IIT 3: Neutrophil and Eosinophil Responses, Immune Complex Disease Flashcards
True or false: Some neutrophils are present in most lesions of acute inflammation.
True
Inflammation is dominated by neutrophils.
What are some causes of neutrophil rich inflammation?
Trauma, foreign material, thrombosis, burns, necrosis, immune complexes.
By what process does thrombin attract neutrophils?
Thrombin is a neutrophil chemoattractant.
What does pus imply?
A bacterial infection.
What are the different kinds of pus?
Purulent and suppurative. These are when neutrophils form pus.
What does neutrophilic mean?
Subtle histologic lesion
What is an abscess?
Localized mass with fibrous capsule, pus in the middle.
Formed by a wall of fibrous tissue surrounding a central cavity of liquefying neutrophils. Formed when a pathogen cannot be eliminated.
What is the first leukocyte to enter inflamed tissues?
Neutrophils
Define pus
Creamy white exudate that implies the presence of bacterial infection.
Define neutrophilic inflammation
Inflammatory processes that are dominated by neutrophils.
What is catarrhal/mucopurulent?
A cloudy white exudate formed by mucus mixed with neutrophils on mucosal surfaces like the respiratory tract.
Are neutrophil responses acute or chronic?
They can be both!
Where are neutrophils produced?
Produced in the bone marrow from myeloid precursor, are released into blood. Don’t ever go back to circulation
What is the timing of suppurative inflammation?
- neutrophils enter tissues within 3-6 hours
- pus takes several days to form
- abscess implies fibrosis, >1 week
What is IL-8?
A chemoattractant that causes neutrophils to leave blood and go to the tissue.
What are the possible outcomes of suppurative inflammation?
- resolution: transient stimulus once clear, response resolves after neutrophil apoptosis
- chronic suppurative inflammation if stimulus stays, ongoing recruitment
- containment - abscess formation (can’t eliminate bacteria, wall off so only small area of inflammation)
- stimulation of fibrosis
When does apoptosis of neutrophils occur (timing)?
After about 24-28 hours by macrophages.
Does suppurative inflammation always have pus?
No
Why is the emigration of neutrophils from blood into tissues not random?
The process is highly regulated. Marginated neutrophils undergo adhesion to endothelium and vessel wall (diapedesis), and chemotaxis through tissues before performing their effector function at the site of inflammation.
How do fibrinous exudates arise?
By fibrin and water spilling out of leaky blood vessels.
What three processes does adhesion to endothelium involve?
- margination
- rolling adhesion
- firm adhesion
In normal animals, where are neutrophils contained?
Half of the blood neutrophils are contained in the rapidly flowing blood, and the remaining marginated pool is loosely adherent to the endothelium.
What happens to the marginated pool of neutrophils during inflammation?
It is increased due to stasis of blood as inflamed venules dilate and fluid leaks into tissue.
What is rolling adhesion?
Neutrophils adhere to specific receptors on endothelial surfaces of small venules. Neutrophils transiently adhere to and are released from endothelial cells in a repetitive manner.
-rolling adhesion involves binding of selections on the surface of endothelial cells, specifically P and E selections, to carbohydrates on the neutrophil surface
What happens after rolling adhesion?
Neutrophils can either be released back into the flowing blood, or undergo firm adhesion to the endothelium.
What is firm adhesion of neutrophils mediated by?
Interactions between integrin adhesion molecules (like B-integrin CD18/CD11a) on the neutrophil surface and intracellular adhesion molecules (ICAMs) on the endothelial cells.
What happens to neutrophils that are firmly adherent to the endothelium?
They are poised to slip between endothelial cells and migrate across the wall of the venule towards the site of inflammation.
Define diapedesis
The process of a neutrophil migrating across the vessel wall.
What happens to neutrophils after they have escaped from blood vessels?
They continue their journey through the tissues towards the site of inflammation. They migrate toward the source of the chemical mediators of inflammation.
Define chemotaxis
The process by which neutrophils undergo directed migration along a chemical gradient, crawling toward a higher concentration of chemoattractant.
What are the most important neutrophil chemoattractants secreted by?
The animal in response to infection. This includes IL-8 and other chemokine, C5a (a fragment of protein C5), leukotriene B4, and platelet activating factor.
What do chemoattractants bind to?
Receptors on the surface of the neutrophil which then extend a pseudopod or lamellipod in the direction in the highest concentration of the chemical.
How does bacteria cause inflammatory mediators?
Bacteria is recognized by phagocytes, macrophages, complement, antibody especially if they are opsonized. Phagocytes take up the bacteria and produce inflammatory mediators that stimulate the endothelial cells and leukocytes.
What are the steps in the neutrophil response to inflammation?
