antibodiesare injected into the blood
to provide immediate but short-lived
protection against specific bacteria, vir-
uses, or toxins. Active immunization, also
called vaccination, primes the body to
make its own antibodies and confers
longer-lasting immunity.
Routine childhood immunization pro-
grammes exist for diseases such as
diphtheria, pertussis, and tetanus (see
DPT vaccination), haemophilus influenza
(Hib), measles, mumps, and rubella (see
MMR vaccination), meningitis C, and
poliomyelitis. Additional immunizations
before foreign travel may also be neces-
sary (see travel immunization).
Most immunizations are given by injec-
tion, and usually have no after effects.
However, some vaccines cause pain and
swelling at the injection site and may
produce a slight fever or flu-like symp-
toms. Some may produce a mild form of
the disease. Very rarely, severe reactions
occur due, for example, to an allergy to
1 of the vaccine’s components. Not all
vaccines provide completeprotection.
Choleraand typhoid fevervaccinations,
in particular, give only partial protection.
People with immunodeficiency disor-
ders, widespread cancer, those taking
corticosteroid drugs,or those who have
previously had a severe reaction to a
vaccine should not be immunized.
Some vaccines should not be given to
young children or during pregnancy.
immunoassayA group of laboratory
techniques, which include ELISA (en-
zyme-linked immunosorbent assay) and
radioimmunoassay, that are used in the
diagnosis of infectious diseases and
allergies, and in the measurement of hor-
monelevels inthe blood.
immunodeficiency disordersDisor-
ders in which there is a failure of the
immune system’sdefences to fight infec-
tion and tumours. They may be due to
an inherited or a congenitaldefect or
may be the result of acquired disease.
The result is persistent or recurrent in-
fection,including those with organisms
that would not ordinarily cause disease,
and an undue susceptibility to certain
forms of cancer. The infections in people
with immunodeficiency disorders are
sometimes called opportunistic infections;
examples include pneumocystic pneu-
monia,fungal infections, and widespread
herpes simplexinfections.
Congenital or inherited deficiencies can
occur in either of the 2 prongs of the
adaptive immune system: humoral or
cellular. Deficiencies of the humoral sys-
tem include hypogammaglobulinaemia
and agammaglobulinaemia. The former
may cause few or no symptoms, depend-
ing on the severity of the deficiency, but
agammaglobulinaemia can be fatal if
not treated with immunoglobulin. Con-
genital deficiencies of T-lymphocytes
may lead to problems such as persis-
tent and widespread candidiasis(thrush).
A combined deficiency of both humoral
and cellular components of the immune
system, called severe combined immuno-
deficiency (SCID), is usually fatal in the
1st year of life unless treatment can be
given by bone marrow transplant.
Acquired immunodeficiency may be
due either to disease processes (such
as infection with HIV, which leads to
AIDS) or damage to the immune system
as a result of its suppression by drugs.
Severe malnutrition and many cancers
can also cause immunodeficiency. Mild
immunodeficiency arises through a natu-
ral decline in immune defences with age.
immunoglobulinA type of protein found
in blood and tissue fluids, also known as
an antibody. Such proteins are produced
by B-lymphocytes (a type of white blood
cell), and their functionis to bind to
substances in the body that are recog-
nized as foreign antigens. This binding is
crucial for the destruction of antigen-
bearing microorganisms. Immunoglob-
ulins also play a key role in allergiesand
hypersensitivityreactions.
Immunoglobulin G (IgG) is the major
class of immunoglobulin of the 5 in the
blood (IgA, IgD, IgE, IgG, and IgM). Its
molecule consists of 2 parts: 1 binds to
an antigen; the other binds to other
cells, which then engulf the microor-
ganisms bearing the antigen.
Immunoglobulins can be extracted
from the blood of people who have rec-
overed from certain infectious diseases
and used for passive immunization.
immunoglobulin injectionAdminis-
tration of immunoglobulinpreparationsIMMUNOASSAY IMMUNOGLOBULIN INJECTION
I