Biology of Disease - Innate Immunity

Death is always caused by failure of which systems?

The brain, heart or lungs

Membrane damage, cytoskeletal damage, reduction in ATP and increase in ROS will all cause what type of cell death?

Necrosis

DNA damage will cause what type of cell death?

Apoptosis

How can free radicals be useful?

They are used by neutrophils and macrophages to kill invading species, but this can damage the host cell

'Free radicals' refers to reactive oxidative species (ROS) and what other compound?

Nitric oxide (NO)

How can recovery from hypoxia result in thrombosis?

Restoration of oxygen to a tissue can create free radicals, which damage the endothelium of blood vessels. Neutrophils and macrophages are recruited (which cause further damage) as well as platelets and thrombin, which cause thrombosis.

Decrease in ATP production results in what three main consequences?

Detachment of ribosomes from the ER, an increase in lactic acid and reduced activity of the Na+/K+ pump

What is the consequence of ribosome detachment from the ER (due to lack of ATP)

Protein synthesis decreases

What is the consequence of an increase in lactic acid in the cell and how does this happen?

Clumping of nuclear chromatin

Increase in lactic acid -> decrease in pH -> disruption of electrostatic attraction between histone proteins and DNA -> clumping of chromatin

What are the two consequences of reduced activity of the Na+/K+ pump (due to lack of ATP) and how do these happen?

1. Swelling of ER and cell:

Sodium accumulates in the cell -> influx of water (osmosis) -> swelling

2. Increased activity of proteases, phospholipases, endonucleases and ATPases:

Sodium accumulates in the cell -> the enzyme that uses the sodium gradient to remove calcium doesn't work -> calcium accumulates in the cell -> increased activity of said enzymes

Why do some cells enter cell death before maximum stress has been reached, especially when this can cause organ failure if occurring on a large scale?

Cells are semi-autonomous, so each cell makes a probability based decision whether to enter cell death or not based on what would be beneficial to the organism in the long term

Give examples on how cells can reversibly adapt under stress conditions

Hypertrophy, atrophy, hyperplasia, dysplasia and metaplasia

Define hypertrophy

Increase in cell size

Define atrophy

Decrease in cell size

Define hyperplasia

increase in number of cells

Define dysplasia

abnormal changes in the size, shape, and organization of mature cells

Define metaplasia

replacement of one cell type with another

Describe the heat shock response

Heat shock factors (HSFs) are released from cytoplasmic complexes to become activated. They move to the nucleus to activate the transcription of heat shock proteins (HSPs), chaperone proteins that bind to partially denatured proteins to keep them functional under stress conditions. This is used in preconditioning, which prepares cells for higher stress situations

Describe the unfolded protein response

Folding chaperone protein synthesis increases in rate and protein translation decreases in rate to ensure that the ER can complete the folding process of protein synthesis

What are the main two stress kinase pathways?

The stress-activated protein kinase (SAPK) pathway and the p38 kinase pathway

What is the aim of a stress kinase pathway?

To modify transcription: the pathways result in the activation of heterodimeric transcription factors (eg AP1). The final result depends on the combination of factors activated, this can range from differentiation to apoptosis

Define and briefly describe apoptosis

Programmed cell death. Cells shrink, selective proteases (caspases) cleave critical proteins for cell function, and the cell releases a signal to inform other cells (eg macrophages) to destroy it via phagocytosis. No inflammatory response happens.

Define and briefly describe necrosis

Uncontrolled cell death. Cells swell and the membranes (both internal and plasma) rupture. The contents released cause neutrophils to carry out an inflammatory response.

Under what condition will an opportunistic pathogen cause disease?

If the host's defence system is compromised

What are the two types of immune response?

Innate (reacts immediately, non-specific) and adaptive (only fast in secondary infection, specific)

Give examples of the barriers in the innate immune system

Skin, mucosal epithelia, and anti-microbial chemicals

Give examples of cells involved in innate immunity

Phagocytes, eosinophils, mast cells and NK cells

Give examples of the soluble components in innate immunity

Complement, cytokines, acute phase proteins and inflammatory mediators

Give examples of barriers in the adaptive immune system

lymphocytes in epithelia, antibodies secreted at surfaces

Give examples of cells in adaptive immunity

B and T lymphocytes

What are the soluble components of adaptive immunity?

Antibodies

How does innate immunity remove a pathogen 0-4hrs after infection?

infection -> recognition by broad agents -> removal of pathogen

How does the early induced innate response remove a pathogen 4-6hrs after infection?

infection-> recruitment of effector cells-> recognition of pathogen and activation of effector cells and inflammation -> removal of pathogen

How does the adaptive response remove a pathogen >96hrs after infection?

infection-> transport of antigen to lymphoid organs-> recognition by naïve B and T cells-> clonal expansion, activation of B and T cells -> removal of pathogen

What is sterile inflammation?

