Inflammation & Healing

Question 1

What are the clinical aspects of inflammation?

Answer 1

• Local signs & symptoms
• Potential systemic signs & symptoms (tachycardia, malaise, anorexia, fever, rigors, chills, weight loss, anaemia if chronic)
• Relevant investigations include a full blood examination, C-reactive protein assessment and erythrocyte sedimentation rate (ESR)
• Relevant Medications include NSAIDS, Panadol, Anti-histamines, Leukotriene antagonists, corticosteroids, TNF and IL-1 inhibitors etc.

Question 2

How does the body protect itself from injury?

Answer 2

The body itself has many mechanisms that aim to protect it from injury such as neural reflexes, fear responses, and immune protection against infections.
- This can include competition amongst commensal organisms, intact epithelial surfaces, secretions onto epithelia surfaces (IgA, lysozyme, acid), mucociliary action in respiratory tract, phagocytic and immune cells/proteins at potential sites of entry (Neutrophils, macrophages, NKs, complement)

Question 3

How do traditional methods of injury protection (competative commensals, epithelia, secretion etc.) differ from inflammation?

Answer 3

Inflammation is the manner in which the body protects itself against injury after it has happened. It is the protective response of living vascularised tissue to that injury. It aims to eliminate the cause and consequence of the injury and is closely associated with repair and healing.
- Healing and repair is variable depending on extent of injury and harm caused to the body by inflammation.

Question 4

List some differences between acute and chronic inflammation?

Answer 4

ACUTE
Earliest response; rapid onset
Short duration; several days but sometimes longer
Features: neutrophils, fluid and protein exudate, vasodilation, macrophages
Non-specific

CHRONIC
Later response
Lasts for weeks/months/years
Features: macrophages, lymphocytes, plasma cells and associate with fibrosis/scarring
Immune responses develop

Both May occur together

Question 5

What are the aims and causes of Acute Inflammation?

Answer 5

Acute inflammation aims to mediate local defenses, destroy any infective agents and remove debris from the site of injury.
Causes include: Certain infections, trauma, foreign material, burns and infarction.

Question 6

What are the components involved in Acute Inflammation?

Answer 6

The components involved are a vascular response, exudate of cells, fluid and proteins as well as variable levels of necrosis.

Question 7

Explain the mechanism of Acute Inflammation?

Answer 7

Infective organisms, foreign material, molecules released from dead cells etc all trigger the release of preformed mediators from mast cells & platelets, as well as exhibiting PAMPs that are recognised by PRRs on tissue macrophages, dendritic cells and epithelial cells which leads to the activation of transcription factors and the production of cytokines and other molecules to initiate the inflammatory response.

Question 8

During Acute Inflammation, what are the vascular responses?

Answer 8

Acute Inflammation causes a vascular response for the delivery of cells, chemical mediators and proteins to the site of injury. This response includes:

- transient arteriolar constriction
- arteriolar, then capillary and venular dilation
- increased vascular permeability
- vasocongestion
- there may also be vascular injury
- endothelial activation also occurs

Question 9

What are the cardinal features of Acute Inflammation?

Answer 9

• Redness/Erythema
• Swelling/Oedema : an abnormal increase in interstitial fluid which may be due to impaired lymphatic drainage, increased permeability (exudate) or increased hydrostatic pressure (transudate)
• Heat
• Pain
• Loss of function

Question 10

What are some key features of endothelium?

Answer 10

Under normal circumstances the endothelium is a semi permeable barrier (cells linked by junctional complexes) that synthesizes the underlying basement membrane. It is replenished by progenitor cells and has a specialised morphology in certain areas.

The endothelium prevents blood clotting by producing nitric oxide and prostacyclin.
It plays a role in the control of vascular tone (through nitric oxide, prostacyclin and endothelin)

It is resistant to leukocyte adhesion normally and is able to produce GFs and cytokines.

Question 11

What is the significance of increasing vascular permeability during inflammation?

Answer 11

When vascular permeability is increased during periods of acute inflammation, the endothelial cells become more permeable to immune cells, cause the vessels to dilate and begin to exhibit adhesion molecules so that leukocytes can be taken out of circulation more easily.

