To start, the inflammatory response is our body?s way to fight
bacterial infection. The immune response is the body?s defense against
viruses. Our body's defense system discerns the type of enemy trying
to invade, and launches the appropriate response, be it inflammatory
or an immune response.
This site has a simple, yet explanatory animation on the inflammatory
response. It?s a good basic way to understand the response. Notice the
white cells, and neutrophils fighting bacteria.
Overall effects of the inflammatory response:
?Blood vessels in the infected area dilate, and as a result blood flow
to the area increases. This makes skin in the area look red and feel
Capillaries in the area become more permeable allowing fluid to seep
into the surrounding tissue. As this occurs oedematous swelling around
the infected site occurs.
The swelling and the effects of some of the chemicals released results in pain.
Hence clinical characteristics of the inflammatory response are known
as redness, heat, oedema and pain.
The inflammatory response (inflammation) occurs when tissues are
injured by bacteria, trauma, toxins, heat, or any other cause.
Chemicals including histamine, bradykinin, serotonin, and others are
released by damaged tissue. These chemicals cause blood vessels to
leak fluid into the tissues, resulting in swelling. This helps isolate
the foreign substance from further contact with body tissues.
The chemicals also attract white blood cells that "eat" microorganisms
and dead or damaged cells. The process where these white blood cells
surround, engulf, and destroy foreign substances is called
phagocytosis, and the cells are collectively referred to as
phagocytes. Phagocytes eventually die. Pus is formed from a collection
of dead tissue, dead bacteria, and live and dead phagocytes.?
Phagocytes are white blood cells, neutrophils usually, to be precise
that destroy organisms. (Phage is of Greek origin, meaning to eat).
?The functions of the inflammatory response include:
1) The delivery of effector molecules and cells to the sites of infection.
2) The formation of a physical barrier to the spread of the
tissue damage or infection.
3) Wound healing and tissue repair.
?Phagocytic cells are the first major type of leucocytes to emigrate
[first neutrophils, followed by macrophages]
Neutrophils are short-lived cells which die within the tissues.
Macrophages are much longer-lived.
Later, lymphocytes (B and /or T) may also enter the site.? This is
when they produce antibodies.
A viral attack is much more complicated to describe. These
illustrations help depict what happens:
?Viruses invade living cells
Although viruses can exist outside a host cell, they can't reproduce.
Once inside a host cell, a virus either lays dormant for some time
(lysogenic infection) or else starts reproducing immediately (lytic
infection). The latter is more common. The tough outer coating of a
lytic virus dissolves when inside the host cell. The virus then
replicates its genetic material until the host cell is so full that it
bursts. The released viruses then invade other host cells.
The body's response to viral infection
Viruses pose a considerable challenge to the body's immune system
because they hide inside cells. This makes it difficult for antibodies
to reach them. However, special immune system cells, called
T-lymphocytes, can recognise and kill cells containing viruses, since
the surface of infected cells is changed when the virus begins to
multiply. Many viruses, when released from infected cells, will be
effectively knocked out by antibodies, produced in response to
infection or previous immunisation.
Antibiotics kill bacteria by interfering with their metabolic
processes, but viruses are so simple they use their host cells to
perform their activities for them. This is why antibiotics are useless
against viral infections. Antiviral drugs work by interfering with the
viral enzymes. Antiviral drugs are currently only effective against a
few viral diseases, such as influenza, herpes, hepatitis B and C and
HIV, but research is ongoing. A naturally occurring protein, called
interferon (which the body produces to help fight viral infections),
can now be produced in the laboratory and is used to treat hepatitis C
Immunization against viral infection is not always possible:
It is possible to vaccinate against many serious viral infections such
as measles, mumps, hepatitis A and hepatitis B. An aggressive
worldwide vaccination campaign, headed by the World Health
Organization (WHO), managed to wipe out smallpox. However, some
viruses - such as those that cause the common cold - are capable of
mutating from one person to the next. This is how an infection with
essentially the same virus can keep dodging the immune system.
Similarly, vaccination for these kinds of viruses is difficult,
because the viruses have already changed their format by the time
vaccines are developed.?
There are 2 immune response, humoral and cell mediated.
