Immunodeficiency WORLD OF MICROBIOLOGY AND IMMUNOLOGY294•
and there are five different types of immunoglobulins (called
IgA, IgG, IgM, IgD, and IgE). The most common type of
immunoglobulin deficiency is selective IgA deficiency. The
amounts of the other antibody types are normal. Some patients
with selective IgA deficiency experience no symptoms, while
others have occasional lung infections and diarrhea. In another
immunoglobulin disorder, IgG and IgA antibodies are defi-
cient and there is increased IgM. People with this disorder
tend to get severe bacterial infections.
Common variable immunodeficiency is another type of
B lymphocyte deficiency. In this disorder, the production of
one or more of the immunoglobulin types is decreased and the
antibody response to infections is impaired. It generally devel-
ops around the age of 10-20. The symptoms vary among
affected people. Most people with this disorder have frequent
infections, and some will also experience anemia and rheuma-
toid arthritis. Many people with common variable immunode-
ficiency develop cancer.
Severe defects in the ability of T lymphocytes to mature
results in impaired immune responses to infections with
viruses, fungi, and certain types of bacteria. These infections
are usually severe and can be fatal.
DiGeorge syndrome is a T lymphocyte deficiency that
starts during fetal development, but it isn’t inherited. Children
with DiGeorge syndrome either do not have a thymus or have
an underdeveloped thymus. Since the thymus is a major organ
that directs the production of T-lymphocytes, these patients have
very low numbers of T-lymphocytes. They are susceptible to
recurrent infections, and usually have physical abnormalities as
well. For example, they may have low-set ears, a small reced-
ing jawbone, and wide-spaced eyes. In some cases, no treatment
is required for DiGeorge syndrome because T lymphocyte pro-
duction improves. Either an underdeveloped thymus begins to
produce more T lymphocytes or organ sites other than the thy-
mus compensate by producing more T lymphocytes.
Some types of immunodeficiency disorders affect both
B lymphocytes and T lymphocytes. For example, severe com-
bined immunodeficiencydisease (SCID) is caused by the
defective development or function of these two types of lym-
phocytes. It results in impaired humoral and cellular immune
responses. SCID is usually recognized during the first year of
life. It tends to cause a fungal infection of the mouth (thrush),
diarrhea, failure to thrive, and serious infections. If not treated
with a bone marrow transplant, a person with SCID will gen-
erally die from infections before age two.
Disorders of innate immunity affect phagocytes or the
complement system. These disorders also result in recurrent
infections.
Acquired immunodeficiency is more common than
congenital immunodeficiency. It is the result of an infectious
process or other disease. For example, the Human Immu-
nodeficiency Virus(HIV) is the virus that causes acquired
immunodeficiency syndrome (AIDS). However, this is not the
most common cause of acquired immunodeficiency. Acquired
immunodeficiency often occurs as a complication of other
conditions and diseases. For example, the most common
causes of acquired immunodeficiency are malnutrition, some
types of cancer, and infections. People who weigh less than70% of the average weight of persons of the same age and
gender are considered to be malnourished. Examples of types
of infections that can lead to immunodeficiency are chicken-
pox, cytomegalovirus, German measles, measles, tuberculo-
sis, infectious mononucleosis(Epstein-Barr virus), chronic
hepatitis, lupus, and bacterial and fungal infections.
Sometimes, acquired immunodeficiency is brought on
by drugs used to treat another condition. For example, patients
who have an organ transplant are given drugs to suppress the
immune system so the body will not reject the organ. Also,
some chemotherapydrugs, which are given to treat cancer,
have the side effect of killing cells of the immune system.
During the period of time that these drugs are being taken, the
risk of infection increases. It usually returns to normal after
the person stops taking the drugs.
Congenital immunodeficiency is caused by genetic
defects, and they generally occur while the fetus is developing
in the womb. These defects affect the development and/or
function of one or more of the components of the immune sys-
tem. Acquired immunodeficiency is the result of a disease
process, and it occurs later in life. The causes, as described
above, can be diseases, infections, or the side effects of drugs
given to treat other conditions.
People with an immunodeficiency disorder tend to
become infected by organisms that don’t usually cause disease
in healthy persons. The major symptoms of most immunode-
ficiency disorders are repeated infections that heal slowly.
These chronic infections cause symptoms that persist for long
periods of time.
Laboratory tests are used to determine the exact nature
of the immunodeficiency. Most tests are performed on blood
samples. Blood contains antibodies, lymphocytes, phagocytes,
and complement components—all of the major immune com-
ponents that might cause immunodeficiency. A blood cell
count will determine if the number of phagocytic cells or lym-
phocytes is below normal. Lower than normal counts of either
of these two cell types correlates with immunodeficiencies.
The blood cells are also checked for their appearance.
Sometimes a person may have normal cell counts, but the cells
are structurally defective. If the lymphocyte cell count is low,
further testing is usually done to determine whether any par-
ticular type of lymphocyte is lower than normal. A lymphocyte
proliferation test is done to determine if the lymphocytes can
respond to stimuli. The failure to respond to stimulants corre-
lates with immunodeficiency. Antibody levels can be meas-
ured by a process called electrophoresis. Complement levels
can be determined by immunodiagnostic tests.
There is no cure for immunodeficiency disorders.
Therapy is aimed at controlling infections and, for some dis-
orders, replacing defective or absent components.
In most cases, immunodeficiency caused by malnutri-
tion is reversible. The health of the immune system is directly
linked to the nutritional health of the patient. Among the
essential nutrients required by the immune system are pro-
teins, vitamins, iron, and zinc. For people being treated for
cancer, periodic relief from chemotherapy drugs can restore
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