Selectin mediated rolling adhesion to endothelium, integrin mediated firm adhesion to endothelium, trans-endothelial migration (diapedesis) and directed migration for chemotaxis toward the inflammatory stimulus (go to tissue). Once it reaches the site of inflammation, the army of neutrophils can confront the invader.
Define neutrophil chemotaxis
Directed migration towards a stimulus.
What are neutrophils drawn towards in chemotaxis?
Toward a higher concentration of the inflammatory mediator (the IM is like a beacon that the NP travels towards).
How exactly are neutrophils drawn towards inflammatory mediators?
By extension of lamellipodia that adhere to tissue matrix (foot like processes).
What are the major roles of neutrophils in acute inflammation?
Phagocytosis (ingestion) and killing of bacteria at the sites of infection.
What enhances the ability of neutrophils to ingest particles and mount an effective killing response?
Opsonization by opsonins.
Define opsonization
The process by which soluble host molecules attach to particles and label them to be more easily recognized and ingested by neutrophils and macrophages.
Essentially, opsonins enhance recognition of bacteria by leukocytes, like an icing on cake that makes cake look better.
What kind of opsonins help with acquired immunity?
IgG (immunoglobulins) bind Fc receptors on the neutrophil surface. They are produced during an immune response to a pathogen.
What kind of opsonins help with both innate and acquired immunity?
Complement fragment C3b, which binds the C3b receptor Mac1 (CD11b/CD18). The complement system may be activated by antigen-antibody complexes or by components of microbes themselves.
What is innate immunity?
When the body hasn’t seen the bacteria before. Collectin proteins in serum and in lung fluids, including mannose binding protein (MBL) and surfactant proteins A and D (SP-A) act as opsonins. Collectins are present without prior exposure to a pathogen.
What happens when neutrophils come in contact with C3b and Fc antibodies?
- neutrophils have receptors for complement and the Fc part of antibody on the cell surface
- when a NP encounters an opsonized bacterium, the opsonin forms a link between the pathogen and these receptors on the np
- the np then extends an arm like pseudopod to enshroud the bacterium and the ingested particle becomes internalized within a phagosome
- soon, this phagosome fuses with the np granules and exposes the ingested bacteria to the toxic contents of the granule
How does mycobacteria inhibit phagocytosis?
Prevent phagosome-lysosome fusion and hide from the immune system in the phagosomes of macrophages.
What are Toll like receptors?
TLRs recognized conserved structures on pathogen surfaces leading to cellular activation such as production of inflammatory mediators. They use patterns to recognize something strange
What are Toll like receptors?
TLRs recognized conserved structures on pathogen surfaces leading to cellular activation such as production of inflammatory mediators. They use patterns to recognize something strange
Are TLRs innate?
Yes they are innate and non adaptive, in contrast to antibody response.
They do have some specificity though.
What is chemotaxis mediated by?
Chemokines, complement fragments, leukotriene B4, or platelet activating factor.
What are the general steps involved in neutrophils killing phagocytosed bacteria?
Generating reactive oxygen species in an oxidative burst, by releasing products from the neutrophil granule into the phagosome, and by releasing NETs and other products into the extracellular space.
What are some examples of antimicrobial proteins in neutrophil granules?
These are directly toxic to bacteria.
- defensins
- cathelicidins
- lysozyme
- lactoferrin
What are summary things that do oxidative killing (free radicles)?
- superoxide anion O2-
- myeloperoxidase (HOCl- production in granules)
- hypochlorite HOCl- (bleach)
What are some examples of proteolytic enzymes?
These degrade bacterial proteins.
- elastase
- collagenase
- cathepsin G
What are the three ways that leukocytes recognize bacterial infections?
- Opsonization (antibody, complement)
- PAMPs (pathogen associated molecular patterns such as toll like receptors)
- Cytokines from other cells
What are the four ways that leukocytes can kill bacteria?
- Oxidative killing
- Proteolytic enzymes
- Bactericidal proteins
- NETs
How can neutrophils kill phagocytosed bacteria by oxidative killing?
- neutrophils undergo oxidative burst within seconds of exposure to a variety of stimuli, including phagocytosis
- burst is energy consuming process that produces superoxide anion, hydroxyl radical and hydrogen peroxide
- primary granules of neutrophils contain myeloperoxidase, which causes H2O2 + Cl- > HOCl-
- HOCl- is hypochlorite or bleach, which kills bacteria and many other pathogens
How do neutrophils kill phagocytosed bacteria by releasing products from the neutrophil granule??
-np granules have lots of antimicrobial peptides and proteins: defensins, cathelicidins, BPI (bactericidal permeability increasing), and others form fatal pores in the membrane of bacteria; lysozyme degrades the peptidoglycan cell wall of many bacteria, and lactoferrin binds iron and prevents its use by pathogens
How do neutrophils kill phagocytosed bacteria with proteolytic enzymes?
