836
c h a p t e r 35
Molecular Immunology
immune
response
without
causing
serious
disease,
e.g., cowpox virus stimulates formation of antibodies and
memory cells that recognize epitopes common to cowpox
and smallpox. Organisms grown under unfavorable con-
ditions (attenuation) so as to become incapable of causing
disease are also used as immunogens; measles, mumps,
rubella, and polioviruses are examples of this approach to
vaccine development. Vaccination must be credited with
the tremendous success in preventing many communica-
ble diseases, particularly those of childhood. Vaccination
is not without risk, however. Contaminants introduced in
the vaccine production, incompletely killed organisms,
and virulence in immune-compromised individuals can
produce serious illness and death in rare cases.
Vaccines against bacterial disease are commonly di-
rected against the toxins produced by the bacteria. The
toxins are purified and treated to prevent them from caus-
ing their debilitating effects on the host (toxoids). The
toxoids retain their immunogenicity and thus their ability
to cause antibody production, which provides immunity
to the bacterial pathogen. A well known example is the
diphtheria toxoid.
Proteins manufactured by recombinant DNA technol-
ogy now enable production of immunogenic molecules
that can be used to stimulate immune response to known
pathogens. These immunogens can be modified so that
they cannot cause disease. Chemically synthesized im-
munogens that present an epitope or epitopes of a pathogen
are also used in the development of vaccines. As the knowl-
edge of the chemical structures of pathogenic molecules
increases, the ability to select suitable structures for vac-
cines becomes increasingly practical. Vaccines prepared
from such molecules, e.g., a hepatitis B vaccine, permits
immunization without risk of hepatitis to the recipient.
DNA vaccines may provide another safe method for
vaccination. Instead of introducing a protein antigen into
a subject, DNA containing a gene for a particular antigen
is introduced into cells. The antigen is synthesized intra-
cellularly and evokes an immune response (also discussed
in Chapter 23).
Prevention of disease caused by infectious agents
through vaccine development offers the best hope for
the elimination of several of the most challenging con-
temporary public health crises. The continuing technical
FIGURE 35-24
(Also see color figure.) Secondary structural features of cytokines.
(A) IFN-a2A (shown with both end and side views of the 5
a
helices).
(B) IL-4, showing the
a
helices from both end and side views. This group
of cytokines is characterized by the 4—6 distinct
a
helices that form the
protein “backbone.” (C) IL-1 showing the ,6-sheet structure that is
characteristic of this group of cytokines.
