use recombinant vaccines because they do not need an animal host to grow the
microorganism. An example is hepatitis B.Diagnosing Diseases
The reaction between an antibody and complementary antigen is used in
conjunction with observing symptoms to diagnosis a disease. You have prob-
ably seen this diagnosis technique used when you were tested for tubercu-
losis. This test required that a suspension of Mycobacterium tuberculosisbe
injected into your skin. If the site becomes red in a couple of days, then you
tested positive for tuberculosis. The redness is a reaction between antibodies
and antigen.
Scientist use eight types of reactions to diagnose diseases. Each determines if
a specific antibody or a specific antigen is present based on its complementary
antibody or antigen. These are:Precipitation reaction. IgG or IgM antibodies are combined with soluble anti-
gens. If the antibody and antigen are in an optional ratio, they form an antigen-
antibody complex called a lattice. The reaction occurs immediately, however
the lattice may not form until minutes after the reaction begins. There are three
commonly used precipitation reaction tests. These are:- Precipitin ring test.Aring appears in the area of the optimal ratio, which
is called the zone of equivalence. - Immunodiffusion test.Aline is visible in the area of the optimal ratio.
- Immunoelectrophoresis test.Uses electrophoresis to identify separated
proteins in human serum. The test is called the Western blot test and is used
in AIDS testing.
Agglutination reaction. Particulate antigen or soluble antigens that adhere par-
ticles are introduced to antibodies to form an aggregate reaction called aggluti-
nation (clumping of cells). There are two types of agglutination reaction tests.
These are:- Direct agglutination test.Uses a plastic microtiter plate to detect antibody
reaction with large cellular antigens. The microtiter plate contains a series
of wells. Each well has the same amount of antigen and successively
diluted serum of the antibody. The direct agglutination test measures the
titer antibodies in the serum. The titer is lower at the onset of the disease
and higher later in the disease.
(^226) CHAPTER 15 Vaccines and Diagnosing Diseases