432 Section 13/ MiscellaneousPassive Immunity
When antibodies produced in one body
are transferred to another to induce
protection against disease, it is known as
passive immunity. It can be acquired
naturally i.e. in foetus receiving mother’s
antibodies through placenta or artificially by
administration from outside in the form of
antisera containing antibodies.
Types of Immunizing Agents
The various preparations employed for
conferring immunity are:
VACCINES
It is an immunobiological substance for
producing specific protection against a
given disease. It stimulates the production
of protective antibodies and other immune
mechanisms. Vaccines may be prepared
from attenuated live organisms, inactivated
or killed microorganisms, toxoids or
combination of these and more recent one
are recombinant vaccines.
Live Vaccines
These are prepared from live organisms
e.g. BCG, measles and polio oral vaccine.
The live vaccines are more potent
immunizing agent because live organisms
multiply in the host and the resulting
antigenic dose is larger than what is
injected and live vaccines have all the major
and minor antigenic components. Besides
that live vaccines engage certain tissues of
the body e.g. intestinal mucosa by polio oral
vaccine.
But there are some limitations with live
vaccines, such as live vaccines should not
be administered in a person with immune
deficiency disease or a person with
leukemia, lymphoma or are on cytotoxic
chemotherapy, radiation or corticosteroid
therapy because of malignancy.
The examples of live vaccines are:- Live (bacterial): BCG, typhoid oral.
- Live (viral): Polio oral vaccine, yellow
fever, measles, rubella, mumps,
influenza. - Live (rickettsial): Epidemic typhus.
Killed or Inactivated Vaccines
These consist of microorganisms killed
by heat or chemicals. Killed vaccines
usually require a primary series of two-
three doses of vaccine to produce an
adequate antibody response and generally
booster dose is required. The duration of
immunity varies from months to years. (e.g.
in case of polio vaccine) The examples are: - Killed (bacterial) vaccine: Typhoid,
cholera, pertussis, plague, meningitis. - Killed (viral) vaccine: Rabies,
influenza, hepatitis B, encephalitis
(Japanese), polio.
Toxoids
These are produced by addition of
formalin to the toxin of microorganisms and
incubating them at 37°C for three to four
weeks. Certain microorganisms produce
endotoxins e.g. tetanus and diphtheria. The
toxins produced by these organism are
detoxicated and used for the preparation
of vaccine. The toxoids have lost their
toxicity but antigenicity is retained.
Polysaccharides
Certain vaccines are prepared from
extracted cellular fractions e.g. meningo-