Granulocytes and monocytes Flashcards
Which cells are the earliest to arrive at a site of injury?
Neutrophils
Which cells are a part of the innate immune response?
Granulocytes (Neutrophils, Eosinophils, Basophils/Mast cells) + Monocytes & monocyte-derived cells (myeloid cells) (monocytes, macrophages, dendritic cells)
What is the life span of neutrophils in humans? in mice?
Around 5 days in humans
around 12 hours in mice
What are the main functions of neutrophils?
- Essential for resistance to invasion by microbes
- Important sentinel cells
- First cells to arrive in any kinds of wounds
What are the steps of neutrophil action?
- recruitment to the site of infection via blood vessels
- Signals released to “call” neutrophils; vascular endothelium changes to become “sticky” - extravasation from blood vessel
- migration through tissue
- activation in response to pathogens, their products or the products of distressed cells (via various pattern recognition receptors (PRRs))
- initiation of mechanisms to eliminate pathogens or infected cells
- interaction with & recruitment of other immune cells to site of infection
- E.g. T cells, monocytes etc. - contribution to resolution of inflammation & tissue repair
How does the vascular endothelium catch neutrophils at the site of infection?
the endothelium starts to express receptors so neutrophils adhere to the vasculature –> e.g. P-selectin, E-selectin)
- Bound on neutrophils by P-selectin glycoprotein ligand-1 (PSGL1) and E-selectin ligand (ESL1) and CD44
What is a chemokine?
chemical messengers which induce directional movement of cells, detected by chemokine receptors
Transmembrane receptors
Name the 3 steps for the adhesion of a neutrophil to the vasculature
a. Interactions between chemokine receptors on the neutrophil and chemokines coating the vessel
b. Interactions between chemokine receptors on the neutrophil and chemokines coating the vessel
c. Activation of integrins
What are the 3 steps in neutrophil recruitment?
- Vascular endothelium changes to become “sticky”
- Adhesion
- Transmigration
How does transmigration occur?
a. Requires integrins
b. Can involve digestion of basement membrane with secreted proteinases that digest extracellular matrix components
c. Can only enter if the junctions have opened a bit.
What is chemotaxis?
chemotaxis: directional movement of cells along a concentration gradient of a chemical stimulus
Chemokines released, gradient is formed – neutrophils can sense gradient and move to areas of higher chemokine concentrations
Name 4/5 examples of neutrophil chemoattractants
- lipid mediator LTB4
- bacteria-derived N-formyl-methionyl-leucyl-phenylalanine (fMLP) – bacterial-derived molecule
- complement component C5a
- CXCL8, CXCL2
What is “swarm initiation”?
First neutrophils that get to the site release more things etc… (cell death, intercellular signal relay,…) Continuous positive loop
What is LAD1?
leukocyte adhesion deficiency: LAD1 is an inherited autosomal recessive disorder with mutations in integrin ITGB2 (b2 integrin, CD18) leading to impaired neutrophil migration, adhesion, and recruitment to site of infection, impaired phagocytosis.
Who discovered phagocytosis?
Elie Metchnikoff
He also hypothesized that this process might have a role in host defense
He was the first immunologist to win a nobel prize in medicine
What are the steps in phagocytosis?
- Attachment
- Direct: by pattern recognition receptors
- Indirect: Antibodies might bind bacteria and be recognized by a receptor on the neutrophil (through recognition of FC domain on antibody); complement might also be bound to bacteria and bind to complement receptor on phagocyte - Engulfment
- Rearrangement of actin; cytoskeleton of cell involved, membrane internalized –> phagosome - Phagosome formation
- Acidification, can merge with lysosome etc… - Formation of phagolysosome
- Digestion of pathogen
- Formation of residual body
- Discharge of waste
What is the role of granules?
Production of antimicrobial peptides and proteolytic enzymes
granules are highly specialized lysosomes which contain many antimicrobial substances:
• prevent growth by limiting availability of essential nutrients inside phagosome or by compromising the integrity of the microorganism
• contents can be released into the phagosomes or extracellularly (degranulation)
what enzymes are present in specific granules?
lactoferrin
hCAP18
lysozyme
what enzymes are present in azurophil granules?
alpha defensin
lysozyme
What is an oxidative burst?
is the rapid release of reactive oxygen species (superoxide radical and hydrogen peroxide) from different types of cells
• takes place at cell membrane or phagosome membrane
• essential microbicidal mechanism
• reactive oxygen intermediates (ROIs)
What important enzymes are used in the formation of oxygen bursts?
