Cell death/repair & acute inflammation Flashcards
Discuss different forms of cell death
Apoptosis → programmed and normally silent to limit damage spread
Necrosis → injurious and can initiate inflammation due to the uncoordinated and unconfined nature of death
What is irreversible injury characterised by?
- extensive cell swelling and resultant blebbing which eventually causes the cell to burst
- protein aggregation
- ER lysis
- spillage of the enzymatic contents into the cytoplasm for autolysis
- further mitochondrial swelling
What does irreversible injury lead to?
necrotic lysis and release of cell contents into the EC space → further damage to other cells and inflammation
Why is there an increase in Ca2+ in necrosis? What can this Ca2+ do?
- loss of membrane function
- can activate enzymes (proteases and phospholipases) which further break down the membrane and there is a vicious cycle
Roles of apoptosis
Normal tissue homeostasis
Embryonic morphogenesis (digits)
Deletion of self-reactive lymphocytes (during T cell development)
What cytokines are release in necrosis and apoptosis?
Apoptosis → TGFB (promote repair)
Necrosis → TNF, IL-1, IL-8 (inflammation)
What are the 5 cardinal signs of inflammation?
1 - Heat (brought about in the tissue by vasodilation and blood flow through peripheral vessels)
2 - Redness (vasodilation)
3 - Swelling (caused by formation of an inflammatory exudate - oedema, resulting from increased capillary permeability)
4 - Pain (released chemical mediators acting on nociceptve fibres)
5 - Loss of function (caused by the inflammation itself and not the processes which it brings about)
How long does acute inflammation last?
Minutes-days
What is the general function of acute inflammation?
To facilitate recruitment of neutrophils to sites of pyogenic bacterial infection and enable them to phagocytose and kill the organisms
Describe the histology of acute inflammation
- vasodilation
- oedema
- adhesion of PMN to venule walls
- cellular infilatration by PMN and macrophages
- Formation of pus
What are the key players for acute inflammation?
Neutrophils and mast cells
What are the key players in chronic inflammation?
Macrophages and lymphocytes
What three classes of mediator are important in acute inflammation?
Cytokines
Peptides and proteinase cascades
Lipids
What are the major proinflammatory cytokines? What do they do?
TNF alpha - leads to activation of vascular endothelial cells and increased vascular permeability, as well as increased blood clotting locally
Interleukin 1B - activates vascular endothelial cells and lymphocytes, results in local tissue destruction
IL-6 - endothelial cell activation
Describe the cascades there are of plasma protein
- Coagulation system - clotting cascade
- Fibrinolysis system - acts to counterbalance clotting
- kinin system - generates porteins capable of sustaining vasodilation and other inflammatory effects (bradykinin)
- Complement system - promotes chemotaxis, opsonisation and formation of the MAC
Describe opsonisation. What is an opsonin?
An opsonin is any molecule that enhances phagocytosis by marking an antigen for an immune response or my marking dead cells for recycling
When antigen is coated with opsonins, binding to immune cells is greatly enhanced
How may lipids be important in acute inflammation?
Membrane phospholipids (e.g. in platelets and leukocytes) provide the substrate (arachidonate) for prostaglandin, thromboxane and leukotriene protein but the COX and lipo-oxygenase pathways respectively
Describe the main roles of the inflammatory mediators? Which mediators have what effects?
Vasodilatation – Histamine and prostaglandins
Vascular leakage – Histamine, Leukotriene C4 (LTC4), LTD4 and C5a
Endothelial cell activation – IL-1, TNF-a, IL-6 and LPS
Chemotaxis – LTB4, C5a, PAF (Platelet Activating Factor) and chemokines
Pain – Bradykinin and prostaglandins
Tissue damage – Free radicals and leukocyte enzymes
What is the process of leukocyte movement from the blood to the tissue called?
Extravasion
What steps does extravasion consist of?
Margination Leukocyte rolling Leukocyte actication Leukocyte tight adhesion Diapedesis (leukocyte extravasion) Chemotaxis
Describe margination
It is movement along the endothelium
Occurs due to stasis - condition characterised by enlarged vessels packed with cells - allows leukocytes to move to the endothelium
Describe leukocyte rolling
- Normal physiological process
- Mediated by low-affinity interactions between L-selectins on the leukocytes and their carbohydrate counter-ligands on the endothelium
- the marginal affinity causes the leukocytes to slow down and begin rolling along the inner surface of the vessel
- during rolling, transitory beongs are formed between selectins and their ligands
What serves to increase rolling during inflammation?
