Date post: | 02-Jan-2016 |
Category: |
Documents |
Upload: | tracy-parks |
View: | 214 times |
Download: | 0 times |
Innate Immune system
Overview of the immune system
Cells of the immune system
Cellular componentsCell Mechanism
Neutrophils Phagocytosis and intracellular killingInflammation and tissue damage
Macrophages Phagocytosis and intracellular killingExtracellular killing of infected or altered self targetsTissue repairAntigen presentation for specific immune response
NK and LAK cells Killing of virus-infected and altered self targets
Eosinophils Killing of certain parasites
Innate Immunity Features
• Preformed: Rapid-Available on Short Notice
• No Memory:Not Enhanced by Prior Exposure:
• Broad Specificity• Dependent on species, strain, sex.
Innate vs. Adaptive Immunity• Innate Immunity• Pathogen recognized by
receptors encoded in the germline: pattern recognition receptors
• Receptors have broad specificity, i.e., recognize many related molecular structures called PAMPs (pathogen-associated molecular patterns)
• Immediate response
• No memory of prior exposure
• Adaptive Immunity• Pathogen recognized by receptors
generated randomly: B-cell (BCR) and T-cell (TCR) receptors for antigen
• Receptors have very narrow specificity; i.e., recognize a particular epitope after processing
• Slow (3 -5 days) response (because of the need for clones of responding cells to develop)
• Memory of prior exposure
Component of Innate Immunity
Innate Immune system
First line Second line1) Mechanical barriers A- cells 2) Chemical & biochemical inhibitors 1- Natural killer3) Normal flora 2- Phagocytes
B- Soluble factors C- Inflammatory barriers
First line1) Mechanical barriers - Intact skin - Mucous coat - Mucous secretion - Blinking reflex and tears - The hair at the nares - Coughing and sneezing reflex
First line2) Chemical & biochemical inhibitors - Sweet and sebaceous secretion - Hydrolytic enzymes in saliva - HCl of the stomach - Proteolytic enzyme in small intestine - Lysozyme in tears - Acidic pH in the adult vagina
Second lineA) cells1- Natural killer (NK)Definition: Large granular lymphocytes Innate cytotoxic lymphocytes
Source : Bon marrow precursors
Location : 10% or 15% of lymphocytes in peripheral blood 1% or 2% of lymphocytes in spleen
Tumor cells
Function : Cytotoxic for Viral infected cells Bacterial, fungal, parasitic infection
Responsible for antibody–dependent cell mediated cytotoxicity (ADCC)
Second line2- Phagocytes Specialized cells for capture, Ingestion and destruction of invading
microorganisms
* Polymorphoniclear leucocytes, mainly neutrophils: granulocytes circulate in blood
* Mononuclear cells (macrophages) - Monocytes in blood
- Histocytes in connective tissues
- Fixed reticuloendothelial cells in liver spleen, lymph nods, bon marrow
Second lineB- Soluble factors
1- Acute phase protein (Plasma protein, CRP=C reactive protein, Fibrin.)
2- Complement (proteins in serum, body fluids)3- Interferons (Proteins against viral infections)4- Properdin (Complement activation)5- Beta lysine (Antibacterial protein from Platelets)6- Lactoferrrin,Transferrin (Iron binding protein)7- Lactoperoxidase (Saliva & Milk)8- Lysozyme (Hydrolyze cell wall)9- Antibiotic peptides , 29-34a.a. and enriched with cys.
(Difensins (Neu, IL-1 and TNF-a is inducer), Cryptocidins (gut))
Complement system
Not Ab mediated
Com
plem
ent 1. Inactive
complement proteins are in constant circulation.
2. Complement proteins are activated by various mechanisms.
3. These are the consequences...
Phagocytosis
The engulfment, digestion, and subsequent processing of microorganisms by macrophages and neutrophils
1) Chemotaxis & attachment: a- Attraction by chemotactic substances (microbes, damaged tissues) b- Attachment by receptors on surfaces of phagocytes
Phagocytosis
2) Ingestion:
* Phagocyte pseudopodia surround organism forming phagosom * Opsinins and co-factors enhance phagocytosis * Fusion with phagocyte granules and release digestive, toxic contents
Phagocytosis
3- Killing (two microbicidal routes) a- Oxygen depended system (powerful microbicidal agents) Oxygen converted to superoxide, anion, hydrogen peroxide, activated oxygen and hydroxyl radicals. b- Oxygen-independent system (anaerobic conditions) Digestion and killing by lysozyme. Lactoferrin, low pH, cationic proteins and hydrolytic and proteolytic enzymes
C) Inflammatory Barriers* Tissue damage by a wound or by invading pathogen
* Inflammatory response: Tissue damageRelease of chemical mediators from Leukocytes (Histamine, fibrin, kinins, cytokines) Invading microbe Redness of tissue Tissue temperature Vasodilatation of capillaries Capillary permeability Influx of fluids Influx of phagocytes into tissues
Infla
mm
atio
n Inflammation gives rise to localized reddening, swelling,
increased temperatures, and pain.
