Immunology - Ch. 4 - Innate Immunity I

Lecture 4, RAHHHH!!!

Human body

has 10^13 human cells, 10^15 bacterial cells, most microbes are beneficial to health

Microbe reproduction

viruses & bacteria - hours to days

humans - decades

microbes can evolve much faster than humans

innate immune system

recognizes evolutionarily conserved structures on microbes,

present in mammals, fish, insects, plants, and even microbes

plants, most non-vertebrates

innate immune system provides protection or the host dies from infection

without a higher circulatory system, adaptive surveillance is a problem

vertebrates, some invertebrates

innate immune system is the first line of protection, informs the adaptive immune system to respond

recognition results in pro-inflammatory response to activate B/T cells,

type of recognition instructs the appropriate adaptive response

epithelia barriers

infection occurs when microbes cross, usually due to physicial damage or loss of anti-microbial defense mechanisms

microbial balance also causes sufficient pathology to cross

innate immune cells are present below to monitor crossed microbes

Cystic Fibrosis

defective chloride channel (CFTR) results in inefficient clearance of mucous to digestive tract, leading to chronic bacterial infection in lung and system infections

Pathogen Associated Molecular Patterns (PAMPs)

microbial structures recognized by the innate immune system receptors

Patter Recognition Receptors (PRRs)

innate receptors that recognize PAMPs

Stereotyped response

PRRs recognition of PAMPS lead to tailored response depending on microbe that has that pamp

LPS (lipopolysaccharide) → anti-bacterial response

dsRNA → anti-viral response

PRR/PAMP system

maintains self/non-self discrimination, allows responses to be tailored to type of microbe

not on self cells = no self response

different types of PRR for different microbes result in different signals to adaptive cells

Mutations of PAMPs

incur significant replicative costs to the microbes,

changing PAMPs would require changing entire biology of microbes

Yeast/bacteria → unique lipid/carbohydrates not found on host cells

Viruses → unique nucleic acids (non-host)

Groups of PRR

Scavenger receptors, lectins, toll like receptors (TLR), RIG-I like receptors (RLR)

Scavenger receptors

recognize extracellular anionic polysaccharides and lipoproteins of bacteria

roles in host maintenance - “scavenger function” and microbe recognition “innate immune function”

“garbage collectors”

Lectins

recognize extracellular polysaccharides on free proteins (scavenger), host (cell signaling), or microbes (innate recognition)

scavenger → glycoproteins recognized, broken down, and reused

host → cell to cell contact and adhesion, signaling

microbe → polysaccharides on bacteria cause cross linking and activation of innate pathways

Toll Like Receptors (TLR)

recognize extracellular and endosomal components of many microbes

RIG-I Like Receptors (RLR)

recognize intracellular nucleic acids from viruses (and some bacteria)

NOD like Receptors (NLR)

recognize intracellular imbalances due to infection

Christiane Nusslein Volhard

showed that Toll proeins direct embryonic cell differentiation in fruit flies

Jules Hoffman

showed different Toll genes conferred resistance to fungi vs bacteria

Bruce Beutler

showed mice with a mutation in TLR4 made them resistant to LPS (sugar on bacteria that causes deadly immune response), but unable to control live bacterial infection

homodimer

two of same receptor, ex: TLR9:TLR9he

heterodimer

two different receptors, ex: TLR2:TLR6E

Extracellular TLR

recognizes intact structures on bacterial, fungal, (parasite?) ligands

TLR 1, 2, 4, 5, 6, 11, 12

Intracellular TLR

expressed in endosomes and recognizes nucleic acids from degraded pathogens, mostly viruses

TLR 3, 7, 8, 9, 13

TLR 1/2

recognizes triacyl lipoproteins

TLR 2/6

recognizes diacyl lipoproteins

TLR 3

recognizes dsRNA (viruses, some bacteria)

TLR 4 (w/MD-2)

recognizes lipopolysaccharides (LPS) (bacteria)

TLR 5

recognizes flagellin (bacteria)

TLR 6/6

recognizes lipopeptides (mycoplasma)

TLR 7

recognizes ssRNA (viruses, much like TLR8)

TLR 8

recognizes ssRNA (viruses, much like TLR 7)

TLR 9

recognizes CpG motifs in dsDNA (viruses, some intracellular bacteria)

TLR 10 or 10/2

recognizes unknown ligand (self/bacteria, anti-inflammatory) brake system

TLR 11 & TLR 12

recognizes profilin (toxoplasma)

TLR 13

recognizes ribosomal RNA (bacteria, some viruses)

mammals

10-15 different TLRs

humans - 10 TLRs (no 11, 12, 13)

mice 12 TLRs (no 13)

