Inflammation

1. Lecture 1-6
INFLAMMATION
Definition and causes.
Inflammation is a fundamentally protective response whose ultimate goal
is to rid the organism of both the initial cause of cell injury (microbes or
toxins) and its consequences. Humans could not long survive injury without
the protective responses of inflammation.
Inflammation is typical pathological process, cause it owns the different
diseases (for example, gastritis, meningitis, nephritis, pneumonia, angina and
others). It is the most numerous pathological process, which has perfected in
evolution as protective response. Different side of this process – own
pathological and defense with various compensatory mechanisms are
presented. Although inflammation and repair are basically defense
mechanisms, they are potentially harmful. Indeed, an over-active inflammatory
response (hypersensitivity) to a bee sting can cause death.
Inflammation has local and common breaches of biochemical,
morphological, structural characters with functional and vascular changes.
This components accounts for the classical sings of acute inflammation,
written by Celsus:
1. heat (calor) 2. redness (rubor) 3. swelling (tumor) 4. pain (dolor)
A fifth clinical sign, loss of function (function laesa), later added by Virchov.
Common clinical manifestation:
1. fever 2. headache 3. neutrophilia 4. sleepless 5. decreased of appetite
6. haemodynamic effects (chock).

3. Causes. Microbes and its toxin, parasites, viruses. Environmental factors –
ultraviolet rays of sunlight, X-rays, nuclear fission, radionuclides, Roentgen
rays.
Injury by chemical agents – mechanical trauma, thermal injury (thermal
burns), electrical injury, by ionizing radiation. Chemical agents – alcohol and
other drug abuse, medicine.
Tissue-destructive enzymes, activation of the B-cell system, as result
production of antibodies, some of which are directed against self-
constitutions.
Inflammation has three major components, which is caused various
exogenous and endogenous stimuli. It is complex reaction with structural and
vascular changes and increased function of connective tissue:
I. Alteration
II. Vascular changes with emigration of the leucocytes and exudation
III. Proliferation

4. I. Alteration
There is primary and secondary alteration. When flogogen (injuring
factor) act on the tissue – the first massive tissue destruction develop.
Following cell death, cell organelles are progressively degraded and there
is leakage of cellular enzymes. Consequences of these disorders are
increased metabolic processes (“the fire of metabolism”), focal hypoxia
and its result acidosis (normal pH equils 7,34 –7,36; under acute
inflammation 5,6 – 6,0; under chronic inflammation – 6,0 – 7,5).
It’s induce lasting tissue damage (secondary alteration) and may also
prolong inflammation because leakage enzymes, chemical mediators and
toxic carbooxygen more breaches metabolism. In the tissue osmotic and
oncotic pressure increased, because developing acidosis stimulate those
processes. Than next phase of inflammation develops.
2.VASCULAR CHANGES. (changes in microcirculation)
The vascular phenomena and changes in microcirculation (it involves
arterioles, precapillares, capillares, venules) breaches local blood
circulation. It's very important phase, because increased blood flow to the
injured area and opening of capillary beds forms exudate and its stimuli to
phagocytosis and repair. Changes in vascular flow and caliber begin very
early after injury and develop at varying rates, depending on the severity of
the injury.

5. The changes occur in the following order:
1) Vasoconstriction of arterioles, lasting a few seconds (it occurs very
rapidly).
Mechanism connected with binding to receptors of sympathetic nervous
system and released adrenalin (noradrenalin), which at once degraded.
2) Arteriole hyperemia (arteriole dilatation) - the longest phase, because it
account for sustained not only nervous but humeral stimuli.
This first involves the arterioles and men results in opening of new
microvascular beds in the area. Thus comes about increased blood flow and the
cause of the heat (calor) and the redness (rubor). This is by fat the most common
mechanism of vascular leakage and is elicited by histamine, bradykinin, H+-ions,
and virtually all other chemical mediators.
3) Venular hyperemia - venular dilatation is characterized by following:
1. Slowing of blood circulation; 2. High hydrostatic pressure; 3. Increased
permeability by mediators of inflammation; 4. The out flow of protein-rich fluid
into the extravascular tissue (its called local sign-swelling); 5. Increased viscosity
of blood; 6. Concentration of red cells in small vessels; 7. Platelet adhesion as
result endothelial cell detachment; 8. Thrombosis (dilated small vessels packed
with red cells; 9. Prestasis; 10. Stasis - it is the last phase.
4) Of the vascular changes. As venous hyperemia develops one begins to see
peripheral orientation of leukocytes, principally neutrophils, along the vascular
endothelium, a process called leukocytic margination.
Leukocytes stick to the endothelium at first transiently then more avidly, and
soon afterward they migrate trough the vascular wall into the interstitial tissue
(process called emigration).
The leukocytes to leave the circulation, chemical mediators may be activated
in consecutive phases of the inflammatory response and account for sustained
and prolonged responses.

