBK1

• TLR3 induces synth of

  • IFN-beta

  • uses TRIF

• triggers antiviral state in host

• NK cell activation

  • prod. IFN-gamma

type 2 interferon & pathogen containment

IFN-gamma = macrophage activation factor

• IL-12 released by activated macrophage cause NK cell to release IFN-gamma

• IFN-gamma activated macrophages v. microbiocidal

  • can form granuloma for intracellular bacterial infections

    • ex. Listeria monocytogenes, Mycobacterium spp., Salmonella spp.

• granuloma formation why pts w/ chronic pulmonary Tb don’t have spread of bacteria

granuloma

focal aggregate of immune cells that forms in response to pathogen or inflamm. stim to wall off pathogen & restrict its spread