?humoral - defends the body against invading antigens through
secretion of special proteins called antibodies
involves specialized cells attack antigens directly
regulates activity of humoral system (26-4)
3.1. Are produced in the bone marrow (B-lymphocytes) and thymus (T-lymphocytes)
3.2. Circulate between the blood, tissue fluid, and lymph
3.3. B Lymphocytes (B-cells) mediate the humoral immune response
3.3.1. Has thousands of antibody molecules mounted in its cell membrane
composed of heavy and light chains (26-5)
binds to two specific antigen molecules (26-6)
3.3.2. Engulfs bound antigens and digests into smaller fragments
3.3.3. Stimulated B-cell (26-7) produces numerous plasma cells which
are antibody factories which secret antibodies identical to those on
these circulate freely in blood and lymph and attack antigens
3.3.4. Stimulated B-cell also produces memory cells which are
lymphocytes like itself these remain in circulation for months and
"remember" the antigen during future exposure.
3.3.5. Agglutination (clumping) of antibodies bound to antigens (26-8)
easier for large phagocytic macrophages in lymph to recognize bound
NK (natural killer) lymphocytes recognize bound antibodies, bind to
them, and secrete powerful chemicals to destroy them
bound antibodies trigger enzymatic reactions (complement cascade)
the leads to cell lysis
3.4. T-Lymphocytes Control the Cell-Mediated Immune Response
3.4.1. T lymphocytes have T-cell receptors instead of antibodies on
3.4.2. T-cell receptors (26-10)
are not secreted but stick to lymphocyte
recognize and bind to only one antigen molecule
for recognition, antigen must be bound to special marker protein
(major histocompatibility complex, MHC) and presented to the T-cell by
a special antigen-presenting cell.
3.4.3. Two types of MHC proteins
MHC-II - found on membranes of b cells, cytotoxic T cells and macrophages
MHC-I - found on membranes of all other cells of the body
Structure and function of MHC molecules (a) (26-11) (b) (26-12) (c) (26-13)
3.4.4. Summary of cell-mediated immune responce (26-14)
Beta cells (26-15)
T Cells (26-16)
3.4.5. Viral infection (26-17)
antigens of virus attach to MCH-I proteins
T-cells bind to antigen- MCH-I complex
T-cells replicate producing memory T cells, Helper T-cells,
Suppresser T cell, and Cytotoxic T-cells helper T-cells produce
cytokines that activate other cells of the immune system (macrophages
and other B and T cells); they also stimulate antigen bound B-Cells to
divide and produce antibodies.
suppresser T-cells inhibit activity of macrophages and other
lymphocytes; they stop the immune response when no longer needed.
cytotoxic T-cells search out abnormal cells (such as cancer cells or
virus-infected cells) and destroy them
?If innate immune cells (dendritic cells) decide that the material is
dangerous (part of a virus or bacteria), then they stimulate a
specialized group of white blood cells causes CD4+ helper T cells to
become activated. CD4+ refers to a surface protein on this class of T
cells. Helper T cells can stimulate another group of white blood cells
called B cells to produce antibodies that bind that specific antigen
and immobilize it, preventing it from causing infection. Antibodies
are specific for only one antigen. B cells must interact with Helper T
cells, other specialized white blood cells, to initiate antibody
production. An important concept is that once activated, memory cells
are produced that insure that a more rapid and stronger immune
response can be made upon re-exposure to the same pathogen. This is
why vaccinations provide lasting protection against disease. Memory
helper T cells are labeled CD4+ CCR5+, to note that the chemokine
receptor (CCR5) is present on the surface of the helper T cell. These
cells migrate and reside in the mucus membranes of our body.?
?The leukocytes circulate through the body between the organs and
nodes by means of the lymphatic (pronounced: lim-fah-tik) vessels.
(You can think of the lymphatic vessels as a type of highway between
the rest stops that are the lymphoid organs and lymph nodes).
Leukocytes can also circulate through the blood vessels. In this way,
the immune system works in a coordinated manner to monitor the body
for substances that might cause problems.
There are two basic types of leukocytes:
·The phagocytes (pronounced: fah-guh-sytes) are cells that chew up
·The lymphocytes (pronounced: lim-fuh-sytes) are cells that allow the
body to remember and recognize previous invaders.
There are a number of different cells that are considered phagocytes.
The most common type is the neutrophil (pronounced: noo-truh-fil).