7. Cellular events: leukocyte exudation and phagocytosis.
A critical function of inflammation is the delivery of leukocytes to the site of
injury. Leukocytes kill bacteria and other microbes and degrade necrotic tissue
and foreign antigens. Unfortunately, leukocytes may also prolong inflammation
and induce tissue damage by releasing enzymes, chemical mediators and toxic
oxygen radicals.
The sequence of events in the leukocyte journey can be divided.
1. Margination. Rolling and adhesion. 2. Emigration toward a chemotactic
stimulus. 3. Phagocytosis and intracellular degradation. 4. Leukocyte activation
with extracellular release of leukocyte products.
Margination, rolling and adhesion.
In normally flowing blood erythrocytes and leukocytes are confident to a
central axial column, leaving a cell-poor layer of plasma in contact with
endothelium. As blood flow slows early in inflammation (as a result of the
increased vascular permeability) white cells fall out of the central column, tumble
slowly and roll along the endothelium of venules and finally rest at some point
where there adhere. The initial process is called margination and in time the
endothelium appears to be virtually lined by white cells, a phenomenon called
pavementing. When the leukocytes adhere, they resemble pebbles or marbles
over which a stream runs without disturbing them. This process of leukocyte-
endothelial adhesion is a necessary prelude to all the subsequent leukocytic
events. Chemical mediators such as interleukin stimulate leukocyte adhesion and
expression on endothelial cells "an endothelium - dependent effect".

9. Emigration and chemotaxis.
Following adhesion leukocytes move along the endothelial surface,
insert pseudopods into the junction between the endothelial cells squeeze
through interendothelial junctions, and assume a position between the
endothelial cell and the basement membrane. Eventually they traverse the
basement membrane and escape into the extravascular space.
Neutrophils, monocytes, lymphocytes, eosinophils and basophils all use
the same pathway.
In most types of acute inflammation, neutrophils emigrate first and
monocytes later. In the first 24 to 48 hours most acute inflammatory
infiltrates are predominantly neutrophilic. By 48 hours, however, monocytes
take over, owing to three factors:
1. Short-liver neutrophils disintegrate and disappear after 24 to 48 hours,
whereas monocytes survive longer.
2. Monocyte emigration is sustained long after neutrophil emigration.
3. Chemotactic factors for neutrofils and monocytes are activated at
different phases of the response.

10. Both exogenous and endogenous substances can act as chemotactic
agents for leukocytes, among them (1) soluble bacterial products; (2)
components of complement system; (3) arachidonic acid (AA) and its product
leukotriene (result disorders metabolism).
But how does the headless leukocyte "see" or "smell" the chemotactic
agents and how do these diverse substances actually induce directed cell
movement? Although not all the answers are known, several important steps
and second messengers are recognized.
Binding of chemotactic agents to specific receptors on the cell membranes
of leukocytes results in activation of phospholipase C (mediated by a unique G
protein) and me release of calcium (intra- and extracellular). It is the increased
cytosolic calcium that triggers the assembly of contractile elements
responsible for cell movement. It also activates phospholipase A2, which as we
shall see converts membrane phospholipids to arachidonic acid. In addition,
DAY and through its activation of protein kinase C, is involved in various
phases of leukocyte activation, degranulation, and secretion, which occur
when these is a very strong chemotactic stimulus or during phagocytosis.