Question 12

What is exudate?

Answer 12

Exudate occurs due to increased vascular permeability

There are different types of acute inflammatory exudate with varying proportions of neutrophils, fluid and fibrin depending on the site and cause. 
There are three main types:
	- purulent/suppurative (abscess)
	- fibrinous
	- serous

Question 13

Explain the key features of Neutrophils?

Answer 13

Neutrophils are the most numerous white cell in the blood with a short life (hours-days) and is not normally found in tissue.

In acute inflammation they are recruited into the tissues from the blood. Stored neutrophils are released from the bone marrow and increased numbers are also produced (neutrophila).

In the first 6-72 hours, they are the predominant cell present and they take on the role of phagocytosing/killing bacteria and debridement (release enzymes that breakdown damaged tissues).

Question 14

Explain the key features of Macrophages?

Answer 14

Macrophages are derived from blood monocytes, are long-lived and reside in various tissues or enter tissues during the inflammatory response.

They are phagocytic and engulf microbes, foreign material, tissue debris etc. and are also antigen presenting playing a role in cellular and humoral immunity.

They secrete mediators including chemokines, proteases for tissue destruction, toxic oxygen metabolites for killing bacteria, cytokines and GFs (TGF-beta, PDGF, FGF) which stimulate repair, IL-1 & TNF for endothelial activation and IL6 for acute phage response.

Question 15

What are the mediators of acute inflammation?

Answer 15

Vasodilation: histamine, prostaglandins (derived from cell membranes), nitric oxide etc.
Increased vascular permeability: histamine, serotonin (from platelets), bradykinin (from activated liver cells), leukotrienes etc.
Endothelial activation: TNF, IL1
Chemotaxis: complement components, bacterial components, certain cytokines(chemokines), leukotriene B4
Tissue damage: neutrophil granule contents, ROS (neutrophils and macrophages produce reactive oxygen species), nitric oxide (made by endothelial cells)
Pain: prostaglandins, bradykinin
Fever: IL1, IL6, TNF, prostaglandins

Question 16

What is the Arachadonic Acid cascade?

Answer 16

Arachadonic acid is an element that is derived from membrane phopholipids. This acid can the be treated with Cyclooxygenase to produce prostaglandins and thromboxane or it can be treated with 5-lipoxygenase to produce leukotrienes.

Both LTs and PGIs are inherently associated with the inflammatory response.

Question 17

What are the outcomes of acute inflammation?

Answer 17

The cause needs to be eradicated and the exudate needs to be dealt with and the damaged cells need to be replaced (either with cells of the same type or with scar tissue) or else inflammation will continue.

The outcome of acute inflammation depends upon:

• Tissue type: different cells have differing abilities to regenerate/replicate (labile [continuously cycling such as epithelial cells or lining the GIT]/stable or facultative dividers[are not normally dividing including hepatocytes and they can be stimulated to go back into the cell cycle and replicate if damage occurs]/permanent [ cannot replicate such as neurons of CNS and myocardial cells]). Cells generally regenerate from stem cells.
• Extent of the damage
• Type/Duration of the injury

Question 18

What is the fate of the exudate after inflammation?

Answer 18

Exudate fluid is drained away from the site into the lymph as well as some of the dead/damaged cells. The lymph, with antigens and damaged cell & exudate travel to the lymph node which may cause an adaptive response and trigger enlargement of the lymph node.

Question 19

What are stem cells?

What are some different types?

Answer 19

self renew and generate different cell lineages and there are various types.
(Embryonic - pluripotent ; Adult/somatic - generate a more limited range of cell lineages)

Question 20

How is Cell proliferation involved with healing?

Answer 20

Healing involves the migration and proliferation of epithelium in epithelial tissues, fibroblasts and myofibroblasts and endothelial cells which form scar tissue.

Question 21

Explain the formation of granulation tissue.