- Endothelial cells have P-selectin and E-selectin which interact with P-selectin ligands and PMN carbohydrates on the leukocyte respectively
- P selectins are released from storage granules of the endothelial cells in response to histamine or thrombin
- E selectin is upregulated by TNF-alpha, IL-1 and LPS
Describe leukocyte activation and tight adhesion
- activation = rapid, occuring in a number of seconds via various GPCRs (chemokine, C5a, fMLP, LTB4 and PAF receptors)
- Activation = increase beta2 integrins which for tight interactions
- these can bind to endothelial cell receptors (e.g. ICLAM)
- this halts rolling
Describe diapedesis
- leukocytes arrested on endothelial surface
- integrins promotes spreading of leukocytes across the endothelial surface
- they extent pseudopodia and migrate through vessel wall
- This migration is driven by chemokines
- After passing through, leukocytes secrete collagenase (macrophages) and elastase (neutrophils) that enables them to pass through the vascular basement membrane
Describe chemotaxis. What substances can be chemotactic? What are these mediators produced in response to?
Bacterial products, particularly peptides with N-formyl-methionine termini
Cytokines, especially those of the chemokine family – E.g. Il-8
Components of the complement system, particularly C5a
Products of the lipoxygenase pathway of arachidonic acid metabolism, particularly LTB4
They are produced in response to infections and tissue damage
How do leukocytes move?
By extending pseudopods that anchor to the ECM and then pull in the direction of the extension
How may leukocytes lead to tissue damage?
- bystander tissues may be damaged in normal defensive reaction
- may be damaged in an attempt to clear dead and damaged tissues
- autoimmunity
Describe the systemic effects of acute inflammation
Fever – Through the action of cytokines such as TNF and IL-1 at the hypothalamus
Chills/rigor
Other CNS – Loss of appetite and fatigue
Cardiovascular system – Tachycardia, increased cardiac output and increased endothelial permeability leading to hypotension
Metabolic – Hepatocytes secrete acute phase proteins, such as C-reactive protein, fibrinogen and complement proteins
Endocrine – Stress response is triggered leading to the secretion of corticosteroids and thyroxin
Leukocytosis – Cytokines stimulate production of leukocytes from precursors in the bone marrow
Plasma cascades – Intravascular coagulation and complement consumption
Long term – Wasting/cachexia
Describe endotoxic shock
The LPS (endotoxin) present on the Gram-negative bacteria binds to the monocyte CD14 receptor, triggering signaling via TLR4 to produce the inflammatory mediators TNF-a, IL-1, IL-6 and IL-8 systemically. The systemic presence of these cytokines leads to a number of systemic effects, including fever, endothelial damage, capillary leakage, hypotension and systemic activation of the coagulation cascade leading to disseminated intravascular coagulation. As a result, there is hypoperfusion of many of the major organs systems, resulting in multiorgan system failure and potentially death.
Describe some inhibitors of proteinases
The main local and systemic defences against PMN-inflicted proteolytic injury include a range of inhibitors of proteinases, such as a2-macroglobulin, a1-antitrypsin and a2-antiplasmin
Role of C3a
Produces anaphylotoxic which activates mast cells and basophils to release histamine
Role of C5a
Chemotaxis
What may macrophages be activated by?
- Endotoxin, IFN-gamma, IL-4, IL-3
- Proinflammatory cytokines (TNF-a, IL-1, IL-6)
- Other cytokines (IL-10, IL-12)
Give an example of non-oxygen dependent tkilling mechanisms employed by neutrophils
Antimicrobial peptides, e.g. LL-37 found in lysosomes
Destroys the lipoprotein membranes of microbes enveloped in phagosome after fusion with lysosomes in macrophages
Describe chronic granulomatous disease
Occurs where cells of the immune system (neutrophils and macrophages) cant form reactive oxygen compounds (most importantly, the superoxide radical due to defective NADPH oxidase)
No respiratory burst
This leads to the formation of granulomas in certain organs
Which components of complement are opsonins?
C3b and C4b
How may the complement cascade interact with the coagulation cascade?
FXa and FXIa also cleave C3 and C5 into C3a and C5a
How does complement interact with the kinin cascade?
They have a common contrl mechanism
the inactivator of C5a and C3a anaphylotoxins is identical to a major plasma bradykinin inactivator