The function of inflammation is to localize tissue damage, localize responses, and then to restore tissue function.
The action of localized leukocytes is augmented (i.e., enhanced) via the attraction of neutrophils and monocytes normally found in circulation.
Microbial materials such as LPS, flagellin (making up bacterial flagella), activated complement, and even bacterial DNA serve as indicators of infection which in turn activates the production of pro-inflammatory cytokines (immune-system activating chemicals).
In addition to the cell-to-cell interactions underlying inflammation, the inflammatory response involves localized increases in blood flow, leakage of blood vessels, and attraction of leukocytes from the blood.
Inflammation
Inflammation
Fev
er Inflammation is a great tool, unless it becomes
chronic or non-localized. Chronic inflammation typically has an underlying
cause (e.g., ongoing infection). Non-localized inflammatory responses gives rise to
body-wide vessel dilation and leakage, resulting in precipitous drops in blood pressure called Shock.
Endotoxin signals inflammatory responses and systemic infections with Gram-negative bacteria can give rise to a very dangerous condition known as Septic Shock.
Fever is the preferred systemic response to bacterial infection.
Fevers are elevated body temperatures induced either by pathogen molecules or by body molecules produced in response to pathogen molecules.
Fever results in temperatures that, ideally, inhibit microbes while enhancing body defenses.
Characteristics:- rapid- does not generate immunologic memory- dependent upon germline encoded receptors recognizing structures common to
many pathogens
Innate Immunity- First Line of Defense
InnateImmunity
Innate immune system recognize 10 3 molecular pattern whereas adaptive immune system recognize more than 10 7 antigens.
Recognition of Microbial Recognition of Microbial NonselfNonself
• Depends on recognition of “Pathogen Associated Molecular Patterns Depends on recognition of “Pathogen Associated Molecular Patterns (PAMPS)”(PAMPS)”– Gene products unique to microbes-Gene products unique to microbes-Molecular Molecular
SignaturesSignatures of microbial invaders of microbial invaders– Conserved among microbes of a given class-InvariantConserved among microbes of a given class-Invariant– Essential for microbial survivalEssential for microbial survival– LPS (Gram negative bacteria); Peptidoglycan (Gram LPS (Gram negative bacteria); Peptidoglycan (Gram
positive bacteria)positive bacteria)
Pattern Recognition Receptors (PRRs)
• Recognize PAMPsRecognize PAMPs• Receptors expressed on macrophages Receptors expressed on macrophages • Signal to induce inflammatory cytokines and activate host Signal to induce inflammatory cytokines and activate host
defense mechanismsdefense mechanismsExamplesExamples: :
Macrophage mannose receptorMacrophage mannose receptorMacrophage Scavenging Receptor-LPS and Gram neg. Scavenging Receptor-LPS and Gram neg. bacteriabacteriaToll-like ReceptorsToll-like Receptors
TLR
2
TLR
2
TLR
1
TLR
6
TLR
3
TLR
4
TLR
5
TLR
9
Pe p
t id
og
lyc a
n (
G+
ve)
Zym
o san
(Y
eas t
)B
a cte
ri al l
ipo p
ept id
es
dsR
NA
LP
S (
G-v
e)
Unm
ethy
late
dC
pG D
NA
Fla
gelli
n
TOLL-LIKE RECEPTORS
Ba c
teri a
l Li p
opro
tei n
sP
a ra s
it e s
urfa
ce p
rote
ins
TLR
7V
iral s
s R
NA
TLR
8
Receptors and Responses of Phagocytes in Innate Immunity
Opsonins and Opsonization
Defect in killing activity in MQ resulted in
Chronic granulomatous disease,CGD
Defect in Phagocyte oxidase enzyme.
Gram Pos. bacteria can not be killed with
MQs.