Tissue damage alone causes inflammation (ie inflammation not caused by a pathogen)

What are the four main symptoms of inflammation? How does each one arise?

Calour- heat, from increased blood flow

Dolor- pain, from stimulated nerve endings

Rubor- redness, from increased circulation/vasodilation

Tumour- swelling, due to increase in fluids in the tissue

Give examples of secretions that act as epithelial barriers in the immune system

Mucous covering all glandular surfaces

Stomach acid (low pH)

Antimicrobial peptides

Enzymes in tears and saliva (lysozyme) and in the stomach (pepsin)

What are leukocytes? Where and how are they made?

Leukocytes are white blood cells. They are made in the bone marrow through a process called haematopoiesis.

What are the two progenitor types a hematopoietic stem cell differentiates into?

Myeloid and lymphoid

What six cell types can a myeloid progenitor produce? Put these into three groups.

Mast cells, eosinophils, macrophages, basophils, dendritic cells and neutrophils.

Group 1: granulocytes: eosinophils, basophils, neutrophils

Group 2: monocytes: macrophages and dendritic cells

Group 3: mast cells

What three cell types can a lymphoid progenitor produce? Which two of these have the same precursor?

NK cells, B cells and T cells.

NK cells and T cells have the same precursor

What are the most abundant white blood cells?

Neutrophils

What are the three ways neutrophils can kill or trap pathogens?

1. Release of chemotaxins (complement factors) to mobilise the site of infection, where they phagocytise microbes then die

2. Degranulation- release of antibacterial proteins into the extracellular space

3. NETs- extruding their DNA to create neutrophil extracellular traps to catch pathogens outside the cell

What are the two extreme types of macrophage?

M1- stimulate inflammatory response by releasing cytokines and pro-inflammatory mediators

M2- more associated with tissue repair and parasite killing

Note- most macrophages exist somewhere between these two types

Give examples of factors that would activate a mast cell

Allergens, danger signals and complement components

How quickly can mast cells degranulate and what do these granules contain?

Mast cells can degranulate in seconds when activated. The granules contain inflammatory mediators such as histamine.

What do eosinophils protect against?

Helminths worms (parasitic worms) and other parasites

What method do eosinophils use to kill microbes?

A type of Antibody Dependent Cell Cytotoxicity (ADCC) to release toxic granule proteins and free radicals

Dendritic cells have little effector function. What is their role?

To create a bridge between the innate and adaptive immune system. They recognise a pathogen and carry information of the interaction to the draining lymph nodes to initiate the adaptive response.

What are the three main components of the innate system?

Phagocytes, complement and NK cells

What type of infection are NK cells most useful for combatting?

Viral infections- NK cells will kill infected cells (viruses exist intracellularly)

How does an NK cell know whether to kill a target cell?

NK cells have both inhibitory and activating receptors. Whether they kill depends on the balance of how many of each receive signals- if the effect on the activating receptors is greater than the inhibitory ones, then the target cell will be killed.

What are the two types of cell an NK cell will kill?

Missing-self: Some viruses prevent cells from expressing MHC class 1 molecules in order to hide from T cells. This means there is nothing stimulating the inhibitory receptor(s) and so the NK cell will attack

Induced-self: when under stress conditions, some cells will produce additional molecules which are received by activating receptors on the NK cell. The effect of the activating signals outweighs the inhibitory and the NK cell attacks.

If a healthy cell produces equal amounts of 'inhibitory' and 'activating' signals, how does an NK cell know not to attack?

The effect of the inhibitory signals is always larger, hence induced-self cells have to produce a large excess of activating signals

What cytokines are released by infected cells? How do these affect surrounding cells, as well as NK cells?

IFN-a (alpha) and IFN-B (beta) are produced. These cause surrounding cells to induce viral replication resistance and stimulate the formation of ligands in the infected cell to be recognised by NK cells. These activate the NK cells to kill the infected cell.

What cytokines are released by local macrophages to recruit NK cells and cause their proliferation?

CXCL8, IL-12, IL-15

Which cytokine is released by activated NK cells to activate macrophages and increase their killing activity?

IFN-y (gamma)

What are the three main NK effector functions?

1. Releasing cytoplasmic granules containing perforin to create holes in the cell walls of microbes. This allows entry of apoptosis-inducing granzymes into the cell

2. ADCC

3. Macrophage activation

Why are innate lymphoid cells (ILCs) important in the early innate response?

They amplify signals given during the early innate response

What are the three major types of ILC and what do they protect against?

ILC1- protects against viruses and other intracellular infections

ILC2- protects against helminths and other parasites

ILC3- protects against bacteria and fungi

What are the three ways in which a cytokine can act/be described as?

