chapter 2 innate immunity

1. Inflammation

   • accumulation and activation of leukocytes and plasma proteins at sites of infections and injury

   • -> act together to kill extracellular microbes and eliminate damaged tissue

2. Antiviral Defense

   • when virus is induced, killing of infectet cell

   • Induced by interferon-1 IFN-1

• Innate immunity against intracellular viruses mediated by

  • NK cells

  • Cytokines type 1 interferons (blocking replication of host cells)

Responds to limited microbial molecules (less than in adaptive immunity)

• Lipopolysachharide,LPS; phagocytes express receptors for these bacterial endotoxins

• Terminal mannose residues (typical for bacteria)

• dsRNA+unmethylated CG-rich oligunucleotides (not in mammalian cells)

• pathogen associated molecular patterns (PAMPs)

DAMPs

• damaged cells release these molecules

• Eliminate these cells

E.g.: high mobility group box protein 1 (HMGB1)

• receptors are specific for microbial structures

  • Some pattern recognition receptors can detect substances present in normals cells like nucleic acids

• Regulatory molecules

Epithelia, providing a physical barrier and antimicrobial molecules and lymphoid cells

Microbes get detected by resident cells like macrophages, dendritic cells, mast cells

• some may release cytokines which initiate inflammation

Complement system (in blood)

• plasma proteins that promote destruction of microbes

Found both on cell surface and endosomes

• membranous: 1,2,4,5,6

• Endosomal: 3,7,8,9 (respond only to nucleic acid)

Different TLRs are specific for different components of microbes

TLR-1/2/6: bacterial/parasitic glycolipids and peptidoglycans

TLR 3/7/8: viral RNAs, ss and ds —> herpesvirus encephalitis

TLR-4: endotoxin / viral bacteria LPS

TLR-5: bacteria flagellin

TLR-9: unmethylated CpG DNA

It activates transcription factors

• NFkB transcription factors —> promotes expression of cytokines, adhesion molecules, costimulators (expression of genes) —> leads to acute inflammation

• Interferone regulatory factors (IRF-3) codes for type 1 interferon —> antiviral cytokine

NOD-1 and NOD-2: specific for peptidoglycans on bacterial cell wall

Both activate NFkB transcription factor

NLRP-3 receptor, adaptor protein, caspase 1 —> (IL-1b)

Pro IL-1B synthesis induced by PAMPs and DAMPs in nucleus

Active caspase 1 cleaves Pro IL-1B to active form IL-1b

• IL-1 causes Inflammation and fever

Microbial products, substances that indicate cell damage and death

• released ATP, Uris acid crystals, changes in intracellular K+ concentration

• Pathogenic signals

• Environmentalists signals

All lead to pyroptosis (inflammation induced cell death) —> leads to extra increase in inflammation by loss of plasma cell integrity and release of infammatory cytokines

Also cell swelling

Gout caused by irate crystal deposition —> inflammation caused IL-1B

Atherosclerosis: inflammation caused by cholesterol —> IL-1b

Viral RNA

—> activates signaling pathways for production of type 1 IFN

STING pathway

• type 1 IFN production and autophagy

Recognizes terminal mannose residues and induces inflammatory response

On phagocytes

• recognizes peptides that begin with N-formylmethionine (specific for bacterial protein)

Skin-> keratinized

Mucus-> prevent interaction of microbe with epithelia

Antimicrobial peptides

• defensins

• Cathelicidins

• neutrophils

• Monocytes/macrophages

Polymorphonucleated leukocytes

4000 to 10000 per müLiter

• production stimulated by CSF (colonising stimulating factor)

• First and most numerous cell type at site of infection

• Do not provide prolonged response (only live several hours in the tissues)

500 to 1000 per müliter

• inflammatory reactions

  • Enter extravasvular tissue and differantiate into macrophages

Many receptors

• TLR an NLR

• Mannose receptors

Functions

• produce cytokines

• Ingest + destroy microbes

• Clear tissue/ initiate tissue repair

• innate immune signals, from TLRs

• Interferon gamma (IFN-y) released by Th1 cells

M1-macrophages —>destroys microbe and triggers inflammation

Occurs in absence of strong TLR signals

• induced by IL-4, IL-13

M2-macrophages —> tissue repair and terminating inflammation

• contain granules, histamine - induces vasodilation and protelitic enzymes for killing microbe/bacteria

