Immune System:
Glossary:
1. Intro
2. Nonspecific Defenses Against Infection
3. How Specific Immunity Arises
4. Immune Responses
5.
Immunity In Health and Disease
6. Cross Word Puzzle
1. Intro:
An animal must protect itself from harmful material such as viruses, bacteria, and
other pathogens. All which could be found in the air, food, and the water. The body
must also protect from rampaging, uncontrollable cells, which can develop into
cancer. There are three lines of defense which protect the body, two of these are nonspecific, as in they do not distinguish one pathogen from another. The first
nonspecific defense is external; this makes up the skin and mucous membrane. The
second line of nonspecific defense is internal, it is put in to play by chemical signals
that make phagocytes and proteins attack invaders that pass through the skin.
Inflammation is a sign that the second line of defense has been put into place.
The Immune system is the third line of defense. The Immune system responds at
the same time as the second line of defense but it responds in a specific matter,
depending on the presence of microorganism, dangerous body cells, toxics, and
substances. The three defenses can easily be compared to a fortress: first the castle
walls, then the army, and finally the commander who identifies infiltrators. The
Immune system produces specific defensive proteins called antibodies, some
examples are lymphocytes.
2. Nonspecific Defenses
Against Infection
A microbe must get past the first line of defense which is the skin and the mucous
membrane. The skin not only prevents bacteria and viruses to enter but also have
chemical defenses, this is seen in the secretion of sebaceous and sweat glands
which give the skin a ph of 3-5. Microbial build up is also minimized by saliva,
tears, and mucous. Theses secretions are filled with proteins such as Lysozyme,
which digest the cell walls of many bacteria entering the respiratory tract and the
eyes.
Mucus traps microbes which prevent the spreading of them. In the trachea, cells
sweep out mucus thus preventing the further spreading of the microbes. Microbes
that are present in your stomach due to the swallowing of mucus, water, or food
has to take the wrath of its acidic environment. The acid destroys most of the
pathogens but there is of course a few survivors such as Hepatitis A.
Pathogens that manage to get pass the first line of defense must now face the
second line of defense. The body’s second line of defense which is nonspecific
depends mostly on Phagocytosis, ingesting of organisms by certain white blood
cells. This action is associated greatly with an inflammation, which are they both
work closely together.
The Neutrophils, make up about 60-70% of all white blood cells (Leukocytes).
Cells which are hurt by the invader release a chemical signal which attracts
neutrophils from the blood. Neutrophils enter the area to destroy pathogens. The
process where they move to the area is called chemotaxis. Due to their tendency
to self-destruct as they kill invaders, their life span is only a few days.
Monocytes, which make up 5% of leukocytes, seem to provide a greater defense.
New monocytes are in the blood for a few hours then they move to tissue, where
they evolve into Macrophages, called big eaters, these are highly effective. The
macrophage engulfs a microbe in a vacuole which then fuses with Lysosome.
Lysosome kills the microbe in two ways, either by making toxic forms of oxygen
or by digesting some of their components. Againthere are some exceptions, such
as bacteria that create an outer capsule which macrophages cannot attach to.
Mycobacterium tuberculosis is ingested but can survive destruction.
Eosinophils, make up about 1.5% of all leukocytes, they contribute to defend
against large parasites, such as a blood fluke. They place themselves against the
wall of the parasite and release enzymes.
Non-Specific defense also involve Natural Killer cells (NK) which attack virusinfected body cells as well as cancerous cells.
Damage to tissue causes Inflammation, which causes precopillaryartenole to
dilate andpostcapillaryvenules to constrict thus the redness and heat felt.
Inflammation is caused by Histamine, which is released by cells when tissue is
injured. Histamine is made by Basophil and Mast cell in the connective tissue.
Increase blood flow enhances the migration of phagocytic cells to the area, which
is the most important result of inflammation. Chemokine, released by blood
vessel endothelia cells, also attract phagocytes.
Neutrophils are the first to arrive, then macrophages that are formed by
monocytes. Macrophages also clean up the dead cells, resulting in puss.
Wide spread response such as fever could take place, this happens by Pyrogens,
which increase the body’s temperature. This is bad for pathogens.
Over whelming the system can lead to septic shock which is as the leading death
in Critical care units.
