L3 Innate Immunity, inflammation and complement

characteristics innate immunity

present in invertebrates and vertebrates

fast response (hours)

non-specific (no antigen specific receptors involved)

no memory

precedes and directs specific immunity

training (epigenetic modifications, memory)

functions innate immunity

prevention of infection

degradation of microbes

cleaning of waste

responds to danger signals

first line of defense, gaining time

activation of specific immunity

effector of specific immunity

no specific memory, but training

always present

physical and biochemical barriers

anatomic, physiologic, phagocytic (cellular) barriers, inflammatory barriers

anatomic barriers

skin and (mucosal) epithalia (large surface exposed to outside world)

cilia

mucus(gut), surfactant proteins(lung)

physiologic barriers

temperature (fever)

low pH in the stomach (HCl)

peristaltic action gut, pooping, coughing, vomiting

enzymes such as lysozyme, phspholipase A

antimicrobial peptides (defensins and catelicidins)

phagocytic (cellular) barriers

specialized cells (monocytes, neutrophils, tissue resident macrophages)

inflammatory barriers

tissue damage and infection lead to influx of phagocytic cells

macrophage - function

phagocytosis, antigen presentation to cells

neutrophil - function

phagocytosis, degranulation (discharge of contents of a cell)

eosinophil

degranulation, release of enzymes, growth factors, cytokines

basophil - function

degranulation, release of histamine, enzymes, cytokiens

mast cell - functions

degranulation, releae of histamine, enzymes, cytokines

monocyte - function

differentiate into macrophages and dendritic cells to elicit an immune response

natural killer (NK) cells

tumour rejection, destruction of infected cells, release of perforin and granzymes which induce apoptosis

T helper (Th) cells, CD4+

function

immune response mediators

Cytotoxic T cells, CD8+

function

cell destruction

pattern recognition receptors and PAMPS/MAMPS

to detect stranger and danger

differntiation between self and foreign

how does the innate immune system recognize pathogens

danger theory polly matzinger (2002)

PAMP: pathogen associated molecular patterns

MAMP: microbial associated molecular patterns

DAMP: danger associated molecular patterns

Pattern recognition receptors (PRRS)

toll like receptors

DC-sign

NLR’s

• nod like receptors(nulcoetiding binding oligomerizatoin domain receptors)

• RIG-like receptors etc

Dectin 1 and 2

NF-kB, IRF3 at the end

Pattern Recognition Receptors (PRRs) are crucial immune system sensors that detect conserved molecular patterns on pathogens (PAMPs) or damaged cells (DAMPs) to initiate innate immune responses, bridging to adaptive immunity, and coordinating inflammation, anti-infection, and tissue repair by activating signaling pathways like NF-κB, leading to pathogen clearance or anti-tumor activities. 

C-type lectins on innate immune cells detect

procaryotic carbohydrate molecules

Toll like receptors and their ligans

pathogen associated molecular pathogens

Lipopolysaccharide (LPS)
lipoteichoic acid (LTA)
peptidoglycan

Bacterial flagella

Bacterial CpG DNA

Viral ssRNA and dsRNA

LPS AND LTA PRESENT IN THE BARN ETC

TLR4 signalling by LPS

NF-kB is a key nuclear transcription facot in M1 macrophages

Myd88 dependent and independent pathways

fast and long term inflammatory responses

chicken lack TRAM (TLR4 signalling is less orbust

IRF-3 is interferon response facotr

Pathogen associated molecular patterns (PAMP)

gram positive

gram negative bacteriaS

PAMPS and DAMPS can act synergistically

true

Danger Associated Molecular Patterns

Mitochondrial DNA and ATP

Histone proteins

Necrotic cells

Heat shock proteins

Uric acid crystals

High mobility group box 1 (HMBG1)

extracellular matrix breakdown products

Inflammasome

cytosolic multiportein complexes

type of inflammasome dependent on nature stimulating agen

caspase 1 converts inactive IL-IB and IL-18 in bioacgive forms

Caspace1 induces pyroptosis, which has features of apoptosis and necrosis

Phagocytes

Monocytes and neutrophils migrate to sites of infection (e.g. bovine mastitis)

use of adhesion molecules : integrins LFA-1 (CD11a/CD18)

chemotaxis along cytokine gradient (e.g. IL-8 (CXCL-8)) and macrophage inflammatory protein1a (MIP-1a)

activation pahgocyte via PAMP and PRR

Phagocytosis and killing pathogen

Macrophages produce nitric oxide (NO) radicals to kill bacteria

Neutrophil extravasation at the site of infection

tethering

rolling

activation

adhesion

transmigration

chemotaxis

Somatic cell count

ase line in healthy cows or height of the response in infected cows

differentiation of cell types - monocytes vs neutrophils

genetics

the SCC may reflect the vulnerability for udder infections

Neutrophil extracellular traps(NETs)

NETs trap bacteria

Nuclear DNA with bound histone proteins, lactoferine, myeloperoxidase, cthepsis etc to kill bacteria

may cause trombosis like problems, probably also in covid infections

Innate lymphoid cells

ILCs and Natural killer cells

Morphologically similar to T cells, but lack antigen specific receptors (TCR)

Thus no MHC restriction

Present at barriers like mucosa

Tissue resident cells, no circulation

ILCs regulate immune responses via cytokine secretion

Detect symptoms of infection, but not the infectious agent itself early sentinels