• Also cytokines and prostaglandins —> inflammation

Responsible for allergic reactions

Class of lymphocyte that recognizes infected or stressed cells and responds by killing

• secrete IFN-gamma to activate macrophages

Contact with infected cell—> secreting granules—> initiate apoptosis

• Interleuking 15 (maturing NK cells)

• type 1 interferon

• Interleukin 12

NK cells+ macrophages act together

• macrophage ingest microbe, secrete IL-12 —> IL-12 activates NK cells—> Nk cells excrete IFN-y to activate more macrophages

ITAMs

• activating receptors on Nk cells that have subunits in cytoplasmic tail

• Downstream pathway leads to production of IFN-y and cytotoxic granules

NKG2D

• Recognizes molecules that resemble MHC class 1 proteins

CD16 (FcyRIIIA)

• specific for Immunoglobulins

• Antibody coated microbes —> ADCC (antibody dependent cellular cytotoxicity)

• Killer cell immunoglobin like receptors (KIR)

• CD94 and NKG2 (lectin)

Mechanisms

• ligand ->phosphorilates ITiMs -> activates tyrosine phosphatase —> remove phosphate groups from tyrosine residues

Counteracts actions of ITAMs

Collection of proteins

3 pathways

1. Alternative

2. Classical

3. Lectin

Main functions

• opsonisation +phagocytosis

• Inflammation

• Cell lysis

Mainly inducing acute inflammation and antiviral Defense

Different microbes elicit different reactions

• extracellular bacteria/fungi

  • Combated with acute inflammatory response (from neutrophils, monocytes and compliment system)

• Intracellular bacteria

  • Eliminated by phagocytes that are activated by binding to TLRs and other receptors and cytokines

• Virus

  • Combated by Type 1 interferon and NK cells

Tissue reaction that delivers mediators of host Defense

1. recruitment of cells (leukocytes+proteins)

2. Leakage of plasma proteins trough blood vessels

3. Engulfment of microbes and dead tissue

4. Destruction of potentially harmful substances

If microbe breaches epithelium—> enters subepithelial space: DC,macrophages,… recognizes them:

• production of cytokines, TNF and IL-1, acts on endothelium of venues -> leukocyte migration

• Rolling of leukocytes: in response to TNF and IL-1 endothelium expresses selectins -> E-Selectin

  • Stimuli (thrombin):rapid translocation of P-Selectin

  • Selectins attract leukocytes, Neutrophils/monocytes express surface carbohydrates —> bind to selectins

  • Cells bind to it but get interrupted by blood flow (not really firm adhesion)

  • Repetitive process

• Firm adhesion

  • Another molecule expressed : integrity

    • Integrins (LFA-1 and VLA-4)

  • In infection chemokines (secreted by macrophages and endothelial cells) increase affinity of leukocytes for integrins

  • —> TNF and IL-1 act ion endothelium to stimulate ligands for integrins including ICAM-1 and VCAM-1

  • Firm adhesion arrests leukocytes on endothelium — cells spreads out

• Leukocyte migration

  • By chemokines

  • Result: leukocyte migrate between endothelia cells trough vessel to site of infection

Intracellular vesicles destroy microbes

1. membrane receptors bind to microbe

2. Extension of plasma membrane around microbe

   • phagosomes is the particle with its membrane around inside the leukocyte

   • Phagosomes+lysosome —> phagolysosom

3. Destruction of microbe by microbicidal substances

   • oxidative burst

     • Phagocytes Oxydase converts O2 to superoxide anion and free radicals (reactive oxygen species) —> kills microbe

   • Inducible nitric oxide synthase (iNOS)

     • Coverings arginine to NO

   • Lysosomal proteases

     • Breaks down microbial proteins

4. Neutrophils produce and secrete neutrophil extracellular traps (NETs)

   • hosting networks

   • Neutrophils die and release their nuclear content

Killing of virus infected cell

• IFN 1

• Plasmacytoid dendritic cell (major source of interferons)

• NK cells (kill cells, induce apoptosis)

Prevents excessive tissue damage

• production of antiinflammatory cytokines by macrophages (M2) and DC

• Interleukin-10 inhibits classical pathway of macrophage activation

• IL-1 receptor antagonist block actions of IL-1

• TLR signaling stimulates production of SOCS proteins (suppressor of cytokine signaling)

• Block action of different cytokines