-proteolytic enzymes degrade the bacterial structural proteins and also proteolytically activate the other antimicrobial peptides
What are NETs?
Neutrophil extracellular traps
- nets of chromatin and antimicrobial proteins that are released during the process of neutrophil cell death
- the net of chromatin entraps bacteria and the attached antimicrobial peptides kill them, all in the extracellular space
What is the benefit of neutrophils in inflammation?
Containment or elimination of infection
What are some negative effects of neutrophils in inflammation?
- impaired organ function
- Injury to host tissue
- stimulation of fibrosis
When is neutrophil mediated tissue injury most apparent?
Immune mediated neutrophilic inflammation, in which the offending antigen does not by itself cause harm to the animal, but provokes a neutrophil inflammatory response that damages tissues and is responsible for clinical signs.
What is immune mediated polyarthritis?
Otherwise harmless antigens incite an aberrant immune response.
- nps infiltrate the joint tissue and result in clinical signs of lameness and swollen joints
- clinical signs may resolve if the inflammatory response is subdued
In immune mediated disease, is there apparent benefit with the neutrophil response?
No, much apparent harm though. In, bacterial infections ups have a bigger role and there has to be a balance between np killing and np injury to tissues
What are situations where np inflammatory responses become harmful?
- infections in anatomic locations where the presence of nps interferes with function (eg pus in eye interferes with vision, in lung alveoli interfere with gas exchange and ventilation) so the body needs to clear the infection but may lose organ function
- overwhelming infection where nps don’t have hope of cleaning infection (eg pneumonia)
- infections with pathogens resistant to attack by nps
What are 4 ways that antibody protects against bacterial infection?
- binds to bacteria and activates complement mediated lysis
- opsonized the bacteria to promote killing by neutrophils and macrophages
- binds bacterial cell adhesion proteins to block colonization of surfaces
- binds and neutralizes bacterial toxins
How can neutrophils injure tissues?
- physical presence of nps in vital anatomic sites like the anterior chamber of eye, alveoli, or brain that can interfere with tissue function
- np granules can degrade tissue (np sometimes release granules to exterior when phagocytosing bacteria that have proteolytic enzymes like elastase and collagenase
- activated nps release oxygen radicals, including hydrogen peroxide, superoxide anion and hypochlorite acid, that cause oxidative injury
- np activation promotes thrombosis from tissue factor which activates the extrinsic pathway of coagulation (secretion by nps of proinflammtory cytokines favour procoagulant state)
In summary how can neutrophils injure tissues?
- large numbers of neutrophils take up functional space
- np secretions can degrade tissue matrix
- nps secrete oxygen radicals that cause oxidative injury to cells
- secretions promote coagulation
- tissues are normally protected against injury from activated nps but defences may be imparired or overwhelmed by severe inflammatory response
Are neutrophil responses often beneficial?
Yes, when the nps have removed the offending agent, the stimulus for inflammation is no longer present, and the inflammatory response subsides.
What may remain after inflammation if the battle was intense?
If there was abundant fibrin exudation or neutrophil mediated tissue injury, a fibrous scar may remain
Where are neutrophils born?
Bone marrow
Where are neutrophils when there is no inflammation?
blood
How may lesions change over time?
Persistent bacterial infections often result in chronic suppurative inflammation, with development of fibrosis as the lesion ages. Ongoing physical trauma may go from acute np response to chronic inflammation with lymphocytes, plasma cells and macrophages, and lead to fibrosis of the affected tissue.
What are the outcomes of suppurative inflammation?
Resolution, abscess formation, chronic ongoing suppurative inflammation, and scarring.
What are type III hypersensitivity reactions?
Complexes of antigen and antibody. They are formed in the circulation, deposit in the walls of blood vessels and incite an inflammatory reaction.
What are circumstances that allow excessive or ongoing formation of immune complexes?
- persistent infections (so immune complexes continue to be formed)
- drug reaction that trigger an immune response
- administration of foreign proteins
- neoplasia (immune responses against abnormal antigens expressed by neoplastic cells)
- abnormal regulation of immune response with loss of tolerance that allows autoimmunity
In scalding injury (boiling water), which are likely reasons for delayed healing?
- lack of reparative cells capable of proliferation (large wound, long Time for epithelium to migrate)
- disruption of connective tissue framework (affects underlying dermal tissue)
- lack of blood supply (infarction from vascular injury)
How does fibrosis of sinusoids affect liver function?
Hepatocytes can’t absorb material from blood, fibrosis would make tougher.
What is an important way that neutrophils damage host tissues?
elastase
-have proteolytic enzymes/protease in granules, one is elastase
What is important for opsonization?
Antibody - allow macrophages to take up