11. The activation and functions of the complement system. Activation of
complement by different pathways leads to cleavage of C3. The functions of
the complement system are mediated by breakdown products of C3 and other
complement proteins, and by the membrane attack complex (MAC).

12. Interrelationships among the four plasma mediator systems triggered by
activation of factor XII (Hageman factor).

13. Sequence of leucocyte events in inflammatin, shown here for neutrophils. The
leukocyte first roll, then become activated and adhere to endothelium, then
transmigrate across the endothelium, pierce the basement membrane, and
migrate toward chemoatractants amanating from the source of injure. Note the
roles of selectins in rolling; chemoattractants in activating the neutrophils to
increase avidity of integrins (in green); ICAM-1 and VCAM-1 in firm adhesion and
PECAM-1 in transmigration.

15. PHAGOCYTOSIS AND DEGRANULATION.
Phagocytosis consists of recognition and attachment of the particle to be
ingested by the leukocyte.
Opsonins, which bind to specific receptors the leukocytes, and other fragment
of complement generated by immune or nonimmune mechanisms.
Pseudopods flow around the object to be engulfed, eventually forming a
phagocytic vacuole. The vacuole then fuses with the limiting membrane of a
lysosomal granule, resulting in discharge of the granule's contents into the
phagolysome and degranulation of the leukocyte.
The ultimate step in phagocytosis of bacteria is killing and degranulation.
Bacterial killing is accomplished largely by reactive oxygen species.
Microbes can also be killed by non oxygendependent substances in the
leukocyte granules, including bacterial permeability - increasing (BPI) protein,
lysozyme, lactoferrin, and a group of newly discovered arginine-rich cationic
peptides called defensins.
The pH of the phagolysosome drops to between 4 and 5 after phagocytosis,
allowing acid hydrolases to degrade me dead microorganisms.
Phagocytosis of the offending agent follows, which may lead to the death of
the microorganism. During chemotaxis and phagocytosis activated leukocytes
may released toxic metabolites and proteases extracellularly, potentially causing
endothelial and tissue damage.
Phagocytosis and degranulation.
Phagocytosis consists of: I. Recognition II. Attachment III. Absorbtion
Attachment
Discharge of the granule’s – degranulation. Bacterial killing is accomplished by
reactive oxygen species. Microbes can also be killed by non – oxygen dependent
substances. The pH of the phagolysosome drops to between 4 and 5 after
phagocytosis, allowing acid hydrolases to degrate the dead microorganism.

16. Summary of the acute inflammatory response.
The vascular phenomena are characterized by increased blood flow
to the injured area, resulting mainly from arteriolar dilatation end opening
of capillary beds. Increased vascular permeability results in the collection
of protein-rich extravascular fluid, which forms the exudate. Plasma
proteins leave the vessels, either through widened interendothelial cell
junction of the venules or by direct endothelial cell injury. The leukocytes,
predominantly neutrophils, first adhere to the endothelium via adhesion
molecules, then leave the microvasculature and migrate to the site of
injury under the influence of chemotactic agent.

19. Inflammation may be:
Serous inflammation is marked by the outpouring of thin fluid that,
depending on the site of injury, is derived from either the blood serum or the
secretions of mesothelial cells lining the peritoneal, pleural, and pericardial
cavities.
Fibrinosis inflammation - it's resulting greater vascular permeability,
larger molecules pass the vascular barrier. A fibrinous exudate is
characteristic of inflammation in body cavities, such as the pericardium and
pleura. Fibrinous exudates may be removed by fibrinolysis, and other debris
by macrophages. This process called resolution, may restore normal tissue
structure, but when the fibrin is not removed it may stimulate the ingrowth of
fibroblasts and blood vessels and thus lead to scarring. Conversion of the
fibrinous exudate to scar tissue (organization) within the pericardial sac will
lead either to opaque fibrous thickening of the pericardium and epicardium in
the area of exudation or, more often, to the development of fibrous strands that
bridge the pericardial space. It is evident, then, that fibrinous exudation may
have more serious consequences than serous exudation.
Purulent inflammation (suppurative) this form of inflammation is
characterized by the production of large amounts of pus or purulent exudate.
A common example of an acute suppurative inflammation is acute
appendicitis, abscesses. Abscess has a central region that appears as a mass
of necrotic white cells and tissue cells. There is usually a zone of preserved
neutrophils about this necrotic focus, and outside this region vascular
dilatation and parenchymal and fibroblastic proliferation occur, indicating the
beginning of repair. In time, the abscess may become walled off by the
connective tissue that limits further spread. Furuncle, carbuncles - purulent
inflammation (called cellulitis) tends to trek rapidly through large areas of
tissue such as an entire arm, the face, or the abdominal wall.