Autocrine, paracrine and endocrine-like

What does an autocrine cytokine do?

Act upon the same cell it was secreted from

What does a paracrine cytokine do?

Act upon a nearby cell

What does an endocrine-like cytokine do?

Enter the circulation to reach a target cell/tissue further away

What four major properties do cytokines show?

Redundancy, pleiotropism, antagonism and synergy

Define redundancy in terms of cytokines

Multiple cytokines can have the same function

Define pleiotropism in terms of cytokines

One cytokine can have multiple different effects

Define antagonism in terms of cytokines

The action of one cytokine can block the action of another

Define synergy in terms of cytokines

Cytokines can work together to create an affect that is larger than their summated effects

What are the three major types of cytokines and what are their functions?

Interleukin (Il)- affect cell activation and behaviour

Interferon (IFN)- antiviral and aids cell activation

Tumour necrosis factor (TNF)- multiple inflammatory functions

Which cells release acute phase proteins? What do they need to be stimulated by to do this?

Hepatocytes release acute phase proteins when stimulated by IL-6.

What are defensins?

Antimicrobial peptides that disrupt the membranes of bacteria, fungi and enveloped viruses

What is the function of pentaxtrins? What are these similar to?

Binding to both pathogens and receptors of phagocytes. This is similar to the function of antibodies.

What molecules is arachidonic acid converted to using the cyclo-oxygenase pathway? What is the function of these molecules?

Prostagladins- trigger vascular dilation and neutrophil chemotaxis

Thromboxane- triggers platelet aggregation and constriction of blood vessels

What molecule is arachidonic acid converted to using the lipo-oxygenase pathway? What is the function of this molecule?

Leukotrienes- trigger bronchial smooth muscle dilation, neutrophil chemotaxis and release of Slow Reacting Substance of Anaphylaxis (SRS-A)

What is the clotting system?

Tissue damage -> activates thrombin -> converts fibrinogen to insoluble fibrin & fibrinopeptides. Fibrin forms a clot to limit spread of infection. Fibrinopeptides induce vascular permeability and neutrophil chemotaxis. Thrombin cleaves both C3 and C5 -> C3a & C5a.

What is the kinin system?

Tissue damage -> results in the generation of Bradykinin which increases vascular permeability, vasodilation, pain, smooth-muscle contraction. The pathway activates complement components C3 and C5.

What is the fibrinolytic system?

Tissue damage -> results in generation of Plasmin, a protease which degrades fibrin into products that recruit neutrophils (chemotactic). Plasmin activates complement C3.

What is the complement system?

Complement cascades is activated by numerous mechanisms. Results in opsonisation, membrane attack complex formation and generation anaphylatoxins (C3a, C4a and C5a)

What properties are shared by PAMPs?

Shared by classes of organisms

Essential for survival of pathogen

Highly conserved

Absent from host cells

Is lipoteichoic acid a PAMP specific to gram-positive or gram-negative bacteria?

Gram-positive

Is lipopolysaccharide a PAMP specific to gram-positive or gram-negative bacteria?

Gram-negative

Which TLRs recognise bacteria?

1:2, 2:6, 4, 5, 9

Which TLRs recognise RNA viruses?

3, 7, 8

Which TLR recognises DNA viruses?

9

Which TLR recognises parasites?

1:2

Which TLR recognises yeast?

2:6

Which TLRs are located on the cell surface?

1, 2, 4, 5, 6, 10

Which TLRs are located in endosomes?

3, 7, 8, 9

Name the three other PRR families

C-type lectin receptors (CLRs)

RIG-I-like receptors (RLRs)

Cytosolic NOD-like receptors (NLRs)

Why is caspase 1 different from other caspases? How is this trait carried out?

It is involved in inflammation rather than apoptosis

It is activated by the inflammasome and activates IL-1B

What are chromatin proteins, ATP, nucleic acid, oxidised LDL and damaged mitochondria examples of?

DAMPs

As well as PRRs, what else are mast cells activated by?

Neurogenic inflammation, responding to substance P from nerve fibres

What are endogenous pyrogens?

Cytokines that induce fever

Which cytokines are produced by macrophages?

IL-1Beta, TNF-alpha, IL-6, CXCL8, IL-12

What are the functions of IL-1?

Activate vascular endothelium

Activate lymphocytes

Local tissue destruction

Fever

Production of IL-6

What are the functions of TNF-alpha?

Increase vascular permeability

Fever

Mobilisation of metabolites

Shock (systemic- sepsis)

What are the functions of IL-6?

Lymphocyte activation

Increased antibody production

Fever

Acute-phase protein production

What is the function of CXCL8?

Create chemical gradients to recruit neutrophils, basophils and T cells

What are the functions of IL-12?

Activate NK cells

Differentiation of CD4 T cells into Th1 cells