Innate immunity: Basics and Phagocytosis Flashcards
How do pathogens enter
Mucosal and epithelial - skin - surfaces
External barrier
How can pathogen cause infection
Pathogen must enter the body - breach one of these barriers
Diff routes of entry
- ex = airborne microorganisms enter through lining of respiratory tract
Why is human skin resistant to colonization by E. coli despite exposure to it
Physical barriers = also chemical barrier
Skin has barrier against it
Describe epithelial surfaces
Provide first barrier against infection = skin, gut lining epithelium, respiratory epithelium, mucosal membranes
Epithelial cells have prrs that bind pamps
What provides innate immunity
Saliva
Hair
Mucus
Tears
What do epithelial layers produce
Protective substances = acidic ph, antimicrobial peptides (defensins)
Name cellular elements of innate immunity
Neutrophils (main) and other granulocytes
Monocytes and macrophages
Dendritic cells
Nk cells and other innate lymphoid cells
Describe monocytes and macrophages
Macrophages = mostly tissue resident
Tissue specific variants = kupffer cells, microglia (macrophages of cns) , intraglomerular mesangial cells
Name types of dendritic cells = 3
Immature
Mature =
conventional
Plasmacytoid
Name some key molecules innate immunity
Antimicrobial enzymes
Antimicrobial peptide s
Complement
Give ex of anti microbial enzyme
Lysozyme= digest peptidoglycan (cell wall gram pos bacteria)
Give ex of anti microbial peptides
Defensins —> disrupt cell membrane (creates pore)
Describe stages of infection and response to it
Pathogens adhere to epithelium
Immune cells activated = local infection, penetration of epithelium
Local infection of tissues
Adaptive immunity
What is definition phagocytosis
Engulfment and internalization of pathogens or their comments upon binding to receptors on cell surface of phagocytes = have to be prompted
Name phagocytes that mediate phagocytosis
Macrophages
Granulocytes:neutrophils
Dendritic cells
What can phagocytosis lead to
Removal and killing of pathogens
Clearing debris= prrs recognize damps (released when cells near during, damage associated molecular patterns)
Generation of peptides for presentation to t cells
Describe macrophage as phagocyte
Also dendritic cells can do phagocytosis and process antigen
Macrophages = presenting peptide antigen to T cell on mhc
Describe receptors involved in phagocytosis
Many are prrs
Not all prrs induce phagocytosis - but many do
Describe indirect phagocytosis
Phagocyte recognition of soluble proteins that are bound to microbial surfaces (opsonins, bind to surface of microbe ) = aka soluble pattern recognition proteins —> enhance phagocytosis (opsonization)
Ex = antibodies and complement proteins, phagocytic cells have receptors for opsonins
Describe phagocytosis - initial
Initiated when receptors interact with ligand/pathogen
Bacterium binds to prrs (pamp binds)
Prompts membrane protrusions that extend = pseudopodia —> leads to engulfment bacteria
Describe phagocytosis - internalized
Pathogen internalized in large membrane enclose endocytic vesicle = phagosome (goes into vesicle)
Describe phagocytosis - fusing
Phagosome fuses with one or more lysosomes —> phagolysosome = lysosomal contents released
Describe phagocytosis - kill
Ph drops and killed
Phagolysosome acidity’s = acquires antimicrobial peptides and enzymes to kill pathogen
Activated enzymes at low ph and chops up bacteria
Describe neutrophils - phagocytosis
Contain dif types of cytoplasmic granules = primary granules and secondary granules
What do granules of neutrophils do
Fuse with phagosome (phagolysosome) and release additional enzymes and antimicrobial peptides that attack the microorganism
How are neutrophils diff from other cells
Macrophages and dendritic cells do not have granules
What happens when Ligand binding/phagocytosis
Triggers signalling and results in change
What do phagolysosomes contain
Products that can kill microbes
Name products that phagolysosomes contain
Low ph/acidification
Hydrologic enzymes from lysozymes and proteases, love low ph
Oxidative attack
Antimicrobial peptides = defensins, Catholicidin
What is oxidative attack
Employs reactive oxygen species = ROS and reactive nitrogen species = RNS = add more oxygen or nitrogen = toxic to pathogen phagocytosed
= damage microbial membranes and intracellular components
How are ROS generated
Free radicals = ROS
Generated by phagocytes unique NADPH oxidase enzyme complex - or phagosome NADPH oxidase
What does ROS production do
By NADPH oxidase increases oxygen consumption —> respiratory burst
T OR F phagolysosome only important organelle for innate immunity
FALSEEEEEEEE
Important organelle for innate and adaptive immunity
How is phagolysosome important organelle for innate immunity
Pathogen killing
Pathogen processes
Pathogen presentation to sensory cytoslic PRRS (some inside cells, tlr, nods)
How is phagolysosome important organelle for adaptive immunity
Antigen degreadtion
Antigen processing
Antigen presentation onto mhc molecules
What can phagocytes do
Clear cells have that undergone apoptosis
Dead/dying cells express damps —> eat me signals, bind to prrs
What do some healthy cells express
Do not eat me signals = CD47
Describe CD47
Will bind to signal regulatory protein alpha (SIRPalpha) on macrophage = transmits signals that inhibit phagocytosis
WHAT DO TUMOUR CELLS EXPRESS
Elevated levels of CD47 —> tumour progression
Novel therapy = antibodies to block CD47 on tumour cells —> hopefully macrophage an phagocytose cancer cell
DESCRibe neutrophils
Another cell capable of phagocytosis = inject and kill microorganisms
Not tissue resident = in circulation, recruited to site of infection
What can neutrophils do
20-60% of neutrophils can produce extra cellular matrix called nets = neutrophil extracellular traps —> trap microorganisms and prevent spread
What is pus
Result of dead and dying neutrophils
Describe whole process of nets
Pamp binds prr = signals from prrs activate neutrophils = leads to intracellular signalling
Degradation of intracellular membrane of neutrophils then chromatins decondense
Cell bursts open and nets released = chromatins attached to some peptides
Nets can trap micoorganisms, stops spread
Compare nets to reg cell
10-15x longer than actual cell
Describe homeostasis - cns resident microglia
Cns resident microglia = macrophages of Brain responsible for establishing proper neuronal connections =
Participate in debris clean up, brain dev, memory, learning
Describe disease multiple sclerosis
Not in homeostasis
Complex inflammatory disease characterized by myelin breakdown = lots of toxic debris built up in brain lesion micro environments
What is required for cns repair
Microglia and peripheral infiltrates of macrophages participate in debris clean up —> various animal models show that this is required for cns repair
Helps homeostasis
Describe receptor binding - microglia
Recognition of cell debris by mouse microglia via receptors leading to pseudopodia
Receptor binding important for initiating phagocytosis
If recpetor KO microglia = no pseudopodia formed
Describe measuring phagocytosis in vitro
We want to know impact of diff conditions on phagocytosis
Dye substrate with a ph sensitive fluorophore —> only fluoresces under low ph conditions = phagolysosome
Fed substrate to macrophage s
Measured fluorescence of macrophages before and after diff condition
Describe key points from research ex
Multiple steps involved in phagocytosis
Diff things may be affected if one step goes wrong, depends which