Adherence and Opsonization
• Adherence to Surface Receptors– Mannose Receptor– Scavenger Receptor
• Opsonins: Greek- “Prepare food for”– Enhance Phagocytosis– Antibodies-Fc Receptors– Complement Proteins-Complement Receptors– MBL and CRP via C1q-R on MQs
• All multi-cellular organisms are able to recognize and eliminate pathogens
• Despite their extreme heterogeneity, pathogens share highly conserved molecules, called “pathogen-associated molecular patterns” (PAMPs)
• Host cells do not share PAMPs with pathogens• PAMPs are recognized by innate immune recognition receptors
called pattern-recognition molecules/receptors (PRMs/PRRs)
Innate Immune Recognition via Patterns
Pathogen-associated molecular patterns
CHALLENGE: How can the host discriminate large numbers of diverse pathogens from each other &/or from self using a restricted number of receptors?
SOLUTION: Evolve variety of receptors that recognize conserved motifs on pathogens that are not found on higher eukaryotes
Pathogen-associated molecular patterns (PAMPs) recognized by pattern recognition receptors (PRRs) or molecules (PRMs)
Two categories of PRRs: Those that mediate capture, uptake & presentation of antigen
(scavenger receptors) Those that lead to the activation of pro-inflammatory
pathways (Toll-like receptors)
TLR1 triacyllipopeptides
TLR2 Bact. Lipoproteins, LTA, Peptidoglycan
TLR3 dsRNA (viral)
TLR4 LPS
TLR5 Flagellin
TLR6 diacyllipopeptides
TLR7 Natural ligand unknown
TLR8 Natural ligand unknown
TLR9 Unmethylated CpG DNA
TLR10 ?
Activation of signal transduction pathways by TLRs induces genes that function in host defense
Pro-inflammatory cytokines
Chemokines
MHC & costimulatory molecules
iNOS & antimicrobial peptides that directly destroy pathogens
TLRs have “shared” & “specific” signal transduction pathways
Shared – all TLRs & IL1R
4 essential components – adaptor proteins MyD88, TOLLIP & TRAF6, & protein kinase IRAK
Specific – some, but not all TLRs…
TLR signaling pathways
Involvement of TLR in Linking Innate Immunity to Adaptive Immunity
Phagocyte response to infection• The SOS signals
– N-formyl methionine-containing peptides
– Clotting system peptides– Complement products– Cytokines released by tissue
macrophages• Phagocyte response
– Vascular adherence– Diapedesis– Chemotaxis– Activation– Phagocytosis and killing
Source: SOM PathMicro online textbook
Phagocytosis
A. Attachment via receptors– FcR, complement R,
scavenger R, Toll-like R
B. Pseudopod extensionC. Phagosome formationD. Granule fusion and
Phagolysosome formation
A
B
C
D
Respiratory burstO2-dependent MPO-independent reactions
Toxic compounds: superoxide anion O2- , hydrogen peroxide H2O2 ,
singlet oxygen 1O2 , hydroxyl radical OH*
G-6-P-dehydrogenase Pentose-P + NADPHGlucose + NADP+
NADPH oxidase
Cytochrome BNADP+ + O2 NADPH + O2
Superoxide dismutase H2O2 + 1O22O2- + 2H+
OH* + OH- + 1O22O2- + H2O2
Respiratory burstO2-dependent MPO-dependent reactions
Toxic compounds: hypochlorous acid OCl-, singlet oxygen 1O2
myeloperoxidase OCl- + H2O H2O2 + Cl-
1O2 + Cl- + H2O 2OCl- + H2O
Respiratory burstDetoxification reactions
Superoxide dismutase H2O2 + O2O2- + 2H+
Catalase H2O + O22H2O2
O2-independent killing
Effector molecule Function
Cationic proteins (cathepsin) Damage to microbial membranes
Lysozyme Hydrolyses mucopeptides in the cell wall
lactoferrin Deprives pathogens of iron
Hydrolytic enzymes (proteases) Digests killed organisms
Summary of intracellular killing pathways
Nitric oxide-dependent killing• Bacteria binds to macrophage• Production of TNF-alpha• Upregulates iNOS• Release of NO
• NO is toxic to infected cells in vicinity of macrophage
• NO sythetase is in the cytosol of activated MQ but noy naïve.
Macrophage
IFN-gammaTNF
O2 + L-arginine NO + citrullineNO synthetase
Phagocytosis“It is the toll-like receptors on macrophages that enable them to sense that the material is microbial in origin, and must therefore be eliminated quickly.”
Chemotaxis = movement toward infections.
FcR-mediated PhagocytosisThree types of FcR
• FcRI(CD16)– monocytes, M. IFN- stim neutrophils– high affinity binds monomeric IgG
• FcRII (CD32) A&B forms– low affinity binds to multimeric IgG– A - phagocytic and NK cells– B - B/T cells
• FcRIII (CD64)– monocytes, M, neutrophils
Innate immunity after combat with microbes, stimulates acquired immunity. So, it’s affect on the nature of acquired immunity and after then acquired immunity improves the function of innate immunity.
