- Indirect agglutination test.Soluble antigens are absorbed onto the surface
of latex spheres where they react to antibodies. This has a relatively short
reaction time, enabling a diagnosis in 10 minutes. Indirect agglutination test
is commonly used to diagnosis streptococci, which cause sore throats.
Hemagglutination reaction. This type of reaction uses red blood cell surface
antigens and complimentary antibodies to determine if red blood cells clump in
reaction to the antibodies. This test is used in typing blood and in diagnosing
infectious mononucleosis. If the antigen is a virus the reaction is called viral
hemagglutination.
Neutralization reaction.This reaction uses antibodies as an antitoxin to block
the extoxin or toxoid of bacteria or a virus. Extoxinis an active toxin and toxoid
is an inactive toxin. A serum containing the antibody for a particular antigen is
placed in a cell culture that contains cells and the antigen. If the antigen does not
destroy (cytopathic effect) cells, then the extoxin is neutralized. Therefore, the
antigen is complementary to the antibody. Tests that use the neutralization re-
action are called vitro neutralization tests. One such test is the hemagglutination
inhibition test, which is used to diagnose a number of infections including measles,
influenza, and mumps.
Complement-fixation reaction. This reaction uses a group of serum proteins
called a complementto bind with the antigen-antibody complex. The serum is
said to be fixed when the serum total binds to the antigen-antibody complex.
Fluorescent-antibody (FA) reaction. This reaction combines fluorescent dyes
with an antibody, making the antibody fluorescent when exposed to ultraviolet
light, and is used to detect a specific antibody in a serum. The fluorescent-antibody
reaction is used to test for rabies. There are two types of fluorescent-antibody re-
action tests. These are:
- Direct FA test. The antigen and the fluorescien-labeled antibodies are
combined on a slide and then incubated. The slide is washed to remove
any antibodies that did not attach to the antigen and then observed under a
fluorescence microscope for yellow-green fluorescence. - Indirect FA test. The antigen and the serum containing the antibody are
combined on a slide. Fluorescein-labeled antihuman immune serum globu-
lin (antiHISG) is also added to the slide, which reacts to human antibody
on the slide. The slide is incubated and washed, then observed under a
fluorescence microscope. If the antigen is fluorescent, then the comple-
mentary antigen is on the slide.
CHAPTER 15 Vaccines and Diagnosing Diseases^227