CHAPTER
17
Immunization and Immune
Testing
Chapter Outline
Immunization (pp. 500–508)
Brief History of Immunization
Active Immunization
Passive Immunotherapy
Serological Tests That Use Antigens and Corresponding Antibodies
(pp. 508–516)
Precipitation Tests
Turbidimetric and Nephelometric Tests
Chapter Summary
Immunization (pp. 500–508)
An individual may be made immune to an infectious disease by two artificial methods: active
immunization, which involves administering antigens to a patient so that the patient actively
mounts an adaptive immune response, and passive immunotherapy, in which a patient acquires
immunity through the transfer of antibodies formed by immune individuals or animals. This sec-
tion discusses these processes in more detail.
Brief History of Immunization
As early as the 12th century, the Chinese adopted a policy of deliberately infecting young chil-
dren with particles of ground smallpox scabs from children who had survived mild cases. This
Instructor’s Manual for Microbiology with Diseases by Taxonomy, 5e
vaccinia, Jenner called the new technique vaccination, and the protective inoculum a vaccine.
We now use the term immunization to refer to the administration of any antigenic inoculum.
In 1879, Pasteur demonstrated that he could make an effective vaccination against Pasteurel-
la multocida, and soon vaccinations against anthrax and rabies followed. After the underlying
Active Immunization
Vaccine Types
Vaccines contain pathogens that have been altered or inactivated, but not all vaccines are equally safe
or effective. Effectiveness can be checked by measuring the titer, the level of antibody in the blood.
The titer can be increased with a booster immunization. Vaccines include the following general types:
Inactivated (killed) vaccines include whole agent vaccines, which are produced with inactive but
whole microbes, and subunit vaccines, which are produced with antigenic fragments of microbes.
For these vaccines, which cannot replicate or retain residual virulence, multiple booster doses must
Toxoid vaccines are chemically or thermally modified toxins that stimulate immunity against
toxins (e.g., tetanus, diphtheria) rather than cellular antigens. Effective immunity requires
multiple childhood doses as well as reinoculations every 10 years of life.
Combination vaccines combine antigens from several pathogens that are administered sim-
ultaneously.
Vaccines using recombinant gene technology are made using a variety of recombinant
Chapter 17 Immunization and Immune Testing
Vaccine Manufacture
Vaccines for bacterial pathogens can be mass-produced by growing large quantities of the mi-
crobes. Viruses must be cultured on cells, and sterile chicken eggs are the most efficient method
of producing large quantities. Research is ongoing to find better methods due to concerns about
patients with egg allergies.
Recommended Immunizations
Vaccine Safety
A common problem associated with vaccines is mild toxicity causing pain at the injection site.
In rare cases, general malaise and fever high enough to induce seizures can occur. A severe
problem associated with immunization is the risk of anaphylactic shock, an allergic reaction to
Passive Immunotherapy
As noted earlier, passive immunotherapy (passive immunization) involves administering pre-
formed antibodies to a patient. Passive immunotherapy does not require the body to mount a re-
sponse; instead, preformed antibodies are immediately available to bind antigen, neutralize, and
opsonize. Antibodies against toxins are called antitoxins or antivenins (in the case of venom).
Serological Tests That Use Antigens and Corresponding Anti-
bodies (pp. 508–516)
Serology is the study and use of serological tests to diagnose and treat disease or identify anti-
bodies or antigens. A wide variety of serological tests visualize antibody-antigen interactions.
Instructor’s Manual for Microbiology with Diseases by Taxonomy, 5e
Precipitation Tests
One of the simplest serological tests relies on the fact that when soluble antigens and antibodies are
mixed in proper proportions, they form huge, insoluble, lattice-like macromolecular immune com-
plexes that precipitate. Cross-linking occurs because antibody molecules can bind two antigens at
Immunodiffusion
Cylindrical wells are cut into an agar plate, serum is placed in one well and soluble antigen in
another. As the molecules move through the agar gel, precipitates form where antigen and anti-
body concentrations are optimal. Immunodiffusion can also be used to detect exposure to com-
plex mixtures of antigens.
Turbidimetric and Nephelometric Tests
Antigen-antibody complexes can be measured by turbidimetry and nephelometry, two methods
Agglutination Tests
Agglutination tests involve the clumping of insoluble particles by antibodies. When the particles are
red blood cells, the reaction is called hemagglutination, and can be used to determine blood type. Ag-
glutination tests can be used to detect the presence of specific antibodies, or to determine the concen-
Neutralization Tests
Neutralization tests work because antibodies can neutralize the biological activity of many
pathogens and their toxins. These are of two types:
1. A viral neutralization test detects the ability of viruses to kill cell cultures, a phenomenon
called cytopathic effect. The virus is mixed with a patient’s serum that is suspected of con-
Chapter 17 Immunization and Immune Testing
The Complement Fixation Test
The complement fixation test is a complex assay based on classical complement activation. It
can be used to determine the presence of specific antibodies in an individual’s serum and detects
smaller amounts than agglutination tests. These tests have been replaced by other serological
methods, such as ELISA or genetic analysis using polymerase chain reaction (PCR).
Labeled Antibody Tests
Fluorescent Antibody Tests
A fluorescent dye molecule can be attached to an antibody without interfering with its ability to
bind antigen. The fluorescent molecules glow when exposed to a specific wavelength. A direct
ELISAs (EIAs)
Enzyme-linked immunosorbent assays (ELISAs) or enzyme immunoassays (EIAs) are a
family of simple immune tests that use an enzyme rather than a dye as the label and can be read-
ily automated and read by a machine. The reactions occur in small wells in plastic plates. An in-
direct ELISA detects the presence of specific antibodies in a serum sample. The basic steps are
Immunoblots
The immunoblot (western blot), can detect the presence of antibodies against multiple antigens;
Instructor’s Manual for Microbiology with Diseases by Taxonomy, 5e
Point-of-Care Testing
Recent years have seen the development of simple immunoassays that give clinicians useful re-
sults within minutes, called point-of-care testing. These immunofiltration and immunochroma-
tographic assays give rapid positive or negative results but are not quantitative.