Neutrophils primarily fight bacteria. So when doctors are worried
about a bacterial infection, sometimes they order a blood test to see
if a patient has an increased number of neutrophils triggered by the
infection. Other types of phagocytes have their own jobs to make sure
that the body responds appropriately to a specific type of invader.
There are two kinds of lymphocytes: the B lymphocytes and the T
lymphocytes. Lymphocytes start out in the bone marrow and either stay
there and mature into B cells, or they leave for the thymus gland,
where they mature into T cells. B lymphocytes and T lymphocytes have
separate jobs to do: B lymphocytes are like the body's military
intelligence system, seeking out their targets and sending defenses to
lock onto them. T cells are like the soldiers, destroying the invaders
that the intelligence system has identified.? There are a lot of
simplified explanations on this page. Keep reading!
?These white blood cells are very important for fighting infection.
They are good at fighting bacteria and fungal infections. They can
·Move to sites of infection in the body
·Stick to invading bacteria or fungi
·Swallow up the invader
·Kill the bacteria they have swallowed with chemicals
B cells and T cells
The white blood cells involved in the acquired immune response are
called 'lymphocytes'. There are two main types of lymphocytes - B
cells and T cells. B and T lymphocytes are made in the bone marrow,
like the other blood cells. They have to fully mature before they can
help in the immune response. B cells mature in the bone marrow. But
the immature T cells travel through the blood stream to the thymus
gland where they become fully developed.
Once they are fully mature, the B and T cells travel to the spleen and
nodes ready to fight infection.
What do B cells do?
B cells react against invading bacteria or viruses by making proteins
called antibodies. The antibody made is different for each different
bug. The antibody locks onto the surface of the invading bacteria or
virus. The invader is then marked with the antibody so that the body
knows it is dangerous and it can be killed off.
The B cells are part of the memory of the immune system. The next
time the same bug tries to invade, the B cells that make the right
antibody are ready for it. They are able to make their antibody more
quickly than the first time the bug invaded.
?The Normal Immune System Response. The inflammatory process is a
byproduct of the body's immune system, which fights infection and
heals wounds and injuries:
·When an injury or an infection occurs, white blood cells are
mobilized to rid the body of any foreign invaders, such as bacteria or
·The masses of blood cells that gather at the injured or infected site
produce factors to repair wounds, clot the blood, and fight any
·In the process, the surrounding area becomes inflamed and some
healthy tissue is injured.
·Under normal conditions, the immune system has other factors that
control and limit this inflammatory process.?
?Lymphocytes include two subtypes known as T-cells and B-cells. Both
types of cells are designed to recognize foreign substances (antigens)
and to launch an offensive or defensive action against them:
·B-cells produce antibodies, which are designed to attack the
antigens. Antibodies can either ride along with a B-cell or travel on
·T-cells have special receptors attached to their surface that
recognize the specific antigen.
T-cells are further categorized as killer T-cells or helper T-cells (TH cells).
·Killer T-cells directly attack antigens found on bacteria or other cells.
·Helper T-cells also recognize antigens, but their role is two fold.
They stimulate B-cells and other white cells to attack the antigen.
They also produce cytokines, powerful immune factors that have an
important role in the inflammatory process.
Helper T-Cells, Cytokines, and the Inflammatory Response. The actions
of the helper T-cells (TH cells) are of special interest. Researchers
have observed high numbers of TH cells in psoriatic plaques:
·The activated TH cells infiltrate the skin cells in psoriasis and, in
the case of psoriatic arthritis, also the joints. (There has been some
debate over whether psoriatic arthritis is a unique disorder, but
evidence now suggests that both psoriatic arthritis and psoriasis are
caused by the same faulty immune process.)
·TH cells normally stimulate B-cells to produce antibodies. In the
case of psoriasis, however, they appear to direct the B-cells to
produce autoantibodies (self antibodies), which are directed against
the body's own cells. In the case of psoriasis, they target self
antigens in skin cells; in psoriatic arthritis, cells in the joints
also come under attack.
·In the resulting autoimmune process, autoantibodies remain in
circulation and continue to mount an immune attack against these
The Lymphatic System
The three primary functions are:
?To collect and return interstitial fluid, including plasma protein to
the blood, and thus help maintain fluid balance,
To defend the body against disease by producing lymphocytes,
To absorb lipids from the intestine and transport them to the blood.
More information on the immune system
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antigenic viral response
bacteria + inflammatory response
viral response immunity