DEFINITION:
The immune response is the way the body defends itself against
microorganisms, cancer cells, and other potentially harmful substances.
THE IMMUNE SYSTEM
The immune system protects the body from potentially harmful substances.
Antigens are large molecules (usually proteins) on the surface of cells,
viruses, fungi, bacteria, and some non-living substances such as toxins,
chemicals, drugs, and foreign particles (such as a splinter). The immune
system recognizes and destroys substances that contain antigens. Even
your own body cells have proteins that are antigens (these include a
group of antigens called HLA antigens). Your immune system learns to see
these antigens as "normal" and does not usually react against
them.
INNATE IMMUNITY AND INFLAMMATION
Innate immunity involves barriers that keep harmful materials from
entering your body. Some of these barriers are: the skin, stomach acid,
mucous (traps microorganisms and small particles), the cough reflex, and
enzymes in tears and skin oils. If an antigen gets past the external
barriers, it is attacked and destroyed by other parts of the immune
system. Innate immunity also includes those things that make humans
resistant to many of the diseases of animals.
The immune system includes certain types of white blood cells. It also
includes chemicals and proteins in the blood (such as complement
proteins and interferon). Some of these directly attack foreign
substances in the body, and others work together to help the immune
system cells.
The inflammatory response (inflammation) is part of innate immunity. It
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 localized swelling.
This helps isolate the foreign substance from 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.
ACQUIRED IMMUNITY
Acquired (adaptive) immunity develops when the body is exposed to
various antigens. It involves a specific type of white blood cell called
a lymphocyte. Actually, there are 2 groups of lymphocytes. B lymphocytes
(also called B cells) produce antibodies. Antibodies attach to a
specific antigen and make it easier for the phagocytes to destroy the
antigen. T lymphocytes (T cells) attack antigens directly, and some T
lymphocytes provide control of the immune response. B cells and T cells
develop that are specific for ONE antigen type. When you are exposed to
a different antigen, different B cells and T cells are formed.
As lymphocytes develop, they normally learn to recognize the body's own
tissues (self) as distinctive from tissues and particles not normally
found in your body (non-self). Once B cells and T cells are formed, a
few of those cells will multiply and provide "memory" for the
immune system. This allows the immune system to respond faster and more
efficiently the next time you are exposed to the same antigen.
PASSIVE IMMUNITY
Passive immunity involves antibodies that are produced in someone's body
other than your own. Infants have passive immunity because they are born
with antibodies that are transferred through the placenta from the
mother. These antibodies disappear between 6 and 12 months of age. Gamma
globulin is another form of getting passive immunity. It's protection is
also temporary.
IMMUNE SYSTEM DISORDERS AND ALLERGIES
Immune system disorders occur when the immune response is inappropriate,
excessive, or lacking. Allergies involve an immune response to a
substance that, in the majority of people, the body perceives as
harmless. Transplant rejection involves the destruction of transplanted
tissues or organs and is a major complication of organ transplantation.
Blood transfusion reaction is a complication of blood administration.
Autoimmune disorders (such as systemic lupus erythematosus and
rheumatoid arthritis) occur when the immune system acts to destroy
normal body tissues. Immunodeficiency disorders (such as inherited
immunodeficiency and AIDS) occur when there is a failure in all or part
of the immune system.
SIGNS OF INFLAMMATORY RESPONSE:
- localized redness
- pain in the area
- swelling of the affected area
- warmth of the affected area
- pus (sometimes)
Note: In many cases, no observable
symptoms develop.
Additional symptoms may include:
- fever
- general discomfort, uneasiness, or
ill feeling (malaise)
- muscle aches
- agitation or confusion
TESTS:
During an infection, a CBC usually shows increased numbers of white
blood cells. A T (thymus derived) lymphocyte count is elevated. A blood
differential count is elevated.
If a problem is suspected, other tests may be performed to determine
complement levels and the levels of specific immunoglobulins
(antibodies).
THERAPIES:
Usually, the immune response is desired. In some cases, suppression of
the immune system is necessary (for example, in the treatment of
autoimmune disorders). This is usually accomplished by administering
corticosteroids and immunosuppressive medications.
Suppression of the immune system may be an undesired side effect of
certain treatments or disorders.
Vaccination (immunization) is way to trigger the immune response. Small
doses of an antigen (such as dead or weakened live viruses) are given to
activate immune system "memory" (activated B lymphocytes and
sensitized T lymphocytes). Memory allows your body to react quickly and
efficiently to future exposures. This means that if you are exposed to a
microorganism, it will be destroyed before it can cause illness.
Passive immunization involves transfusion of antiserum, which contains
antibodies that are formed by another person (or animal). It provides
immediate protection against an antigen, but does not provide
long-lasting protection. Gamma globulin and equine (horse) tetanus
antitoxin are examples of passive immunization.
COMPLICATIONS:
An efficient immune response protects against many diseases and
disorders. Inefficient immune response allows diseases to develop.
Inadequate, inappropriate, or excessive immune response causes immune
system disorders.
Complications related to altered immune response include:
- disease development
- allergy/hypersensitivity
- anaphylaxis
- autoimmune disorders
- blood transfusion reaction
- immunodeficiency disorders
- serum sickness
- transplant rejection
- graft versus host disease
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