Drosophila

9 different TLRs

Sea Urchin

222 different TLRs

Ruslan Medshitov & Charles Janeway

showed that TLR4 induced inflammatory cytokines in human cells

Step 1 - Cellular consequences of TLR signals

stop pinocytosis/phagocytosis - recognized microbe already. ensures response is specific to microbe

Step 2 - Cellular consequences of TLR signals

increasing expression of antigen presentation (MHC) and costimulatory proteins, become ready to stimulate adaptive immune response

Step 3 - Cellular consequences of TLR signals

decrease expression of adhesion molecules that retain cells in periphery so that they migrate to draining lymph nodes

Step 4 - Cellular consequences of TLR signals

produce cytokines that activate adaptive immune cells

MyD88 protein

Most TLRs signal through this protein

TRIF protein

TLR3 signals through this protein

MyD88 / TRIF proteins

TLR4 can signal through either of these proteins

Different types of inflammatory responses

depending on which TLR is activated, initiated to tailor the response to the type of pathogen being recognized

dependent on type of cell expressing the activated TLR

Deficiency in MyD88

leads to susceptibility to bacterial infection

Deficiency in TRIF

leads to susceptibility to some viral infections (herpesvirus)

Cytokines produces in response to TLR signals

Tumor Necrosis Factor (TNF), Interleukin 12 (IL-12), Type I Interferons (IFN-1), Interleukin 6 (IL-6)

Tumor Necrosis Factor (TNF)

general inflammation, cell recruitment, cell death

Interleukin 12 (IL-12)

immune responses to extracellular pathogens, inflammation, initiation of adaptive response

Type I Interferons (IFN-1)

immune respones to intracellular pathogens, poise cells for infection, initiation of adaptive response

causes dendritic cells to migrate to draining lymph nodes, stimulates adaptive immune response

Interleukin 6 (IL-6)

general effects, acts on hypothalamus to increase body temperature

RIG-I Like Receptors (RLR) & NOD Like Receptors (NLR)

expressed in cytoplasm to recognize intracellular bacterial and viral products

Shizuo Akira

showed that RIG-I protein bound dsRNA and triggered inflammatory response (IFN-I)

Michael Gale Jr

showed that RIG-I protein made cells resistant to viral infection

mammals (RLRs)

8 known RLRs

IPS-1 protein

Most (all) RLRs signal through this protein, an adaptor protein on mitochondria

results in production of type I interferons (IFN-I)

IFNs Role

make infected and surrounding cells non-permissive for virus growth, similar to TLR induced IFN-I

Sensing (infected cell)

Recognition of dsRNA by RIG-I leads to activation of IRF3 (via IPS-1) and transcription of IFN-I that is secreted by the cell

Poising (neighbor cell)

IFN-I binding to IFN-receptor increases expression of protein kinase R (PKR) and 2’-5’ oligoadenylate synthetase (OAS)

Blocking (infection of neighbor cell)

Binding of dsRNA to PKR results in activation, then phosphorylation and inactivation of eIF-2a to shut down protein synthesis

Binding of dsRNA to 2-5OAS convers ATP to 2’-5’ oligoadenylate, which binds and activates RNAseL to destroy viral & host RNA, shutting down virus replication and host protein expression

BOTH pathways induce apoptosis

Dana Philpott

showed NOD1 and NOD2 proteins recognize bacterial peptidoglycans

Gabriel Nunez

showed NALP3 recognizes peptidoglycans

NLR Binding

wide variety of host and microbial ligands, also sense changes in temperature or intracellular ions, induce apoptosis, inflammatory cytokines, or cellular differentiation

Human NLRs

22 known NLRs

Mice NLRs

33 known NLRs

Direct Ligand Binding

binding (microbial or due to cell damage) results in oligomerization of NLR, recruitment of adapter proteins (ASC) and activation of pro-Caspase-1 to Caspase-1

Casepase-1

converts pro-cytokines into active versions that are secreted from the cell

IL-1B and IL-18

main cytokines, potent activators of inflammation (vasodilation, cell recruitment, and innate activation)

TLR poise NLR signaling

TLR signals increases expression of pro-IL-1B and pro-IL-18

NLR signals result in Caspase-1 conversion of pro-IL-1B to active IL-1B

NLR poise TLR signaling

Secreted IL-1B binds to IL-1B receptor, further increasing expression of MyD88 and IRAK4li

lipids, carbohydrates (extracellular) and nucleic acids (endosomal)

TLR → MyD88 or TRIF → NFkB → IL-12 or Type I IFN, IL-6, TNFn

nucleic acids (cytoplasm)

RLR → IPS-1 → IRF3/7 → Type I IFN

nucleic acids, pH, stress (cytoplasm)

NRL → ASC → Caspase 1 → IL-12, IL-1B, IL-18