Groups of innate lymhoid celles (deze nog verder uitsplitsen, zodat ik het goed kan otnhoudne)

ILC 1, NK CELLS, ILC1, IFN-Y, TNF, viral defense, tumour surveillance, infammation

ILC2, ILC2, IL-4, IL-5, IL-9, IL-13, defense against parasites, allergy, tissue repair
ILC3, LTi cells, IL-17 IL22, defencse against bacteria/fungi, lymphoid organ development

NK cells

kill infected or unwanted cells sometimes together with antibodies (ADCC)

inhibitory receptor detect self MHC class I on healthy cells

Cells with down regulated MHCI molecules are targets for NK cells - is called missing self recognition

Down regulation of MHCI can be caused by viruses and in tumor cells

NK-cells: early detection of infected cells

IFN-gamma causes enhanced expression of MHCI

Inflammation

increasing evidence that chronic inflammation is related to diseases on the long term

Stimuli of acute inflammation

pathogens (bacteria, viruses, parasites)

microbial associated molecular patterns (MAMP)
danger associated molecular patterns (DAMP)

necrotic cells/tissues

chemical agents/poisons

Heat or cold

Injury (cut, needle, splinter)

Sequence of events in acute inflammation

Stinulus

mediators

vascular

cellular

repair/resolution

mediators of inflammation

pro and anti-inflammatory components

pro-ifnlamamtory components

• proinflammatory cytokines (interferon-y, il-1b, il-6, TNFa, IL8

• complement facotors C5a

• Acute phase proteins (CRP, haptoglobin)

• prostaglandins

• reactive oxygen species (ROS)

anti-inflammatory components → downregulated autoimmune response

• anti-inflammaotry cytokines (IL-19, TGFB)

• Interleukin 1 receptor anatonis (IL1Ra)

  • Natural (auto) antibodies

Prostaglandins

prostocyclin, thromboxane

phospholipase A2 → COX1, COX2 (NSAIDs) → prostaglandins

NSAIDs (e.g. ibuprofen, aspirin) block COX enzymes, reducing prostaglandin synthesis, reduce pain, reduce fver, reduce inflammation

Adhesion, rolling and diapedesis of neutrophils

Adhesion molecules involved in rolling adhesion and diapedesis:

• E-selectin and P-selectin

• ICAM

• Integrins

  • Extracellular matrix proteins

SOCS: suppressors of cytokine signaling

negative feedback regulation of cytokine signalig by 8 different SOC proteins

what kind of inflammation is this

acute - neutrophils (macrophages)

No T/B cells

what kind of inflammation is this

chronic

mononuclear cells, macrophages/monocytes, lymphocytes, palsma cells

T/B cells

in chronic infoammaiton is specific immunity involved

five symptoms of acute inflammation

heat (color)

redness (rubor)

swelling (tumor)

pain (dolor)

funciton loss (functio laesa)

Acute phase response

positive acute phase protines: their levels increase in response ot inflammation (e.g. CRP, SAA, haptoglobin)

Function of positive acute phase:

• enahcning immune function, modulating the inflamamtory response, promoting tissue repair

negative acute phase proteins: their levels decrease during inflammation (e.g. albumin)

function of negative acute phase proteins:

• regulating inflmmation to maintain homeostasis

produced in the liver

Complement system

functions

Opsonisation of bacteria and unwanted cells (C3b) resulting in clearance of immune complexes

stimulating inflammation (C3a, C5a)

• increase vascular permeability

• release of histamine from mast cells and basophils

cell lysis (membrane attack complex)

Complement deficiencies

vulnerable for infectious diseases

autoimmune diseases (e.g. systemic lupus erythmeatosus (SLE), renal failure kidneh)

3 complement pathways

classical - via antigen-antibody complexes

lectin pathway - via MBL-MASP complexes

Altenative pathway - via spontaenous C3 hydrolysis

C3a - pro-inflammatory action

C3b - opsonization

C5B - membrane attack complex

Around 30 plasma proteins, self assembling csacase

all 3 pathwasy end up in C3 convertase, which is the start of the terminal pathway, the membrane attack complex (MAC)

3 complement pathways + opsonization

T

Tick over phase: to prevent killing of healthy host cells

C3 produced in the liver

In extracellular fluid C3 is cleaved sponataneously in C3b and C3a

C3b deposited on healhty cell surface is removed by MCP and DAF

The alternative pathway

Trigger surface (e.g. bacterial cell wall) permits deposition from C3b

C3b is generated form the thick over phase

C3 in extracellular fluid is hydrolized spontaenously in C3b + C3a

C3b on healthy cells inactived by MCP(CD46) and DAF(CD59)
C3 convertase: factor B binds C3b. B is cleaved by factor D into Bb and Ba. C3bBb is formed

Properdin stabilizes the C3bBb complex

endproduct is C5 convertase: C3bBbC3b

C5 convertase cleaves C5 in C5a and C5b

The lectin pathway

Mannose binding lectin (MBL) is acute phase protien

ACtives C4 (C4a and C4b)

C4b binds to pathogen surface and binds C2

C2 is cleaved into C2a and C2b

C4bC2b = classival C3 convertase

C4bC2bC3b = C5 convertase

The classical pathway

antigen specific antibodies form immune complexes

The terminal pathway

C3a and C5a have a clear role in local inflammatory responses

Which complement is involved in inflammation and opsonization?but alos cytolysis?