Proteins can help kill microbes such as 20 serums proteins known as the
Complement System, which take steps to lyse microbes.
Another set of proteins that provide defense are Interferons, which are released
by virus-infected cells. This makes close cells release chemicals that inhibit the
spread of the virus in the cells
Nonspecific defense made up of skin and mucous, phagocytes, NK cells,
inflammation and proteins. Both do not distinguish between pathogens.
3. How Specific Immunity
Arises
Lymphocytes provide the specificity and diversity of the immune system
The body is made up of two main Lymphocytes, B cells and T
cells, concentrated in the spleen, lymph nodes, and lymphatic
tissue. They display specificity since they respond to particular
microbes. A foreign substance that causes a specific response by
lymphocytes is called an antigen. One way antigens elicit a
response by the immune system is by activating b cells to secret
Antibodies. Specific antibodies interact with specific antigens.
The way which B and T cells recognize specific antigens is by
their Antigen receptors. In B cells it is called membrane
antibodies but in T cells it is called T cell receptors which
recognize antigens, not secreted, have about 100,000 receptors.
Antigens interact specifically with lymphocytes causing an
immune response and immunological memory.
Antigens only interact with lymphocytes specific to it, causing the
lymphocyte to divide and differentiate. One clone consist of
Effector cells, short lived cells made to fight, the other clone is
made up of Memory cells, long lived cells bearing receptors for
the specific antigen. This process mentioned above is called
Clonal selection.
The selective differentiation of lymphocytes that occurs first time
around is called primary immune response—10 to 17 days are
needed to make the most effective effector cell response, in this
rime B cells and T cells produce antibody producing effector B
cells, Plasma cells, and effector T cells. When the same antigen is
seen it takes 2 to 7 days to the response to take into place,
Secondary Immune response.
Lymphocyte development allows the immune system to
distinguish between self and not self. Lymphocytes originate in
Bone Marrow and if they migrate ti the thymus they are then called
T cells, if they do not then they are B-cells.
While maturing B and T cells are tested to see if their receptors
react to molecules already present in the body, if they do then they
are destroyed.
T cells have a great interaction with cells surface glycoproteins,
encoded by MHC, major histocompatibility complex, in humans it
is known as HLA. 2 classes of MHC mark body cells as self, Class
I MHC molecules and Class II MHC molecules found in
specialized cells.
Antigen presentation, MHC molecules present a protein antigen to
an antigen receptor on a T cells. T cells are then alerted. Two main
type of T cells, each respond to one of the two classes of MHC.
Cytotoxic T cells have antigen receptors that bind to peptides
displayed by I MHC molecules. Helper T cells have receptors that
bind to peptides displayed by the body’s class II MHC molecule.
Class I MHC molecules present fragments of proteins made by
invaders to cytotoxic T cells, which then kill infected cells. Class II
MHC molecules only made by a few cells. These cells called
Antigen-presenting cells (APC’s) ingest pathogens. Remnants are
given to helper T cells that signal others to fight.
Maturing T-cells in the thymus interact with mature T cells and
depending on which class it has more affinity to they will become
cytotoxic cells or helper T cells.
4. Immune Responses
Can have two types of responses to antigens, a humoral response and a cell
mediated response, Humoral Immunityinvolves B cells activation and results
from production of antibodies, Cell-Mediated Immunity is where T cells are
transferred from Animals to Animals. Circulations of antibodies defend
against bacteria, toxins, and viruses, while T cells in C-M response area active
against viruses and bacteria in a cell and againstfungi, protozoa, and worms.
Helper T Lymphocytes Function in both humoral and cell mediated immunity.
The interaction between an APC and Helper T cell is greatly enhanced by a T
cells surface protein CD4. It binds to part of the II MHC.
When activated the Tn differentiates into active helper T cells and memory
helper T cells. Active Helper T cells secrete Cytokines, proteins that stimulate
other lymphocytes.
Cells-mediated response, cytotoxic T cells counter pathogens.
Cytotoxic T lymphocytes kill cancer cells and cells infected with viruses.
Interaction of cytotoxic T cells and class I MHC is enhanced by CD8, kills by
releasing proteins that make holes in the target cell membrane, Tumor antigen
causes detection of cancer cells.
In the humoral response, B cells make antibodies against extracellular
pathogens.
