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Saturday, November 22, 2008
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What
Are Primary Immunodeficiency Diseases?
Primary immunodeficiency diseases are caused
by intrinsic defects in the cells of the immune system and are
often caused by inherited genetic defects. This is in contrast
to secondary immunodeficiency diseases such
as acquired immunodeficiency syndrome caused by infection with
human immunodeficiency virus. The hallmark of primary immunodeficiency
diseases is increased susceptibility to infection, but they
can cause other problems as well. These diseases are grouped
according to what part of the immune system is affected.
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B lymphocytes and
plasma cells producing
proteins called antibodies |
Antibody
Deficiencies
Antibodies are proteins made by white blood cells called B lymphocytes
and plasma cells. The function of antibodies is to recognize and
mark bacteria, viruses, and other foreign invaders so that other
parts of the immune system will respond to these invaders by killing
them. One example of an antibody deficiency is:
- X-linked
Agammaglobulinemia-an inherited deficiency that appears
in the first 3 years of life. Infants with this deficiency
develop recurrent pus-producing infections of the ears, lungs,
sinuses, and bones and can get infections in the bloodstream
and internal organs. They are also susceptible to certain
viruses such as hepatitis and polio.
Combined
Immunodeficiencies
T lymphocytes are white blood cells that are critical to a healthy
immune system. Some T lymphocytes develop into killer cells that
destroy infected cells while others become helper cells that communicate
with other immune cells and instruct B lymphocytes to make antibodies.
People who lack both killer T lymphocytes and antibodies to fight
against foreign invaders develop severe illnesses. The most common
such deficiency is:
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Regulatory T lymphocytes
produce molecules called
cytokines |
Killer T lmphocytes
produce molecules that
kill infected cells |
- X-linked
Severe Combined Immunodeficiency - an inherited deficiency
caused by a defective gene for a T lymphocyte molecule important
for T cell growth. Patients are diagnosed within the first
year of life with frequent and severe infections often caused
by organisms that do not affect people with healthy immune
systems.
Complement Deficiencies
The complement system consists of a group of proteins that attach
to antibody-coated foreign invaders like bacteria and viruses.
 |
| Complement proteins
kill antibody-coated bacteria and viruses |
These proteins work
together to disable and kill invading pathogens. People deficient
in one or another of these proteins have a diminished ability
to kill invaders, resulting in increased infections. Such people
may also develop antibodies that react against the body's own
cells and tissues, resulting in autoimmune diseases with immune-mediated
damage to the body. The most common of these deficiencies is:
- C2 Deficiency-an
inherited defect in the gene for the complement protein called
C2. This defect can cause an autoimmune disease such as systemic
lupus erythematosus or can result in severe infections such
as meningitis. The illnesses usually appear in childhood or
in early adulthood.
Phagocytic
Cell Deficiencies
Phagocytes include white blood cells called neutrophils and macrophages
that engulf and kill antibody-coated foreign invaders. Phagocytes
can be defective either in their ability to kill pathogens or
in their ability to move to the site of an infection. In either
case, the defect results in increased infections. The most severe
form of phagocytic cell deficiency is:
-
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Phagocytic cells
ingest antibody- and/or
complement-coated bacteria and kill them |
Chronic
Granulomatous Disease-inherited deficiencies of molecules
needed by neutrophils to kill certain infectious organisms.
These illnesses usually appear early in childhood but may
appear as late as adolescence. People with chronic granulomatous
disease develop frequent and severe infections of the skin,
lungs, and bones and develop localized, swollen collections
of inflamed tissue called granulomas.
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December 9, 1999
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