NADPH oxidase complex is the one forming ROIs (aka NOX/Phox)
• Transfers electrons from the cytosolic NADPH to oxygen –> releases superoxide species
• Can be released in phagosome itself or outside cell (hydroxyl radical groups, hypochloride
• When bound to membrane of bacteria, will force them to burst open
What disease occurs when neutrophils are unable to make reactive oxygen intermediates?
- chronic granulomatous disease: defective phagocyte NADPH oxidase (PHOX) leading to reduced reactive oxygen production – recurrent & atypical infections
Name 2 other ways in which neutrophils can kill/affect other cells
Neutrophil extracellular traps (NETs)
Cytokine secretion
What are Neutrophil extracellular traps (NETs)?
Extracellular killing mechanism first described in 2004 [Brinkmann]
• neutrophil activation triggers them to undergo a specific type of cell death:
o nuclei swells, chromatin are dissolved and the decondensed DNA is expelled from the cell (NETosis)
• DNA is coated in histones & antimicrobial proteins from neutrophilic granules
• NETs form sticky traps that can kill pathogens
o Immobilizes cells and makes them accessible for phagocytosis
• So far from what we know, only neutrophils can do this.
What is a cytokine? Name cytokines produced by neutrophils
cytokine: a protein secreted by an immune cell that has an effect on nearby cells expressing the appropriate receptor
• IL1a and IL1b (proinflammatory)
• TNFa (proinflammatory)
• IL-17 (proinflammatory)
• VEGF (important in endothelial regeneration; wound healing)
What recruits eosinophils into tissues?
IL-5
CCR3-CCL11 (eotaxin)
which type of immune response are eosinophils related to?
TH2 CD4 T cell responses
How are granules useful in eosinophils?
• granule content release involved in anti-parasitic responses: contain enzymes, growth factors, cytokines, chemokines; clear worm infection
o Release various factors resulting in muscle contraction, mucus release to get rid of big particles that cells cannot phagocytose
o Allergic reactions
What are the functions of eosinophils?
- associated with TH2 CD4 T cell responses
- produce inflammatory lipid mediators
- contribute to airway dysfunction in lung during asthma
- granule content release involved in anti-parasitic responses
What is the difference between basophils and mast cells?
- Basophils are recruited from the blood while mast cells reside in tissues (already there)
- basophils have bi-lobed, mast cells single lobed nucleus & both have large numbers of cytoplasmic granules (stain dark blue)
- mast cells localized in tissues around blood vessels & nerves, basophils are recruited from blood
What are the functions of basophils and mast cells?
- Both produce histamines (immunity, T cell responses, allergens responses)
- associated with TH2 CD4 T cell responses
- provide protective immunity to helminths & ticks
- implicated in responses to allergens
WHat are lipid mediators and what are they derived from?
• Locally acting bioactive lipids
• Derivatives of arachidonic acid
–> leukotrienes and prostaglandins
What is the main function of leukotrienes?
leukocyte recruitment (LTB4)
What is the main function of prostaglandins?
inhibition of platelet aggregation, promote vasodilation & vascular leakage (PGE2); platelet aggregation (thromboxane A2)
Both homeostatic roles + role during inflammation
What are lipid mediators produced by?
eosinophils, neutrophils, mast cells, macrophages, endothelial cells & others…
Which enzymes are used to make prostaglandins?
COX1 and COX2
What is targeted by aspirin and what is the effect?
• COX-1 and COX-2 are targeted by various drugs (e.g. aspirin) which has an important anti-inflammatory effect and delays blood clotting (less likely to have a stroke)
Which enzyme is used to make leukotrienes?
Lipoxygenase
What are monocytes and where are they found? Where are they generated?
mononuclear cells, kidney-shaped nucleus, 4-10% of WBCs
o mostly in blood but pools exist in spleen that can be mobilized
o continuously generated in bone marrow
What is monocyte development dependent on in mice?
o development in mice dependent on colony stimulating factor 1 (CSF-1/M- CSF)
What are the 2 types of monocytes and their function?