Y
Endosome
YNaive T Cell
MHC B7
Inflammatory and effectorcytokines
PRR
PAMP
Activated T Cell
CD40L, FasL, CD30L, CD27L
B Cell
Phagocytosis
APC
Direct Bactericidal ActivityPhagocytosisOxygen burstAnti-microbial peptides
Pathogen-specific Antibody
Complement
Determinants recognized by theinnate immune system
Immune response to damage• Dependent on what, where and how bad• Phased response with critical timing
– Requires chemokine signalling, receptor binding, etc
Days: 0 4 7 Weeks: 2 4 6
Non-specific killer cellsNK cells
EosinophilsMast cells
Innate response to virus infection and altered self
• Infected or altered self (transformed) cell downregulated MHC
• NK does not receive inhibitory signal
• Signals kill infected cell
NK cell
Infected/transformed cell
No MHC
Inhibitory RNK R
Innate response to extracellular microorganisms (parasites)
• Activated eosinophils release granule components– Major basic protein
• Major component of granules
– Eosinophil peroxidase• Cationic hemoprotein
– Eosinophil cationic protein• ribonuclease
Eosinophil
Natural Killer (NK) Cells- First identified by having the ability to lytically kill certain tumor cell lines
without prior sensitization
- Kill target cell by release of cytotoxic granules containing granzymes and perforin which penetrate target cell membrane and induce programmed cell death
- Can mediate Antibody-Dependent Cellular Cytotoxicity (ADCC) with CD16 that bind to IgG1,3
- Kill virally-infected cells with missing MHC class I
- Activated by IFN-/ or IL-12,18 (produced rapidly by activated macrophages) and proliferate with IL-15.
- Activated NK cells secrete IFN, acts on macrophages to increase microbial phagocytosis and killing
Antibody-Dependent Cellular Cytotoxicity
NK cell receptorsInhibitory Receptors:- germ-line encoded, no combinatorial diversity as seen with T/B cell receptors
- inhibit cytotoxicity to prevent killing of normal host cells
- specific for MHC class I alleles
- binding to class I sends inhibitory signal to NK cells
Activating Receptors:- germ-line encoded
- recognize carbohydrate structures on self proteins
NK Cell Cytotoxicity• Schematic representation
of NK cell receptors and killing. Normal cells are not killed because inhibitory signals from MHC class I molecules override activating signals. In tumor cells or virus-infected cells, reduced expression or alteration of MHC molecules interrupts the inhibitory signals, allowing activation of NK cells and lysis of target cells.
Virus-infected or
NK produces IFN-gamma for MQs and it produce IL-12 for NK.
Natural Killer-T Cells (NK-T Cells)- Minor subset of -T cells originally described by expression of NK-cell associated
markers
- Majority express invariant TCR (V14-J18/V8.2), remaining express diverse TCR
- Rapidly release large amounts of IL-4 and IFN, can interact with/influence other “innate immune” lymphocytes (NK cells, -T cells)
- Recognize self and foreign glycolipids presented by CD1
- Crystal structure analysis of CD1d indicates the presence of an MHC-like fold with a large, hydrophobic binding groove
- Due to the unique glycolipid antigen binding ability of CD1 molecules, it has been speculated that CD1 acts as an alternative mechanism for surveillance of foreign and altered-self glycolipids that would otherwise escape conventional class I and II pathways
“Innate” Lymphocytes- Unique, minor subsets of T and B lymphocytes that undergo receptor gene
rearrangements to generate receptor diversity (unlike NK cells)
- These subsets express limited receptor diversity, utilizing only a small number of receptor gene segments
- Tend to found in specific locations in the body, usually sites that encounter exogenous antigens or pathogens
Cytokines
-The most important cells in innate immunity
that produce cytokine are MQs, Neu, NK.
-IFN-a & B (control of viral infection)
-TNF-a & IL-1 (pro-inflammatory cytokines)
- IL-12 & IL-15 (NK activator)
-IFN-gamma (MQ activator)
- IL-6 (Neu production and from BM and CRP)
InterferonsProteins usually produced by virally infected cells
* Types of interferons:
1- Alpha interferon Secreted by Macrophages Induced by Viruses or Polynucleotide
2- Beta interferon Secreted by Fibroblasts, Viruses
3- Gamma interferon T- lymphocytes, Specific antigens
dsRNA
Interferon: An AntiviraldsRNA normally is not present in cells.
Thanks