Answer 21

Granulation tissue is an Intermediate tissue in the formation of scar tissue and occurs during healing. It has many components which include:

Inflammatory cells:

• macrophages (phagocytic, kill debris/necrotic tissue and secrete GFs, cytokine and mediators to drive the healing process)
• lymphocytes (produce cytokines to drive the response)

New Blood Vessels:

• degradation of basement membrane by matrix metalloproteinases (MMP) and loss of cell to cell contact between endothelial cells
• migration and proliferation of endothelial cells toward angiogenic stimulus
• maturation of cells, recruitment of pericytes and smooth muscle cells
• new vessels are leaky
• VEGF secreted by various mesenchymal cells important

Fibroblasts:
- fibroblast migration and proliferation involves various growth factors and cytokines (PDGF, TGF-beta, FGF)

ECM:
- deposited towards the end of healing

Granulation tissue is initially very cellular and vascular, later they become fibrous and eventually mature scar forms. Fibrin is seen in acute inflammation but not in granulation tissue. Because scar tissue is not overly vascular, it appears pale macroscopically.

Question 22

How does healing occur?

Answer 22

Normal healing can occur by primary intention ( healing of narrow, closely opposed wounds - which is why suturing is used) or by secondary intention (larger wounds which required granulation tissue to fill in the gaps and results in large scars)

Question 23

Explain how Growth factors are used in healing?

Answer 23

-Released by various cell types (macrophages, mesenchymal cells, endothelial cells, platelets)
(Epidermal GF, vascular endothelial GF (thought to be important in tumours and diabetic eye disease), Fibroblast GF, Platelet derived GF, transforming GF-beta.)
- Function as ligands that bind to receptors on specific cells
- Mostly these receptors are the type with intrinsic tyrosine kinase activity
- Binding of GF activates signal transduction pathways that activate transcription of transcription factors that control entry to the cell cycle and progression (c-MYC, c-JUN, p53)
- Lead to proliferation of epithelium, endothelium, fibroblasts etc.

Question 24

What are some mechanisms of extracellular signalling?

Answer 24

• Juxtacrine - between gap junctions/between cells and ECM
• Autocrine - signal that is released by a cell and acts on itself/same cell type (IL2 made by lymphocytes and activates lymphocytes)
• Paracrine - cell that acts on nearby cells of a different type (such as growth factors made by macrophages that activates fibroblasts to proliferate)
• Endocrine - hormones go into the blood and effect target cells that may be far away from the producing cell.

Question 25

Some of the factors that influence healing are…?

Answer 25

Local:

• foreign material
• infection
• blood flow
• extensive necrosis
• radiation exposure
• movement
• size, location and type of wound

Systemic:

• nutrition
• immune impairment (AIDS, diabetes, corticosteriods)

Question 26

Some adverse outcomes of a lack of healing include:

Answer 26

Keloid: non preventable; common with genetic predisposition, excessive scarring (TGF beta is important in the development)

Dehiscience: protrusion of internal structure through the wounds

Contracture: scar tissue forms and contracts impairing movement; burns.

Non-healing ulcer: associated with diabetes and may need amputation

Question 27

How does Chronic Inflammation arise?

Answer 27

Chronic inflammation arises in several ways. It may follow acute inflammation or it may have an insidious onset following certain infections, autoimmune diseases (such as diabetes type I) or repeat/prolonged exposure to potentially toxic (asbestos exposure) and sometimes unknown agents (such as inflammatory bowel disease which the antigen is unknown for).

Ongoing inflammation and tissue damage proceed at the same time as attempts at healing and will persist until the damaging stimulus is eradicated. If this is done, then repair/healing may occur however in many diseases, tissue is destroyed and scarred thus impairing function.

Question 28

What are some disease processes that are associated with chronic inflammation?

Answer 28

• atherosclerosis
  
  • asthma (although it is an allergic condition, there are chronic inflammatory components that are often present between the exacerbations)
  • tuberculosis
  • fibrosing lung disease
  • chronic hepatitis and cirrhosis
  • inflammatory bowel disease
  • coeliac disease
  • peptic ulceration
  • rheumatoid arthritis
  • rheumatic heart disease
  • and more…

Question 29

How are macrophages involved with Chronic Inflammation?

Answer 29

Macrophages are long lived cells that are derived from blood monocytes, residing in various tissues/entering tissues during an inflammatory response. They are phagocytic and also antigen presenting giving them roles in both innate and adaptive immunity. They also secret mediators including: chemokines, proteases, killing secretions etc.