25. 3. Repair - proliferation.
After leukocyte exudation and phagocytosis begins repair - endothelial
cells proliferate and form new blood vessels (granulation tissue). Death is
born life. For the life threading loss of fluid, the endothelial cells
differentiate and form intercellular junction - it's characteristic of healing
inflammation. Death will be born life.
During repair, endothelial cells proliferate and form new blood vessels
(granulation tissue). These capillary sprout remain leaky until the
endothelial cells differentiate and form intercellular junctions, accounting
for the edema characteristic of healing inflammation.
It should be noted that although these four mechanisms are separable
all may play a role m response to one stimulus. For example, in various
stages of a thermal bum, leakage results from chemically mediated
endothelial contraction as well as direct and leukocyte dependent injury -
and from regenerating capillaries when the bums heal. This accounts for
the life threatening loss of fluid in severally burned patients. In addition,
different mechanisms may be actived killing mediated by anti-donor
immunoglobulin plus complement (C). Modification of the endothelium by
the direct effect of lymphokines contributes, as well.

27. The major components of the extracellular matrix (ECM), including collagens,
proteoglycans, and adhesive glycoproteins. Note that although there are some
overlaps in their constituents, basement membrane and interstitial ECM have
different general compositions and architecture. Both epithelial and
mesenchymal cells (e.g., fibroblasts) interact with ECM via integrins. For the
sake of simplification, many ECM components have been left out (e.g., elastin,
fibrillin, hyaluronan , syndecan).

28. Proteoglycans in the ECM
and on cells act as reservoirs
for growth factors. Heparan
sulfate binds basic fibroblast
growth factor (FGF-2)
secreted into the ECM. Any
subsequent injury to the
ECM can release FGF-2,
which stimulates the
recruitment of inflammatory
cells, fibroblast activation,
and new blood vessel
formation. Syndecan is a cell
surface proteoglycan with a
transmembrane core protein
and attached extracellular
glycosaminoglycan side
chains. The
glycosaminoglycan chains
can also bind free FGF-2
from the ECM and mediate
interactions with cell surface
FGF receptors. The
cytoplasmic tail of syndecan
attaches to the intracellular
actin cytoskeleton and helps
maintain the architecture of
epithelial sheets.

29. Mechanisms by which ECM
components (e.g., fibronectin
and laminin) and growth
factors can influence cell
proliferation, motility,
differentiation, and protein
synthesis. Integrins bind ECM
and interact with the
cytoskeleton at focal
adhesion complexes (protein
aggregates that include
vinculin, α-actin, and talin).
This can initiate the
production of intracellular
second messengers or can
directly mediate nuclear
signals. Cell surface
receptors for growth factors
activate signal transduction
pathways that overlap with
those activated by integrins.
Signals received from growth
factors and ECM components
are integrated by the cell to
yield various responses,
including changes in cell
proliferation, locomotion, and
differentiation.

30. Phases of wound healing. Wound contraction occurs only in healing by
second intention.

31. Steps in wound
healing by first
intention (left) and
second intention
(right). In the
latter, note the
large amount of
granulation tissue
and wound
contraction.

33. Macrophage-lymphocyte interactions in chronic inflammation. Activated
lymphocytes and macrophages stimulate each other, and both cell types
release inflammatory mediators that affect other cells. IFN-γ - interferon-γ;
IL-1 - interleukin 1; TNF- tumor necrosis factor.

34. Comparison of the morphologic features of RA and osteoarthritis