Macrophages Flashcards
Haematopoiesis is?
Haematopietic stem cells found in bone marrow of adults differentiate into various cells
Features of HSCs
Sustain blood cells throughout life
Capable of self-renewal
Multipotent - stem cells generate other cells of multiple lineages
Two main lineages generated are lymphoid and myeloid cells
Determining factors for Cells produced by HSC
Cellular environment
Transcription factors
Soluble mediators in the environment
How does Pattern Associated Molecular Patterns(PAMPs) help microbe recognition
PAMP receptors recognise PAMPs
Works on principle there is difference between cell and pathogenic cells
PAMP also recognised indirectly
Examples of Bacterial PAMPs
Cell wall components
Such as LPS and LTA
Examples of viruses PAMPs
ssRNA and dsRNA that form part of viral life cycle
Examples of yeast PAMPs
Sugars
B-glucans
Examples of helminths PAMPs
Sugars e.g Chitin
Proteins
Where are PRRs encoded?
Germline encoded in genes for multicellular organisms
Highly abundant in cells of innate immune response
- phagocytes(macrophages neutrophils and dendritic cells)
Where are PRRs located
Soluble
Exposed on cell surface
In cytoplasm
In vacuoles
What are Toll Like Receptors
Best characterises PRRs
Recognise wide range of pathogens which lead to appropriate signalling and responses
How many TLRs are there
10
What is TLR1
Ligand and target microbes
Triacyl lipopeptides
Mycobacteria
What is TLR2
Ligand
Target microbes
Peptidoglycans - Gram positive bacteria
GPI-linked proteins - Trypanosomes
Lipoproteins - mycobacteria
Zymosan - yeasts and other fungi
What is TLR3 ligand and target microbes
dsRNA - Viruses
What is TLR4 ligand and microbes?
LPS - Gram-negative bacteria
F-protein - Respiratory Syncytial virua
What is TLR5 ligand and microbe
Flagellin - bacteria
What is TLR6 ligand and target microbes
Diacyl lipopeptides - mycobacteria
Zymosan- yeast and other fungi
What is TLR7 and TLR8 ligand and target microbes?
ssRNA - Viruses
What is TLR9 ligand and target microbes?
CpG unmethylated dinucleotides and dinucleotides - Bacterial DNA
Herpesvirus infection - Some herpesviruses
What are the major classes of PRR besides TLR’s and what they bind to?
Dectin-1 Receptors binds to B-glucans
Mannose receptor bind to mannose
Scavenger receptor bind to lipids/proteins
Major roles of macrophages
Pattern recognition
Phagocytosis
Killing infected cells
Cytokines release
Direct both innate and adaptive immune response through secretion of cytokines and chemokines plus antigen presentation to T cells
Where do Macrophages derive
Where are macrophages found
HSC from myeloid lineage
Myeloid precursor bone marrow cells
Macrophages found in all tissues within body
What cells have myeloid precursors
Neurtrophils
Monocytes
Macrophages
What is role of Monocytes
Released into circulation so can enter tissues and replace resident tissue macrophages
What control myeloid differentiation
Sequential TFs
Soluble mediators
Micro-environmental factors
What are tissue resident macrophages?
Macrophages that establish in tissue during early embryogenesis to produce resident cells that proliferate
Have different expression patterns that can be analysed by microarray
What are DAMPs
Damage associated molecular patterns from stressed cells and allow recognition of healthy cells from damaged cells
Usually from contents of damaged cell spilling out.
Macrophages integrate a large number of stimuli which result in different types of activation
Why?
Enhances effector functions and ensure a directed and appropriated response
How does classically activated macrophage work?
Tissue macrophage recognises e.g LPS with TLR or IFNy released by cells when they recognise viruses
This causes differentiation of macrophage into a classically activate macrophage
How can you recognise a classically activated macrophage?
Surface markers and phenotypic features
E.g. Lots of MHC Class II on the surface
Produce many antimicrobials
E.g. Hydrogen peroxide, nitric oxide
Th1 cytokines
IL-6, IL-23 leads to Th17 cells
What are wound healing macrophages
What do they do and how
Macrophages that cause tissue damage repair
Produce precursors of collagen for tissue
By
Increasing transcription and translation of arginase which will convert to arginine to ornithine a precursor for polyamide an collagen for matrix regeneration
Increase apoptosis
What activates Wound healing macrophages
Inflammatory cytokines or Th2 cytokines such as IL4
How can pathogens skew wound healing macrophages
M.tb increases arginase production for survival
What are Regulatory Macrophages?
For parts like eyes,brain and tested where we do not want excessive inflammatory response to prevent excess damage
Anti-inflammatory Macrophages produce anti-inflammatory cytokines IL-10, TGF-B to calm down response
What are Tumor associated macrophages?
And how do they work?
Macrophages are hijacked by tumors
Found in tumors
Differentiate to produce environment beneficial for tumour E.g increase VEGF to increase vascularise to tumour cells to encourage growth
Suppress immune response so tumours not killed.
Produce growth factors to encourage tumour development
Macrophage normally indicate poor prognosis for tumours
Macrophages recognise pathogen via
Directly or opsonic Receptors
What is phagocytosis
Main mechanism for uptake and destruction of microbes and apoptosis cells
Three major steps of macrophage phagocytosis
Initial recognition (receptor mediated)
Uptake, signalling and actin-driven cytoskeletal remodelling
Processing-killing, presentation or non inflammatory removal
Name pathogens that evade phagocytosis
Yersinia, salmonella, clostridium toxins that block Rho-family of GTPases
How does uptake via opsonic phagocytosis work?
Particles coated in complement or soluble pattern recognition Receptors (MBL, collections,MFG-8) or antibodies
Receptors recognise coated pathogens and phagcytose it
E.g. Binding by FC receptor and zipper hypothesis
What are main Fc Receptors?
FcyRI( CD64) has high affinity to momomeric IgG
FcyRIIandRIII(CD32 and 16) – low affinity – polymeric IgG
Stages of phagocytosis
Ligand binding
Activation of phagocytic cell
Engulfment
Internalisation /fusion with lysosomes
How does phagosome maturation progress
Phagosome matures and gradually acidified via fusion with lysosomes from endocytic pathway
Rab protein 5,7,11 essential for vesicular fusion
Final degradation through generating phagolysosome
Pathogen components either presented on surface to initiate further immune response or degraded in cell
What pathogen blocks phagolysosome formation
M.tb by inhibiting sphingosine kinase signalling
Autophagy how it occurs
And what is it
Initiated via starvation or stress from viral infection
Cell packages cut solid contents in double membrane vehicle and delivers to lysosomes for degradation
Growing evidence cells use same machinery against invading microorganism
Killing mechanisms of macrophages ?
Reactive oxygen species/ reactive nitrogen species
Proteolytic and hydrolytix enzymes -e.g proteases
Antimicrobial peptides
Nutrient deprivation
What are antimicrobial peptides?
Defensins and cathelicidins
-short peptides, between 12 and 50 aminonacids
Positively charges and bind electrostatically to form multimeric pores killing microbes
Also act as chemoattractants
What increases acidity in phagosmal maturation
Acidity increased via V-ATPase
Name hydrolytic enzymes
Lysozymes, cathespin D, lipases
What does the deprivation of nutrients macrophage kills mechanism?
IDO metabolise tryptophan
Arginase metabolises arginine
Vitamin B12 binding protein and lacroferrin being B12 and iron