Stimulated by antigens and cytokines, the B ell differentiates into a clone of
antibody secreting plasma cells and memory B cells. Antigens that evoke this
type of response are known as T-dependent antigens since they stimulate
antibody production with T H cells.
Other antigens function as T-independent antigens such are presents in some
bacteria capsule. The repeated subunits bind to a number of antibodies on B
cell. This causes antibody secretion, but it is weaker than the other.
Antibodies interact with an accessible portion of the antigen called an
Epitope. Intruders usually have several epitopes.
Antibodies constitute a group of globular serum proteins called
Immunoglobulins (IgS). Each molecule consists of four polypeptide chains,
two identical Heavy Chains and two identical Light Chains.
Antibody specificity has been used in lab research. Some of these antibody
tools are polyclonal: products of different clones. Others are monoclonal:
from single clone. Since they are identical the Monoclonal Antibodies
produced are specific to the same epitope.
Antigen-Antibody complex where the antibody binds to an antigen is the basis
of disposal of the intruder. Neutralization is where the antibody binds to and
blocks the activity of the antigen. For example they can stop the production of
toxins in bacteria. The antigen covered in antibodies is eliminated by
phagocytosis. In a process called opsonization, the bound antibodies enhance
the macrophage attachment.
Antibody-mediated clumping or Agglutination of bacteria or viruses
neutralizes microbes. This is due to the fact that each antibody has at least two
antigen binding sites.
Most important is Complement fixation, the activation of the complement
system by antigen-antibody complexes. There is the classical pathway
triggered by the antibodies bound to the antigen, and the alternate pathway
which is triggered by substances naturally present in bacteria.
Invertebrates have a rudimentary immune system, in which they have no
specific immune system except for a few exceptions. It will always react to an
invader in the same amount of time.
5. Immunity in Health and
Disease
Immunity can be achieved naturally or artificially,
Immunity gained by getting an infectious disease such as chicken
pox is called Active Immunity, it is thus naturally acquired. It can
also be acquired artificially by Immunization also known
asVaccination. Vaccines include dead or weakened viruses or
bacteria. When the patient gets the disease the person’s immune
system will respond quicker.
Antibodies can be transferred from one individual to another,
resulting in Passive Immunity; it can be passed through the
placenta or the mom’s milk. It can also be vaccinated though it is
temporal.
Immune system’s capacity to distinguish self from oneself limits
successfulness of blood transfusions.
ABO Blood Groups, include an individual with type A blood has
A antigens on the surface of his red blood cells. B blood types have
B antigens and O blood types have neither antigen. If an A blood
type receives B blood, the A blood will have antibodies against
that blood.
Due to inducing a T-independent response they produce no
memory cells, producing IgM which does not cross the placenta
bringing no harm to the baby. Yet another blood cell antigen the
RH factor cause trouble since antibodies produced to it or IgG
class, can cross the placenta which can be dangerous. When a
mother is Rh-negative but has a fetus that is Rh-positive, the fetus’
blood may mix with the mother causing a T-dependent response.
When the mother has another RH positive baby the IgG can cross
the placenta and destroy the fetus.
The NHC molecules are responsible for the rejection of tissue thus
the best match is from a twin or sibling. Nevertheless medicine is
needed to suppress the immune response. The graft versus host
reaction is limited if the MHC Molecules are well matched
Allergies are hypersensitive response to the environmental
antigens. One hypothesis states that the origins of allergies are that
they are remnants of the immune system’s response to parasitic
worms.
The most common allergies involve antibodies of the IgE class.
They bind to most cells and when allergens attack the mast cell
degranulate releasing histamine. Acute allergic responses result in
Maphylactic Shock, a life threatening reaction to allergens where
the blood pressure drops significantly.
Sometimes the immune system loses tolerance to self which lead to
lupus or even multiple sclerosis.
There are many Immunodeficiencies and it is not always an inborn
condition. Stress and depression can lead to a suppressed immune
system.
AIDS is an immune deficient disease caused by HIV.
Acquired Immunodeficiency Syndrome gives rise to
opportunistic diseases allowing for an easy target.Human
Immunodeficiency Virus causes AIDS, due to it being a retrto
virus and its constant mutation it is extremely hard to cure. The
way it lowers defenses is by attacking CD$ cells on T-cells since it
is a receptor for the virus.