Macrophages are though to have more inclination toward playing a role in defense (phagocytosing) or expression/secretion of chemical mediators. After phagocytosis, the macrophage can take on different histological appearances. (After lipid ingestion, they can appear foamy; carbon from the lung can make macrophages black in colour and cluster them.)

Question 30

How are lymphocytes associated with Chronic Inflammation?

Answer 30

Lymphocytes are found normally in lymphoid tissues and so they are no inherently seen only in chronic inflammation (where they need to be in excessive numbers or in tissues that are not often associated with lymphoid activity).
There are many different subtypes of lymphocytes that are dependant upon the function of that lymphocytes.
Histologically, they are dark and densely nucleated.

Question 31

How are plasma cells associated with Chronic Inflammation?

Answer 31

They are seen normally in immune response in mucosa, associated lymphoid tissue and lymph nodes but during chronic inflammation.
Nucleus is similar in size to the lymphocyte nucleus but it is situated down one end. There is a pale region near the nucleus where the golgi apparatus called the paranuclear hof. They often have clockface chromatin which shows a distribution of chromatin around the edges of the nuclear. The cytoplasm contains a lot of RNA and as such they appear purple.

Question 32

How are germinal centres associated with Chronic Inflammation?

Answer 32

During the inflammatory response of some pathologies, there can be humoral mediated immune responses where they are not usually expected and thus germinal centres form in those locations. (Rheumatoid arthritis where germinal centres can be seen in joint capsules)

Rheumatoid arthritis is associated with pain, loss of function etc. NSAIDs, anti-TNFs, corticosteriods are all used in an attempt to medicate/treat and downregulate the immune response.

In liver Cirrhosis, the causation can be diabetic related, alcoholism, viral hepatitis etc. It generally take more than 20 years to develop through a chronic inflammatory process. Usually it does not present until there is a very serious outcome such as liver failure.

Question 33

What is granulomatous inflammation?

Answer 33

This is important pathologically and clinically. There are two types: immune and foreign body. It develops in response to certain persistent or non-degradable antigens. It is characterised by epithelioid macrophages and frequently multinucleate giant cells with or without necrosis.

Diseases in which granulomatous inflammation occurs include:

• Certain infections - generally intracellular and non-viral (tuberculosis, leprosy, syphilis, fungal, parasitic)
• Unknown Cause (sarrcoidosis, Crohn’s disease)
• Lymphomas
• Deposition of exogenous or endogenous irritant materials (suture, urate (gout) crystals, keratin)

There is also immune mediated granulomatous inflammation, in that it is a cell mediated response (delayed type hypersensitivity). Macrophages present antigen to CD4 T cells which release IFN-gamma which activated macrophages and IL2 which activates T cells as part of the Th1 response.

Diagnosis of granulomatous inflammation is done histologically and so biopsies are quite often taken. They key indicators are epithelioid macrophages and multinucleate giant cells as well as lymphocytes. They may also be fibroblasts and necrosis (due to phagocytosing macrophages that can release enzyme, and oxygen derived free radicals that can cause necrosis) When there is a well circumscribed collection of these cells it is called a granuloma.

Question 34

What are the systemic effects of IL1, TNF and IL6?

Answer 34

-Fever, rigors, chills: exogenous and endogenous pyrogens leading to prostaglandin synthesis in the hypothalamus leading to resetting of the thermostat.
- Malaise, anorexia
- Leukocytosis: neutrophilia in acute inflammation
- Increased acute phase proteins synthesised by hepatocytes:
>Including C reactive protein (CRP), fibrinogen, serum amyloid A (SAA) protein, complement factors, hepcidin etc.
>May act as opsonins, antimicrobial functions
>Fibrinogen (and immunoglobulins) bind the RBCs leading to rouleaux formation which in turn causes sediment more rapidly - the basis for Erythrocyte Sedimentation Rate (ESR) test.
>Elevated SAA if prolonged may lead to secondary amyloidosis
>Chronically elevated hepcidin leads to a limited availability of iron and anaemia of chronic disease
- CRP and ESR : Non specific tests for inflammation
- Weight loss
- Very high levels in certain situations which leads to systemic endothelial activation, vasodilation and shock.