- Patrolling monocytes (mice: Ly6cLow, humans: CD16+) maintain blood vessel integrity, detect pathogens
- Inflammatory monocytes (mice: Ly6c+, humans: CD14+) are rapidly recruited to sites of infection or injury; participate in response
What happens to monocytes when they enter the tissues?
• When they get in the tissue, they can differentiate into macrophages or dendritic cells upon recruitment into tissues during inflammation (transient populations)
What are macrophages and where are they located?
o large (15–85 mm), professional phagocytes, are resident within tissues o early paradigm: monocytes replenish macrophages in tissues o recent insight: most macrophage populations are seeded during embryogenesis & replenished by division within tissues (reside there; important role in tissue homeostasis)
Name a macrophage of the lung
alveolar macrophages (lie along airways)
Name a macrophage of the liver and their function
Kupffer cells – clearance of aged erythrocytes (critical in filtering out old erythrocytes)
Name a macrophage of the CNS and their function
microglia – synaptic remodelling & removal of dead neurons
Name a macrophage of the bone and their function
osteoclasts – resorb bone
Name functions of the macrophages in adipose tissues
regulation of metabolism, insulin resistance
Name a macrophage of the spleen and their function
white-pulp, red-pulp, marginal zone and metallophilic macrophages – erythrocyte clearance, immune surveillance, iron metabolism
Name a macrophage of the lymph nodes
CD169+ subcapsular sinus macrophages
What are the main roles of macrophages?
Play a critical role in maintaining tissue homeostasis
But also response to infection
Macrophages also participate in host response
They move but are much slower cells.
Macrophages can prevent neutrophils from coming into the tissue if its only a small site of damage
Arms of macrophage will cover small lesion and prevent neutrophils from coming to the site.
Explain the M1/M2 paradigm
depending on their exposure to activating stimuli, as well as other signals from host tissues macrophages can become (can be anywhere on the spectrum, not black or white)
- Differentiation difference in macrophages arise as a result of cytokine milieu generated by other immune cells
- Can become something between M1 and M2 macrophages
What is an M1 macrophage, what is it produced by and what are their function?
M1 macrophages: (aka classically activated macrophage)
Interferon-gamma produced by TH1 cells, CD8 T cells or NK cells, and tumor necrosis factor-a produced by APCs
= Have microbicidal activity, produce IL-1, IL-6 and IL-23: pro-inflammatory
What is an M2 macrophage, what is it produced by and what are their function?
aka alternatively activated macrophages
IL-4 produced by TH2 cells or by granulocytes = wound-healing activity & tissue repair, produce extracellular matrix proteins, can be immunosuppressive
What are dendritic cells and what are their functions?
- Stellate/dendritic morphology
- Specialized antigen-processing & presenting cells (activate T cells)
- Express MHC-II and MHC-I, as well as pattern-recognition receptors which enable their activation in response to microbial stimuli –> can talk directly to T cells
- Have dendrites (long arms)
- Dendritic cells also live in lymph nodes
What are the different types of dendritic cells?
• Heterogeneous population with many subsets defined by distinct phenotypes/anatomic location (diff types)
o cDC – classical/myeloid: APCs initiating T/B immunity
o pDC – plasmacytoid: secrete large amounts of type I interferon (IFNa) during viral infections
What are the functions of dendritic cells?
Can live in tissues, get activated by pattern recognition receptors they express when pathogen is encountered
• initiate, coordinate and regulate adaptive immune responses, maintain tolerance to self
• Resident populations in tissue take up antigen
• Migrate to lymphatics and then traffic to secondary lymphoid organs (e.g. local lymph nodes) where initiate adaptive immune responses
What are 4 treatments for disorders of granulopoiesis?
• Prophylactic methods to reduce exposure to infections
• Antimicrobial drugs to prevent and treat infections
• Administration of colony stimulating factors (if too little granulocytes present)
– G-CSF
– GM-CSF
• Bone marrow transplantation (most common): Ablation of bone marrow of affected individual with cytotoxic drugs, followed by transplantation of healthy donor cells – bone marrow, cord blood or enriched hematopoietic stem cells.
